TonB and the gram-negative dilemma

Mol Microbiol. 1990 Dec;4(12):2019-25. doi: 10.1111/j.1365-2958.1990.tb00561.x.


TonB protein serves as an energy transducer to couple cytoplasmic membrane energy to high-affinity active transport of iron siderophores and vitamin B12 across the outer membranes of Gram-negative bacteria. The biochemical mechanism of the energy transduction remains to be determined, but important details are already known. TonB is targeted to and anchored in the cytoplasmic membrane by a single membrane-spanning domain and spans the periplasm to physically interact with outer-membrane receptors of the transport ligands. TonB-dependent energy transduction is modulated by ExbB protein, which stabilizes TonB, and possibly by several other proteins including ExbC, ExbD, and TolQ. TonB has a relatively short functional half-life that is accelerated when rates of active transport across the outer membrane are increased. A model that incorporates this information, as well as some tempered speculation, is presented.

Publication types

  • Review

MeSH terms

  • Anti-Bacterial Agents / metabolism
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Biological Transport, Active
  • Cell Membrane / metabolism
  • Energy Transfer
  • Gene Expression Regulation, Bacterial
  • Gram-Negative Bacteria / genetics
  • Gram-Negative Bacteria / metabolism*
  • Iron / metabolism
  • Iron Chelating Agents / metabolism
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mutation
  • Siderophores
  • Vitamin B 12 / metabolism


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Iron Chelating Agents
  • Membrane Proteins
  • Siderophores
  • tonB protein, Bacteria
  • Iron
  • Vitamin B 12