Stereochemical criteria for polypeptide and protein chain conformations. Part I. Evaluation of helical parameters

Ramakrishnan, C. (1964) Stereochemical criteria for polypeptide and protein chain conformations. Part I. Evaluation of helical parameters Proceedings of the Indian Academy of Sciences, Section A, 59 (5). pp. 327-343. ISSN 0370-0089

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Official URL: http://www.ias.ac.in/j_archive/proca/59/vol59conte...

Related URL: http://dx.doi.org/10.1007/BF03046447

Abstract

A large number of configurations are possible for a polypeptide structure depending upon the relative orientations of the two peptide groups linked at an α-carbon atom. If the linkages at the α-carbon atoms are identical, then the structure assumes a regular helical form. Such a regular helical structure can be specified by two parameters φ, φ' which are the angles of rotation of the two groups about the N−αC and αC−C' bonds meeting at an α-carbon atom. In this paper, a method of evaluating the helical parameters of a structure, namely, the number of residues per turn n, the unit translation along the axis of the helix h and the direction cosines of the helical axis with respect to a suitably chosen co-ordinate system, is described making use of rotation matrices. The evaluation has been done for three different values of the angle NαCC at the α-carbon atom, namely, 105°, 110° and 115°. The results are shown graphically in the form of curves for constant n and constant h in the φ-φ' plane.

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