ExbB
StructureStructure
ExbB consists of three transmembrane domains (spanning from residues 16-39, 128-155 and 162-194), with two large portions of the protein representing the majority of the protein in the cytoplasm and two smaller portions in the periplasm[1].
ExbB can exist in the TonB system either in a complex with ExbD (to a ratio of 3.5:1) or on its own (where no ExbD is present), which has been suggested to play a part in the diverse roles of TonB[2].
ExbB has a similar sequence and physiological structure to TolQ and is therefore thought to be evolutionarily linked[3].
FunctionFunction
ExbB is essential for TonB-dependent energy transduction as the absence of ExbB prevents TonB responding to the proton motive force, as well as the change of the high-affinity association of TonB for the outer membrane to the cytoplasmic membrane[2].
Loss of ExbB function can be partially replaced by TolQ and vice versa - reduced activities of either of these proteins via a mutant form can be reversed by introducing double mutants[3].
ReferencesReferences
- ↑ 1.0 1.1 Kampfenkel K, Braun V. Topology of the ExbB protein in the cytoplasmic membrane of Escherichia coli. J Biol Chem. 1993 Mar 15;268(8):6050-7. PMID:8449962
- ↑ 2.0 2.1 Held KG, Postle K. ExbB and ExbD do not function independently in TonB-dependent energy transduction. J Bacteriol. 2002 Sep;184(18):5170-3. PMID:12193634
- ↑ 3.0 3.1 Braun V, Herrmann C. Point mutations in transmembrane helices 2 and 3 of ExbB and TolQ affect their activities in Escherichia coli K-12. J Bacteriol. 2004 Jul;186(13):4402-6. PMID:15205446 doi:10.1128/JB.186.13.4402-4406.2004