Structural basis for the action of thermolysin

High resolution X-ray crystallography has been used to determine the modes of binding to thermolysin of a series of different inhibitors including dipeptides, mercaptans, hydroxamates, N-carboxymethyl peptides and phosphonamidates. The interactions displayed by such inhibitors illustrate interactions that are presumed to occur between the enzyme and its substrates during catalysis. The crystallographic analysis, together with model building, suggest a detailed stereochemical mechanism of action for thermolysin and, by analogy, other zinc proteases such as carboxypeptidase A and the angiotensin converting enzyme. Analysis of a series of phosphonamidates, which are presumed to be transition-state analogues, has shown that chemically similar inhibitors can adopt dissimilar modes of binding. These different configurations provide a rationalization for large differences in the kinetics of binding that are observed for these inhibitors. Experiments with thermolysin as a test case suggest that knowledge of the three-dimensional structure of an enzyme or receptor will greatly facilitate the rational design of drugs directed at such targets.