More than a century after the discovery of Treponema pallidum (Tp), syphilis remains a major threat to global public health. Our limited understanding of this sexually transmitted disease reflects the many peculiarities of its etiologic agent, most notably an inability to replicate in vitro, a labile outer membrane (OM), and an extremely narrow host range. We showed during prior funding intervals that the molecular architecture of Tp differs radically from that of Gram-negative bacteria. The spirochete's highly unusual OM is the ultrastructural basis for its designation as the "stealth pathogen" and the prime determinant of its capacity to evade innate and adaptive immune responses. The experimental data derived from our in silico mining of the Tp genome during the current funding interval have yielded compelling evidence that the particles visualized in the Tp OM by freeze-fracture EM more than 20 years ago are integral OMPs and canonical ?-barrels. Three developments now enable us to carry this work forward to an integrated structural, functional, and immunological investigation of Tp rare OMPs. One is the characterization of TP0326/BamA, an ortholog for the central component of the molecular machine that chaperones precursor OMPs from the periplasm into the OM. Because of its potential to illuminate both the biogenesis and composition of the Tp OM, we liken TP0326 to the treponemal equivalent of the Rosetta Stone. The second is the demonstration that TprC/D is a trimeric, channel-forming protein and functional E. coli OmpF ortholog. We now hypothesize that the molecule's bipartite domain structure represents a potential topological-functional paradigm for other members of the Tpr family. The third is the generation of a robust list of candidate OMPs that, when more fully investigated, will yield a comprehensive picture of the surface weaponry Tp deploy to establish and maintain persistent infection. Our long-term objective is to continue to refine our model for the molecular architecture of the Tp cell envelope as a conceptual framework for elucidating the complex and shifting balance between pathogen and host that characterizes human syphilis. We have formulated Specific Aims to maintain our momentum towards this overarching goal: (i) further characterization of TP0326/BamA;(ii) further characterization of TprC and its closely related Tpr family members, TprI and TprF;and (iii) using our roster of candidate OMPs to expand our knowledge of Tp's OMP repertoire and the contributions of novel OMPs to host-pathogen interactions during syphilitic infection.

Public Health Relevance

Syphilis is a chronic sexually transmitted disease caused by the noncultivatable spirochete Treponema pallidum (Tp). In a number of previously published studies, we have demonstrated that the outer membrane (OM) of Tp differs markedly from those of Gram-negative bacteria, such as Escherichia coli, most notably with respect to its paucity of integral membrane proteins. The experiments in this proposal will identify the repertoire of surface-exposed OM proteins Tp uses to establish and maintain persistent infection in its obligate human host.

Agency
National Institute of Health (NIH)
Type
Research Project (R01)
Project #
5R01AI026756-26
Application #
8648950
Study Section
Bacterial Pathogenesis Study Section (BACP)
Program Officer
Hiltke, Thomas J
Project Start
Project End
Budget Start
Budget End
Support Year
26
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Connecticut
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
City
Farmington
State
CT
Country
United States
Zip Code
06030
Radolf, Justin D; Deka, Ranjit K; Anand, Arvind et al. (2016) Treponema pallidum, the syphilis spirochete: making a living as a stealth pathogen. Nat Rev Microbiol 14:744-759
Luthra, Amit; Anand, Arvind; Radolf, Justin D (2015) Treponema pallidum in Gel Microdroplets: A Method for Topological Analysis of BamA (TP0326) and Localization of Rare Outer Membrane Proteins. Methods Mol Biol 1329:67-75
Seña, Arlene C; Zhang, Xiao-Hui; Li, Trudy et al. (2015) A systematic review of syphilis serological treatment outcomes in HIV-infected and HIV-uninfected persons: rethinking the significance of serological non-responsiveness and the serofast state after therapy. BMC Infect Dis 15:479
Luthra, Amit; Anand, Arvind; Hawley, Kelly L et al. (2015) A Homology Model Reveals Novel Structural Features and an Immunodominant Surface Loop/Opsonic Target in the Treponema pallidum BamA Ortholog TP_0326. J Bacteriol 197:1906-20
Anand, Arvind; LeDoyt, Morgan; Karanian, Carson et al. (2015) Bipartite Topology of Treponema pallidum Repeat Proteins C/D and I: OUTER MEMBRANE INSERTION, TRIMERIZATION, AND PORIN FUNCTION REQUIRE A C-TERMINAL β-BARREL DOMAIN. J Biol Chem 290:12313-31
Kenedy, Melisha R; Luthra, Amit; Anand, Arvind et al. (2014) Structural modeling and physicochemical characterization provide evidence that P66 forms a *-barrel in the Borrelia burgdorferi outer membrane. J Bacteriol 196:859-72
Harman, Michael; Vig, Dhruv K; Radolf, Justin D et al. (2013) Viscous dynamics of Lyme disease and syphilis spirochetes reveal flagellar torque and drag. Biophys J 105:2273-80
Anand, Arvind; Luthra, Amit; Edmond, Maxwell E et al. (2013) The major outer sheath protein (Msp) of Treponema denticola has a bipartite domain architecture and exists as periplasmic and outer membrane-spanning conformers. J Bacteriol 195:2060-71
Silver, Adam C; Dunne, Dana W; Zeiss, Caroline J et al. (2013) MyD88 deficiency markedly worsens tissue inflammation and bacterial clearance in mice infected with Treponema pallidum, the agent of syphilis. PLoS One 8:e71388
Cruz, Adriana R; Ramirez, Lady G; Zuluaga, Ana V et al. (2012) Immune evasion and recognition of the syphilis spirochete in blood and skin of secondary syphilis patients: two immunologically distinct compartments. PLoS Negl Trop Dis 6:e1717

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