Donor strand exchange and conformational changes during E. coli fimbrial formation

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Fimbriae and pili are essential macromolecular surface structures in Gram-negative bacteria, mediating cellular adhesion.
• Understanding their assembly is key to deciphering bacterial pathogenesis and developing targeted therapeutics.

Purpose of the Study:

• To elucidate the high-resolution structure of a complex of Escherichia coli fimbrial proteins (FimH, FimG, FimF, FimC).
• To provide the most complete model to date of native fimbrial subunit arrangement and assembly.
• To investigate conformational changes during the usher/chaperone assembly process.

Main Methods:

• X-ray crystallography at 2.7Å resolution.
• Analysis of protein-protein interactions via donor strand complementation.
• Comparison of chaperone-bound complexes with the assembled fimbrial structure.

Main Results:

• A detailed 2.7Å resolution structure of the FimH, FimG, FimF, and FimC complex was determined.
• The FimH, FimG, and FimF proteins form the fimbrial tip, with FimC acting as a chaperone.
• Significant conformational changes, including shifts up to 14Å, were observed in non-chaperone subunits upon chaperone replacement and during assembly, particularly in the FimH domains and the donor strand binding groove.

Conclusions:

• The study provides an unprecedented structural model for fimbrial assembly in E. coli.
• Observed conformational shifts in FimH domains and other subunits are critical for subunit-subunit interactions and likely dictate specificity.
• These findings offer insights into the mechanism of bacterial adhesion and potential targets for antimicrobial strategies.