Delocalizing trypsin specificity with metal activation

Recognition for proteolysis by trypsin depends almost exclusively on tight binding of arginine or lysine side chains by the primary substrate specificity pocket. Although extended subsite interactions are important for catalysis, the majority of binding energy is localized in the P-1 pocket. Analysis of the interactions of trypsin with the P-1 residue of the bound inhibitors ecotin and bovine pancreatic trypsin inhibitor suggested that the mutation D189S would improve metal-assisted trypsin N143H, E151H specificity toward peptides that have a Tyr at P-1 and a His at P-2'. In the presence of transition metals, the catalytic efficiency of the triple mutant Tn N143H, E151H, D189S improved toward the tyrosine-containing peptide AGPYAHSS. Trypsin N143H, E151H, D189S exhibits a 25-fold increase in activity with nickel and a 150-fold increase in activity with zinc relative to trypsin N143H, E151H on this peptide. In addition, activity of trypsin N143H, E151H, D189S toward an arginine-containing peptide, YLVGPRGHFYDA, is enhanced by copper, nickel, and zinc. With this substrate, copper yields a 30-fold, nickel a 70-fold, and zinc a 350-fold increase in activity over background hydrolysis without metal. These results demonstrate that the engineering of multiple substrate binding subsites in trypsin can be used to delocalize protease specificity by increasing relative substrate binding contributions from alternate engineered subsites.