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Updated: Sep 9, 2026

The Importance of Correct Protein Concentration for Kinetics and Affinity Determination in Structure-function Analysis
Published on: March 17, 2010
Crystal structure of carboxypeptidase A complexed with D-cysteine at 1.75 A - inhibitor-induced conformational
D M van Aalten1, C R Chong, L Joshua-Tor
1W. M. Keck Structural Biology, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
Abstract:
D-Cysteine differs from the antiarthritis drug D-penicillamine by only two methyl groups on the beta-carbon yet inhibits carboxypeptidase A (CPD) by a distinct mechanism: D-cysteine binds tightly to the active site zinc, while D-penicillamine catalyzes metal removal. To investigate the structural basis for this difference, we solved the crystal structure of carboxypeptidase A complexed with D-cysteine (D-Cys) at 1.75-A resolution. D-Cys binds the active site zinc with a sulfur ligand and forms additional interactions with surrounding side chains of the enzyme. The structure explains the difference in potency between D-Cys and L-Cys and provides insight into the mechanism of D-penicillamine inhibition. D-Cys binding induces a concerted motion of the side chains around the zinc ion, similar to that found in other carboxypeptidase-inhibitor crystal structures and along a limited path. Analysis of concerted motions of CPD and CPD-inhibitor crystal structures reveals a clustering of these structures into distinct groups. Using the restricted conformational flexibility of a drug target in this type of analysis could greatly enhance efficiency in drug design.
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