Amino acid similarity coefficients for protein modeling and sequence alignment derived from main-chain folding angles

A set of "similarity-parameters" was calculated that reflects the influence of the proteinogenic amino acids on the structure of the protein backbone. The parameters were derived from a detailed analysis of the amino acid specific main-chain torsion angle distributions as they are found in proteins (highly resolved protein structures from the Brookhaven Protein Data Bank). The purpose of these parameters is threefold: (1) they should help in estimating the structural effect of an amino acid substitution during the design of new mutants in protein-engineering; (2) in modeling by homology they should mark places in the protein where changes in the folding are expected; and (3) they should form a scoring matrix in protein sequence alignment superior to identity scoring. The usability of the "structure derived correlation matrix (SCM)" for these purposes is assessed and demonstrated for some examples in the paper.