Attachment of LcrV from Yersinia pestis at Dual Binding Sites to Human TLR-2 and Human IFN-γ Receptor

The virulence antigen (V-antigen, LcrV) of Yersinia pestis, the causative agent of bubonic plague, is an established protective antigen known to regulate, target, and mediate type III translocation of cytotoxic yersiniae outer proteins termed Yops; LcrV also prompts TLR2-dependent upregulation of anti-inflammatory IL-10. In this study, we determined the parameters of specific interaction of LcrV with TLR2 expressed on human transfected HEK293 cells (TLR2+/CD14-), VTEC2.HS cells (TLR2+/CD14-), primary monocytes (TLR2+/CD14+), and THP-1 cells (TLR2+/CD14+). The IRRL314 - 317 motif of the extracellular domain of human and mouse TLR2 accounted for high-affinity binding of LcrV. The CD14 co-receptor did not influence this interaction. LcrV did not bind to human U937 (TLR2-/CD14-) and alveolar macrophages (TLR2-/CD14+) in the absence of receptor-bound human IFN-γ or a synthetic C-terminal fragment (hIFN-γ132 - 143). The latter, but not mouse IFN-γ (or synthetic control peptides), shared a GRRA138 - 141 site necessary for high-affinity specific binding. LcrV of Y. pestis shares the N-terminal LEEL32 - 35 binding site of Yersinia enterocolitica and also has an exposed internal DEEI203 - 206 binding site. Comparison of binding constants and consideration of steric restrictions indicate that binding is not cooperative and only the internal site binds LcrV to target cells. Both the LEEL32 - 35 and DEEI203 - 206 binding sites are removed by five amino acids from DKN residues associated with biological activity of bound LcrV. LcrV of Y. pestis promoted both TLR2/CD14-dependent and TLR2/CD14-independent amplification of IL-10 and concomitant downregulation of TNF-α in human target cells. The ability of LcrV to utilize human IFN-γ (a major inflammatory effector of innate immunity) to minimize inflammation is insidious and may account in part for the severe symptoms of plague in man. Keywords: plague • Yersinia pestis • virulence antigen LcrV • Toll-like receptor TLR2 • interferon-γ