4xp8

Publication Abstract from PubMed

The Gram-negative bacterium enteropathogenic Escherichia coli (EPEC) uses a syringe-like type III secretion system (T3SS) to inject virulence or effector proteins into the cytoplasm of host intestinal epithelial cells. In order to assemble, the T3SS must traverse both bacterial membranes, as well as the peptidoglycan layer. Peptidoglycan is made of repeating N-acetylmuramic acid and N-acetyl glucosamine disaccharides crosslinked by pentapeptides to form a tight mesh barrier. Assembly of many macromolecular machines requires a dedicated peptidoglycan lytic enzyme (PG-lytic enzyme) to locally clear peptidoglycan. Here we have solved the first structure of a T3SS-associated PG-lytic enzyme, EtgA from EPEC. Unexpectedly, the active site of EtgA has features in common with both lytic transglycosylases and hen egg-white lysozyme (HEWL). Most notably, the beta-hairpin region resembles that of lysozyme, and contains an aspartate that aligns with lysozyme Asp52 (a residue critical for catalysis), a conservation not observed in other previously characterized lytic transglycosylase families which the conserved T3SS enzymes had been presumed to belong to. Mutation of the EtgA catalytic glutamate, Glu 42, conserved across lytic transglycosylases and HEWL, and this differentiating aspartate diminishes type III secretion in vivo, supporting its essential role in clearing the peptidoglycan for T3SS assembly. Finally, we show that EtgA forms a 1:1 complex with the building block of the polymerized T3SS inner rod component, EscI, and that this interaction enhances PG-lytic activity of EtgA in vitro, collectively providing the necessary strict localization and regulation of the lytic activity to prevent overall cell lysis.

Structural analysis of a specialized type III secretion system peptidoglycan-cleaving enzyme.,Burkinshaw BJ, Deng W, Lameignere E, Wasney GA, Zhu H, Worrall LJ, Finlay BB, Strynadka NC J Biol Chem. 2015 Feb 12. pii: jbc.M115.639013. PMID:25678709^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.