InterPro domain: IPR018385

Escherichia coli contains four different secondary carriers (DcuA, DcuB, DcuC, and DctA) for C4-dicarboxylates [ 1 , 2 , 3 , 4 ] DcuA is used for aerobic growth on C4-dicarboxylates [ 5 , 5 ], whereas the Dcu carriers (encoded by the dcuA, dcuB, and dcuC genes) are used under anaerobic conditions and form a distinct family of carriers [ 6 , 6 , 7 , 8 , 8 , 9 ]. Each of the Dcu carriers is able to catalyze the uptake, antiport, and possibly also efflux of C4-dicarboxylates. DcuB is the major C4-dicarboxylate carrier for fumarate respiration with high fumarate-succinate exchange activity. It is synthesized only in the absence of oxygen and nitrate and in the presence of C4-dicarboxylates [ 9 , 9 , 10 , 11 ]. DcuA is expressed constitutively in aerobic and anaerobic growth and can substitute for DcuB [ 12 , 12 ]. These proteins are members of the C4-dicarboxylate Uptake C (DcuC) family. DcuC has 12 GES predicted transmembrane regions, is induced only under anaerobic conditions, and is not repressed by glucose. DcuC may therefore function as a succinate efflux system during anaerobic glucose fermentation. However, when overexpressed, it can replace either DcuA or DcuB in catalyzing fumarate-succinate exchange and fumarate uptake [ 12 , 12 ]. DcuC shows the same transport modes as DcuA and DcuB (exchange, uptake, and presumably efflux of C4-dicarboxylates) [ 13 ].

1. Inactivation and regulation of the aerobic C(4)-dicarboxylate transport (dctA) gene of Escherichia coli. J. Bacteriol. 181, 5624-35
2. Anaerobic fumarate transport in Escherichia coli by an fnr-dependent dicarboxylate uptake system which is different from the aerobic dicarboxylate uptake system. J. Bacteriol. 174, 5533-9
3. Escherichia coli possesses two homologous anaerobic C4-dicarboxylate membrane transporters (DcuA and DcuB) distinct from the aerobic dicarboxylate transport system (Dct). J. Bacteriol. 176, 6470-8
4. Identification of a third secondary carrier (DcuC) for anaerobic C4-dicarboxylate transport in Escherichia coli: roles of the three Dcu carriers in uptake and exchange. J. Bacteriol. 178, 7241-7
5. The uptake of C4-dicarboxylic acids by Escherichia coli. Eur. J. Biochem. 18, 274-81
6. Transport of C4-dicarboxylates by anaerobically grown Escherichia coli. Energetics and mechanism of exchange, uptake and efflux. Eur. J. Biochem. 222, 605-14
7. Molecular phylogeny as a basis for the classification of transport proteins from bacteria, archaea and eukarya. Adv. Microb. Physiol. 40, 81-136
8. Alternative respiratory pathways of Escherichia coli: energetics and transcriptional regulation in response to electron acceptors. Biochim. Biophys. Acta 1320, 217-34
9. Identification and characterization of a two-component sensor-kinase and response-regulator system (DcuS-DcuR) controlling gene expression in response to C4-dicarboxylates in Escherichia coli. J. Bacteriol. 181, 1238-48
10. Transcriptional regulation and organization of the dcuA and dcuB genes, encoding homologous anaerobic C4-dicarboxylate transporters in Escherichia coli. J. Bacteriol. 180, 6586-96
11. Fumarate regulation of gene expression in Escherichia coli by the DcuSR (dcuSR genes) two-component regulatory system. J. Bacteriol. 180, 5421-5
12. Functioning of DcuC as the C4-dicarboxylate carrier during glucose fermentation by Escherichia coli. J. Bacteriol. 181, 3716-20