title: The TprK protein of Treponema pallidum is periplasmic and is not a target of opsonic antibody or protective immunity.
abstract: The finding that Treponema pallidum, the syphilis spirochete, contains 12 orthologs of the Treponema denticola outer membrane major sheath protein has engendered speculation that members of this T. pallidum repeat (Tpr) family may be similarly surface exposed. In this regard, the TprK protein was reported to be a target of opsonic antibody and protective immunity and subject to immunologically driven sequence variation. Despite these findings, results from our previous analyses of treponemal outer membranes in concert with computer-based predictions for TprK prompted us to examine the cellular location of this protein. TprK-alkaline phosphatase fusions expressed in Escherichia coli demonstrate that TprK contains a signal peptide. However, opsonophagocytosis assays failed to indicate surface exposure of TprK. Moreover, results from three independent methodologies, i.e., (a) indirect immunofluorescence analysis of agarose-encapsulated organisms, (b) proteinase K treatment of intact spirochetes, and (c) Triton X-114 phase partitioning of T. pallidum conclusively demonstrated that native TprK is entirely periplasmic. Consistent with this location, immunization with the recombinant protein failed to induce either protective immunity or select for TprK variants in the rabbit model of experimental syphilis. These findings challenge the notion that TprK will be a component of an efficacious syphilis vaccine.
authors.affiliation: Center for Microbial Pathogenesis, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
authors.forename: K R
authors.initials: KR
authors.lastname: Hazlett
authors.forename: T J
authors.initials: TJ
authors.lastname: Sellati
authors.forename: T T
authors.initials: TT
authors.lastname: Nguyen
authors.forename: D L
authors.initials: DL
authors.lastname: Cox
authors.forename: M L
authors.initials: ML
authors.lastname: Clawson
authors.forename: M J
authors.initials: MJ
authors.lastname: Caimano
authors.forename: J D
authors.initials: JD
authors.lastname: Radolf
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000276:immunology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D002462:Cell Membrane / Q000378:metabolism; D018387:Codon, Initiator; D004269:DNA, Bacterial; D019286:Endopeptidase K / Q000378:metabolism; D005798:Genes, Bacterial; D014644:Genetic Variation; D008969:Molecular Sequence Data; D019897:Periplasm / Q000378:metabolism*; D014176:Protein Biosynthesis; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D013587:Syphilis / Q000517:prevention & control; D014158:Transcription, Genetic; D014210:Treponema pallidum / Q000235:genetics / Q000276:immunology*; D014611:Vaccination
chemical_list: D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D018387:Codon, Initiator; D004269:DNA, Bacterial; C406409:Tpr protein, Treponema; D019286:Endopeptidase K