Architecture of the type IVa pilus machine

Area of Science:

• Bacteriology
• Microbial cell biology
• Structural biology

Background:

• Type IVa pili are essential filamentous appendages on bacterial surfaces.
• These pili mediate crucial cellular processes like motility and adhesion through extension and retraction.
• Understanding the molecular machinery behind pilus dynamics is key to deciphering bacterial behavior.

Purpose of the Study:

• To visualize the in situ structure of the type IVa pilus machine (T4PM) in Myxococcus xanthus.
• To map the precise locations of T4PM core components and minor pilins within the cell.
• To gain mechanistic insights into the assembly, structure, and function of type IVa pili.

Main Methods:

• Cryo-electron tomography was employed to image intact Myxococcus xanthus cells.
• High-resolution (3-4 nm) imaging was performed on both piliated and nonpiliated cells.
• Mutant strains lacking specific T4PM proteins and tagged protein fusions were analyzed.

Main Results:

• The T4PM structure was resolved, revealing an outer membrane pore, periplasmic and cytoplasmic rings, and cytoplasmic/periplasmic components.
• The locations of all 10 core T4PM proteins and minor pilins were systematically mapped.
• Distinct structural differences were observed between piliated and nonpiliated states.

Conclusions:

• The study provides a high-resolution, in situ structural model of the type IVa pilus machine.
• Component mapping elucidates the spatial organization and potential roles in pilus biogenesis.
• These findings advance our understanding of bacterial motility mechanisms mediated by type IVa pili.