ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A survey has been made, by using computer methods, of the types of helices which polypeptide chains can form, taking into account steric requirements and intramolecular hydrogen-bonding interactions. The influence on these two requirements, of small variations in the bond angles of the peptide residues, or of small changes in the overall dimensions of the helix (pitch and residues per turn), have been assessed for the special case of the α-helix. Criteria for the formation of acceptable hydrogen bonds have also been applied to helices of other types, viz., the 310-, γ-, ω-, and π-helices. It was shown that the N—H … O and H … O—C angles in hydrogen bonds are sensitive to changes in either the NCαC′ bond angle or in the rotational angles about the N—Cα and Cα—C′ bonds. However, the variants of the α-helix observed experimentally in myoglobin can all be constructed without distortion of the hydrogen bonds. For α-helices, the steric and hydrogen bonding requirements are more easily fulfilled with an NCαC′ bond angle of 111°, rather than 109.5°. The decreased stability observed for the left-handed α-helix relative to the right-handed one for L-amino acids is due essentially only to interactions of the Cβ atom of the side chains with atoms in adjacent peptide units in the backbone, and interactions with atoms in adjacent turns of the helical backbone are not significantly different in the two helices. Restrictions in the freedom of rotation of bulky side chains may have significant kinetic effects during the formation of the α-helix from the “random coil” state.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1966.360040806
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