A Predictive Model of Strong Hydrogen Bonding in Proteins: The Nδ1−H−Oδ1Hydrogen Bond in Low-pH α-Chymotrypsin and α-Lytic Protease

A computational QM/MM methodology for the systematic study of various structural and spectroscopic properties of strong hydrogen bonds in enzymes is presented. The theoretical model is applied to the N δ1 −H−O δ1 hydrogen bond between His57 and Asp102 in the active sites of low-pH α-chymotrypsin and α-lytic protease. The minimum energy structures of both enzymes reproduce the experimental N δ1 −O δ1 distance and are used to obtain computational values for the H−D fractionation factor ( φ ), the proton chemical shift (δ H ) of the H δ1, and changes in δ H upon isotope substitution ( Δδ H - D and Δδ H - T ). For both enzymes, calculated parameters are in good agreement with available experimental data. Predictions are made for other properties for which experimental values are not available.