title: BopB is a type III secreted protein in Bordetella bronchiseptica and is required for cytotoxicity against cultured mammalian cells.
abstract: The cytotoxicity of Bordetella bronchiseptica to infected cells is known to be dependent on a B. bronchiseptica type III secretion system. Although the precise mechanism of the type III secretion system is unknown, BopN, BopD and Bsp22 have been identified as type III secreted proteins. In order to identify other proteins secreted via the type III secretion machinery in Bordetella, a type III mutant was generated, and its secretion profile was compared with that of the wild-type strain. The results showed that the wild-type strain, but not the type III mutant, secreted a 40-kDa protein into the culture supernatant. This protein was identified as BopB by the analysis of its N-terminal amino acid sequence. Severe cytotoxicity such as necrosis was induced in L2 cells by infection with the wild-type B. bronchiseptica. In contrast, this effect was not observed by the BopB mutant infection. The haemolytic activity of the BopB mutant was greatly impaired compared with that of the wild-type strain. The results of a digitonin assay strongly suggested that BopB was translocated into HeLa cells infected with the wild-type strain. Taken together, our results demonstrate that Bordetella secretes BopB via a type III secretion system during infection. BopB may play a role in the formation of pores in the host plasma membrane which serve as a conduit for the translocation of effector proteins into host cells.
authors.affiliation: Laboratory of Bacterial Infection, Kitasato Institute for Life Sciences, Kitasato University, Shirokane, Tokyo, Japan.
authors.forename: Asaomi
authors.initials: A
authors.lastname: Kuwae
authors.forename: Minako
authors.initials: M
authors.lastname: Ohishi
authors.forename: Mineo
authors.initials: M
authors.lastname: Watanabe
authors.forename: Masaaki
authors.initials: M
authors.lastname: Nagai
authors.forename: Akio
authors.initials: A
authors.lastname: Abe
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D016950:Bordetella bronchiseptica / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D002352:Carrier Proteins / Q000235:genetics; D002460:Cell Line; D003470:Culture Media; D004072:Digitonin / Q000494:pharmacology; D017353:Gene Deletion; D005798:Genes, Bacterial; D006461:Hemolysis; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D010566:Virulence Factors, Bordetella / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C114406:BscN protein, Bordetella bronchiseptica; D002352:Carrier Proteins; D003470:Culture Media; D010566:Virulence Factors, Bordetella; D004072:Digitonin