title: A conserved TLR5 binding and activation hot spot on flagellin.
abstract: Flagellin is a bacterial protein that polymerizes into the flagellar filament and is essential for bacterial motility. When flagellated bacteria invade the host, flagellin is recognized by Toll-like receptor 5 (TLR5) as a pathogen invasion signal and eventually evokes the innate immune response. Here, we provide a conserved structural mechanism by which flagellins from Gram-negative γ-proteobacteria and Gram-positive Firmicutes bacteria bind and activate TLR5. The comparative structural analysis using our crystal structure of a complex between Bacillus subtilis flagellin (bsflagellin) and TLR5 at 2.1 Å resolution, combined with the alanine scanning analysis of the binding interface, reveals a common hot spot in flagellin for TLR5 activation. An arginine residue (bsflagellin R89) of the flagellin D1 domain and its adjacent residues (bsflagellin E114 and L93) constitute a hot spot that provides shape and chemical complementarity to a cavity generated by the loop of leucine-rich repeat 9 in TLR5. In addition to the flagellin D1 domain, the D0 domain also contributes to TLR5 activity through structurally dispersed regions, but not a single focal area. These results establish the groundwork for the future design of flagellin-based therapeutics.
authors.affiliation: Division of Biomedical Convergence, College of Biomedical Science, Kangwon National University, Chuncheon 24341, Republic of Korea.
authors.forename: Wan Seok
authors.initials: WS
authors.lastname: Song
authors.affiliation: Division of Biomedical Convergence, College of Biomedical Science, Kangwon National University, Chuncheon 24341, Republic of Korea.
authors.forename: Ye Ji
authors.initials: YJ
authors.lastname: Jeon
authors.affiliation: Division of Biomedical Convergence, College of Biomedical Science, Kangwon National University, Chuncheon 24341, Republic of Korea.
authors.forename: Byeol
authors.initials: B
authors.lastname: Namgung
authors.affiliation: Division of Biological Science and Technology, Yonsei University, Wonju 26493, Republic of Korea.
authors.forename: Minsun
authors.initials: M
authors.lastname: Hong
authors.affiliation: Division of Biomedical Convergence, College of Biomedical Science, Kangwon National University, Chuncheon 24341, Republic of Korea.|Institute of Bioscience and Biotechnology, Kangwon National University, Chuncheon 24341, Republic of Korea.
authors.forename: Sung-Il
authors.initials: SI
authors.lastname: Yoon
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D005408:Flagellin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D051198:Toll-Like Receptor 5 / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D051198:Toll-Like Receptor 5; D005408:Flagellin