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 γ-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) O157 at 2.6 Å resolution. The asymmetric unit
consists of two protein molecules and each monomer represents the common α/β fold of metallocarboxypeptidases
(MCP). The Tyr133-Asp143 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 Val204-Thr211 loop. The reported structure provides a starting point for the
molecular mechanism of MpaA in a significant human pathogen.
Keywords: PG, Mtp, E. coli O157, mtp amidase, MpaA, crystal structure.
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