title: Role of the C-terminal cytoplasmic domain of FlhA in bacterial flagellar type III protein export.
abstract: For construction of the bacterial flagellum, many of the flagellar proteins are exported into the central channel of the flagellar structure by the flagellar type III protein export apparatus. FlhA and FlhB, which are integral membrane proteins of the export apparatus, form a docking platform for the soluble components of the export apparatus, FliH, FliI, and FliJ. The C-terminal cytoplasmic domain of FlhA (FlhA(C)) is required for protein export, but it is not clear how it works. Here, we analyzed a temperature-sensitive Salmonella enterica mutant, the flhA(G368C) mutant, which has a mutation in the sequence encoding FlhA(C). The G368C mutation did not eliminate the interactions with FliH, FliI, FliJ, and the C-terminal cytoplasmic domain of FlhB, suggesting that the mutation blocks the export process after the FliH-FliI-FliJ-export substrate complex binds to the FlhA-FlhB platform. Limited proteolysis showed that FlhA(C) consists of at least three subdomains, a flexible linker, FlhA(CN), and FlhA(CC), and that FlhA(CN) becomes sensitive to proteolysis by the G368C mutation. Intragenic suppressor mutations were identified in these subdomains and restored flagellar protein export to a considerable degree. However, none of these suppressor mutations suppressed the protease sensitivity. We suggest that FlhA(C) not only forms part of the docking platform for the FliH-FliI-FliJ-export substrate complex but also is directly involved in the translocation of the export substrate into the central channel of the growing flagellar structure.
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan. tohru@fbs.osaka-u.ac.jp
authors.forename: Tohru
authors.initials: T
authors.lastname: Minamino
authors.forename: Masafumi
authors.initials: M
authors.lastname: Shimada
authors.forename: Mayuko
authors.initials: M
authors.lastname: Okabe
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Saijo-Hamano
authors.forename: Katsumi
authors.initials: K
authors.lastname: Imada
authors.forename: May
authors.initials: M
authors.lastname: Kihara
authors.forename: Keiichi
authors.initials: K
authors.lastname: Namba
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005407:Flagella / Q000378:metabolism*; D005408:Flagellin / Q000378:metabolism*; D006358:Hot Temperature; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D006180:Proton-Translocating ATPases / Q000378:metabolism; D019779:Salmonella enterica / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013489:Suppression, Genetic
chemical_list: D001426:Bacterial Proteins; C080688:FlhA protein, Bacteria; C085668:FlhB protein, Bacteria; D008565:Membrane Proteins; D005408:Flagellin; C069250:fliH protein, Bacteria; C069251:fliI protein, bacteria; C069253:fliJ protein, Bacteria; D006180:Proton-Translocating ATPases