title: The muramidase EtgA from enteropathogenic Escherichia coli is required for efficient type III secretion.
abstract: Enteropathogenic Escherichia coli (EPEC) is an important cause of infectious diarrhoea. It colonizes human intestinal epithelial cells by delivering effector proteins into the host cell cytoplasm via a type III secretion system (T3SS) encoded within the chromosomal locus of enterocyte effacement (LEE). The LEE pathogenicity island also encodes a lytic transglycosylase (LT) homologue named EtgA. In the present work we investigated the significance of EtgA function in type III secretion (T3S). Purified recombinant EtgA was found to have peptidoglycan lytic activity in vitro. Consistent with this function, signal peptide processing and bacterial cell fractionation revealed that EtgA is a periplasmic protein. EtgA possesses the conserved glutamate characteristic of the LT family, and we show here that it is essential for enzymic activity. Overproduction of EtgA in EPEC inhibits bacterial growth and induces cell lysis unless the predicted catalytic glutamate is mutated. An etgA mutant is attenuated for T3S, red blood cell haemolysis and EspA filamentation. BfpH, a plasmid-encoded putative LT, was not able to functionally replace EtgA. Overall, our results indicate that the muramidase activity of EtgA is not critical but makes a significant contribution to the efficiency of the T3S process.
authors.affiliation: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, D.F., 04510, Mexico.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: García-Gómez
authors.affiliation: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, D.F., 04510, Mexico.
authors.forename: Norma
authors.initials: N
authors.lastname: Espinosa
authors.affiliation: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, D.F., 04510, Mexico.
authors.forename: Javier
authors.initials: J
authors.lastname: de la Mora
authors.affiliation: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, D.F., 04510, Mexico.
authors.forename: Georges
authors.initials: G
authors.lastname: Dreyfus
authors.affiliation: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, D.F., 04510, Mexico.
authors.forename: Bertha
authors.initials: B
authors.lastname: González-Pedrajo
mesh_terms: D001433:Bacteriolysis; D054308:Enteropathogenic Escherichia coli / Q000201:enzymology* / Q000378:metabolism*; D004912:Erythrocytes / Q000187:drug effects; D029968:Escherichia coli Proteins / Q000378:metabolism*; D015870:Gene Expression; D055786:Gene Knockout Techniques; D006461:Hemolysis; D006801:Humans; D006868:Hydrolysis; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009113:Muramidase / Q000378:metabolism*; D010457:Peptidoglycan / Q000378:metabolism; D033903:Periplasmic Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D014774:Virulence; D037521:Virulence Factors / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D010457:Peptidoglycan; D033903:Periplasmic Proteins; D011994:Recombinant Proteins; D037521:Virulence Factors; D009113:Muramidase