Conformational analysis of the right-hand twisted antiparallel beta-structure.

The conformational analysis of a pair of two-linked peptide units in the anti-parallel arrangement is reported here with a view to study the effect of association of one chain with the other. The pair of two-linked peptide units were fixed in space through the hydrogen bonds between them, in accordance with certain hydrogen bond criteria. Model building was undertaken to ascertain whether the proximity of the side-chains could be used to eliminate any one of the right-hand twisted, left-hand twisted or regular beta-structures. Stereochemically, it was found possible with all of them. The preference for a right-hand twisted beta-structure, however, was indicated by the classical energy calculations. The relevance of the results thus obtained is discussed in the context of the preferential right-hand twist of the beta-pleated sheets present in globular proteins. The agreement between the minimum energy conformations obtained for the pair of two-linked peptide units and the globular protein data is also indicated.