R. Fronzes, Eva
Schafer, Luchun Wang, Helen Saibil, Elena Orlova, and Gabriel Waksman*.
Structure of type IV secretion system core complex
Science.
323:266-268.
* indicates corresponding author
Type IV secretion systems (T4SSs) are important virulence factors used by Gram-negative bacterial pathogens to inject effectors into host cells or spread plasmids harbouring antibiotic resistance genes. We report the 15 Å resolution cryo-electron microscopy structure of the core complex of a T4SS. The core complex is composed of three proteins, each present in 14 copies and forming a ~1.1 MDa two-chambered, double membrane-spanning channel. Remarkably, the structure is double walled, open on the cytoplasmic side and constricted on the extracellular side. The double walled structure in which each component appears to span a large part of the entire channel provides a novel and elegant means of regulating channel opening. Overall the T4SS core complex structure is very different in both architecture and composition from that of the type III secretion needle complex, the only other double membrane spanning secretion system that has been structurally characterized.