Correlation between chemical structure and biological activities of Porphyromonas gingivalis synthetic lipopeptide derivatives

Summary We recently separated a PG1828‐encoded triacylated lipoprotein (Pg‐LP), composed of two palmitoyl and one pentadecanoyl groups at the N‐terminal of glycerocysteine from Porphyromonas gingivalis , a periodontopathic bacteria, and found that Pg‐LP exhibited definite biological activities through Toll‐like receptor (TLR) 2. In the present study, we synthesized 12 different Pg‐LP N‐terminal peptide moieties (PGTP) using four combinations of glyceryl ( R and S ) and cysteinyl ( l and d ) stereoisomers, and three different acyl group regioisomers, N ‐pentadecanoyl derivative (PGTP1), S ‐glycero 2‐pentadecanoyl derivative (PGTP2) and S ‐glycero 3‐pentadecanoyl derivative (PGTP3). All the PGTP compounds (RL, SL, SD, RD) tested showed TLR2‐dependent cell activation. The activating capacities of the PGTP‐R compounds were more potent than those of the PGTP‐S compounds, whereas there were no differences between the PGTP‐L and ‐D compounds. Furthermore, the production of interleukin (IL)‐6 following stimulation with the PGTP1‐RL, PGTP2‐RL and PGTP3‐RL compounds was impaired in peritoneal macrophages from TLR2 knock‐out (KO), but not those from TLR1 KO or TLR6 KO mice. These results suggest that P. gingivalis triacylated lipopeptides are capable of activating host cells in a TLR2‐dependent and TLR1‐/TLR6‐independent manner, and the fatty acid residue at the glycerol position in the PGTP molecule plays an important role in recognition by TLR2.