Figure 2.
The curli biogenesis system possesses a unique outer membrane secretion apparatus. The CsgG pore is composed of eight subunits (the front three have been removed to improve clarity) with a 2nm wide central pore. Both CsgE and CsgF interact directly with the CsgG pore. CsgE is periplasmic and required for directing soluble CsgA to the CsgG pore for secretion while CsgF is surface exposed and contributes to the assembly of CsgB into a surface associated, amyloid-templating conformation. Once outside the cell, CsgA interacts with CsgB and assembles into an amyloid fiber.