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Figure 2 | Microbial Cell Factories

Figure 2

From: Immunomodulatory mechanisms of lactobacilli

Figure 2

TLR2 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].

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