Type IV secretion systems span the two membranes of Gram-negative bacteria, with three proteins —— VirB7, VirB9 and VirB10 — assembled into a 1.05 megadalton core spanning the inner and outer membranes. Here, the crystal structure of an outer-membrane complex is presented. The structure is the largest determined for an outer-membrane channel and is unprecedented in being composed of three proteins.
- Vidya Chandran
- Rémi Fronzes
- Gabriel Waksman