title: CsgE is a curli secretion specificity factor that prevents amyloid fibre aggregation.
abstract: Curli are extracellular amyloid fibres produced by Escherichia coli that are critical for biofilm formation and adhesion to biotic and abiotic surfaces. CsgA and CsgB are the major and minor curli subunits, respectively, while CsgE, CsgF and CsgG direct the extracellular localization and assembly of curli subunits into fibres. The secretion and stability of CsgA and CsgB are dependent on the outer membrane lipoprotein CsgG. Here, we identified functional interactions between CsgG and CsgE during curli secretion. We discovered that CsgG overexpression restored curli production to a csgE strain under curli-inducing conditions. In antibiotic sensitivity and protein secretion assays, CsgG expression alone allowed translocation of erythromycin and small periplasmic proteins across the outer membrane. Coexpression of CsgE with CsgG blocked non-specific protein and antibiotic passage across the outer membrane. However, CsgE did not block secretion of proteins containing a 22-amino-acid putative outer membrane secretion signal of CsgA (A22). Finally, using purified proteins, we found that CsgE prohibited the self-assembly of CsgA into amyloid fibres. Collectively, these data indicate that CsgE provides substrate specificity to the curli secretion pore CsgG, and acts directly on the secretion substrate CsgA to prevent premature subunit assembly.
authors.affiliation: Department of Molecular Microbiology and Microbial Pathogenesis, Washington University School of Medicine, Campus Box 8230, 660 S. Euclid Avenue, St Louis, MO 63110, USA.
authors.forename: Ashley A
authors.initials: AA
authors.lastname: Nenninger
authors.forename: Lloyd S
authors.initials: LS
authors.lastname: Robinson
authors.forename: Neal D
authors.initials: ND
authors.lastname: Hammer
authors.forename: Elisabeth Ashman
authors.initials: EA
authors.lastname: Epstein
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Badtke
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Hultgren
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Chapman
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011489:Protein Denaturation; D025941:Protein Interaction Mapping; D055503:Protein Multimerization
chemical_list: D001426:Bacterial Proteins; C109182:CsgB protein, E coli; C561979:CsgE protein, E coli; C534546:CsgG protein, E coli; D029968:Escherichia coli Proteins; D008074:Lipoproteins; D026901:Membrane Transport Proteins; C489688:csgA protein, E coli; C077481:Crl protein, Bacteria