title: VirK is a periplasmic protein required for efficient secretion of plasmid-encoded toxin from enteroaggregative Escherichia coli.
abstract: Despite the autotransporter (AT) moniker, AT secretion appears to involve the function of periplasmic chaperones. We identified four periplasmic proteins that specifically bound to plasmid-encoded toxin (Pet), an AT produced by enteroaggregative Escherichia coli (EAEC). These proteins include the 17-kDa Skp chaperone and the 37-kDa VirK protein. We found that the virK gene is present in different Enterobacteriaceae. VirK bound to misfolded conformations of the Pet passenger domain, but it did not bind to the folded passenger domain or to the β domain of Pet. Assays with an EAECΔvirK mutant and its complemented version showed that, in the absence of VirK, Pet was not secreted but was instead retained in the periplasm as proteolytic fragments. In contrast, Pet was secreted from a Δskp mutant. VirK was not required for the insertion of porin proteins into the outer membrane but assisted with insertion of the Pet β domain into the outer membrane. Loss of VirK function blocked the EAEC-mediated cytotoxic effect against HEp-2 cells. Thus, VirK facilitates the secretion of the AT Pet by maintaining the passenger domain in a conformation that both avoids periplasmic proteolysis and facilitates β-domain insertion into the outer membrane.
authors.affiliation: Department of Cell Biology, Centro de Investigación y de Estudios Avanzados del IPN-CINVESTAV-IPN, México DF, Mexico.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Tapia-Pastrana
authors.forename: Lucia
authors.initials: L
authors.lastname: Chavez-Dueñas
authors.forename: Humberto
authors.initials: H
authors.lastname: Lanz-Mendoza
authors.forename: Ken
authors.initials: K
authors.lastname: Teter
authors.forename: Fernando
authors.initials: F
authors.lastname: Navarro-García
mesh_terms: D001427:Bacterial Toxins; D002460:Cell Line; D004768:Enterotoxins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D022781:Hepatocytes / Q000187:drug effects; D006801:Humans; D008970:Molecular Weight; D033903:Periplasmic Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding; D012697:Serine Endopeptidases / Q000378:metabolism*
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D033903:Periplasmic Proteins; C574497:VirK protein, E coli; C530786:Pet protein, E coli; D012697:Serine Endopeptidases