title: Divergent roles of amino acid residues inside and outside the BB loop affect human Toll-like receptor (TLR)2/2, TLR2/1 and TLR2/6 responsiveness.
abstract: TLR2 specifically recognizes a wide range of ligands by homodimerizing or heterodimerizing with TLR1 or TLR6. However, the molecular basis of the specific signalling transduction induced by TLR2 homodimerization or heterodimerization with TLR1 or TLR6 is largely unknown. In this study, we found three amino acid residues, two (663L and 688N) outside and one (681P) inside the BB loop, which were conserved in all of the TLRs, except for the TLR3 toll/IL-1R(TIR) domain. The responsiveness of human TLR2/2, TLR2/1 or TLR2/6 was completely lost when 663L and 688N were replaced with the corresponding amino acid residues in the TLR3 TIR domain, respectively. However, the response of TLR2 (P681A) to the high concentration of TLR2/TLR6 agonist was almost intact, but the activity of TLR2 (P681A) was greatly reduced when stimulated with the TLR2/1 agonist or the TLR2/2 agonist. Although the surface expression of TLR2 (L663E) was sharply reduced, both the intracellular distribution and the surface expression of all of the other TLR2 mutants were unchanged. The ability of all three TLR2 mutants to recruit MyD88, was consistent with their responsivenesses. Computer modelling indicated that the surface negative charge of all of the TLR2 mutants' BB loops was reduced. Thus, our data demonstrated that the 663L and 688N residues outside of the BB loop were essential for the responsiveness of TLR2/2, TLR2/1 and TLR2/6, but the 681P residue inside of the BB loop exhibited divergent roles in TLR2/2, TLR2/1 and TLR2/6 signalling transduction, thereby providing clues regarding the specific signalling transduction of TLR2/2, TLR2/1 and TLR2/6.
authors.affiliation: Department of Pathogenic Biology, Third Military Medical University, Chongqing, P. R. China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Qiu
authors.forename: Yan
authors.initials: Y
authors.lastname: Ding
authors.forename: Lingyun
authors.initials: L
authors.lastname: Zou
authors.forename: Zhangping
authors.initials: Z
authors.lastname: Tan
authors.forename: Taiping
authors.initials: T
authors.lastname: Liu
authors.forename: Xiaolan
authors.initials: X
authors.lastname: Fu
authors.forename: Wenyue
authors.initials: W
authors.lastname: Xu
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000596:Amino Acids / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D017124:Conserved Sequence; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D053594:Myeloid Differentiation Factor 88 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D016415:Sequence Alignment; D015398:Signal Transduction / Q000235:genetics*; D055672:Static Electricity; D051194:Toll-Like Receptor 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051195:Toll-Like Receptor 2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051216:Toll-Like Receptor 6 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D000596:Amino Acids; C507779:MYD88 protein, human; D053594:Myeloid Differentiation Factor 88; C495342:TLR2 protein, human; C495368:TLR6 protein, human; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051216:Toll-Like Receptor 6