Quantumchemical study of the catalytic triad in subtilisin: the influence of amino acid substitutions on enzymatic activity.

In the catalytic reaction of serine proteases the basicity of a histidine and the nucleophilicity of a serine, both residues together with an aspartate residue belonging to the catalytic triad, are of great importance. The influence of amino acid substitution on the basicity and the fast nucleophilicity of these important amino acids was investigated using a very simple and fast procedure. The amino acids of the triad were calculated at an ab initio level with the environment residues represented by point charges obtained with the CHelpG population analysis. Basicity trends were found to be reflected by the charge on the basic nitrogen and the "protonation energy", calculated for the triad. The serine nucleophilicity was found to correlate with the charge on the hydroxyl atom and with the minimum of the Molecular Electrostatic Potential in the vicinity of this oxygen.