Chaperone Recycling in Late-Stage Flagellar Assembly

Area of Science:

• Microbiology
• Structural Biology
• Molecular Biology

Background:

• The bacterial flagellum is a complex nanomachine essential for motility in Gram-negative bacteria.
• Flagellar assembly involves precise secretion and self-assembly of extracellular components, guided by molecular chaperones.
• The role of the export controller protein FliJ in chaperone-substrate trafficking at the export gate is crucial but poorly understood.

Purpose of the Study:

• To structurally and biophysically characterize the interaction between late-stage flagellar chaperones FliT and FlgN and the export controller FliJ.
• To elucidate the mechanism by which FliJ controls substrate delivery and chaperone recycling during flagellar assembly.

Main Methods:

• Structural characterization of chaperone-FliJ interactions.
• Biophysical assays to determine binding affinity and cooperativity.
• Cell-based experiments to assess functional impact on flagellar assembly.

Main Results:

• FliT and FlgN bind FliJ cooperatively with high affinity at specific sites.
• Chaperone binding induces a conformational change in FliJ, disrupting its coiled-coil structure.
• Altered FliJ structure affects its interaction with the flagellar export gate.

Conclusions:

• FliJ acts as a critical regulator, mediating substrate release from chaperones during late-stage flagellar assembly.
• The disruption of FliJ's structure by chaperones is key to controlling protein delivery to the export gate.
• This mechanism provides a basis for chaperone recycling, ensuring efficient flagellar construction.