Structures of two thermolysin-inhibitor complexes that differ by a single hydrogen bond.

The mode of binding to thermolysin of the ester analog Cbz-GlyP-(O)-Leu-Leu has been determined by x-ray crystallography and shown to be virtually identical (maximum difference 0.2 angstrom) with the corresponding peptide analog Cbz-GlyP-(NH)-Leu-Leu. The two inhibitors provide a matched pair of enzyme-inhibitor complexes that differ by 4.1 kilocalories per mole in intrinsic binding energy but are essentially identical except for the presence or absence of a specific hydrogen bond.