title: FliH and FliI ensure efficient energy coupling of flagellar type III protein export in Salmonella.
abstract: For construction of the bacterial flagellum, flagellar proteins are exported via its specific export apparatus from the cytoplasm to the distal end of the growing flagellar structure. The flagellar export apparatus consists of a transmembrane (TM) export gate complex and a cytoplasmic ATPase complex consisting of FliH, FliI, and FliJ. FlhA is a TM export gate protein and plays important roles in energy coupling of protein translocation. However, the energy coupling mechanism remains unknown. Here, we performed a cross-complementation assay to measure robustness of the energy transduction system of the export apparatus against genetic perturbations. Vibrio FlhA restored motility of a Salmonella ΔflhA mutant but not that of a ΔfliH-fliI flhB(P28T) ΔflhA mutant. The flgM mutations significantly increased flagellar gene expression levels, allowing Vibrio FlhA to exert its export activity in the ΔfliH-fliI flhB(P28T) ΔflhA mutant. Pull-down assays revealed that the binding affinities of Vibrio FlhA for FliJ and the FlgN-FlgK chaperone-substrate complex were much lower than those of Salmonella FlhA. These suggest that Vibrio FlhA requires the support of FliH and FliI to efficiently and properly interact with FliJ and the FlgN-FlgK complex. We propose that FliH and FliI ensure robust and efficient energy coupling of protein export during flagellar assembly.
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Minamino
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Kinoshita
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
authors.forename: Yumi
authors.initials: Y
authors.lastname: Inoue
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.|Quantitative Biology Center, RIKEN, 6-2-3 Furuedai, Suita, Osaka, 565-0874, Japan.
authors.forename: Yusuke V
authors.initials: YV
authors.lastname: Morimoto
authors.affiliation: Center for Gene Research, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan.
authors.forename: Kunio
authors.initials: K
authors.lastname: Ihara
authors.affiliation: Departments of Food Science and Nutrition, Faculty of Human life and Science, Doshisha Women's College of Liberal Arts, Kyoto, 602-0893, Japan.
authors.forename: Satomi
authors.initials: S
authors.lastname: Koya
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
authors.forename: Noritaka
authors.initials: N
authors.lastname: Hara
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Nishioka
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Kojima
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Homma
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.|Center for Gene Research, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Namba
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D005407:Flagella / Q000378:metabolism*; D016680:Genome, Bacterial / Q000235:genetics; D021381:Protein Transport; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*; D012475:Salmonella / Q000235:genetics / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D014733:Vibrio / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; C064971:FliA protein, Bacteria; C099486:FliK protein, Bacteria; C077389:FliN protein, Bacteria; D012808:Sigma Factor; C069250:fliH protein, Bacteria; C069251:fliI protein, bacteria; C069253:fliJ protein, Bacteria; C071266:FlgM protein, Bacteria; D006180:Proton-Translocating ATPases
keywords: Bacterial flagella; FlhA; Type III protein export; cross-complementation; mutational robustness