Cryo-EM analysis of the SctV cytosolic domain from the Enteropathogenic E.coli T3SS injectisome.
The bacterial injectisome and flagella both rely on type III secretion systems for their assembly. The syringe-like injectisome creates a continuous channel between the bacterium and the host cell, through which signal-modulating effector proteins are secreted. The inner membrane pore protein SctV controls the hierarchy of substrate selection and may also be involved in energizing secretion. We present the 4.7 Å cryo-EM structure of the SctV cytosolic domain (SctVC) from the enteropathogenic Escherichia coli injectisome. SctVC forms a nonameric ring with primarily electrostatic interactions between its subunits. Molecular dynamics simulations show that monomeric SctVC maintains a closed conformation, in contrast with previous studies on flagellar homologue FlhA. Comparison with substrate-bound homologues suggest that a conformational change would be required to accommodate binding partners.