title: TprC/D (Tp0117/131), a trimeric, pore-forming rare outer membrane protein of Treponema pallidum, has a bipartite domain structure.
abstract: Identification of Treponema pallidum rare outer membrane proteins (OMPs) has been a longstanding objective of syphilis researchers. We recently developed a consensus computational framework that employs a battery of cellular localization and topological prediction tools to generate ranked clusters of candidate rare OMPs (D. L. Cox et al., Infect. Immun. 78:5178-5194, 2010). TP0117/TP0131 (TprC/D), a member of the T. pallidum repeat (Tpr) family, was a highly ranked candidate. Circular dichroism, heat modifiability by SDS-PAGE, Triton X-114 phase partitioning, and liposome incorporation confirmed that full-length, recombinant TprC (TprC(Fl)) forms a β-barrel capable of integrating into lipid bilayers. Moreover, TprC(Fl) increased efflux of terbium-dipicolinic acid complex from large unilamellar vesicles and migrated as a trimer by blue-native PAGE. We found that in T. pallidum, TprC is heat modifiable, trimeric, expressed in low abundance, and, based on proteinase K accessibility and opsonophagocytosis assays, surface exposed. From these collective data, we conclude that TprC is a bona fide rare OMP as well as a functional ortholog of Escherichia coli OmpF. We also discovered that TprC has a bipartite architecture consisting of a soluble N-terminal portion (TprC(N)), presumably periplasmic and bound directly or indirectly to peptidoglycan, and a C-terminal β-barrel (TprC(C)). Syphilitic rabbits generate antibodies exclusively against TprC(C), while secondary syphilis patients fail to mount a detectable antibody response against either domain. The syphilis spirochete appears to have resolved a fundamental dilemma arising from its extracellular lifestyle, namely, how to enhance OM permeability without increasing its vulnerability to the antibody-mediated defenses of its natural human host.
authors.affiliation: Departments of Medicine, University of Connecticut Health Center, Farmington, Connecticut, USA.
authors.forename: Arvind
authors.initials: A
authors.lastname: Anand
authors.forename: Amit
authors.initials: A
authors.lastname: Luthra
authors.forename: Star
authors.initials: S
authors.lastname: Dunham-Ems
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Caimano
authors.forename: Carson
authors.initials: C
authors.lastname: Karanian
authors.forename: Morgan
authors.initials: M
authors.lastname: LeDoyt
authors.forename: Adriana R
authors.initials: AR
authors.lastname: Cruz
authors.forename: Juan C
authors.initials: JC
authors.lastname: Salazar
authors.forename: Justin D
authors.initials: JD
authors.lastname: Radolf
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D011134:Polysaccharides; D011487:Protein Conformation; D017510:Protein Folding; D011817:Rabbits; D011994:Recombinant Proteins; D013587:Syphilis / Q000276:immunology / Q000382:microbiology; D014210:Treponema pallidum / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*
chemical_list: D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D011134:Polysaccharides; D011994:Recombinant Proteins