Peter Pauling at Cambridge, 1953-1954

Peter Pauling, 1954.

[The life of Peter Pauling, part 5 of 9]

In the first months of 1953, with his office mates scrambling to determine the molecular structure of DNA before his own father could beat them to it, Peter Pauling was mostly concerned with the English weather. He had been at Cambridge University since the fall of 1952 when he began his PhD program in physics at the university’s Cavendish Laboratory, and in that time he judged that he had seen a mere two full days of sun and was now officially fed up.

His father, by contrast, was mostly concerned with finishing his most recent edition of The Nature of the Chemical Bond, for which he had often solicited Peter as a source to provide example problems and solutions prior to his departure for England. As he was now beginning his graduate research, however, Peter was too busy to provide much assistance for this edition.

Instead, he was mostly occupying himself with a muscle camera developed by Hugh E. Huxley, a molecular biologist studying the physiology of muscle with Max Perutz’ Medical Research Council (MRC) Unit of Molecular Biology at Cambridge. Taking pictures of fibrous and globular proteins – beginning with insulin and tropomyosin – Peter applied the Cochran-Crick theory, with the goal of determining the helical structure of these protein molecules. This inquiry was, in principle, made possible by Linus Pauling’s work from less than a decade prior.

Since 1947, when the MRC unit was founded by Sir Lawrence Bragg, John Kendrew and Max Perutz had endeavored to use x-ray crystallography to determine the molecular structure of hemoglobin in sheep. By the time that Peter arrived at Cambridge, however, hemoglobin had proven to be an untenable object of study, and Kendrew’s focus had shifted to myoglobin. Whereas hemoglobin is found mostly in the blood, myoglobin is generally found only in muscle tissue. Both are proteins that carry oxygen to cells. Problematically, myoglobin is one fourth the size of hemoglobin, and too small for the era’s techniques of x-ray analysis.

To solve this issue, sperm whale myoglobin was used in hopes that the molecular details of the larger, oxygen-rich proteins of a diving mammal would be more observable with the tools then available. “Stranded whales are the property of the Queen,” Peter explained to his father as he discussed this work, “but we have an agreement with her to get a piece of meat if one comes ashore.” Nonetheless, though availed of samples from beached whales in the United Kingdom and from countries as far afield as Peru, Kendrew could not render the x-ray diffraction patterns with complete certainty.

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Sperm whale myoglobin image created by John Kendrew.

In 1953, Perutz realized that by comparing the diffraction patterns of natural whale myoglobin crystals to crystals soaked in heavy metal solutions – a procedure called multiple isomorphous replacement – the positions of the atoms in myoglobin could be more accurately determined. Accordingly, Peter was tasked with making countless measurements in support of this effort.

Peter wrote to his father often over the next two years as he struggled to complete this project, which was the focus of his PhD. In particular, Peter asked for advice on how one might best get heavy metal atoms onto myoglobin, detailing his attempts to use everything from saltwater to telluric acid, which was used to produce salts rich in metallic contents, such as the element Tellurium.

Indeed, Peter’s work proceeded slowly, not least of all because of his knack for keeping things entertaining. Shortly after Watson and Crick’s discovery of DNA, for example, he fabricated a letter of invitation from his father, Linus Pauling, to Francis Crick, requesting Crick’s presence at an upcoming conference on proteins at Caltech. “Professor Corey and I want you to speak as much as possible during the meeting,” the impostor Pauling said to Crick in the fake letter, even urging him to consider lecturing at Caltech as a visiting professor. Linus Pauling had appeared to sign the letter himself, his signature skillfully forged. The letter proved so convincing that Crick actually replied, accepting the invitation to speak at the conference.

Before long, it became apparent that the entire communication was, in fact, a practical joke. Lawrence Bragg, the director of the Cavendish Laboratory, where Crick himself worked, was scheduled to speak at the proteins conference in the same time slot that the fake letter had proposed for Crick. Were it not for this, the deception might have gone even farther, since upon seeing his son’s forgery Linus himself was almost convinced that he had written the letter and had simply forgotten about it amidst the relentless pace of his schedule.

Ever a stickler for the details, however, Pauling noticed a grammatical error in the document that he would never have made. From there, he deduced the letter as having been authored by his mischievous son. For this transgression, Linus subtracted a five-pound fine from the $125.00 check that he sent to Peter each month.

Peter Pauling and the Discovery of the Double Helix, 1952-1953

Peter Pauling, 1954.

[The life of Peter Pauling: Part 4 of 9]

With Winter break coming fast and Linus Pauling having apparently solved the structure of DNA, Jim Watson and Francis Crick extinguished any hope of modeling their own structure. Eager to take advantage of a few days off, their Cavendish office mate, Peter Pauling, headed for the continent in the company of a friend whom he described as “a mad Rhodes scholar” who had “wooed” him with his “insane plan” for exploring Europe.

On this trip, which was indeed ambitious, Peter visited Munich, Vienna, Linz, Brussels, Frankfurt, and Bavaria, hitchhiking his way from location to location. Crossing Germany, Peter saw neighborhoods still littered with the rubble of the Second World War, alongside industrious people struggling to rebuild. His mode of travel, he confessed to his mother in a letter, had seemed a better idea when its low cost was his only consideration. In person, however, spending several hours standing in or walking through the snow had a way of changing one’s priorities.

Nonetheless, the whole escapade proved a romantic adventure for the young Peter Pauling. He spent Christmas Eve in a gas house belonging to the director of an iron company somewhere in Leoben, Austria. Resting there and watching the snow fall, he wrote again to his mother:

I look out the window to the lovely white mountains. It is grand. Considering the possibilities, Christmas and your birthday [Ava Helen was born on December 24, 1903] could hardly have been spent in a nicer place. Considering impossibilities, I can think of places where I would much prefer to be. Sometimes it is sad to grow up.

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[Triple Helix animation and narration created by Cold Springs Harbor Laboratory]

With the arrival of the new year, the Cavendish researchers put their skis away, shook the snow from their coats, and resumed their work.  It wasn’t long into the term before Peter learned, from two letters received in February, that his father was, in fact, having difficulty with some of the van der Waals distances hypothesized to be near the center of his DNA model. In response – and almost as an afterthought – Peter casually asked his father for a manuscript of the DNA proposal, mentioning that his coworkers in Max Perutz’ unit would like to give it a read. Upon receiving the paper, Peter promptly revealed to Watson and Crick that the Pauling-Corey model was a triple helix, a concept similar to one that Watson and Crick had developed themselves – and rejected – back in 1951.

This moment was a major turning point for Watson and Crick, who only then realized that they still had a chance to discover the structure before Linus Pauling. That said, what followed may not have been quite the race as it was made out to be after the fact. At least, Peter Pauling did not see it that way, and the casual manner in which his father interacted with him (and with others at the Cavendish) seems also to belie such a dramatization.

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[Jim Watson recalls learning of the Pauling-Corey triple helical model. Video created by Cold Springs Harbor Laboratory.]

Near the end of February 1953, while wishing his father a happy birthday, Peter noted that his office still felt that Linus’ structure required sodium to be located somewhere near the oxygens, whose negative charges would have to cancel out to hold the molecule together. “We agree that everything is a little tight,” he said, referring to the small atomic distances between Pauling’s three polynucleotide chains with phosphate groups in the middle.

