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<i>In vivo</i> tests of the <i>E. coli</i> TonB system working model-interaction of ExbB with unknown proteins, identification of TonB-ExbD transmembrane heterodimers and PMF-dependent ExbD structures.

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The Intrinsically Disordered Region of ExbD Is Required for Signal Transduction.

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Going Outside the TonB Box: Identification of Novel FepA-TonB Interactions <i>In Vivo</i>.

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From Homodimer to Heterodimer and Back: Elucidating the TonB Energy Transduction Cycle.

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The TonB system uses proton energy to transport nutrients across bacterial outer membranes. TonB carboxy terminus interactions are key for transporter binding, with monomeric TonB being essential for activity.

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Biochemistry

Background:

  • Gram-negative bacteria utilize the TonB system for active transport across the outer membrane, a process crucial for nutrient acquisition.
  • This system converts proton motive force from the cytoplasmic membrane into mechanical energy for nutrient uptake.
  • The TonB system is a target for developing antibiotics, particularly for combating iron acquisition in pathogenic bacteria.

Purpose of the Study:

  • To elucidate the mechanism of energy transduction by the TonB system in Gram-negative bacteria.
  • To investigate the role of TonB's amino-terminal and carboxy-terminal domains in its function and interaction with other proteins.
  • To understand how TonB interacts with outer membrane transporters and the ExbB/ExbD complex.

Main Methods:

  • Site-directed mutagenesis of TonB, focusing on residue H20.
  • Analysis of TonB homodimerization through its amino-terminal and carboxy-terminal domains.
  • Investigating the functional consequences of trapping TonB in different conformational states.

Main Results:

  • TonB homodimers formed via the amino terminus retained activity, while those formed via the carboxy terminus were inactive.
  • Inactive TonB H20A mutations affected carboxy-terminal homodimer formation, suggesting monomeric interaction with transporters.
  • Evidence suggests a separate pool of ExbD homodimers involved in initiating the energy transduction cycle.

Conclusions:

  • The TonB carboxy terminus interacts with outer membrane transporters as a monomer.
  • The ExbD carboxy terminus plays a role in modulating these interactions.
  • A proposed model details the initiation and progression of the TonB energy transduction cycle involving homodimers of TonB and ExbD.