Linus Pauling and the Structure of Proteins: A Documentary History Narrative  
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Herman Branson
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In the past few years there has been some controversy concerning the role of Herman Branson in what happened during this phase of Pauling's protein work. It is worth reviewing his contributions in as much detail as possible given the fact that there is paucity of primary material – lab notes, memos, and so forth – covering Branson's visit to Pauling's lab in 1948-49.

What is known is this: Branson, a professor of physics and chair of the physics department at Howard University, arrived in 1948 and spent roughly a year in Pasadena working with Pauling's group. During that time he was asked by Pauling to determine all helical structures for protein chains that satisfied certain restrictions and requirements. Among these it is likely that Pauling insisted that all peptide bonds be planar (a condition that Pauling had first considered likely theoretically, based on his understanding of resonance structures, and then demonstrated experimentally, through Corey's work on small peptides); that bond lengths and angles conform to the precise figures Corey had obtained for amino acids and peptides; and that structures allow for as many hydrogen bonds as possible between turns of the helix, in order to stabilize the structure. In addition, Pauling wanted to tie Branson's work to the available x-ray data; for this purpose the visiting professor was assisted in his calculations by Sidney Weinbaum, Pauling's long-time assistant and a "human calculator" when it came to analyzing x-ray patterns. Finally, it is likely (although documentation has not been found) that Pauling advised Branson not to be hampered by the idea that there had to be an integral number of amino acids per turn. Pauling had long known that nature, at least at the level of molecules, did not always fit itself into neat, whole numbers; that concept might have permeated his laboratory (as the lure of integral repeats permeated the Cavendish) without him having to stress it.

These guidelines separated Pauling's approach from the British work being done at the same time. Without them, the British had come up with many models and little of value. Using them, however, Branson narrowed the field, presenting Pauling with only two candidates, one a more loosely wound structure (called the gamma helix) with 5.1 amino acids per turn, and a tighter helix, alpha, which had 3.7 amino acids per turn. The maddening fact remained that neither one matched the experimental evidence from Astbury's x-ray studies. Astbury had found a 510 picometer repeat in his keratin fibers; Branson's and Corey's models came in at 540 picometers – a significant difference in structures as precisely modeled as these.

Branson wrote up his results late in 1949, turned them in to Pauling, and returned to Howard University and other work. Pauling held on to the results, hesitating to publish because of the 510-540 discrepancy, and rechecking the data. Then he saw Bragg's group groping toward the goal and made the fateful decision to push ahead and publish what he had.

Branson, for his part, gave proteins little thought until he received a note from Pauling in late 1950 along with a draft copy of a paper on the alpha and gamma helixes. "Dr. Weinbaum did a great amount of work, based on your original notes, and I think that a discussion of the configurations of the spirals is in good shape," Pauling wrote, asking for Branson's suggestions on the manuscript before he sent it in for publication Branson was listed as third author, after Pauling and Corey.

There is no record of a reply. Branson went on to a significant career, staying on as chair of the physics department at Howard University for many years, and later serving as president of two colleges. In 1984, however, as he was nearing retirement, Branson wrote Pauling biographers Victor and Mildred Goertzel implying that his contribution had been greater than the final paper indicated. "I took my work to Pauling who told me that he thought they [the proposed alpha and gamma helices] were too tight, that he thought that a protein molecule should have a much larger radius so that water molecules could fit down inside and cause the protein to swell," he wrote. "I went back and worked unsuccessfully to find such a structure." When he received Pauling's note and the draft manuscript, Branson wrote, "I interpreted this letter as establishing that the alpha and gamma in my paper were correct and that the subsequent work done was cleaning up or verifying. The differences were nil." He added in his letter to the Goertzels that he "resented" the later attention lavished on Pauling and Corey. In an interview just before his death in 1995, Branson added that he thought Corey had nothing to do with the discovery of the helixes.

Arguments over priorities in scientific discoveries are more common than most people think. Sometimes it takes years for old resentments to surface, as they appear to have done with Herman Branson. The issue might be resolved if Branson's original report to Pauling could be found. But because it is not available, and because of the overall paucity of the written record, it might never be possible to firmly place proper credit in the discovery of the alpha and gamma helixes.

So we are left with interpretation. It seems, in the opinion of this writer, that while the order of the authors on the resulting paper might be questioned, the names of all three men are appropriate. In light of what is known about the operation of Pauling's laboratory and the general role played by Robert Corey, it is clear that Branson was assigned and carried out significant work. That work, however, was invented by Pauling, made possible by Pauling, directed by Pauling, and most important guided by chemical restrictions set by Pauling. Without Pauling's assignment of the problem, Branson would not have worked on protein structures at all. Without Pauling's laboratory support, Weinbaum's help, for instance, and the other talent available there for suggestions, review, and interpretation of his work, Branson might not have been able to accomplish his task. Without Pauling's restrictions on possible structures – again, the key to the problem - Branson would likely have come up with little or nothing in the way of results, just as the British had.

A final note: Branson's memory that Corey had little to do with the final results seems unlikely. Branson was in his mid-thirties, still relatively young when the work was done, and had relatively little experience in building molecular models from x-ray data. Corey, seventeen years his senior, was unsurpassed in the world at that time in turning difficult-to-interpret x-ray patterns into solid, proven, precise molecular models. According to Branson's much-later memory, he started building models on his own before Corey got involved, then, "One day Corey came by with some large F-H atomic models. We attached them as the alpha helix. Corey's response on viewing the spiral was 'Well, I'll be damned.'" That image of a relative novice astonishing a master of the craft seems unlikely, given their relative levels of experience and the technical difficulties involved in this sort of model building. While Branson undoubtedly used his mathematical skills and knowledge of physics to narrow the possible helixes, it is difficult to imagine that Corey's work would not have been indispensable in achieving the highly accurate, very precise models that were eventually published.

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See Also: Letter from Herman Branson to Linus Pauling. October 10, 1950. 

Click images to enlarge 

Herman Branson in his office, Lincoln University of Pennsylvania. 1970s.

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Letter from Linus Pauling to Herman Branson. October 6, 1950.

"On my return to Pasadena in the fall of 1948 I talked with Professor Corey about the alpha helix and the gamma helix, and also with Dr. Herman Branson, who had come for a year as a visiting professor. I asked Dr. Branson to go over my calculations, and in particular to see if he could find any third helical structure. He reported that the calculations were all right, and that he could not find a third structure."

Linus Pauling
September 1982
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