Structure of the S pilus periplasmic chaperone SfaE at 2.2 Å resolution

Stefan D. Knight, Devapriya Choudhury, Scott Hultgren, Jerome Pinkner, Vivian Stojanoff, Andrew Thompson

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S pili are sialic acid binding hair-like appendages expressed by pathogenic strains of Escherichia coll The presence of S pili has been implicated as a virulence factor in both urinary-tract infections and new-born meningitis. Assembly of S pili proceeds via the ubiquitous chaperone/usher pathway. Previously, structures of the homologous chaperones PapD and FimC involved in assembly of P and type-1 pili, respectively, have been solved. Here, the 2.2 Å X-ray structure of the S pilus chaperone SfaE is reported. SfaE has the same overall L-shaped structure as PapD and FimC, with two immunoglobulin-like domains oriented at about a 90° angle to each other. Conserved residues in the subunit-binding cleft known to be critical for chaperone function occupy essentially identical positions in SfaE, FimC and PapD. As in free PapD and FimC, the long F1-G1 loop connecting the two last strands of the N-terminal domain is disordered. SfaE crystallizes as a dimer with an extensive dimer interface involving the subunit-binding surfaces of the chaperone. Dimerization via these regions has previously been observed for PapD and might be a general side effect arising from the subunit-binding properties of periplasmic chaperones. The domain interface contains an extended hydrogen-bond network involving three invariant charged residues and two structurally conserved water molecules. It is suggested that disruption of the domain interactions may destabilize the N-terminal domain through exposure of three conserved hydrophobic residues, thereby promoting release of pilus subunits during pilus assembly.

Original languageEnglish
Pages (from-to)1016-1022
Number of pages7
JournalActa Crystallographica Section D: Biological Crystallography
Issue number6 II
StatePublished - 2002
Externally publishedYes


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