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Related Experiment Video

Updated: Jun 5, 2026

X-Ray Crystallography to Study the Oligomeric State Transition of the Thermotoga maritima M42 Aminopeptidase TmPep1050
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Published on: May 13, 2020

The TonB dimeric crystal structures do not exist in vivo.

Kathleen Postle1, Kyle A Kastead, Michael G Gresock

  • 1Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA. kup14@psu.edu

Mbio
|December 24, 2010
PubMed
Summary
This summary is machine-generated.

The TonB protein

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Area of Science:

  • Microbiology
  • Structural Biology
  • Biochemistry

Background:

  • The TonB system in Escherichia coli energizes nutrient transport across the outer membrane using proton motive force (PMF).
  • ExbB and ExbD proteins harvest PMF and transfer energy to TonB.
  • The TonB carboxy terminus interacts with outer membrane transporters for ligand translocation.

Purpose of the Study:

  • To investigate the in vivo conformation of the TonB carboxy terminus.
  • To identify functionally important and irreplaceable residues within the TonB carboxy terminus.
  • To reconcile discrepancies between in vitro crystal structures and in vivo function.

Main Methods:

  • Cysteine scanning mutagenesis of the entire TonB carboxy terminus.
  • Analysis of disulfide-linked dimer formation in vitro.
  • Phenotypic analysis of Cys substitution mutants in various assays.

Main Results:

  • Cysteine substitutions at predicted dimer interfaces did not form disulfide bonds.
  • Mutations at distant sites in crystal structures efficiently formed dimers.
  • Seven functionally important residues were identified, but none were irreplaceable.
  • Mutant phenotypes varied depending on the assay and specific residue substitution.
  • All identified residues showed synergistic effects.
  • Observed properties contradicted the buried nature of residues in solved crystal structures.

Conclusions:

  • The previously solved dimeric crystal structures of the TonB carboxy terminus likely do not represent the in vivo conformation.
  • Aberrant structures may result from the absence of the TonB transmembrane domain, ExbB, ExbD, and/or PMF during structural determination.
  • Further studies are needed to elucidate the true in vivo structure and mechanism of TonB-mediated transport.