As communicated in an earlier letter to his son, Linus Pauling had already identified these structural arrangements as a weakness of the model, and he was in the midst of attempting to correct the issue. Peter confided to his father that, at that time, the Cambridge office had nothing better to offer. He added simply that “We were all excited about the nucleic acid structure,” and concluded with his many thanks for the paper.

In response, Linus Pauling asked for updates on any progress that Watson and Crick were making with their own model, and casually requested that Peter also remind Watson that he should arrive for a scheduled protein conference at Caltech by September 20^th. Peter clarified only that the Cavendish group had successfully built the Pauling-Corey model and that Watson and Crick had then discarded it, becoming very involved in their own efforts and “losing objectivity.” It would be up to them, Peter said, to communicate the details of their structure. Shortly thereafter, Watson and Crick sent a letter to Linus Pauling, outlining their structure and including the short article that they had submitted for publication in Nature.

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Crystallographic photo of Sodium Thymonucleate, Type B. “Photo 51.” Taken by Rosalind Franklin, May 1952.

It has been well-established that Pauling and Corey made basic errors in their own modeling  of the structure of DNA. But in March 1953, having no knowledge of the x-ray crystallographic photographs of DNA that had been taken by Rosalind Franklin at Kings College, Pauling felt bewildered by the certainty with which Watson and Crick had rejected his triple helical model. Upon learning its details, Pauling agreed that the double helix model was at least as likely, and he considered it to be a beautiful molecular structure, but he could not understand why his own structure was being ruled out entirely.

At the heart of his confusion lay the fact that he did not believe that any x-ray evidence existed that proved that the phosphate groups might somehow be located on the outside, rather than in the core, of the DNA molecule. Pauling did not believe that this evidence existed because he hadn’t seen it yet; crucially, Watson and Crick had. Indeed, from the point of their realization that Pauling had modeled the structure incorrectly, Watson and Crick worked fervently to once again convince Maurice Wilkins to provide them with Rosalind Franklin’s data.

(On one occasion, they met with Wilkins for lunch at the Crick home, where Peter could often be found for brunch on the weekends. On certain of these earlier brunch occasions, while in the home’s basement dining room, Watson and Crick discussed the feasibility of redoubling their efforts to model DNA while Peter, casually eating biscuits and sipping tea at the table, offered that if they didn’t do it soon, his father would take another shot at it. After the embarrassment of a failed attempt, he assured them, Linus Pauling was a strong bet to get it right the second time around.)

Within a month’s time, and with Rosalind Franklin having left his lab, Wilkins finally consented to providing Watson and Crick with all of the relevant data that he had requested. This proved to be the final piece that the duo needed in building their correct structural model of DNA.

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Pauling en route to Europe, 1953.

While all of this went on, Linus himself was seemingly unconcerned by any “race” for the structure of DNA. In fact, the only racing on his mind was a jaunt across Western Europe in a new sports car.

While Watson and Crick frantically worked to unravel the secrets of DNA before Linus Pauling beat them to it, Linus Pauling himself was debating the virtues of British, German, and Italian motor vehicles. Preparing for multiple trips overseas and in the market for some new wheels, Pauling’s plan was to select a car while in Europe during the Spring for the Solvay Conference, and then to actually pick it up in August, when he and Ava Helen would return to Europe for the International Congress of Pure and Applied Chemistry in Stockholm and Uppsala. The couple would then tour the continent in style before returning to the United States on a Scandinavian freighter and driving across the country from either New York or New Orleans to their California home.

While Peter advised his father that a Jaguar Mark VII was absolutely the best buy of the season, Linus expressed a preference for the slightly more modest convertible Sunbeam-Talbot. Peter countered with the possibility of an Austin A-40 Sports 4-Seater, and Linus finally agreed to have Peter look into purchasing the car on his behalf and scheduling a delivery of sorts. Seeing that his father was finally taking the bait, Peter attempted to spring a trap: “Might you be in need of a chauffeur, mechanic, linguist, travelling companion, navigator, break repairer, tire changer, witty conversationalist etc. on your trip next summer?” he wondered. “I know just the fellow. Good friend of mine.”

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A segment of the original Watson and Crick DNA model. 1953.

As the end of March rolled around and the Solvay Conference approached, Linus Pauling alerted his son to the fact that he had not made hotel reservations or, really, any plans for his visit to Cambridge. This responsibility he delegated wholly to Peter, who was somewhat distracted at the time, writing to his father about the blue sky and sun that had finally begun to break up the English winter gloom, and announcing with pride that he had gone to two balls in one week, getting along quite well with the Scandinavian girls. “As a sensible young American, I stand out in this town of pansy Englishmen,” he declared with impunity.

When Linus finally arrived at Cambridge in April, however, he found his son’s sensibilities to be somewhat lacking. Peter had in fact not made the requested hotel reservations, and while campus accommodations were fine for the son, they were not so wonderful for the elder Pauling. Watson later joked that, “the presence of foreign girls at breakfast did not compensate for the lack of hot water in his room.”

When the moment of truth finally came, Peter and his father strode into the Cavendish offices to see the model that Watson and Crick had constructed. Upon inspection, Linus reiterated the interpretation that he had given to his son earlier: the structure was certainly possible, but to be certain, Pauling would first need to see the quantitative measurements that Wilkins had provided. By way of response, Watson and Crick produced “Photo 51,” Rosalind Franklin’s now-famous image that enabled crucial measurements concerning the structure of the B-form of DNA.

Presented with this evidence, Linus Pauling quickly conceded that Watson and Crick had solved the problem. Later that night, the Paulings, together with Watson, had dinner with the Cricks at their home at Portugal Place to celebrate. To quote Watson, each “drank their share of burgundy.”

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So was it a race? And if so, what was Peter Pauling’s role? Was he a double agent or an informant? Or merely an unwitting accomplice, ignorant of the full implications of his actions?

In trying to answer these questions, it is important to emphasize that, for Peter, the “race for DNA” had never been a race at all. His father, he believed, was only interested in the nucleic acids as an interesting chemical compound. Linus Pauling clearly didn’t attack the structure with the same tenacity as Watson, in particular, who regarded the genetic material as the holy grail of biology, the secret of life. As Peter would write two decades later in New Scientist 

The only person who could conceivably have been racing was Jim Watson. Maurice Wilkins has never raced anyone anywhere. Francis Crick likes to pitch his brains against difficult problems… For Jim, however…the gene was the only thing in life worth bothering about and the structure of DNA was the only real problem worth solving.

In 1966, Jim Watson, then in the process of writing his book on the discovery of DNA, The Double Helix, sent Peter Pauling an early draft. His concern, he explained, was that he accurately portray Peter’s role in the entire affair; that, and he didn’t want Peter to sue him for defamation.

Peter laughed and told his old office mate that he thought it was a very good book; certainly very exciting. However, he pointed out that Watson should ask Linus Pauling for an agreement not to sue him, too. After all, Peter said, “He has more experience than I do.”

Peter Pauling: The Race that Wasn’t, 1952

Peter Pauling with his parents, ca. 1950s.

[The life story of Peter Pauling. Part 3 of 9]

“This tub moves steadily but slowly along.” So wrote Peter Pauling in a letter to his mother, Ava Helen Pauling, riding somewhere in the Atlantic in the hull of a cargo ship that had been built in 1926. “It took us two and a half days to reach the open sea.”

