title: Structural stability of flagellin subunit affects the rate of flagellin export in the absence of FliS chaperone.
abstract: FliS chaperone binds to flagellin FliC in the cytoplasm and transfers FliC to a sorting platform of the flagellar type III export apparatus through the interaction between FliS and FlhA for rapid and efficient protein export during flagellar filament assembly. FliS also suppresses the secretion of an anti-σ factor, FlgM. Loss of FliS results in a short filament phenotype although the expression levels of FliC are increased considerably due to an increase in the secretion level of FlgM. Here to clarify the rate limiting step of FliC export in the absence of FliS, we isolated bypass mutants from a Salmonella ΔfliS mutant. All the bypass mutations were identified in FliC. These bypass mutations increased the export rate of FliC by ca. twofold, allowing the bypass mutant cells to produce longer filaments than the parental ΔfliS cells. Both far-UV CD measurements and limited proteolysis revealed that the bypass mutations significantly destabilize the folded structure of FliC monomer. These results suggest that an unfolding step of FliC limits the export rate of FliC in the ΔfliS mutant, thereby producing short filaments. We propose that FliS promotes FliC docking at the FlhA platform to facilitate subsequent unfolding of FliC.
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Furukawa
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: Department of Food Science and Nutrition, Faculty of Human Life and Science, Doshisha Women's College of Liberal Arts, Kyoto, 602-0893, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Sakaguchi
authors.affiliation: Department of Food Science and Nutrition, Faculty of Human Life and Science, Doshisha Women's College of Liberal Arts, Kyoto, 602-0893, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Mori
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
authors.forename: Takuma
authors.initials: T
authors.lastname: Fukumura
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.|Quantitative Biology Center, RIKEN, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Miyata
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan. tohru@fbs.osaka-u.ac.jp.|Quantitative Biology Center, RIKEN, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan. tohru@fbs.osaka-u.ac.jp.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Namba
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan. keiichi@fbs.osaka-u.ac.jp.
authors.forename: Tohru
authors.initials: T
authors.lastname: Minamino
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D005407:Flagella / Q000378:metabolism; D005408:Flagellin / Q000096:biosynthesis / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D012486:Salmonella typhimurium / Q000378:metabolism; D012808:Sigma Factor / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D018832:Molecular Chaperones; D012808:Sigma Factor; D005408:Flagellin; C076734:FliS protein, Bacteria