Linus Pauling and the Structure of Proteins: A Documentary History Narrative  
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Bragg's Challenge
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Sir Lawrence Bragg, the great British crystallographer, had for years crossed Pauling's path. Both had been interested in the molecular structure of minerals in the late 1920s and early 1930s. Both had grown to have an interest in proteins. Bragg had shared a Nobel Prize as a young man for virtually inventing x-ray crystallography with his father, and had been named to succeed Ernest Rutherford as the Cavendish Professor at Cambridge in the late 1930s. It was a powerful position. While most of Bragg's attention remained fixed on inorganic molecules, he was also interested in extending crystallography's reach as far as it could go, even to molecules as huge as proteins. After the War, money from Britain's Medical Research Council (the equivalent of the US's National Institutes of Health) became available for establishing crystallographic studies into molecular biology; the result was a small unit operating under Bragg's direction on the fringes of the Cavendish. It was small, somewhat shabby by today's standards, and for the first few years had only two permanent members: Max Perutz and John Kendrew. It would prove enough to change the history of science.

Pauling visited and saw the set-up during his time at Oxford. He recognized that Perutz and Kendrew were dedicated, talented, and equipped to make great advances (although he continued to believe that it would take years before they would solve any complete protein structures with their top-down approach). He came home with great respect for the British.

So it is likely that he had a feeling of foreboding when he read their latest paper. The title made it sound as if they might have made an important breakthrough. But he quickly saw that they had not. It was a laundry list of possible structures for the basic pattern found in Astbury's studies of protein fibers. Some were helixes, others kinked chains, and none of them, Pauling realized, was satisfactory. The paper represented work in progress. At the end, Bragg's group halfheartedly endorsed Astbury's old idea of a folded ribbon. But there was not enough evidence to reach a firm conclusion.

Pauling might have been interested to see how the British were using his bottom-up approach – model building based on an understanding of the structural elements involved – to solve the problem. He, in turn, had started to use some of the British techniques after his return from England, starting Corey to work on a whole protein, lysozyme, and encouraging the work of a new Caltech faculty member, Jack Kirkwood, who was looking at the charge distribution and general properties of globular proteins.

But the British did not play Pauling's game as well as Pauling himself. They had not been strict enough about the planarity of the peptide bond, for instance, allowing it to bend and twist in ways Pauling thought unlikely. They also assumed a restriction that Pauling thought unnecessary. The British insisted that each turn of a proposed protein spiral, or each kink in a ribbon, had to include an integral number of amino acids – most likely two or three amino acids per repeat. Pauling saw no reason to insist on integral repeats. He had told Branson to ignore them in his model building.

The paper by Bragg's group has receded into the background of history. But it had one important effect: It refocused Linus Pauling's attention on protein structures.

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See Also: Letter from Linus Pauling to W.L. Bragg. July 16, 1951. 

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Picture
Portrait of Sir William Lawrence Bragg, approx. 1960.


Page 1
Letter from W.L. Bragg to Linus Pauling. June 13, 1951.

"It was one of those papers you publish mainly because you've done all that work."

Max Perutz
January 31, 1976
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