Quantum mechanical modeling of aspartic proteinase interactions: Difference in binding of diastereomeric statine models

Quantum mechanical calculations were carried out for the interaction of two diastereomeric model inhibitors of aspartic proteinases with a model for the active site, based on crystallographic coordinates of endothiapepsin. The model inhibitor is formamide N-(2-hydroxy 3-methyl propane) and the active site is represented by the full backbone and most of the side chains of the two partial sequences D32-T33-G34-S35 and D215-T216-G217-T218. Those calculations demonstrate that the best binding mode for this short inhibitor is consistent with the X-ray experiments and somewhat stronger with the inhibitor in a 2(S) configuration, compared to 2(R). Another binding mode is possible for this model inhibitor only in the 2(S)-configuration, and is weaker than the first.