Quantitative estimation of activities of mutant enzymes

Computational method for the design of enzymes with altered substrate specificity

A combination of enzyme kinetics and X-ray crystallographic analysis of site-specific mutants has been used to probe the determinants of substrate specificity for the enzyme alpha-lytic protease. We now present a generalized model for understanding the effects of mutagenesis on enzyme substrate specificity. This algorithm uses a library of side-chain rotamers to sample conformation space within the binding site for the enzyme-substrate complex. The free energy of each conformation is evaluated with a standard molecular mechanics force field, modified to include a solvation energy term. This rapid energy calculation based on coarse conformation sampling quite accurately predicts the relative catalytic efficiency of over 40 different alpha-lytic protease-substrate combinations. Unlike other computational approaches, with this method it is feasible to evaluate all possible mutations within the binding site. Using this algorithm, we have successfully designed a protease that is both highly active and selective for a non-natural substrate. These encouraging results indicate that it is possible to design altered enzymes solely on the basis of empirical energy calculations.