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Gonzalez-Pedrajo, B; Minamino, T; Yoshimura, SDJ; Morimoto, YV; Kami-ike, N; Namba, K (2009)

ROLES OF THE EXTREME N-TERMINAL REGION OF FLIH FOR EFFICIENT LOCALIZATION OF THE FLIH-FLII COMPLEX TO THE BACTERIAL FLAGELLAR TYPE III EXPORT APPARATU

MOL MICROBIOL 74(6):1471-1483
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P>Most bacterial flagellar proteins are exported by the flagellar type III protein export apparatus for their self-assembly. FliI ATPase forms a complex with its regulator FliH and facilitates initial entry of export substrates to the export gate composed of six integral membrane proteins. The FliH-FliI complex also binds to the C ring of the basal body through a FliH-FliN interaction for efficient export. However, it remains unclear how these reactions proceed within the cell. Here, we analysed subcellular localization of FliI-YFP by fluorescence microscopy. FliI-YFP was localized to the flagellar base, and its localization required both FliH and the C ring. The ATPase activity of FliI was not required for its localization. FliI-YFP formed a complex with FliH Delta 1 (missing residues 2-10) but the complex did not show any localization. FliH Delta 1 did not interact with FliN, and alanine-scanning mutagenesis revealed that only Trp-7 and Trp-10 of FliH are essential for the interaction with FliN. Overproduction of the FliH-FliI complex improved the export activity of the fliN mutant whereas neither of the FliH(W7A)-FliI nor FliH(W10A)-FliI complexes did, suggesting that Trp-7 and Trp-10 of FliH are also required for efficient localization of the FliH-FliI complex to the export gate.