Title : Lateral clustering of
TLR3 :dsRNA signaling units revealed by
TLR3 ecd:3Fabs quaternary structure
Abstract :
- Toll-like receptor 3 ( TLR3 ) recognizes dsRNA and initiates an innate immune response through the formation of a signaling unit (SU) composed of one double-stranded RNA (dsRNA) and two TLR3 molecules
- We report the crystal structure of human TLR3 ectodomain (TLR3ecd) in a quaternary complex with three neutralizing Fab fragments
- Fab15 binds an epitope that overlaps the C-terminal dsRNA binding site and, in biochemical assays, blocks the interaction of TLR3 ecd with dsRNA, thus directly antagonizing TLR3 signaling through inhibition of SU formation
- In contrast, Fab12 and Fab1068 bind TLR3 ecd at sites distinct from the N- and C-terminal regions that interact with dsRNA and do not inhibit minimal SU formation with short dsRNA
- Molecular modeling based on the co-structure rationalizes these observations by showing that both Fab12 and Fab1068 prevent lateral clustering of SUs along the length of the dsRNA ligand
- This model is further supported by cell-based assay results using dsRNA ligands of lengths that support single and multiple SUs
- Thus, their antagonism of TLR3 signaling indicates that lateral clustering of SUs is required for TLR3 signal transduction