The Tol-Pal proteins of the Escherichia coli cell envelope: an energized system required for outer membrane integrity?

Res Microbiol. Jul-Aug 2001;152(6):523-9. doi: 10.1016/s0923-2508(01)01226-8.


The outer membrane of gram-negative bacteria acts as a barrier against harmful lipophilic compounds and larger molecules unable to diffuse freely through the porins. However, outer membrane proteins together with the Tol-Pal and TonB systems have been exploited for the entry of macromolecules such as bacteriocins and phage DNA through the Escherichia coli cell envelope. The TonB system is involved in the active transport of iron siderophores and vitamin B12, while no more precise physiological role of the Tol-Pal system has yet been defined than its requirement for cell envelope integrity. These two systems, containing an energized inner membrane protein interacting with outer membrane proteins, share similarities.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Amino Acid Sequence
  • Bacterial Outer Membrane Proteins*
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / physiology*
  • Escherichia coli / chemistry
  • Escherichia coli / genetics
  • Escherichia coli / physiology*
  • Escherichia coli Proteins*
  • Lipoproteins / chemistry
  • Lipoproteins / genetics
  • Lipoproteins / physiology*
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / physiology*
  • Molecular Sequence Data
  • Peptidoglycan / chemistry
  • Peptidoglycan / genetics
  • Proteoglycans*
  • Sequence Alignment
  • Sequence Homology, Amino Acid


  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • Escherichia coli Proteins
  • ExcC protein, E coli
  • Lipoproteins
  • Membrane Proteins
  • Peptidoglycan
  • Proteoglycans
  • tolA protein, E coli
  • tonB protein, Bacteria
  • tonB protein, E coli
  • PplA protein, Legionella pneumophila