"The structure of the synthetic a-polypeptides"

Date:
[1953]-1954
Reference:
PP/CRI/H/1/18
Catalogue details

Licence: In copyright

Credit: "The structure of the synthetic a-polypeptides". Source: Wellcome Collection.

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    The Structure of the Synthetic «-Polypeptides F.H.C. Crick B.Sc. Ph.D. Protein Structure Project, Polytechnic Institute of Brooklyn, U.S.A The classic work of Astbury has shown that structurally the fi brous proteins fall into two main groups: the keratin-myosin-epidermin- fibrinogen group, known for short as k-m-e-f, and the collagens. The distinction between them is displayed most clearly by their wide-angle X-ray diffraction patterns. These also show that the k-m-e-f group can exist in two forms, known as « and ß, which under certain circumstances can be converted into each other. Astbury suggested many years ago that the ß form corresponded to an extended configuration of the poly peptide chain, and that the g form contained chains folded so that their overall length was approximately halved. This explanation is now general ly accepted as being correct, at least in outline. In recent years it has been possible to prepare synthetic polypep tides in which all the sldechains are the same, and to study them by X-rays and infra-red. These, too, show a ß t or extended form and an o, or folded form. The X-ray pattern of the latter is similar to, but not identical with the a pattern of the k-m-e-f fibrous proteins. n Until 1951 the exact nature of the fold of the a-polypeptides was not known, although several configurations had been suggested. In that year a structure of a novel type, known as the e-helix, was proposed * by Pauling, Corey and Branson. Recent developments have left no doubt that this structure is basically correct. The main object of the present article is to review the evidence in favour of the «-helix, and in particular to explain why it is con sidered correct although the agreement with the experimental evidence is not yet perfect. A brief description of the a-helix is given first to enable the reader to grasp the general nature of it. The a-helix was originally deduced by Pauling, Corey and Branson from a set of plausible stereochemical postulates, but it can also be derived in dependently from the broad features of the experimental evidence. The strength_of_tlie_case_for_the_c,-he 1 i_x_lies_in_the_fa.ct_that_both methods of^aggroach_giye_the_same_answer• It is at first sight sur- prising that a structure of such apparent complexity can be solved at ^On leave of absence from the Medical Research Council Unit, Cavendish Laboratory, Cambridge, England.