Purification, characterization, and primary structure of a novel cell wall hydrolytic amidase, CwhA, from...

A novel bacteriolytic enzyme CwhA (cell wall hydrolytic amidase) was purified by ion exchange and gel-filtration chromatographies from a commercial bacteriolytic preparation from Achromobacter lyticus. CwhA exhibited optimal pH at 8.5 and lysed CHCl(3)-treated Escherichia coli more efficiently than Micrococcus luteus, Staphylococcus aureus, Enterococcus faecalis, and Pediococcus acidilactici. The enzyme was inhibited by 1,10-phenanthroline strongly and by EDTA to a lesser extent, suggesting that it is probably a metalloenzyme. Amino acid composition and mass spectrometric analyses for the CwhA-derived M. luteus muropeptides revealed that CwhA is N-acetylmuramoyl-L-alanine amidase [EC 3.5.1. 28]. The complete amino acid sequence of CwhA was established by a combination of Edman degradation and mass spectrometry for peptides obtained by Achromobacter protease I (API) digestion and cyanogen bromide (CNBr) cleavage. The enzyme consists of a single polypeptide chain of 177 amino acid residues with one disulfide bond, Cys114-Cys121. CwhA was found to be homologous to N-acetylmuramoyl-L-alanine amidase from bacteriophage T7 (BPT7). Its sequence identity with BPT7 is 35%, but the amino acid residues functioning as zinc ligands in BPT7 are absent in CwhA. These results suggest that CwhA is a new type of N-acetylmuramoyl-L-alanine amidase.