Energy Requirements for Protein Secretion via the Flagellar Type III Secretion System.

Protein transport across the cytoplasmic membrane is coupled to energy derived from adenosine triphosphate hydrolysis or the protein motive force (pmf). A sophisticated, multi-component type III secretion system exports substrate proteins of both the bacterial flagellum and virulence-associated injectisome system of many Gram-negative pathogens. The type-III secretion system is primarily a pmf-driven protein exporter. Here, I describe methods to investigate the export of substrate proteins into the culture supernatant under conditions that manipulate the pmf.