A mono-acyl phospholipid (20:1 lyso-PS) activates Toll-Like Receptor 2/6 hetero-dimer

Toll-like receptor 2 (TLR2) is an important pattern recognition receptor on the surface of host immune cells that binds a variety of ligands that are released by microorganisms as well as by damaged or dying host cells. According to the current concept, TLR2/1 and TLR2/6 heterodimers are activated by tri- or di-acylated ligands, respectively. However, also mono-acyl phospholipid containing lipid fractions derived from parasites, were reported to be able to activate TLR2. In order to provide conclusive evidence for the TLR2 activating capacity of mono-acyl phospholipids derived from pathogens, we developed a biosynthetic method to enzymatically convert commercially available phospholipids into several mono-acyl-phospholipid variants that were examined for their TLR2 activating capacity. These investigations demonstrated that 1-(11Z-eicosenoyl)-glycero-3-phosphoserine 20:1 (20:1 lyso-PS) is a true agonist of the TLR2/6 heterodimer and that its polar headgroup as well as the length of the acyl chain are crucial for TLR2 activation. In silico modelling further confirmed 20:1 mono-acyl PS as a ligand for TLR2/6 heterodimer, as this predicted that multiple hydrogen bonds are formed between the polar headgroup of 20:1 mono-acyl PS and amino acid residues of both TLR2 and TLR6. Future studies can now be performed to further assess the functions of 20:1 lyso-PS as an immunological mediator, because this enzymatic method enables its preparation in larger quantities than is possible by isolation from the parasite that naturally produces this compound, Schistosoma mansoni, the source of the original discovery (Van der Kleij et al., 2002).