Having said goodbye to the nightlife of Montreal, and having entrusted his brother Crellin with the needle to his old turntable, Peter took to the sea without much to his name save a bottle of duty free Canadian Rye Whiskey; which, he lamented, did not keep him as warm onboard the cold ship as a good overcoat might have done. (Ava Helen, ever concerned for her son’s well-being, would see to it that he would have money to pick up some warmer clothes once he had arrived in Cambridge, paid for in matured war bonds.) Onboard the ship, Peter shared his cramped cabin space with three roommates: a Scot, a “very pleasant and hard-working” Englishman, and an 18 year old “pipsqueak” just out of rugby. Ever the charismatic socialite, Peter must have been excited to spend his days at sea with such an assortment of characters.

Arriving in England in the fall of 1952, Peter began his studies at Cambridge University, working under John Kendrew, a Peterhouse Fellow in Max Perutz’ Molecular Biology Unit at the Cavendish laboratory for physics. Although the Cavendish traditionally had not extended its focus beyond physics and physical chemistry to questions of biology, Sir Lawrence Bragg – director of the Cavendish and chair of the university’s Physics department – had recently supported an expansion of the lab’s scope to include the mapping of biological molecular structures.

This new Molecular Biology Unit would spearhead several important discoveries, among them Kendrew’s and Perutz’ work on the atomic structure of proteins, the program of research that Peter was brought on to support and an accomplishment significant enough to garner the 1962 Nobel Prize in Chemistry. That same year, two other former Cavendish researchers – James Watson and Francis Crick – would receive their shared Nobel Prize in Physiology or Medicine for their discovery of the double helical structure of DNA, a breakthrough that Peter Pauling certainly observed from a front row seat, and even, perhaps, helped to make possible.

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Francis Crick and James Watson, walking along the the Backs, Cambridge, England. 1953. (Image Credit: The James D. Watson Collection, Cold Springs Harbor Laboratory Archives.)

When Peter Pauling first moved into the office that he shared with James Watson, Francis Crick, and Jerry Donahue, Watson noted that Peter was “more interested in the structure of Nina, Perutz’s Danish au pair girl, than in the structure of myoglobin.” Crick, too, felt that the young Pauling was “slightly wild,” but still the office mates hit it off immediately. According to Watson, Peter’s presence meant that, “whenever more science was pointless, the conversation could dwell on the comparative virtues of girls from England, the Continent, and California.” Watson and the young Pauling even made a point of visiting The Rex art house cinema together to watch the 1933 romantic film Ecstasy, which Watson referred to affectionately as, “Hedy Lemarr’s romps in the nude.”

Women aside, Peter was most concerned by the day-to-day troubles that were typical of English life in the early 1950s. He wrote to his mother about the lack of a bathtub in the small, cold, damp room that he now inhabited, and complained about the space’s perpetual lack of sunlight. He did praise his fortune at having scoured London and finding a suitable teapot, and he requested that Ava Helen kindly make him a pair of curtains for his window (which she happily obliged).

In letters to his father, Peter preferred to talk about cars, or his recent dinners with the Braggs and their daughter Margaret, rather than his own research pursuits. Linus, on the other hand, was immediately curious about the intellectual climate at the Cavendish and was especially interested in the work of Francis Crick, who a year earlier had been part of a collaborative effort to develop a theory of mathematical representation for x-ray diffraction that was fast becoming a standard in the field.

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Linus Pauling and Robert Corey examining models of protein structure molecules. approx. 1951. (Image credit: The Archives, California Institute of Technology)

The previous year, 1951, Linus Pauling had bested Bragg and the physical chemists at Cambridge in becoming the first to publish the alpha helical structure of many proteins. Despite the desire prevailing at the Cavendish to eventually beat Linus Pauling at his own game, Watson and Crick had been warned to keep away from the study of DNA by the head of the lab. Bragg knew that Maurice Wilkins and Rosalind Franklin, of King’s College London, were already working on the problem using Franklin’s photos and crystallographic calculations of the A and B forms (low and high hydration levels, respectively) of DNA.

Wilkins’ and Franklin’s work was proceeding slowly, however, and Peter Pauling and Jerry Donahue – another Caltech graduate now stationed overseas as a post-doc – were both in regular communication with Linus Pauling. These contacts provided Watson and Crick with insight into what was going on in Pasadena. In his correspondence, Peter joked about the mounting competition between Caltech and the researchers at the Cavendish and King’s College. “I was told a story today,” he said to his father. “You know how children are threatened ‘You had better be good or the bad ogre will come get you?’ Well, for more than a year, Francis and others have been saying to the nucleic acid people at King’s, ‘You had better work hard or Pauling will get interested in nucleic acids.'”

While Watson and Crick urged Wilkins to provide them with Franklin’s images and calculations so that they might model the structure themselves, Peter stoked the fires of their urgency, assuring them that his father was no doubt only moments away from solving the problem. Donahue was equally convinced: for him, Linus Pauling was the only scientist likely to produce the right structure.

By December, the fate that Jerry Donahue and Peter Pauling had been predicting seemed to come true: a letter from Linus to his son claimed that he had indeed determined the structure of DNA. The letter gave no details, simply confirming for Watson and Crick that Pauling and his Caltech partner Robert Corey had somehow solved the problem. Watson later recounted his colleague’s distress in hearing this news, recalling that Crick “began pacing up and down the room thinking aloud, hoping that in a great intellectual fervor he could reconstruct what Linus might have done.” But it seemed to be too late. Pauling’s DNA paper was set to appear in the February 1953 issue of Proceedings of the National Academy of Sciences. In all likelihood, it would be time to move on to new projects.

Alexander Rich, 1924-2015

Alexander Rich. Photo by Donna Coveney.

Today we remember Dr. Alexander Rich, a student and colleague of Linus Pauling who passed away in April at the age of 90. Rich and Pauling were among the group of scientists who embarked on one of the most exciting scientific quests of the 20th century – the so-called “race for DNA.” Rich’s friends and colleagues also remember him for his endless desire to know more about the processes propelling life, a trait that is evident in his career as a biochemist. According to Pauling, this holistic interest in and understanding of science allowed Rich to make invaluable contributions to multiple disciplines.

Nucleic acids – the carriers of genetic information within a cell’s nucleus – were first identified in 1868 when Friedrich Miescher isolated the DNA compound for the first time. For some eighty-five years, however, the structure of DNA remained undescribed. In the 1940s and 1950s, scientists around the world began to focus more on the problem, working to build an accurate model of the DNA molecule in hopes of fully understanding its role in the process of gene expression.

In 1953, using Rosalind Franklin’s experimental data, James Watson and Francis Crick published their proposal of a double helical structure for the DNA molecule, and quickly became scientific celebrities once their model was deemed correct. Like Rosalind Franklin and, indeed, Linus Pauling, Alexander Rich was among the many researchers whose work and contributions to the understanding of proteins and nucleic acids abetted Watson and Crick’s discovery of the DNA molecule’s structure.

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Born in Hartford, Connecticut in 1924, Alexander Rich served in the U.S. Navy during World War II, then went on to Harvard University, where he received a bachelor’s degree in biochemical sciences in 1947 and graduated from Harvard Medical School in 1949. Soon after receiving his medical degree, he moved to Pasadena, where he worked as a research fellow in Linus Pauling’s lab at the California Institute of Technology, and where he lived with future Nobel laureate Martin Karplus, a fellow student of Pauling’s.

