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Paolo Rossi1, Qiong Xing2, Elisabetta Bini1

  • 1Deparment of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, United States.

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Bacterial flagellar assembly relies on precise protein transport. This study reveals how late-stage chaperones FliT and FlgN bind the export controller FliJ, controlling substrate delivery and chaperone recycling for flagellar construction.

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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.