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Conformational constraints of amino acid side chains in α‐helices
Author(s) -
Piela Lucjan,
Nemethy George,
Scheraga Harold A.
Publication year - 1987
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360260805
Subject(s) - steric effects , conformational isomerism , chemistry , side chain , helix (gastropod) , hydrogen bond , alanine , stereochemistry , amino acid , crystallography , molecule , biochemistry , ecology , organic chemistry , snail , biology , polymer
The conformational freedom of amino acid side chains is strongly reduced when the side chains occur on an α‐helix. A quantitative evaluation of this freedom has been carried out by means of conformational energy computations for all naturally occurring amino acids and for α‐aminobutyric acid when they are placed in the middle of a right‐handed poly( L ‐alanine) α‐helix. One of the three possible rotameric states for rotation around the C α C β bond (viz. g + ) is excluded completely on the helix because of steric hindrance, and the relative populations of the other two rotamers ( t and g − ) are altered because of steric interactions and the reduction of hydrogen‐bonding possibilities. The computed tendencies of the changes in distributions of rotamers, on going from an ensemble of all backbone conformations to the α‐helix, agree with the observed tendencies in proteins. Minimum‐energy side‐chain conformations in an α‐helix have been tabulated for use in conformational energy computations on polypeptides.