Blessed with a nimble mind, Rich was able to jump back and forth between chemistry and biology as his research interests progressed, all the while paying close attention to the broader implications of his research for the field of medicine. Rich became particularly well-known for his work on the structure and chemistry of fiber compounds, research which quickly became useful to the study of nucleic acids. By isolating strands of nucleic acids within fibrous compounds, Rich was able to produce images of their structure.

Though his pictures were not as clear or impactful as those captured by Rosalind Franklin, many have since posited that his work could have been of equal significance to Franklin’s had Caltech housed more fine-focus x-ray equipment.  Regardless, Rich was held in high esteem by Watson and Crick who, before publishing their DNA structure, asked that Rich review their work and corroborate their ideas.

Collagen model built by Alexander Rich and Francis Crick. September 1955.

In the wake of Watson and Crick’s triumph, the structure of nucleic acids continued to intrigue Rich. This time around however, it was RNA that caught his attention. Like DNA, RNA carries genetic material and is vital to the formation of proteins. It is thus necessary to understand the structure and function of RNA to fully comprehend DNA’s role in protein formation.

Rich began research in this area during James Watson’s brief stay at Caltech, and some now speculate that Rich’s interest in RNA images led Watson to focus entirely on RNA. While in Pasadena, Rich and Watson collected different images of RNA in an attempt to understand its physical structure, but the x-ray crystallographic photographs available at the time were not sufficient enough to discern a conclusive model.

Rich’s stint at Caltech came to an end in 1954 and he subsequently moved into his own laboratory at the National Institute of Mental Health (NIMH). While there he continued to delve into questions regarding the structure and composition of RNA. At the NIMH Rich was, at long last, successful in creating an image of RNA that provided hints about its structure. Rich concluded that RNA consists of a single-stranded nucleic acid that binds with complementary strands of RNA to form a temporary double helix – a process he described as molecular hybridization. Many were skeptical that a single-stranded nucleic acid could temporarily form a double helix, but Rich was able to show that this is made possible by the shedding of water molecules that comes about when the two strands bind.

Not only did this finding contribute enormously to the understanding of RNA’s structure and function, but Rich’s contributions to the understanding of molecular hybridization in nucleic acids has opened up many more possibilities. For example, polymerase chain reaction, a process used to identify genes, is based on the principle of hybridization. Today, methods of this sort are fundamental to all sorts of work in biotechnology and to the analysis of DNA.

Alexander Rich with Linus Pauling, among others, at a scientific meeting in the Soviet Union. Image Source: Alexander Rich Collection.

Following his tenure at the NIMH, Rich became a professor of Biophysics at the Massachusetts Institute of Technology, beginning in 1958 and lasting until his death. His investigations there included the discovery of Z-DNA, which is a type of DNA molecule that takes a zigzag form and follows a left-handed wind rather than the more common right-handed wind. His work at MIT also showed that protein synthesis occurs in a polysome – the name given to a cluster of Ribosomes that work together.

Alexander Rich received high honors for his contributions, including election to the National Academy of Sciences and receipt of the 1995 National Medal of Science – the highest scientific honor bestowed by the U.S. government.  It is no wonder then that Linus Pauling recalled his former pupil with great pride. “Of the several men with MD degrees who have worked with me,” he once noted, “I think that Dr. Rich may well be the one with the broadest grasp of science as a whole.”

Pauling and Perutz in the Golden Age of Protein Research

Max Perutz, 1987. Image Credit: Graham Wood.

[Part 3 of our series celebrating the Perutz centenary.]

In 1939 Max Perutz’s girlfriend gave him a book token for Christmas. Working on finishing his dissertation on the structure of hemoglobin, Perutz used that token to purchase Linus Pauling’s recently published text, The Nature of the Chemical Bond.

In the obituary of Pauling that he wrote some fifty-five years later, Perutz described how the “book transformed the chemical flatland of my earlier textbooks into a world of three-dimensional structures” and “fortified my belief, already inspired by J. D. Bernal, that knowledge of three-dimensional structure is all-important and that the functions of living cells will never be understood without knowing the structures of the large molecules composing them.”  The purchase of Pauling’s book marked the beginning of a long, fruitful and sometimes contentious correspondence between the two men, working on separate continents but united by similar interests.

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Not until 1946 did Perutz first write to Pauling, asking for assistance as he labored through his research on the structure of hemoglobin. The Cavendish Laboratory, where Perutz was located, did not have the latest equipment that was available to Pauling at Caltech. In particular, Perutz needed a Hollerith punch-card machine to carry out calculations of the three-dimensional Patterson-Fourier synthesis. Perutz knew that Pauling’s lab was already conducting calculations of this sort and that the work Perutz was doing “would have to be done sooner or later, if the molecular structure of the proteins is to be worked out.”

As such, Perutz hoped that someone in Pauling’s lab might do the calculations for him. Pauling was not moved enough by Perutz’s request to offer the labor of his own team, replying that enlisting someone do such work in a “routine way” could lead to confusion. Pauling did offer that Perutz come to Pasadena, or send a surrogate to do the work, if he could find the money. Perutz was unable to support such an undertaking and so ended that conversation.

Linus Pauling and Lord Alexander R. Todd. Cambridge, England. 1948.

Two years later, in 1948, Pauling was in England, enjoying a stint as George Eastman Professor at Oxford. It was during this time that he and Perutz met for the first time in person. Perutz described his first experiences of Pauling’s lectures, in which

he would reel off the top of his head atomic radii, interatomic distances and bond energies with the gusto of an organist playing a Bach fugue; afterwards he would look around for applause, as I had seen Bertrand Russell do after quoting one of his eloquent metaphors.

The two also found time to talk together about their own particular research projects.

Pauling’s work at Oxford touched directly on Perutz’s own program, in what would become a oft-noted story in twentieth century history of science. As Pauling lay in bed with a cold, he did not stop working, choosing to spend his time making planar peptide models with paper chains. From his paper folding exercises, Pauling, according to Perutz’s obituary, “found a satisfactory structure by folding them into a helix with 3.6 residues per turn.” (A story that Pauling relayed many times himself.) The structure would come to be known as the alpha helix.

After Pauling recovered from his illness, Perutz showed him his own model of a polypeptide chain which was part of his larger hemoglobin model and was similar to fibers described by William Astbury. To Perutz’s “disappointment, Pauling made no comment,” and gave no hint as to his own breakthrough, which he announced the next year in a “dramatic lecture.”  That later unveiling of the alpha helix gave rise to a famous Perutz anecdote, which later informed the title of a book of essays that Perutz published.

When I saw the alpha-helix and saw what a beautiful, elegant structure it was, I was thunderstruck and was furious with myself for not having built this, but on the other hand, I wondered, was it really right?

So I cycled home for lunch and was so preoccupied with the turmoil in my mind that I didn’t respond to anything. Then I had an idea, so I cycled back to the lab. I realized that I had a horse hair in a drawer. I set it up on the X-ray camera and gave it a two hour exposure, then took the film to the dark room with my heart in my mouth, wondering what it showed, and when I developed it, there was the 1.5 angstrom reflection which I had predicted and which excluded all structures other than the alpha-helix.

So on Monday morning I stormed into my professor’s office, into [William Lawrence] Bragg’s office and showed him this, and Bragg said, ‘Whatever made you think of that?’ And I said, ‘Because I was so furious with myself for having missed that beautiful structure.’ To which Bragg replied coldly, ‘I wish I had made you angry earlier.’

