Abstract
Curli, an adhesive surface fibre produced by Escherichia coli and salmonellae, was proposed on the basis of genetic evidence to follow a distinct assembly pathway involving an extracellular intermediate of the fibre subunit CsgA, the polymerization of which can be induced at the cell surface by a 'nucleator' protein (CsgB). Here we show biochemically that CsgA is actively secreted to the extracellular milieu and that CsgB is surface located. We demonstrate that the putative curli assembly factor CsgG is an outer membrane-located lipoprotein. CsgG is highly resistant to protease digestion both in vivo and in vitro. During curli assembly, CsgG is required to maintain the stability of CsgA and CsgB. In line with this, it is possible to modulate the steady-state levels of CsgA and CsgB by varying intracellular levels of CsgG. This suggests that, in the absence of CsgG, CsgA and CsgB are proteolytically degraded. Moreover, curli production and steady-state levels of CsgA and CsgB can be increased above wild-type levels by overexpression of CsgG, meaning that the quantity of assembled curli fibres can be controlled by this lipoprotein.
Publication types
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Comparative Study
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Research Support, Non-U.S. Gov't
MeSH terms
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Alkaline Phosphatase / genetics
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Alkaline Phosphatase / metabolism
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Amino Acid Sequence
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Anti-Bacterial Agents / pharmacology
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Bacterial Outer Membrane Proteins / genetics
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Bacterial Outer Membrane Proteins / metabolism*
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Bacterial Proteins / genetics
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Bacterial Proteins / metabolism*
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Blotting, Western
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Cloning, Molecular
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Electrophoresis, Polyacrylamide Gel
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Endopeptidase K / metabolism
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Escherichia coli / metabolism*
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Escherichia coli Proteins*
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Fibronectins / metabolism*
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Gene Expression Regulation, Bacterial
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Lipoproteins / genetics
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Lipoproteins / metabolism*
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Membrane Proteins / analysis
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Membrane Proteins / metabolism
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Molecular Sequence Data
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Palmitic Acid / metabolism
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Peptides*
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Protease Inhibitors / pharmacology
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Sodium Dodecyl Sulfate / pharmacology
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Urea / pharmacology
Substances
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Anti-Bacterial Agents
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Bacterial Outer Membrane Proteins
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Bacterial Proteins
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CsgB protein, E coli
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Escherichia coli Proteins
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Fibronectins
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Lipoproteins
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Membrane Proteins
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Peptides
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Protease Inhibitors
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Recombinant Fusion Proteins
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csgA protein, E coli
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Crl protein, Bacteria
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Palmitic Acid
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Sodium Dodecyl Sulfate
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globomycin
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Urea
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Alkaline Phosphatase
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Endopeptidase K