Structure-function Relationship of Mycoplasmal Lipoproteins/lipopeptides and Their Recognition by Toll-like Receptor 2

Recent evidence has been accumulated that microbial lipoprotein (LP) plays pathological roles in bacterial infection. The part of LP responsible for the expression of biological activities has been demonstrated to be the N-terminal lipopeptide moiety. Mycoplasmas, wall-less microorganisms, also possess LP capable of activating macrophages or fibroblasts. We have found that M. salivarium LP activates normal human gingival fibroblasts and macrophages to induce production of inflammatory cytokines, and we have purified a 44-kDa LP (LP44) responsible for the activity. In addition, the structure of the N-terminal lipopeptide moiety of LP44 has been determined to be S-(2,3-bispalmitoyloxypropyl) Cys-Gly-Asp-Pro-Lys-His-Pro-Lys-Ser-Phe-Thr-Gly-Trp-Val-Ala-. The lipopeptide S- (2,3-bispalmitoyloxypropyl) Cys-Gly-Asp-Pro-Lys-His-Pro-Lys-Ser-Phe (FSL-1) was synthesized. The lipopeptide FSL-1 activated human gingival fibroblasts and macrophages to produce inflammatory cytokines as LP44 did. Experiments using FSL-1 and its derivatives revealed that the diacylglyceryl and peptide portions of FSL-1 are indispensable for the activation of macrophages and for the recognition by Toll-like receptor 2 (TLR2) and TLR6. We have recently demonstrated that each of several leucine residues located at a leucine-rich repeat of TLR2 play a key role in the recognition of the diacylated lipopeptide FSL-1, mycoplamal LP and S. aureus peptidoglycan.