Crystal Escherichia Structure of Murein-Tripeptide Amidase MpaA from Escherichia coli O157 at 2.6 Å Resolution

Peptidoglycan (PG) is an essential component of the cell wall, and undergoes reconstruction by various PG hydrolases during cell growth, development and division. The murein- tripeptide (Mtp) amidase MpaA belongs to PG hydrolase family and is responsible for cleaving the y-D-Glumeso-Dap amide bond in the Mtp released during PG turnover. The current paper reports the crystal structure of MpaA from Escherichia coli (E. coli) 0157 at 2.6 angstrom resolution. The asymmetric unit consists of two protein molecules and each monomer represents the common a/13 fold of metallocarboxypeptidases (MCP). The Tyr(133)-Asp(143) loop appears to mediate the entrance and binding of the substrate into the active groove. A structural comparison of MpaA with its homologue from Vibrio harveyi showed that MpaA has narrower active pocket entrance with a smaller surface opening, which is determined by the Val(204)-Thr(211) loop. The reported structure provides a starting point for the molecular mechanism of MpaA in a significant human pathogen.