Figure 2From: Immunomodulatory mechanisms of lactobacilliTLR2 recognition of lipoproteins and LTA. Recognition of LTA and lipoproteins is mediated through binding of the lipid chains which anchor these molecules in the membrane. a). All lipoproteins possess a specific N-terminal lipoprotein signal which targets the protein for secretion and post-translational modification. In Gram-positive bacteria and Gram-negative bacteria the Lgt enzyme transfers a diacylglyceride group to the cysteine sulfhydryl group adjacent to the signal peptide cleavage site. Subsequently the signal peptide is cleaved just before the cysteine residue by LspA yielding a mature di-acylated lipoprotein. However, in Gram-negative bacteria and mycobacteria the Lnt enzyme attaches a third acyl group to the amino group of the N-terminal cysteine promoting its transport to the outer membrane. b). The diacyl lipid chains added by Lgt bind in a hydrophobic pocket in the extracellular domain of TLR2 and the head group of the peptide interacts with TLR6 to promote hetero-dimerization and signalling. In the case of tri-acylated lipoproteins the third lipid chain interacts with a hydrophobic channel in TLR1 to promote dimerization and signalling. This diagram is a modified version of Figure 1 published by Schenk et al., 2009 [101].Back to article page