[W1-6] Energy coupling mechanism of the bacterial flagellar type III secretion system
The bacterial flagellum is a supramolecular motility machine consisting of a reversible rotary motor, a universal joint and a helical propeller. Flagellar building blocks are transported via the flagellar type III secretion system (fT3SS) from the cytoplasm to the distal end of the growing structure where their assembly occurs. The fT3SS is composed of a transmembrane export gate complex powered by proton motive force across the cell membrane and a cytoplasmic ATPase ring complex. FlhA is a transmembrane export gate protein consisting of the N-terminal transmembrane domain with eight transmembrane helices and the C-terminal cytoplasmic domain. FlhA not only acts as a voltage-gated proton channel to couple proton flow with protein export but also ensures the strict order of protein export for efficient flagellar assembly. The C-terminal cytoplasmic domain of FlhA undergoes cyclic domain motions during flagellar protein export, and such domain motions are critical for rapid and efficient proton-coupled protein export. In this workshop, I will discuss our current understanding of the energy coupling mechanism of the fT3SS.