Purification, crystallization and preliminary X-ray analysis of TP0435 (Tp17) from the syphilis spirochete Treponema pallidum

MiR-216a-5p-containing exosomes suppress rTp17-induced inflammatory response by targeting TLR4

Syphilis caused by Treponema pallidum (T. pallidum) infection is accompanied by inflammatory injury of tissue, and has a worldwide distribution and increasing incidence over the past decade. Tp17 has been reported to be a strong membrane immunogen, and was initially observed to play a role in inflammation during syphilis, reacting intensely with human syphilitic sera. We therefore used recombinant Tp17 (rTp17) as a stimulator in our study. Increasing evidence has demonstrated that microRNA (miRNA)-containing exosomes have emerged as a potential effective therapeutic target for many diseases. However, the biological functions and molecular mechanisms of miR-216a-5p in syphilis pathogenesis remain unknown. Our study first identified dramatically decreased miR-216a-5p in plasma of syphilis patients compared with the healthy control, which was negatively correlated with the expression of inflammatory cytokines, including IL-1β, IL-6, and TNF-α. Moreover, endothelial cells treated with miR-216a-5p-containing exosomes significantly attenuated the rTp17-induced inflammatory response. More importantly, we identified that miR-216a-5p could bind to the 3′-untranslated region (UTR) of Toll-like receptor (TLR) 4 (TLR4), and overexpression of TLR4 largely rescued the miR-216a-5p-mediated suppression of rTp17-induced inflammatory cytokine production and the TLR4-MYD88 signaling pathway. Thus, our results reveal a novel role of miR-216a-5p-containing exosomes in endothelial cells, implying a potential therapeutic target for inflammation in syphilis patients.

Novel Treponema pallidum Recombinant Antigens for Syphilis Diagnostics: Current Status and Future Prospects

The recombinant protein technology considerably promoted the development of rapid and accurate treponema-specific laboratory diagnostics of syphilis infection. For the last ten years, the immunodominant recombinant inner membrane lipoproteins are proved to be sensitive and specific antigens for syphilis screening. However, the development of an enlarged T. pallidum antigen panel for diagnostics of early and late syphilis and differentiation of syphilis stages or cured syphilis remains as actual goal of multidisciplinary expertise. Current review revealed novel recombinant antigens: surface-exposed proteins, adhesins, and periplasmic and flagellar proteins, which are promising candidates for the improved syphilis serological diagnostics. The opportunities and limitations of diagnostic usage of these antigens are discussed and the criteria for selection of optimal antigens panel summarized.

Insights into the potential function and membrane organization of the TP0435 (Tp17) lipoprotein from Treponema pallidum derived from structural and biophysical analyses

The sexually transmitted disease syphilis is caused by the bacterial spirochete Treponema pallidum. This microorganism is genetically intractable, accounting for the large number of putative and undercharacterized members of the pathogen's proteome. In an effort to ascribe a function(s) to the TP0435 (Tp17) lipoprotein, we engineered a soluble variant of the protein (rTP0435) and determined its crystal structure at a resolution of 2.42 Å. The structure is characterized by an eight-stranded β-barrel protein with a shallow "basin" at one end of the barrel and an α-helix stacked on the opposite end. Furthermore, there is a disulfide-linked dimer of the protein in the asymmetric unit of the crystals. Solution hydrodynamic experiments established that purified rTP0435 is monomeric, but specifically forms the disulfide-stabilized dimer observed in the crystal structure. The data herein, when considered with previous work on TP0435, imply plausible roles for the protein in either ligand binding, treponemal membrane architecture, and/or pathogenesis.