Interaction of a bacterial flagellar chaperone FlgN with FlhA is required for efficient export of its cognate substrates

• Published in: Molecular microbiology 2012-02, Vol.83 (4), p.775-788
• Main Authors: Minamino, Tohru, Kinoshita, Miki, Hara, Noritaka, Takeuchi, Shiori, Hida, Akira, Koya, Satomi, Glenwright, Helen, Imada, Katsumi, Aldridge, Phillip D., Namba, Keiichi
• Format: Article
• Language: English
• Subjects: Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Gene Deletion; Gene expression; Membrane Proteins - genetics; Membrane Proteins - metabolism; Microbiology; Miscellaneous; Models, Biological; Models, Molecular; Mutant Proteins - genetics; Mutant Proteins - metabolism; Mutation; Protein Binding; Protein Interaction Mapping; Protein Transport; Proteins; Suppression, Genetic
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2011.07964.x

Summary FlgN chaperone acts as a bodyguard to protect its cognate substrates, FlgK and FlgL, from proteolysis in the cytoplasm. Docking of the FlgN–FlgK complex with the FliI ATPase of the flagellar type III export apparatus is key to the protein export process. However, a ΔfliH‐fliI flhB(P28T) mutant forms some flagella even in the absence of FliH and FliI, raising the question of how FlgN promotes the export of its cognate substrates. Here, we report that the interaction of FlgN with an integral membrane export protein, FlhA, is directly involved in efficient protein export. A ΔfliH‐fliI flhB(P28T) ΔflgN mutant caused extragenic suppressor mutations in the C‐terminal domain of FlhA (FlhAC). Pull‐down assays using GST affinity chromatography showed an interaction between FlgN and FlhAC. The FlgN–FlgK complex bound to FlhAC and FliJ to form the FlgN–FlgK–FliJ–FlhAC complex. The FlgN–FlhAC interaction was enhanced by FlgK but not by FliJ. FlgN120 missing the last 20 residues still bound to FlgK and FliJ but not to FlhAC. A highly conserved Tyr‐122 residue was required for the interaction with FlhAC. These results suggest that FlgN efficiently transfers FlgK/L subunits to FlhAC to promote their export.