Interactions between Yersinia pestis V-antigen (LcrV) and human Toll-like receptor 2 (TLR2) in a modelled protein complex and potential mechanistic insights

Background Yersinia pestis, the etiological pathogen of plague, is capable of repressing the immune response of white blood cells to evade phagocytosis. The V-antigen (LcrV) was found to be involved in this process by binding to human Toll-like Receptor 2 (TLR2). The detailed mechanism behind this LcrV and TLR2 mediated immune response repression, however, is yet to be fully elucidated due to the lack of structural information. Results In this work, with protein structure modelling, we were able to construct a structure model of the heterotetramer of Y. pestis LcrV and human TLR2. Molecular dynamics simulation suggests the stability of this structure in aquatic environment. The LcrV model has a dumbbell-like structure with two globule domains (G1 at N-terminus and G2 away from membrane) connected with a coiled-coil linker (CCL) domain. The two horseshoe-shape TLR2 subunits form a V-shape structure, are not in direct contact with each other, and are held together by the LcrV homodimer. In this structure model, both the G1 and CCL domains are involved in the formation of LcrV homodimer, while all three domains are involved in LcrV-TLR2 binding. A mechanistic model was proposed based on this heterotetrameric structure model: The LcrV homodimer separates the TLR2 subunits to inhibit the dimerization of TLR2 and subsequent signal transfer for immune response; while LcrV could also inhibit the formation of heterodimers of TLR2 with other TLRs, and leads to immune response repression. Conclusions A heterotetrameric structure of Y. pestis LcrV and human TLR2 was modelled in this work. Analysis of this modelled structure showed its stability in aquatic environments and the role of LcrV domains and residues in protein-protein interaction. A mechanistic model for the role of LcrV in Y. pestis pathogenesis is raised based on this heterotetrameric structure model. This work provides a hypothesis of LcrV function, with which further experimental validation may elucidate the role of LcrV in human immune response repression.