Membrane Voltage-dependent Activation of the Transmembrane Export Gate Complex in the Bacterial Flagellar Type III Secretion System

Abstract

Many structural subunits of the bacterial flagellum are transported to the distal end of the growing flagellar structure via a unique and specific protein export apparatus to construct a supramolecular motility machine on the cell surface. The flagellar export apparatus is composed of a transmembrane export gate complex and a cytoplasmic ATPase ring complex. The export gate complex utilizes the transmembrane electrical potential difference of protons, which is defined as membrane voltage, as the energy source to drive proton-coupled protein export. In this review, we describe our current understanding of the membrane voltage-dependent activation mechanism of the export gate complex.