 

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Once Pauling returned to Pasadena, he and Perutz fell into a minor quarrel. In December 1950, Perutz had heard that Pauling had been “annoyed” by Perutz and John Murdoch Mitchison’s paper, “State of Hæmoglobin in Sickle-Cell Anæmia,” which had been published in Nature that October. Pauling was upset that Perutz and Mitchison had suggested that crystallization caused cells to sickle without properly citing his own seminal work on the subject.

In a December letter, Perutz said he was “very disappointed” that Pauling was upset with the publication, not only because there was a reference to Pauling, et al. in its introductory paragraph, but “particularly because all the new experimental evidence we report seemed to fit in so beautifully with the basic ideas set out in” Pauling’s co-authored Science article, “Sickle Cell Anemia, a Molecular Disease,” published in November 1949. Perutz explained his position in more detail, noting,

There is perhaps a slight difference between our points of view. Whereas you regard the sickling as being due to an aggregation and partial alignment of hæmoglobin molecules by a lock and key mechanism, an interlocking of specific groups in neighbouring molecules, we regard the cause of the sickling as being simply a crystallization, due to abnormally low solubility of the reduced hæmoglobin. No specific interaction of the kind you mention need be involved in the second process, though it obviously may be…I am sorry that this misunderstanding between us should have arisen, particularly as I have spent much effort trying to convert unbelievers to your scheme.

Pauling waited until the following February to respond and explained his feeling that readers of Perutz’s article might conclude that Perutz was making an original proposal. Having made this statement, Pauling, in his own way, moved beyond the quarrel by telling Perutz about his more recent work showing that “hemoglobin is not crystallized in the sickle cells, but is only converted to the nematic [or liquid crystal] state.” The ice broken, Perutz quickly responded by inviting Pauling to take part in informal discussions about protein structure at the Cavendish Laboratory before an annual conference, to be held in Stockholm. Pauling, however, could not attend.

The next year, Pauling attempted to visit England, this time to speak at a conference about the alpha helix, but was delayed due to his passport renewal being denied on account of his political activities. Perutz wrote that Pauling’s “absence had a sadly damping effect on our meeting at the Royal Society, and it made the discussion rather one sided as there was no none to answer the various objections to the α-helix raised by the Astburites and Courtlauld people” since Pauling’s supporters were unprepared to defend Pauling’s position without him. Perutz was also keen to show Pauling his own progress, an eagerness that Pauling reciprocated. By July Pauling had cleared up his passport problems and was able to spend time in person discussing his and Perutz’s work.

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By 1953 Perutz and Pauling were quarrelling again over proper citation, though this time it was Perutz suggesting that Pauling had not given Francis Crick enough credit regarding the coiling of alpha helixes. Pauling explained to Perutz that, while he was at Cambridge the previous summer, he had talked with Crick and John Kendrew at length. During that conversation, according to Pauling,

There was only brief discussion of α keratin at this time, and, if my memory is correct, only a few sentences were said about the coiled coil, as Crick calls it. We discussed the fact that the 5.15-Å meridional reflection offers some difficulties of explanations, and that also there seemed to be a discrepancy in the density of α keratin. The discussion was very brief. Then Mr. Crick asked me if I had ever thought of the possibility that the α helixes were twisted about one another. I answered that I had. So far as I can remember, nothing more was said on this point.

Pauling went on to emphasize that “the idea was not a new one to me then” and that his own description of it in Nature was different from Crick’s understanding. Perutz ceded this point, adding that Pauling’s differences with Crick “stimulated Crick to clarify his own” ideas on the coiling of alpha helixes. More generally, Perutz found that the competition that arose between the two labs as they worked on similar problems helped to push each forward, thus leading to positive advances.

The famous group photo of the Pasadena Conference on the Structure of Proteins, September 1953. Pauling stands front row, third from left. Perutz stands two rows behind Pauling. [Image credit: The Archives, California Institute of Technology]

That September, Perutz made his first visit to California in order to deliver a paper at the Pasadena Conference on the Structure of Proteins, at which were gathered all of the world’s major figures in the field, including Jim Watson and Francis Crick, newly famous for their double helical structure of DNA. Perutz told his wife, Gisela, that his paper was “well received.” Additionally, with all of the different perspectives presented, there was “an atmosphere of soberness, and a realization that no-one’s solution of the protein problem was complete, and every approach was still fraught with complications.” Perutz was also quite taken with the Paulings’ home and their hospitality, pointing out that Ava Helen had invited him “after one of the meetings for a swim in their garden.”

Correspondence between Perutz and Pauling dipped a bit after the conference, though Pauling did take a moment to congratulate Perutz on being elected to the Royal Society the following Spring. While the exchange was brief, it reflected the long relationship built up between the two over the preceding years and, in particular, a confluence of work that had boosted the esteem of both scientists.

Perutz had begun looking at the structure of wool proteins back in 1951, thinking that there might be similarities to hemoglobin. He became excited after finding Pauling’s work on alpha helixes in fibers, thinking that the structure might be present in wool as well. His initial studies resulted in disappointment, but after adjusting the angle at which he was taking his x-rays by 30 degrees, he compiled new data that confirmed Pauling’s alpha helix structure. After applying it to his own work on hemoglobin, Perutz told Pauling “the discovery of this reflexion in haemoglobin has been the most thrilling discovery of my life…there is no doubt that it is a universal feature at least of all fibers of the α type. Whether all crystalline proteins show it remains to be seen.” Not suprisingly, Pauling was also “very pleased” with this discovery.

This research opened the door for Perutz to be considered by the Royal Society. But it was his development of a technique for determining a three-dimensional view of structures derived from x-ray crystallography that assured his election. He did this be attaching mercury atoms to hemoglobin, which allowed him to figure out where the crest and trough of a given x-ray was in relation to the structure that appeared on the photos. Perutz later said that after he finished the work and published it in Nature at the end of 1959, he went skiing in the Alps, and by the time he returned he was famous, assuring his fellowship in the Royal Society.

Perutz’s Hemoglobin Breakthroughs and Later Work

Perutz with his hemoglobin molecule, 1959. Image credit: Life Sciences Foundation.

[Part II of our survey of the life of Max Perutz, this time focusing on the years 1941-2002. Published in commemoration of the Perutz centenary, May 2014.]

Knowing that his parents were safe from Nazi persecution and able to return to the United States, circumstances began improving for Max Perutz. The Rockefeller Foundation reactivated his grant, allowing him to support himself while stateside as well as his parents in Cambridge, England. Perutz’s father was also able to find work as a laser operator during the war and afterwards qualified for a pension.

In September 1941, Perutz met Gisela Peiser, who was an accountant at the Society for the Protection of Science and Learning, an organization that assisted Jewish and other academic refugees fleeing from the Nazis. After a quick courtship, they were married the following March and, in December 1944, welcomed their daughter Vivien into the world. That same year, Perutz also found himself back in good stead with the British government and recruited to research ice strength for potential ice stations in the North Atlantic. The research did not work out, so Perutz returned to his work on hemoglobin at Cambridge. The next few years were spent trying to put together a secure source of income for him and his growing family. In the interim, he took out more loans and found a temporary fellowship.

Meanwhile, Perutz’s health continued to suffer. As his chronic gastrointestinal attacks became more unbearable, interfering with his daily activities more and more, Perutz began to seek out help. Most doctors he saw told him it was a psychological problem, but eventually one doctor recognized that the symptoms could be treated by a mixture of atropine and codeine. The remedy helped enough for Perutz to live more or less undisturbed by the problem for several years, though eventually that would change.

