Dissecting the Role of -Glycan at N413 in Toll-like Receptor 3 via Molecular Dynamics Simulations.

Toll-like receptor 3 (TLR3) is an endosomal receptor involved in initiating immune responses upon viral infection by directly recognizing double-stranded RNA (dsRNA). As one of the most heavily glycosylated TLR family members, the role of glycan at N413 of TLR3 in ligand recognition has been in debate for decades. Herein, to investigate the role of glycans in TLR3, specifically at amino acid residue N413, molecular dynamic simulations were performed. The loop region of LRR12 (residues 323-355), which protrudes from the dsRNA binding TLR3 lateral surface was found to be vital for interacting with dsRNA via the formation of hydrogen bonds. The glycan at N413 not only prevented dsRNA from being exposed to the bulk water during the binding process but further stabilized dsRNA in the TLR3 binding site. When N413 was in the glycosylated form, the binding free energy of TLR3 interacting with dsRNA was significantly lower than that of TLR3 in the N413 unglycosylated form. Additionally, as the glycan at N413 functioned to alter the dynamics of the dsRNA binding process, its flexibility was meanwhile influenced by dsRNA. In all, these results demonstrate that the size, length, and branch of glycan at N413 affect the thermodynamics and dynamics of TLR3 recognition with dsRNA. This study further extends our understanding of the biological role of glycans in the innate immune recognition of dsRNA by TLR3 and provides a new perspective for modulating TLR3 function.