Secretion of curli fibre subunits is mediated by the outer membrane-localized CsgG protein.
Produced by many Enterobacteriaceae spp., curli are biologically important amyloid fibres that have been associated with biofilm formation, host cell adhesion and invasion, and immune system activation. CsgA is the major fibre subunit and CsgE, CsgF and CsgG are non-structural proteins involved in curli biogenesis. We have characterized the role of CsgG in curli subunit secretion across the outer membrane. Directed mutagenesis of CsgG confirmed that its activity is dependent on localization to the outer membrane. Rotary Shadow electron microscopy of purified CsgG suggested that this protein assembles into an oligomeric complex with an apparent central pore. Oligomeric CsgG complexes were confirmed using co-purification experiments. Antibiotic sensitivity assays demonstrated that overexpression of CsgG rendered Escherichia coli susceptible to the antibiotic erythromycin. A 22-amino-acid sequence at the N-terminus of CsgA was sufficient to direct heterologous proteins to the CsgG secretion apparatus. Finally, we determined that CsgG participates in an outer membrane complex with two other curli assembly proteins, CsgE and CsgF.
Robinson
Lloyd S
LS
Department of Molecular Microbiology and Microbial Pathogenesis, Box 8230, Washington University School of Medicine, 660S. Euclid Ave, St Louis, MO 63110, USA.
Ashman
Elisabeth M
EM
Hultgren
Scott J
SJ
Chapman
Matthew R
MR
D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D050356:Lipid Metabolism; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation
D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C489688:csgA protein, E coli