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Perutz and John Kendrew, 1962. Image credit: Nobel Foundation.

In 1947, the war now completed, Perutz, along with John Kendrew, was appointed to head the new Research Unit for the Study of the Molecular Structure of Biological Systems (Perutz later shortened the unit’s name to Molecular Biology Research) at the recently established Medical Research Council. Situated at the Cavendish Laboratory in the physics department, the group expanded on Perutz’s earlier application of x-ray crystallography to biological materials. Perutz, in this new administrative role, described his lab management as one where he would “leave people free to do what they wanted…if they were good scientists.”

One of the several student researchers that came through the lab was Francis Crick, who started work in 1949. Perutz had Crick look at the validity of his hemoglobin model, which was the culmination of roughly six years of research. Crick applied his mathematical training to show that the model was “nonsense.” Perutz accepted Crick’s assessment and later reflected that only in England at that time could a student be so critical of their principal investigator. Crick was eventually drawn away from hemoglobin research by James Watson, who came to the lab in 1951 to work under Kendrew on molecular structure, but his impact on the development of Perutz’s hemoglobin structure was long-lived.

Throughout the late 1940s, Perutz also continued his work on glaciers in the Alps and helped found the Glacier Physics Committee in 1947. Though he had trouble recruiting able assistants who could also ski (the first two broke their legs), the work gave Perutz and his family the opportunity to spend summers in the mountains. Perutz’s research led him to conclude that glaciers flowed faster at the surface than at the bottom.

Perutz’s digestive attacks began increasing in intensity in the early 1950s to the point where, in 1954, he was hospitalized for ten days. While there, doctors looked for possible causes but came up empty and could only prescribe bismuth, with little effect. What did help, for reasons Perutz did not understand, was visiting the Alps, and so he arranged for a trip after being released from the hospital. Unfortunately the attacks resumed as soon as he returned to Cambridge, pushing Perutz to his limits – he considered resignation and even contemplated suicide. In desperate straits, he arranged for another trip to the Alps that spring but, once there, continued to get worse and, as an added complication, came down with scurvy.

When he returned, Perutz sought out other doctors who might be able to help, eventually visiting Werner Jacobson, who was also at Cambridge. Jacobson thought Perutz’s symptoms sounded like those of Celiac disease. He suggested that his patient stop eating wheat, or more specifically gluten, which immediately improved Perutz’s condition. Whenever the symptoms appeared again, as they did in the early 1960s, Perutz could trace them back to gluten; he eventually stopped eating any form of bread, since even gluten-free flour contained small amounts of gluten that negatively affected his health.

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Perutz in lecture. Image credit: Nature.

Perutz’s improved physical condition coincided with the final years of his triumphant work on a determination of the structure of hemoglobin. After working out a solution to interpret x-ray diffraction photos of proteins three-dimensionally, Perutz came upon the structure in September 1959, submitting his findings to Nature before heading to the Alps to ski over the winter break. By the time he returned, he was famous.  It was quickly and widely acknowledged that his work comprised a major breakthrough for both chemistry and biology.  As Hugh E. Huxley wrote, in 2002

He was the first person to find out how to determine protein structure by X-ray crystallography, after many years of patient struggle, and he applied the technique to solve the structure of haemoglobin, the oxygen-carrying protein in blood….The results showed that it was possible to see, in the atomic detail necessary to understand mechanisms, the structure of the macromolecules that carry out many of the functions of a living cell. Such knowledge is basic to the revolution that has swept through biology in the past 50 years, and to modern medicine and biotechnology.

By Fall 1962 there were rumors that Perutz would be awarded the Nobel Prize for chemistry. As October arrived, he began receiving calls from the press, but did not quite trust them. As the calls continued, Perutz received a telegram and thought, along with the rest of the lab, that it may be from the Nobel committee. Alas, the message was only from Nature asking how many reprints of his article Perutz wanted. That afternoon however, Perutz received another telegram, the one he had been waiting for. The lab celebrated with a champagne party as Perutz and Kendrew had been awarded the Nobel Prize for Chemistry, and Watson and Crick, along with Maurice Wilkins, would receive the Nobel Prize in Physiology and Medicine.

Perutz continued to work on the hemoglobin structure after his rise to fame, next turning to the question of how the structure changed with the uptake of oxygen. His Nobel lecture described this continued research on the four subunits within hemoglobin that changed their structure as oxygen was taken up; the first description of how proteins changed in structure.

In the years that followed, Perutz focused more on why this change occurred. Aided by automated x-ray diffraction machines and able assistants, Perutz’s lab was able to turn out more measurements than ever before. But the measurements, as Perutz later related, did not make any sense. After one of his research assistants completed his postdoc, Perutz looked closer at his results and realized that the new x-ray instruments had not been calibrated correctly.

In 1967, with all the bugs fixed, Perutz and his team put together the first atomic model of hemoglobin, but Perutz’s questions about why the structure changed still were not answered. By 1970, the lab was able to construct an oxygen-free model, allowing Perutz to compare it with the oxygenated model. As Perutz later described “there came this dramatic moment when between them, the models revealed the whole mechanism.” What he was able to see was how a slight movement of the iron atom triggered a change in the whole molecule. Thus, Perutz felt he was able to explain “all the physiological functions of hemoglobin on the basis of its structure.” The results were published in Nature.

Within the field, objections to Perutz’s explanation were numerous and he spent much of the next two decades refuting criticisms and refining his own explanation. At the same time, his celebrity also rose among scientists as he was increasingly invited to give lectures all over Europe and North America. By 1975 Perutz’s fame outside of scientific circles had grown such that Queen Elizabeth II invited him to visit with her at Buckingham Palace. Afterwards, Perutz expressed his regrets to the Queen’s secretary that “she had made me talk away like an excited little boy about my own doings and that I never asked her anything about hers.” Nonetheless, Perutz did hope that the Queen would enjoy his gift, the autobiography of Charlie Chaplin.

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Max Perutz with his hemoglobin model. Image credit: BBC.

By 1980 Perutz had begun to reach out to broader audiences more intentionally. Shortly after retiring from the chair of the Laboratory of Molecular Biology, Perutz wrote a memoir of his time there. This, in turn, inspired him to compile an account of his experiences during World War II and submit it to the New Yorker. Penned in 1980 but not published until 1985, “Enemy Alien” helped bring Perutz greater levels of fame, as he received more letters after its publication than he did congratulations for his Nobel Prize.

An Italian pharmaceutical company also approached Perutz in 1980 to give a lecture on the social implications of molecular biology. According to a 2001 interview, Perutz told the company that “molecular biology has no social implications,” but that he could talk about “science as a whole.” This spurred him to take more of an interest in broader scientific questions, ultimately leading him to adopt controversial stances combatting criticism of the Green Revolution, DDT use and nuclear power, among other issues in the headlines. It also evolved into an interest in philosophy – Karl Popper’s Open Society and its Enemies proved particularly impactful. By 1989, Perutz expanded his popular lectures into a book of essays, Is Science Necessary? which included writings that he had also done for the New York Review of Books as well as “Enemy Alien.”

