Site-specific effect of polar functional group-modification in lipids of TLR2 ligands for modulating the ligand immunostimulatory activity

Toll-like receptor 2 (TLR2), a member of the TLR innate immune receptor family, recognizes lipoproteins from bacteria and modulates the immune response by inducing the expression of various cytokines. TLR2 has a large hydrophobic pocket that recognizes long fatty acyl groups on TLR2 ligands. However, few studies have focused on the property of the hydrophobic TLR2 pocket. Based on the X-ray crystal structure of TLR2, small polar regions were found in the hydrophobic TLR2 pocket. Interactions between the polar residues and ligands were explored here by designing and synthesizing a Pam₂CSK₄ derivative of the TLR2 ligands, containing an amide group within the lipid moiety. We evaluated the binding affinities and immunomodulatory activities of these ligands. Results suggested that the amide groups in the lipid chain interacted with the polar residues in the hydrophobic lipid-binding pocket of TLR2.