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Gene Review:

ECs3889 - biopolymer transport protein ExbD

Escherichia coli O157:H7 str. Sakai

Killmann, H. et al., Higgs, P.I. et al., Sauter, A. et al., Higgs, P.I. et al., Traub, I. et al., et al.

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Disease relevance of ECs3889

The ExbB protein together with the ExbD and TonB proteins is involved in energy-coupled transport across the outer membrane of Escherichia coli [1].
Escherichia coli and related Gram-negative bacteria contain an energy-coupled transport system through the outer membrane which consists of the proteins TonB, ExbB, ExbD anchored in the cytoplasmic membrane and receptors in the outer membrane [2].

High impact information on ECs3889

Rather, FecA and the TonB, ExbB and ExbD proteins are involved in induction of the fec transport genes independent of their role in ferric citrate transport across the outer membrane [3].
Since no energy source is known in the outer membrane it is assumed that energy is provided through the action of the TonB, ExbB and ExbD proteins, which are anchored to the cytoplasmic membrane [4].
This implies that in wild-type cells ferrichrome transport through the outer membrane is the rate-limiting step and that TonB, ExbB and ExbD are only required for outer membrane transport [4].
ExbB and ExbD, despite being encoded from the same operon, were not equimolar, being present at 2463 +/- 522 and 741 +/- 105 copies respectively [5].
In this study, we report the per cell numbers of TonB, ExbB, ExbD and FepA for cells grown under iron-replete and iron-limited conditions [5].

Biological context of ECs3889

Dimer formation was reduced but not abolished in a mutant lacking ExbB and ExbD, suggesting that these complex components may influence dimerization but are not strictly required and that the N-terminal cytoplasmic membrane anchor and the C-terminal region are important for dimer formation [6].
The cytoplasmic membrane proteins ExbB and ExbD support TonB-dependent active transport of iron siderophores and vitamin B12 across the essentially unenergized outer membrane of Escherichia coli [7].

Anatomical context of ECs3889

It is concluded that the only hydrophobic segment of ExbD, encompassing residues 23 to 43, forms a transmembrane domain and that residues 1 to 22 are located in the cytoplasm and residues 44 to 141 are located in the periplasm [8].

Associations of ECs3889 with chemical compounds

In this study, in vivo formaldehyde cross-linking analysis was used to investigate the interactions of T7 epitope-tagged ExbB or ExbD proteins [7].

References

Topology of the ExbB protein in the cytoplasmic membrane of Escherichia coli. Kampfenkel, K., Braun, V. J. Biol. Chem. (1993) [Pubmed]
Activity domains of the TonB protein. Traub, I., Gaisser, S., Braun, V. Mol. Microbiol. (1993) [Pubmed]
Signal transfer through three compartments: transcription initiation of the Escherichia coli ferric citrate transport system from the cell surface. Härle, C., Kim, I., Angerer, A., Braun, V. EMBO J. (1995) [Pubmed]
Conversion of the FhuA transport protein into a diffusion channel through the outer membrane of Escherichia coli. Killmann, H., Benz, R., Braun, V. EMBO J. (1993) [Pubmed]
Quantification of known components of the Escherichia coli TonB energy transduction system: TonB, ExbB, ExbD and FepA. Higgs, P.I., Larsen, R.A., Postle, K. Mol. Microbiol. (2002) [Pubmed]
In vivo evidence for TonB dimerization. Sauter, A., Howard, S.P., Braun, V. J. Bacteriol. (2003) [Pubmed]
Interactions in the TonB-dependent energy transduction complex: ExbB and ExbD form homomultimers. Higgs, P.I., Myers, P.S., Postle, K. J. Bacteriol. (1998) [Pubmed]
Membrane topology of the Escherichia coli ExbD protein. Kampfenkel, K., Braun, V. J. Bacteriol. (1992) [Pubmed]

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