While continuing to write for the New York Review of Books up to the end of his life, Perutz also pursued new research on proteins and hemoglobin, taking a particular interest in neurodegenerative diseases like Parkinson’s and Alzheimer’s. In 2001, right before he passed away, Perutz was still at the lab seven to eight hours a day (including lunch and tea), preparing a publication for the Proceedings of the National Academy of Sciences on the common structure of insoluble protein deposits in neurodegenerative diseases. He passed away at the age of 87, unable to reconcile his initial structure with x-ray diffraction photos which showed contradicting features that Perutz concluded arose from three different structures. The results were published in 2002, after Perutz had died, in two separate articles.

Caltech, Cambridge and Coiled-Coils

Coiled-coil illustration from Pauling and Corey’s Nature publication of January 10, 1953.

Within the overarching saga of the race for DNA between Linus Pauling’s Caltech lab and Sir William Lawrence Bragg‘s Cambridge lab, the Cavendish, there existed a small yet interesting story of controversy and intrigue: the case of the coiled-coils.

In August 1952, Linus Pauling visited England during the final leg of a larger European tour largely devoted to touting his important new discovery, the alpha helix. Lecturing about his proposed protein structure inevitably led to Pauling’s visiting all of the major centers for research in England that were focusing on proteins. One of these centers was the Department of Physics at Cambridge University – the Cavendish – directed by Bragg, a Nobel laureate and Pauling’s long-time scientific rival. While visiting the Cavendish, Pauling also met with a non-traditional graduate student with whom he had communicated only a few times, via letter. This student was Francis Crick, the British scientist who, together with his American colleague James Watson, would go on discover the double-helical structure of DNA the following year.

Francis Crick, 1955.

One afternoon during Pauling’s visit, Crick and Pauling shared a taxi cab as they traveled around the premises of Cambridge.  During this jaunt, the two discussed several topics of mutual interest, including Pauling’s alpha helix. Eventually this conversation turned to an examination as to why Pauling’s model of the alpha helix lacked the 5.1 angstrom repeating turn (all helices, by definition, twist) found in x-rays of keratin, a fibrous protein structure that makes up the outer layer of human skin. Pauling’s model predicted a turn every 5.4 angstroms. This mystery had remained a thorn in Pauling’s model since his publication of the alpha helix a year prior.

During their cab ride, Crick is reputed to have asked Pauling about the possibility that alpha helices are coiled around one another. Pauling, according to a letter recounting the event, replied that he had, and that this reply marked the end of the discussion of coiled-coils between the two scientists. Crick, however, claimed in a later letter that the conversation was longer and more detailed. Whether or not the conversation was brief or of greater length, this was the beginning of a controversy.

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His tour completed, Pauling returned to Caltech and renewed work on the angstrom reflection problem dogging the alpha helix. He and Robert Corey, the biochemist with whom Pauling and Herman Branson had collaborated to develop the alpha helix, soon found that if two to seven alpha helices were wound “like a piece of yarn around a finger, into a sort of coiled-coil” the resulting structure would match the 5.1 angstrom reflection found in x-rays of keratin. This addition to the alpha helix hypothesis built upon an undated idea of Pauling’s that was written down in a travel journal that he kept during the European tour. The notes describe a structure that Pauling named “AB6” – six alpha helices (B6) coiled around a seventh (A).

Pauling’s first notes on what would later be described as “coiled-coils.”

Meanwhile, back at Cambridge, Peter Pauling – one of Linus and Ava Helen’s three sons – was working at the Cavendish as a graduate student alongside Crick and Watson, having arrived the same summer as his father. Peter told Crick – who was also working on “coiled-coils” of the alpha helix – of his father’s research in Pasadena. This news undoubtedly felt to Crick like Linus Pauling had built upon the ideas that Crick brought up in their conversation.

In a rush to be published first, Crick hurriedly finished his research and dashed off a note to the journal Nature in October 1952, only to discover that Pauling’s own manuscript had arrived just a few days before. However, in a surprise twist, Crick’s manuscript was published first, likely due to two factors: 1. Crick’s paper was shorter, and 2. it was sent with a cover letter from Max Perutz, a supporter of Crick and part of Bragg’s Cavendish team, requesting high-speed publication.

The following month, Pauling wrote a letter to Jerry Donohue, a former Caltech doctoral student who had worked with Pauling since the 1940s and was, at the time, working at the Cavendish on a Guggenheim Fellowship. The communication was in reply to a letter that Donohue had written to Pauling reporting on Crick’s Nature submission.  In his reply Pauling explained that he remembered the conversation with Crick involving the alpha helix during the past summer. Cognizant of the controversy brewing over the provenance of the coiled-coil idea, Pauling specifically wrote that the conversation with Crick was brief.

A few months later, in March 1953, Pauling wrote a similar letter to Max Perutz, this one containing more detail on the matter. Pauling mentions in the letter that he had thought of Crick’s suggestion prior to their conversation, but had not fully fleshed it out; a claim perhaps supported by Pauling’s travel journal.

Pauling to Perutz, March 29, 1953.

Francis Crick was given a copy of Pauling’s letter to Perutz. In response, Crick recalled the taxi cab conversation as having been longer than Pauling remembered, and more in depth on the subject of the coiled-coils, thus leading him to the assumption that Pauling had built upon his ideas. This would have been fine, Crick wrote, had Pauling simply informed Crick so that the two scientists could publish simultaneously, giving credit where credit was due as well as bolstering each other’s work.

Crick to Pauling, April 14, 1953.

Crick did admit that Pauling’s paper was more detailed and thorough than was his own, and also came to different conclusions on key points. These factors were enough for both Caltech and the Cavendish to declare that Pauling and Crick had generated their ideas on coiled-coils independent of one other, if simultaneously.

Linus Pauling and the Structure of Proteins: A Documentary History

Today is Linus Pauling’s birthday – he would have been 112 years old.  Every year on February 28th we try to do something special and this time around we’re pleased to announce a project about which we’re all very excited: the sixth in our series of Pauling documentary history websites.

Launched today, Linus Pauling and the Structure of Proteins is the both latest in the documentary history series and our first since 2010’s The Scientific War Work of Linus C. Pauling. (we’ve been a little busy these past few years)  Like Pauling’s program of proteins research, the new website is sprawling and multi-faceted.  It features well over 200 letters and manuscripts, as well as the usual array of photographs, papers, audio and video that users of our sites have come to expect.  A total of more than 400 primary source materials illustrate and provide depth to the site’s 45-page Narrative, which was written by Pauling biographer Thomas Hager.

Warren Weaver, 1967.

That narrative tells a remarkable story that was central to many of the twentieth century’s great breakthroughs in molecular biology.  Readers will, for example, learn much of Pauling’s many interactions with Warren Weaver and the Rockefeller Foundation, the organization whose interest in the “science of life” helped prompt Pauling away from his early successes on the structure of crystals in favor of investigations into biological topics.

So too will users learn about Pauling’s sometimes caustic confrontations with Dorothy Wrinch, whose cyclol theory of protein structure was a source of intense objection for Pauling and his colleague, Carl Niemann.  Speaking of colleagues, the website also delves into the fruitful collaboration enjoyed between Pauling and his Caltech co-worker, Robert Corey.  The controversy surrounding Pauling’s interactions with another associate, Herman Branson, are also explored on the proteins website.

Linus Pauling shaking hands with Peter Lehman in front of two models of the alpha-helix. 1950s.

