Enzyme:substrate hydrogen bond shortening during the acylation phase of seine protease catalysis

The refinement of the structure of the canonical inhibitor complex formed between crayfish trypsin (CFT) and trypsin inhibitor (SGTI), which is assumed to be a simple model for studying the catalytic Michaelis complex, is reported in which the substrate peptide forms an antiparallel beta sheet with the enzyme in order to position the scissile peptide bond in the active site. In the Michaelis complex the electron distribution of the carbonyl bond is distorted toward the oxygen atom compared to other peptide bonds in the structure, which indicates the polarization effect of the oxyanion hole.