Bacterial Chaperones CsgE and CsgC Differentially Modulate Human α-Synuclein Amyloid Formation via Transient Contacts.

Amyloid formation is historically associated with cytotoxicity， but many organisms produce functional amyloid fibers (e.g.， curli) as a normal part of cell biology. Two E. coli genes in the curli operon encode the chaperone-like proteins CsgC and CsgE that both can reduce in vitro amyloid formation by CsgA. CsgC was also found to arrest amyloid formation of the human amyloidogenic protein α-synuclein， which is involved in Parkinson's disease. Here， we report that the inhibitory effects of CsgC arise due to transient interactions that promote the formation of spherical α-synuclein oligomers. We find that CsgE also modulates α-synuclein amyloid formation through transient contacts but， in contrast to CsgC， CsgE accelerates α-synuclein amyloid formation. Our results demonstrate the significance of transient protein interactions in amyloid regulation and emphasize that the same protein may inhibit one type of amyloid while accelerating another.