Abstract

Innate immunity is the first defensive wall a pathogen needs to beat to flourish in our body. Mammal Toll-like receptors (TLRs) regulate the inflammatory and tissue repair responses to injury by specifically and effectively recognizing pathogen-associated molecular patterns to elicit immune cell signaling. In particular, TLR4, together with the myeloid differentiation factor 2 (MD-2), recognise lipopolysaccharides of Gram-negative bacteria whilst TLR2, together with TLR1 or TLR6, are activated by lipoteichoic acids of Gram-positive bacteria and bacterial lipoproteins. Of much significance is the link of TLRs to critical diseases like cancer and auto-immune disorders. Therefore, the therapeutic modulation of innate immunity has emerged as a main strategy for the treatment of pathologies. For the development of immunomodulators it is of paramount importance to deepen into the functioning of TLRs at the atomic-molecular level. We here report the development of new monosaccharide-based synthetic glycolipids with agonistic activity towards TLR4/MD-2 and useful as vaccine adjuvants. Based on our docking calculations and molecular dynamics simulations, we proposed a novel mechanism for their biological activity determined from their chemical structure, 3D shape and fatty acid chains length. Further, we have applied methods of computational chemistry to characterize plausible dimerization modes of the transmembrane (TMD) and juxtamembrane (JMD) domains of human TLR2/TLR1 and TLR2/TLR6 complexes in liquid-order and liquid-disordered membrane models to account for their recruitment in lipid rafts. We have gathered evidence of differential behaviour of TMD depending on the membrane composition and we have characterized the particular structures of JMD which are critical for signal transduction. All together, these results aid in the understanding of the activation mechanism of TLR-related innate immunity to characterize and promote the development of new TLR modulators.