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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.

The protective effect of Brazilian propolis and its extract Artepillin C against ferric nitrilotriacetate (Fe-NTA)-induced renal lipid peroxidation and carcinogenesis was studied in male ddY mice. Fe-NTA-induced renal lipid peroxidation leads to a high incidence of renal cell carcinoma (RCC) in mice. Administration of propolis by gastric intubation 2 h before or Artepillin C at either the same time, 2 h, or 5 h before the intraperitoneal injection of Fe-NTA (7 mg Fe/kg) effectively inhibited renal lipid peroxidation. This was evaluated from the measurement of renal thiobarbituric acid-reactive substances (TBARS) or histochemical findings of 4-hydroxy-2-nonenal (4-HNE)-modified proteins and 8-hydroxy-2'-deoxyguanosine (8-OHdG). Repeated injection of Fe-NTA (10 mg Fe/kg per day, twice a week for a total of 16 times in 8 weeks) caused subacute nephrotoxicity as revealed by necrosis and pleomorphic large nuclear cells in the renal proximal tubules, and gave rise to RCC 12 months later. A protective effect from carcinogenicity was observed in mice given propolis or Artepillin C. Furthermore, the mice given Fe-NTA only developed multiple cysts composed of precancerous lesions with multilayered and proliferating large atypical cells. Mice treated with propolis and Artepillin C also had cysts, but these were dilated and composed of flat cells. These results suggest that propolis and Artepillin C prevent oxidative renal damage and the carcinogenesis induced by Fe-NTA in mice.

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