The FlgN chaperone activates the Na+-driven engine of the Salmonella flagellar protein export apparatus
Tohru Minamino, Miki Kinoshita, Yusuke V. Morimoto, Keiichi Namba
Abstract
Abstract The bacterial flagellar protein export machinery consists of a transmembrane export gate complex and a cytoplasmic ATPase complex. The gate complex has two intrinsic and distinct H + -driven and Na + -driven engines to drive the export of flagellar structural proteins. Salmonella wild-type cells preferentially use the H + -driven engine under a variety of environmental conditions. To address how the Na + -driven engine is activated, we analyzed the fliJ( Δ 13 – 24) fliH( Δ 96 – 97) mutant and found that the interaction of the FlgN chaperone with FlhA activates the Na + -driven engine when the ATPase complex becomes non-functional. A similar activation can be observed with either of two single-residue substitutions in FlhA. Thus, it is likely that the FlgN-FlhA interaction generates a conformational change in FlhA that allows it to function as a Na + channel. We propose that this type of activation would be useful for flagellar construction under conditions in which the proton motive force is severely restricted.