Related Experiment Videos
Structure of the S pilus periplasmic chaperone SfaE at 2.2 A resolution
Stefan D Knight1, Devapriya Choudhury, Scott Hultgren
1Department of Molecular Biology, Uppsala Biomedical Centre, Swedish University of Agricultural Sciences, Box 590, S-753 24 Uppsala, Sweden. stefan@xray.bmc.uu.se
Abstract:
S pili are sialic acid binding hair-like appendages expressed by pathogenic strains of Escherichia coli. 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 A 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 degrees 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.
Insights
The S pilus chaperone SfaE shares a similar structure with other pili chaperones, crucial for bacterial assembly. Its dimerization mechanism may regulate pilus subunit release during assembly in pathogenic E. coli.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- S pili are critical virulence factors in pathogenic Escherichia coli, contributing to urinary tract infections and meningitis.
- These pili assemble via the chaperone/usher pathway, a common mechanism in bacteria.
Purpose of the Study:
- To determine the X-ray structure of the S pilus chaperone SfaE.
- To compare the structural features of SfaE with homologous chaperones PapD and FimC.
- To elucidate the potential role of SfaE dimerization in pilus assembly regulation.
Main Methods:
- X-ray crystallography was used to determine the 2.2 Å structure of SfaE.
- Structural comparisons were made with previously solved structures of PapD and FimC.
- Analysis of the SfaE dimer interface and conserved residues was performed.
Main Results:
- SfaE exhibits an L-shaped structure with two immunoglobulin-like domains, similar to PapD and FimC.
- Conserved residues in the subunit-binding cleft are identically positioned across these chaperones.
- SfaE crystallizes as a dimer, with the interface involving subunit-binding surfaces, a feature also seen in PapD.
Conclusions:
- SfaE's structure and conserved residues highlight its role in the chaperone/usher pathway.
- The observed dimerization of SfaE may be a general property of periplasmic chaperones, potentially regulating pilus assembly.
- Disruption of the dimer interface could destabilize SfaE, facilitating pilus subunit release.