Structural Similarities of dAminopeptidase to Carboxypeptidase DD and bLactamases

The nucleotide sequence of the D-aminopeptidase gene was determined and analyzed to study the structural relationship to other proteins. The gene consisted of an open reading frame of 1,560 nucleotides, which specifies a protein of Mr of 57,257 (28). The deduced primary structure is considerably similar to that of Streptomyces R61 carboxypeptidase DD (30) (27% identical over 287 amino acids) and class C /-lactamase from E. coli (22% identical over 234 amino acids) (31,32) (Fig. 3). The enzyme is also structurally related to class A /-lactamases (33,34), penicillin-binding proteins (35-40), and class D/-lactamases (41,42). The sequence Ser-Xaa-Xaa-Lys is perfectly conserved among this class of enzymes (Fig. 4). With carboxypeptidase DD and class C /-lactamase, the sequences at the highly similar area, Ser-Val-Xaa-Lys-Xaa-Phe-Xaa-Ala-Xaa-Val-Leu-Leu (30) and Ser-Val-Ser-Lys-Xaa-Phe-Tyr (31), respectively, are well conserved. Furthermore, some of the residues scattered around the conserved region are similar among the enzymes. The Met-57 located four residues upstream from the Ser-61 is found similarly in the carboxypeptidase DD and /-lactamases as a hydrophobic residue Phe. A common observation regarding D-aminopeptidase and the /-

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