In Escherichia coli Xuzhou21, curli subunits are produced and secreted into the outer membrane through the CsgG secretion channel. Curli are a unique group of functional amyloids, which are crucial for host cell adhesion, biofilm formation and colonization of inert surfaces. They are involved in harmful diseases in humans, since they share similar structural and biochemical characteristics with amyloid fibers. Curli subunits are secreted into the outer membrane through the CsgG secretion channel. The crystal structure of CsgG showed that it is a symmetric nonameric channel, composed of monomers each having four strands spanning the outer membrane. A 36-stranded ß barrel is formed from nine CsgG monomers. CsgG could perhaps reduce the biofilm formation by controlling Curli secretion and that is why it is studied as a putative antibiotics target.

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