Carboxyl proteinase from Pseudomonas defines a novel family of subtilisin-like enzymes

The crystal structure of a pepstatin-insensitive carboxyl proteinase from P seudomonas sp. 101 (PSCP) has been solved by single-wavelength anomalous di ffraction using the absorption peak of bromide anions. Structures of the un inhibited enzyme and of complexes with an inhibitor that was either covalen tly or noncovalently bound were refined at 1.0-1.4 Angstrom resolution. The structure of PSCP comprises a single compact domain with a diameter of sim ilar to 55 Angstrom, consisting of a seven-stranded parallel beta -sheet fl anked on both sides by a number of helices. The fold of PSCP is a superset of the subtilisin fold, and the covalently bound inhibitor is linked to the enzyme through a serine residue. Thus, the structure of PSCP defines a nov el family of serine-carboxyl proteinases (defined as MEROPS S53) with a uni que catalytic triad consisting of Glu 80, Asp 84 and Ser 287.