Disease relevance of ECs3890

• Topology of the ExbB protein in the cytoplasmic membrane of Escherichia coli [1].
• We note sequence similarity between MotA and ExbB, a cytoplasmic-membrane protein that energizes outer-membrane transport in Gram-negative bacteria [2].

High impact information on ECs3890

• It is postulated that FecA, TonB, ExbB and ExbD transfer the signal across the outer membrane, while the regulatory protein FecR transmits the signal across the cytoplasmic membrane to FecI in the cytoplasm [3].
• 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].
• 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].
• 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, deletion of valine 17 within the aminoterminal transmembrane anchor of TonB resulted in complete loss of TonB activity, as well as loss of detectable in vivo crosslinking into a 59 kDa complex believed to contain ExbB [6].

Chemical compound and disease context of ECs3890

• Replacement of glutamate 176, the only charged amino acid in the third transmembrane helix of ExbB, with alanine (E176A) abolished ExbB activity in all determined ExbB-dependent functions of Escherichia coli [7].

Biological context of ECs3890

• The deduced amino acid sequence of P. putida ExbB showed 58.6% homology with its E. coli homologue, but, unlike the E. coli protein, it has a N-terminal extension of 91 amino acids [8].
• Point mutations in transmembrane helices 2 and 3 of ExbB and TolQ affect their activities in Escherichia coli K-12 [7].
• 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 [9].
• Cells with mutations in both exbB and tolQ had no measurable cobalamin transport and thus had a phenotype that was essentially the same as TonB-. I conclude that the ExbB protein is a normal component of the energy coupling system for the transport of cobalamin across the outer membrane [10].
• 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 [11].

Anatomical context of ECs3890

• 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].

Associations of ECs3890 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 [11].
• The signal elicited by ferric citrate crosses the outer membrane via TonB, ExbB, and ExbD [12].

References