Abstract
Curli are surface organelles of Escherichia coli. These fibrous proteins, formed by polymerization of a 15-kDa subunit, are expressed by E. coli strains associated with severe infections in humans. A remarkable property of curli is their ability to interact with a wide range of human proteins, interactions that contribute to the enhanced virulence of curli-expressing E. coli. To define the protein-binding region(s) of curli, we investigated the binding properties of overlapping synthetic peptides covering the curli subunit. Two peptides, one covering a 24-amino acid residue sequence in the NH(2)-terminal half of the subunit (NNS24) and one corresponding to the 26 COOH-terminal residues (VDQ26), were found to bind a number of human proteins. Physiochemical analysis revealed that NNS24 adopts a thermally stable beta-structure, and in solution the peptide forms soluble multimers, predominantly octamers. Intact curli are known to activate the proinflammatory and procoagulant contact system, and when added to human plasma, the NNS24 and VDQ26 peptides induced the release of the potent vasoactive peptide bradykinin. The results map important curli functions to the regions corresponding to the NNS24 and VDQ26 sequences.
Highlights
Some strains of Escherichia coli and Salmonella express fibrous surface proteins that aggregate into matrix-like structures attached to the bacterial surface
This difference in expression suggests a role for curli in E. coli pathogenicity, a notion that is further supported by findings that curli induce proinflammatory cytokines and that anti-CsgA antibodies are found in serum samples from patients with E. coli sepsis [14]
Available data indicate that the CsgA subunit is responsible for most of these interactions, which in some cases have been shown to contribute to E. coli virulence
Summary
Some strains of Escherichia coli and Salmonella express fibrous surface proteins that aggregate into matrix-like structures attached to the bacterial surface. Intact curli are known to activate the proinflammatory and procoagulant contact system, and when added to human plasma, the NNS24 and VDQ26 peptides induced the release of the potent vasoactive peptide bradykinin.
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