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Atomic Coordinates and Structure Factors for Two Helical Configurations of Polypeptide Chains. March 31, 1951

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Title:	Atomic Coordinates and Structure Factors for Two Helical Configurations of Polypeptide Chains
Creator:	Pauling, Linus, 1901-
Contributor:	Corey, Robert
Publisher:	National Academy of Sciences
Date:	1951-05-00
Subject:	Chemical bonds
Description:	Reprinted from the Proceedings of the National Academy of Sciences, Vol. 37, No. 5, pp. 235-240.
Type:	Text
Format:	text/plain
Language:	en
Identifier:	paulingcorey1-pg01.jpg
Source:	Master scanned with Epson GT-10000+ flatbed scanner at 600 dpi.
Rights:	http://osulibrary.orst.edu/specialcollections/coll/pauling/dna/copyright.html
Full Text:	Reprinted from the Proceedings of the NATIONAL ACADEMY OF SCIENCES, Vol. 37, No. 5, pp. 235-240.¦ay, 1951 ATOMIC COORDINATES AND STRUCTURE FACTORS FOR TWO HELICAL CONFIGURATIONS OF POLYPEPTIDE CHAINS BY LINUS PAULING AND ROBERT B. COREY GATES AND CRELLIN LABORATORIES OF CHEMISTRY,* CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CALIFORNIA Communicated March 31, 1951 During recent years we have been gathering information about interatomic distances, bond angles, and other properties of simple substances related to proteins, and have been attempting to formulate configurations of the polypeptide chain that are compatible with this information and that might constitute a structural feature of proteins. We have reported the discovery of two helical configurations that satisfy these conditions. In the following paragraphs we discuss the atomic positions for these configurations, and their form factors for diffraction of x-rays in the equatorial direction. The γ Helix.—Let us first discuss the 5.1-residue helix.­his configuration is obtained by coiling a polypeptide chain into a helical form, in such a way that the planar amide groups, [diagram], are in the trans configuration (the carbonyl group being almost directly opposed to the imino group), and each amide group forms hydrogen bonds with the fifth more distant group in each direction along the chain. The structure is represented diagrammatically in figure 1, and a drawing of it has been recently published .°e base our discussion on the values of interatomic distances and bond angles given in figure 4; these differ from those described earlier only in the change from 120° to 123° for the angle C'—N—C*. The fifth amide group beyond a given group in the helix is nearly directly above it, and if the hydrogen bonds determine the orientation of the plane of the amide groups there seems to be no reason for this plane not to be parallel to the axis of the helix.­he following calculations are made