Redetermination and refinement of the complex of benzylsuccinic acid with thermolysin and its relation to the complex with carboxypeptidase A

The complex of benzylsuccinic acid with thermolysin has been redetermined at 1.7-Å resolution and refined to a crystallographic residual of 15.7%. In contrast to the prior study, which was to 2.3-Å resolution, and without the benefit of refinement (Bolognesi, M. C. and Matthews, B. W. (1979) J. Biol. Chem. 254, 634-639), the present analysis shows that it is the D- rather than the L-isomer of benzylsuccinic acid that binds. The stereochemistry of the zinc-carboxylate interaction is now seen to be syn, as is also observed in all known zinc-carboxylate complexes of both thermolysin and carboxypeptidase A. The mode of binding of the β-carboxylate resembles the presumed geometry of the tetrahedral transition state and, as such, is consistent with the commonly accepted mechanism of action of thermolysin and of carboxypeptidase A.