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Conformational constraints of amino acid side chains in α-helices

✍ Scribed by Lucjan Piela; George Nemethy; Harold A. Scheraga

Publisher
Wiley (John Wiley & Sons)
Year
1987
Tongue
English
Weight
678 KB
Volume
26
Category
Article
ISSN
0006-3525

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✦ Synopsis

The conformational freedom of amino acid side chains is strongly reduced when the side chains occur on an a-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 a-aminobutyric acid when they are placed in the middle of a right-handed poly(lalanine) a-helix. One of the three possible rotameric states for rotation around the C" -C @ 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 hydrogenbonding possibilities. The computed tendencies of the changes in distributions of rotamers, on going from an ensemble of all backbone conformations to the a-helix, agree with the observed tendencies in proteins. Minimum-energy side-chain conformations in an a-helix have been tabulated for use in conformational energy computations on polypeptides.

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