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FimC is a periplasmic PapD-like chaperone that directs assembly of type 1 pili in bacteria
C H Jones1, J S Pinkner, A V Nicholes
1Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110.
Abstract:
Biogenesis of the type 1 pilus fiber in Escherichia coli requires the product of the fimC locus. We have demonstrated that FimC is a member of the periplasmic chaperone family. The deduced primary sequence of FimC shows a high degree of homology to PapD and fits well with the derived consensus sequence for periplasmic chaperones, predicting that it has an immunoglobulin-like topology. The chaperone activity of FimC was demonstrated by purifying a complex that FimC forms with the FimH adhesion. A fimC1 null allele could be complemented by the prototype member of the chaperone superfamily, PapD, resulting in the production of adhesive type 1 pili. The general mechanism of action of members of the chaperone superfamily was demonstrated by showing that the ability of PapD to assemble both P and type 1 pili was dependent on an invariant arginine residue (Arg-8), which forms part of a conserved subunit binding site in the cleft of PapD. We suggest that the conserved cleft is a subunit binding feature of all members of this protein family. These studies point out the general strategies used by Gram-negative bacteria to assemble adhesins into pilus fibers, allowing them to promote attachment to eukaryotic receptors.
Insights
Escherichia coli uses the FimC chaperone protein to build type 1 pili fibers, essential for bacterial attachment. This chaperone is crucial for assembling adhesins into pili, enabling bacteria to bind to host cells.
Area of Science:
- Microbiology
- Bacterial pathogenesis
- Protein structure and function
Background:
- Type 1 pilus biogenesis in Escherichia coli is essential for bacterial adhesion.
- The fimC gene product plays a critical role in this process.
- Periplasmic chaperones are known to be involved in pilus assembly.
Purpose of the Study:
- To characterize the FimC protein as a periplasmic chaperone.
- To elucidate the mechanism of type 1 pilus assembly mediated by FimC.
- To investigate the conserved mechanisms of pilus biogenesis in Gram-negative bacteria.
Main Methods:
- Sequence homology analysis of FimC.
- Purification and characterization of FimC-FimH complexes.
- Complementation studies using PapD chaperone.
- Site-directed mutagenesis to identify critical residues.
Main Results:
- FimC was identified as a periplasmic chaperone with homology to PapD and an immunoglobulin-like fold.
- FimC forms a complex with the FimH adhesin, demonstrating its chaperone activity.
- PapD, a known chaperone, could complement fimC null mutations, producing functional type 1 pili.
- An invariant arginine residue (Arg-8) in PapD's conserved cleft was crucial for pilus assembly.
Conclusions:
- FimC is a key periplasmic chaperone in type 1 pilus biogenesis in E. coli.
- The conserved cleft in chaperones like PapD and FimC is vital for subunit binding and pilus assembly.
- These findings reveal general strategies employed by Gram-negative bacteria for assembling adhesins into pili for host cell attachment.