Much is known about Pauling’s famously lost “race for DNA,” contested with Jim Watson, Francis Crick and a handful of others in the UK.  Less storied is the long running competition between Pauling’s laboratory and an array of British proteins researchers, waged several years before Watson and Crick’s breakthrough.  That triumph, the double helix, was inspired by Pauling’s alpha helix, discovered one day when Linus lay sick in bed, bored and restless as he fought off a cold. (This was before the vitamin C days, of course.)

Illustration of the antibody-antigen framework, 1948.

Many more discoveries lie in waiting for those interested in the history of molecular biology: the invention of the ultracentrifuge by The Svedberg; Pauling’s long dalliance with a theory of antibodies; his hugely important concept of biological specificity; and the contested notion of coiled-coils, an episode that once again pit Pauling versus Francis Crick.

Linus Pauling and the Structure of Proteins constitutes a major addition to the Pauling canon. It is an enormously rich resource that will suit the needs of many types of researchers, students and educators. It is, in short, a fitting birthday present for history’s only recipient of two unshared Nobel Prizes.

Happy birthday, Dr. Pauling!

The Alpha Helix

Space-filling model of the alpha helix.

[The Paulings in England: Part 5 of 5]

It has been said that sometimes blessings come in disguise, and so it may be that we have the damp English spring to thank for the elucidation of the alpha-helix structure of alpha-keratin – a fundamental and ubiquitous secondary structure pattern found in many proteins.

Linus Pauling was plagued by sinusitis for much of his time in England, and for three days in March 1948 it had become severe enough to put him in bed (as he was fond of saying over the years, this was before his vitamin C days). After a day spent devouring mystery novels, Pauling asked Ava Helen if she would bring him some paper and his slide rule, at which point he started trying to figure out how polypeptide chains might fold up into a satisfactory protein structure.

Pauling’s canvas was just an ordinary 8 1/2 by 11 inch sheet of paper. His first step was to draw the correct bond angles and distances onto the sheet, as determined from previous x-ray crystallographic work on polypeptides. Next he folded the sheet along parallel lines into a sort of squared-off tube. Doing so allowed him to add in representations of hydrogen bonds, which the impromptu model suggested would form between amino acid residues and, as a result, hold the turns of the polypeptide together.

The model made sense and pretty quickly it was clear that Pauling had discovered something important.  As he later wrote, his folded creation “turned out to be the structure of hair and horn and fingernail, and also present in myoglobin and hemoglobin and other globular proteins, a structure called the alpha-helix .”

Reconstruction of the alpha-helix paper model. Drawn and folded by Linus Pauling, 1982.

Pauling kept this idea to himself until his return to the United States because something didn’t match up quite right with the current laboratory data. Specifically, the turns of Pauling’s helix didn’t mirror the 5.1 angstrom repeat found in all of William T. Astbury‘s x-ray patterns. Pauling’s structure came close, but made a turn every 5.4 angstroms, or every 3.7 amino acid residues.

After his return home, with the assistance of colleagues Robert Corey and Herman Branson, Pauling continued refining his alpha helix structure and developing others, including the beta sheet. Simultaneously, the Caltech group’s chief British rivals at the Cavendish Laboratory published a paper titled “Polypeptide Chain Configurations in Crystalline Proteins.” The paper promised more than it delivered though, and while it listed many possible structures, Pauling found none of them to be likely. The competition was still on.

Pauling was finally convinced to publish when he received word that a British chemical firm called Courtaulds had created a synthetic polypeptide chain that showed no sign of Astbury’s 5.1 angstrom reflection in x-ray diffraction images. This was enough evidence for Pauling to decide that the 5.1 angstrom repeat was, perhaps, not a vital component of all polypeptide chains.  And so it was that in April 1951 Pauling, Corey and Branson published “The structure of proteins: Two hydrogen-bonded helical configurations of the polypeptide chain,” in the Proceedings of the National Academy of Sciences.

After devouring the Pauling group’s results shortly after their publication, Max Perutz headed to the Cavendish lab at Cambridge to check the data himself. Having confirmed the structure in images of horsehair, porcupine quill, synthetic polypeptides, hemoglobin and, for good measure, some old protein films that had been tucked away, Perutz wrote to Pauling, “The fulfillment of this prediction and, finally, the discovery of this reflection in hemoglobin has been the most thrilling discovery of my life.” He then published an analysis of his own data, concluding, “The spacing at which this reflexion appears excludes all models except the 3.7 residue helix of Pauling, Corey and Branson, with which it is in complete accord.”

Video Link: Pauling Recounts His Discovery of the Alpha Helix

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It wasn’t until a year later that the mystery of Astbury’s 5.1 angstrom reflection was finally solved. In 1952, on a visit to the Cavendish, Pauling met Francis Crick, the then-graduate student who would go on to play a huge part in the discovery of the structure of DNA. The two maintained similar interests and during a taxi ride around Cambridge found themselves discussing the matter of the alpha helix. “Have you thought about the possibility,” Crick asked Pauling, “that alpha helixes are coiled around one another?” Whether Pauling had or had not considered this possibility remains a point of contention, but Pauling remembered replying that he had, because he had been considering a number of higher-level schemes for his helixes, including some which wound around each other.

Regardless, Pauling returned to Caltech and both he and Crick set to work on the problem. With help from Corey, Pauling discovered a means by which the alpha helixes could wrap around each other in a coiled-coil to produce the problematic 5.1 angstrom found in Astbury’s pictures of natural keratin.  Crick, in the meantime, was conducting a very similar study.  Pauling and Crick, independent of one another, ultimately submitted the solution to this puzzle for publication within days of each other, and at first there was a bit of grumbling as to whom the credit should be awarded. Though Crick’s note was published first, the Cavendish camp eventually conceded that Pauling’s paper included considerably more detail of consequence, and it was finally settled that both scientists had independently come to the same general conclusion.

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Pauling receiving his honorary degree from the University of Paris, 1948.

After Pauling’s two fruitful terms as Eastman Professor at Oxford were up in July, the family split their remaining time between travels in Amsterdam, Switzerland and Paris. Pauling rounded off the trip by receiving yet another honorary degree from the University of Paris, and on August 25, 1948, the Paulings set sail once more on the Queen Mary.

His eight months in Europe had been productive and enlightening, but Pauling was ready to return to Pasadena where he could share the myriad ideas he had generated and gathered during his time away from Caltech. As we have seen, he was especially eager to get back to work on proteins, writing shortly before his departure that “I have continued to work on my theory of metals, and have been doing nothing about proteins. However, I am looking forward to being back home, and to thinking about that subject again.”

The Triple Helix

“We have seen Paulings paper on Nucleic Acid. Have you? It contains several very bad mistakes. In addition, we suspect he has chosen the wrong type of model.”

-James Watson, letter to Max Delbrück, February 20, 1953.

We were very interested to see that a model of the Pauling-Corey “triple helix” structure of DNA has been built by Farooq Hussain.  As Hussain notes on his website, the model was constructed based on drawings published by Linus Pauling and Robert Corey in their paper detailing the incorrect structure.

The proposed triple helix structure of DNA. Model by Farooq Hussain.

Hussain’s representation of the triple helix is striking; especially so when compared with Watson and Crick’s far more elegant and intuitive double helix, surely the most famous molecule in history.

Double helix model, courtesy of P. Shing Ho.

Indeed, Watson was well within his right to feel confident in his February letter to Delbrück.  As he noted before closing, “Today I am very optimistic since I believe I have a very pretty model, which is so pretty I am surprised no one has thought of it before.”

For more on the triple helix, see our write-up on the subject, published in April 2009.