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. 1981 Jun;78(6):3408–3412. doi: 10.1073/pnas.78.6.3408

Zinc environment and cis peptide bonds in carboxypeptidase A at 1.75-A resolution.

D C Rees, M Lewis, R B Honzatko, W N Lipscomb, K D Hardman
PMCID: PMC319577  PMID: 6943549

Abstract

The structure of the metalloenzyme carboxypeptidase A (peptidyl-L-amino-acid hydrolase, EC 3.4.17.1) has been refined at 1.75 A by a restrained least-squares procedure to a conventional crystallographic R factor of 0.162. Significant results of the refined structure relative to the catalytic mechanism are described. In the native enzyme, the zinc coordination number is five (two imidazole N delta 1 nitrogens, the two carboxylate oxygens of glutamate-72, and a water molecule). In the complex (at 2.0-A resolution) of carboxypeptidase A with the dipeptide glycyl-L-tyrosine, however, the water ligand is replaced by both the carbonyl oxygen and the amino nitrogen of the dipeptide. The amino nitrogen also statistically occupies a second position near glutamate-270. Consequently, the coordination number of zinc may vary from five to six in carboxypeptidase A-substrate complexes. Implications of these results for the catalytic mechanism of carboxypeptidase A are discussed. In addition, three cis peptide bonds, none of which involves proline as the amino nitrogen donor, have been located fairly near the active site.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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