Treponema pallidum subsp. pallidum TP0136 Protein Is Heterogeneous among Isolates and Binds Cellular and Plasma Fibronectin via its NH2-Terminal End

Abstract

Adherence-mediated colonization plays an important role in pathogenesis of microbial infections, particularly those caused by extracellular pathogens responsible for systemic diseases, such as Treponema pallidum subsp. pallidum (T. pallidum), the agent of syphilis. Among T. pallidum adhesins, TP0136 is known to bind fibronectin (Fn), an important constituent of the host extracellular matrix. To deepen our understanding of the TP0136-Fn interaction dynamics, we used two naturally-occurring sequence variants of the TP0136 protein to investigate which region of the protein is responsible for Fn binding, and whether TP0136 would adhere to human cellular Fn in addition to plasma Fn and super Fn as previously reported. Fn binding assays were performed with recombinant proteins representing the two full-length TP0136 variants and their discrete regions. As a complementary approach, we tested inhibition of T. pallidum binding to Fn by recombinant full-length TP0136 proteins and fragments, as well as by anti-TP0136 immune sera. Our results show that TP0136 adheres more efficiently to cellular Fn than to plasma Fn, that the TP0136 NH2-terminal conserved region of the protein is primarily responsible for binding to plasma Fn but that binding sites for cellular Fn are also present in the protein’s central and COOH-terminal regions. Additionally, message quantification studies show that tp0136 is highly transcribed during experimental infection, and that its message level increases in parallel to the host immune pressure on the pathogen, which suggests a possible role for this protein in T. pallidum persistence. In a time where syphilis incidence is high, our data will help in the quest to identify suitable targets for development of a much needed vaccine against this important disease.

Syphilis

“…Spirochetes directly penetrate mucous membranes or enter through abrasions in skin, which is less heavily keratinized in peri-genital and peri-anal areas than skin elsewhere 8,68 . To establish infection, T. pallidum must adhere to epithelial cells and extracellular matrix components; in vitro binding studies suggest that fibronectin and laminin are key substrates for these interaction 76,97–99 . Once below the epithelium, organisms multiply locally and begin to disseminate through the lymphatics and bloodstream.…”

Treponema pallidum, the syphilis spirochete: making a living as a stealth pathogen

“…In addition to being an adhesin, TP0751 is a zinc-dependent metalloprotease (hence, was named “pallilysin”) that forms a complex with TP0751 (which contains a Von Willebrand factor type A domain) capable of degrading clots and extracellular matrix, which could facilitate both dissemination and attachment 74,75 . The lipoprotein TP0136 is a fibronectin-binding adhesin with sequence heterogeneity among T. pallidum strains (Table 1) 76,77 . Most recently, elegant gain of function experiements using B. burgdorferi as a surrogate genetic host have shown that the lipoprotein TP0435 (Tpp17) functions as a cytadhesin 78 .…”

Recombinant Treponema pallidum protein Tp0136 promotes fibroblast migration by modulating MCP‐1/CCR2 through TLR4

“…Tp0136 is one of a few proteins produced by Treponema pallidum ( T. pallidum ) that bind and adhere to fibronectin, and the transcription level of Tp0136 is significantly elevated during the healing period in a rabbit model of syphilis. Therefore, we suggest that Tp0136 may contribute to the healing of syphilitic lesions . However, the related mechanism is still unclear.…”

“…Therefore, we suggest that Tp0136 may contribute to the healing of syphilitic lesions. 14 However, the related mechanism is still unclear. Therefore, we postulate that Tp0136 promotes MCP-1/CCR2 expression through TLR4, leading to fibroblast migration, which plays an important role in the pathophysiology of syphilis.…”