Side chain characteristic main chain conformations of amino acid residues

Main chain conformation characteristics of the respective side chains of the 20 naturally occurring amino acid residues were obtained by the analysis of (phi, psi)-data from the crystal structures of 38 different globular proteins. The following observations are of interest: (i) For amino acids other than Glu, Thr and aliphatic amino acids, at least one main chain conformation is stabilised solely by side chain atoms. Such conformations are listed. (ii) In globular proteins, the main chain conformations which are significantly destabilised by side chain atom interactions are observed. The stabilising force for those conformations seems to come from main chain atom interactions. (iii) A set of conformations for which the main chain and side chain interactions are almost equal but in opposite directions, is listed and these conformations will be taken by residues mainly due to the effect of surroundings. The results can be used to study the folding of polypeptide chains and they also provide an insight into the role of the respective side chains on main chin conformations of amino acid residues.