Cell surface-localized CsgF condensate is a gatekeeper in bacterial curli subunit secretion

• Published in: Nature communications 2023-04, Vol.14 (1), p.2392-13, Article 2392
• Main Authors: Swasthi, Hema M., Basalla, Joseph L., Dudley, Claire E., Vecchiarelli, Anthony G., Chapman, Matthew R.
• Format: Article
• Language: English
• Subjects: 631/326/46; 631/45/470/2284; 82/1; 82/29; 82/83; Amino acids; Amyloid; Amyloid - metabolism; Amyloidogenesis; Assembly; Bacteria; Bacterial Proteins - metabolism; Biosynthesis; Cell surface; Condensates; E coli; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - metabolism; Fimbriae, Bacterial - metabolism; Humanities and Social Sciences; multidisciplinary; N-Terminus; Nucleation; Phase separation; Phenylalanine; Proteins; Science; Science (multidisciplinary); Secretion
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-38089-1

Curli are functional amyloids present on the outer membrane of E. coli . CsgF is required for the proper assembly of curli. Here, we found that the CsgF phase separates in vitro and that the ability of CsgF variants to phase-separate is tightly correlated with CsgF function during curli biogenesis. Substitution of phenylalanine residues in the CsgF N-terminus both reduced the propensity of CsgF to phase-separate and impaired curli assembly. Exogenous addition of purified CsgF complemented csgF   − cells. This exogenous addition assay was used to assess the ability of CsgF variants to complement csgF   ‒ cells. CsgF on the cell surface modulated the secretion of CsgA, the curli major subunit, to the cell surface. We also found that the CsgB nucleator protein can form SDS-insoluble aggregates within the dynamic CsgF condensate. We propose that these multicomponent CsgF-B condensates form a nucleation-competent complex that templates CsgA amyloid formation on the cell surface. In this work, the authors show that the phase separation of a cell surface-associated protein called CsgF is critical to mediate the secretion and assembly of the amyloidogenic curli subunits.