title: Crystal structure of FliC flagellin from Pseudomonas aeruginosa and its implication in TLR5 binding and formation of the flagellar filament.
abstract: Pseudomonas aeruginosa is one of leading opportunistic pathogens in humans and its movement is driven by a flagellar filament that is constituted through the polymerization of a single protein, FliC flagellin (paFliC). paFliC is an essential virulence factor for the colonization of P. aeruginosa. paFliC activates innate immune responses via its recognition by Toll-like receptor 5 (TLR5) and adaptive immunity in the host. Thus, paFliC has been a vaccine candidate to prevent P. aeruginosa infection, particularly for cystic fibrosis patients. To provide structural information on paFliC and its flagellar filament, we have determined the crystal structure of paFliC, which contains the conserved D1 and variable D2 domains, at 2.1 Å resolution. As observed for Salmonella FliC, the paFliC D1 domain is folded into a rod-shaped structure, and paFliC was demonstrated by gel filtration and native PAGE analyses to directly interact with TLR5. Moreover, a structural model of the paFliC-TLR5 complex suggests that paFliC D1 would provide major TLR5-binding sites, similar to Salmonella FliC. In contrast to the D1 domain, the paFliC D2 domain exhibits a unique structure of two β-sheets and one α-helix that has not been found in other flagellins. An in silico construction of a flagellar filament based on the packing of paFliC in the crystal suggests that the D2 domain would be exposed to solution and could play an important role in immunogenicity. Our biophysical and structure-based modeling study on paFliC, the paFliC-TLR5 complex, and the paFliC filament could contribute to the improvement of vaccine design to control P. aeruginosa infection.
authors.affiliation: Department of Systems Immunology and Institute of Antibody Research, College of Biomedical Science, Kangwon National University, Chuncheon 200-701, Republic of Korea.
authors.forename: Wan Seok
authors.initials: WS
authors.lastname: Song
authors.affiliation: Department of Systems Immunology and Institute of Antibody Research, College of Biomedical Science, Kangwon National University, Chuncheon 200-701, Republic of Korea. Electronic address: sungil@kangwon.ac.kr.
authors.forename: Sung-il
authors.initials: SI
authors.lastname: Yoon
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005407:Flagella / Q000378:metabolism*; D005408:Flagellin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D063347:Native Polyacrylamide Gel Electrophoresis; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D051198:Toll-Like Receptor 5 / Q000235:genetics / Q000378:metabolism*; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D015800:Protozoan Proteins; D051198:Toll-Like Receptor 5; D029961:Zebrafish Proteins; D005408:Flagellin
keywords: Flagellar filament; Flagellin; FliC; Pseudomonas aeruginosa; Structure; TLR5