X-RAY-DIFFRACTION STUDY OF THE INTERACTION BETWEEN CARBOXYPEPTIDASE-A AND (S)-(+)-1-AMINO-2-PHENYLETHYL PHOSPHONIC ACID

The structure of the carboxypeptidase A complex with the inhibitor (S)-(+)-1-amino-2-phenylethylphosphonic acid has been determined at 0.23 nm resolution. The DELTA-F map shows electron-density peaks both in the S1 and S1' sites, where the inhibitor molecule can be modeled in two different orientations with approximate 50% occupancy. In the proposed model, the phosphonate group binds to the zinc ion in a monodentate fashion. Other anchoring groups for the inhibitor molecule are Arg127 (hydrogen bonds with the phosphonate oxygen atoms) and Glu270 (hydrogen bond with the amino group in one of the two orientations). A recent spectroscopic investigation of the complex between cobalt(II) carboxypeptidase A and (S)-(+)-1-amino-2-phenylethylphosphonic acid is essentially in agreement with our results.