Identification of MpaA, an Amidase in Escherichia coli That Hydrolyzes the γ-d-Glutamyl-meso-Diaminopimelate Bond in Murein Peptides

MpaA amidase was identified in Escherichia coli by its amino acid sequence homology with the ENP1 endopeptidase from Bacillus sphaericus. The enzymatic activity of MpaA, i.e., hydrolysis of the γ-d-glutamyl-diaminopimelic acid bond in the murein tripeptide l-alanyl-γ-d-glutamyl-meso-diaminopimelic acid, was demonstrated in the cell extract of a strain expressing mpaA from a multicopy plasmid. An mpaA mpl (murein peptide ligase) double mutant accumulated large amounts of murein tripeptide in its cytoplasm, consistent with the premise that MpaA degrades the tripeptide if its recycling via the peptidoglycan biosynthetic pathway is blocked.