title: Virulence plasmid of Rhodococcus equi contains inducible gene family encoding secreted proteins.
abstract: Rhodococcus equi causes severe pyogranulomatous pneumonia in foals. This facultative intracellular pathogen produces similar lesions in immunocompromised humans, particularly in AIDS patients. Virulent strains of R. equi bear a large plasmid that is required for intracellular survival within macrophages and for virulence in foals and mice. Only two plasmid-encoded proteins have been described previously; a 15- to 17-kDa surface protein designated virulence-associated protein A (VapA) and an antigenically related 20-kDa protein (herein designated VapB). These two proteins are not expressed by the same R. equi isolate. We describe here the substantial similarity between VapA and VapB. Moreover, we identify three additional genes carried on the virulence plasmid, vapC, -D, and -E, that are tandemly arranged downstream of vapA. These new genes are members of a gene family and encode proteins that are approximately 50% homologous to VapA, VapB, and each other. vapC, -D, and -E are found only in R. equi strains that express VapA and are highly conserved in VapA-positive isolates from both horses and humans. VapC, -D, and -E are secreted proteins coordinately regulated by temperature with VapA; the proteins are expressed when R. equi is cultured at 37 degrees C but not at 30 degrees C, a finding that is compatible with a role in virulence. As secreted proteins, VapC, -D, and -E may represent targets for the prevention of rhodococcal pneumonia. An immunologic study using VapA-specific antibodies and recombinant Vap proteins revealed no evidence of cross-reactivity despite extensive sequence similarity over the carboxy terminus of all four proteins.
authors.affiliation: Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington 99164-7040, USA. bab@vet.purdue.edu
authors.forename: B A
authors.initials: BA
authors.lastname: Byrne
authors.forename: J F
authors.initials: JF
authors.lastname: Prescott
authors.forename: G H
authors.initials: GH
authors.lastname: Palmer
authors.forename: S
authors.initials: S
authors.lastname: Takai
authors.forename: V M
authors.initials: VM
authors.lastname: Nicholson
authors.forename: D C
authors.initials: DC
authors.lastname: Alperin
authors.forename: S A
authors.initials: SA
authors.lastname: Hines
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D003429:Cross Reactions; D004268:DNA-Binding Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008562:Membrane Glycoproteins / Q000235:genetics*; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010957:Plasmids; D016929:Rhodococcus equi / Q000235:genetics* / Q000472:pathogenicity; D013696:Temperature; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D008562:Membrane Glycoproteins; D037521:Virulence Factors; C077517:VapB protein, Bacteria