"The structure of the synthetic alpha-polypeptides"

Date:
1954
Reference:
PP/CRI/H/1/27
Catalogue details

Licence: In copyright

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

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    i j/ßH a M & p ; r, / - fe: Nif The Structure of the Synthetic a-Polypeptides — ~ / ^ 'f ^ / ° FiHJC. Crick, d.ac., m.u. iff fVi'f'' ' y J ~ /S- ''Protein St rue tu re. Project^ Po lyte c hnic Institute of Brooklyn, U.S.A . I The classic work of Astburjíjias 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^'i and ¿3, 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 a 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 sidechains are the same, and to study them by \ w X-rays and infra-red^TThese^ too^ show a ß, or extended^ form # and an a, 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.. 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 a-helix, was proposed by Pauling, Corey and Bransori/. 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 a-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 the case for the_a-he 1 ix_lies_in__the_fact_that_both methods of approach_give_the_same_answer. It is at first sight sur- prising that a structure of such apparent complexity can be solved at t. > I çjïdn leave of absence from the -edics 1 ' Research Council Unit, Cavendish J/ j Laboratory, Cambridge, England.