A conserved TLR5 binding and activation hot spot on flagellin

• Published in: Scientific reports Vol. 7; no. 1; p. 40878
• Main Authors: Song, Wan Seok, Jeon, Ye Ji, Namgung, Byeol, Hong, Minsun, Yoon, Sung-il
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 20.01.2017; Nature Publishing Group
• Subjects: 631/250/262; 631/45/612; 631/535/1266; 82; Alanine; Arginine; Bacteria; Binding sites; Complementarity; Crystal structure; Flagella; Flagellin; Gram-positive bacteria; Humanities and Social Sciences; Immune response; Innate immunity; Leucine; multidisciplinary; Mutagenesis; Pathogens; Proteins; Radiation; Salmonella; Scanning; Science; Science (multidisciplinary); Structural analysis; TLR5 protein; Toll-like receptors; Vaccines
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep40878

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 ( bs flagellin) 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 ( bs flagellin R89) of the flagellin D1 domain and its adjacent residues ( bs flagellin 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.