title: Three conserved MyD88-recruiting TLR residues exert different effects on the human TLR4 signaling pathway.
abstract: Stimulation of Toll-like receptor (TLR) 4 leads to the activation of both MyD88-dependent and MyD88-independent pathways through the recruitment of adaptors TIRAP/MyD88 and TRIF/TRAM, respectively. However, the molecular basis of the TLR4 Toll/interleukin-1 receptor (TIR) domain in recruiting these downstream adaptors is still not entirely clear. Here, we identify three amino acid residues (714P in the BB loop, 696L in the αA helix and 721N in the αB sheet) conserved in all MyD88-recruited TLRs, but not the TLR3 TIR domain, as being critical for TLR4 responsiveness to LPS. These results were based on the substitution of each residue with a residue of the opposite type (hydrophilic/hydrophobic). However, the responsiveness of the TLR4 mutants to LPS was only partially decreased when each residue was replaced with a residue having the same hydrophilicity/hydrophobicity. This result is likely associated with an alteration in the BB-loop conformation of each TLR4 mutant and its ability to recruit the downstream adaptor TRAM. Thus, we identified three amino acids essential for TLR4 signaling, and their replacement with a residue of the same or opposite hydrophilicity/hydrophobicity greatly affected TLR4 signaling. This study furthers our understanding of the molecular mechanism by which the TLR4 TIR domain modulates TLR4 signaling and also provides new insight for the design of antisepsis therapy.
authors.affiliation: Department of Pathogenic Biology, Third Military Medical University, 30 Gaotanyan Zhengjie, Shapingba District, Chongqing, 400038, People's Republic of China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Ding
authors.forename: Yuan
authors.initials: Y
authors.lastname: Qiu
authors.forename: Linyun
authors.initials: L
authors.lastname: Zou
authors.forename: Zhangping
authors.initials: Z
authors.lastname: Tan
authors.forename: Jigang
authors.initials: J
authors.lastname: Dai
authors.forename: Wenyue
authors.initials: W
authors.lastname: Xu
mesh_terms: D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D017124:Conserved Sequence; D015870:Gene Expression; D006801:Humans; D016899:Interferon-beta / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D053594:Myeloid Differentiation Factor 88 / Q000737:chemistry / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D016415:Sequence Alignment; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051193:Toll-Like Receptors / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D016899:Interferon-beta