Aggregative adherence fimbriae form compact structures as seen by SAXS.

Area of Science:

• Microbiology
• Structural Biology
• Biophysics

Background:

• Bacterial colonization relies on fimbriae, hair-like appendages on the bacterial surface.
• Enteroaggregative E. coli use aggregative adherence fimbriae, composed of major and minor pilin subunits, for colonization.
• The precise structure and the role of the minor pilin subunit in fimbriae assembly are not well understood.

Purpose of the Study:

• To elucidate the structural morphology of purified aggregative adherence fimbriae in solution.
• To investigate the role of the minor pilin subunit in the assembly and structure of these fimbriae.

Main Methods:

• Small-angle X-ray scattering (SAXS) was employed to determine the structure of purified fimbriae.
• Structural analysis focused on the arrangement of Agg5A (major) and Agg3B (minor) pilin subunits.

Main Results:

• Aggregative adherence fimbriae adopt a compact, pairwise assembled structure on a flexible string, deviating from a straight filament model.
• The absence of the minor subunit (Agg3B) resulted in less compact fimbriae but did not alter their length.
• The minor subunit's importance lies in influencing the overall global structure, not solely at the fimbriae tip.

Conclusions:

• The study reveals novel insights into the structural morphology and assembly dynamics of aggregative adherence fimbriae.
• The minor pilin subunit plays a significant role in the global structural integrity of the fimbriae.
• Findings challenge the previous speculation regarding the minor subunit's localization at the fimbriae tip.