Novel roles in human MD-2 of phenylalanines 121 and 126 and tyrosine 131 in activation of Toll-like receptor 4 by endotoxin.

摘要: Potent mammalian cell activation by Gram-negative bacterial endotoxin requires sequential protein-endotoxin and protein-protein interactions involving lipopolysaccharide-binding protein, CD14, MD-2, Toll-like receptor 4 (TLR4). TLR4 simultaneous binding of MD-2 to (E) the ectodomain TLR4. We now describe mutants recombinant human that bind react with E.CD14 but do not support cellular responsiveness endotoxin. The F121A/K122A Y131A/K132A only when co-expressed Single K122A K132A each +/- promote TLR4-dependent suggesting Phe(121) Tyr(131) are needed for TLR4-independent transfer from CD14 also bound E.MD-2. mutant F126A reacts as well wild-type E.MD-2(F126A) binds high affinity (K(d) approximately 200 pm) does activate instead acts a potent antagonist, inhibiting HEK/TLR4 cells These findings reveal roles in and, together Phe(126), strongly suggest structural properties E.MD-2, E alone, determine agonist or antagonist effects on