Studies on the conformation of amino acids VII. Backbone and side-chain conformations of N-terminal residues in peptides

Abstract

Potential energy calculations have been made to predict the preferred conformations of N-terminal residues in polypeptide chains. Nonbonded, electrostatic and torsional energies have been computed using appropriate energy functions and their role assessed. The effects of β-, γ-, and δ-atoms in the side chain on the backbone conformation are discussed. A conformation in which the plane of the peptide group is coplanar with the plane through the atoms N, C^α and C' is preferred for the N-terminal glycyl residue, and this coplanarity is affected by the presence of β- and γ-atoms only and not beyond. The side-chain conformations about the C^α---C^β and C^β---C^γ bonds are nearly the same as those predicted for the corresponding free amino acid examples. The observed conformations of N-terminal residues in the crystal structures are compared with the theoretical predictions and the agreement is found to be good.