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2.A.13 The C4-Dicarboxylate Uptake (Dcu) Family

Several proteins of the Dcu family have been sequenced as of 1/1998, but all are from Gram-negative bacteria. Two are from E. coli, one is from Haemophilus influenzae, one is from Serratia marscesens and one (a large, N-terminally truncated fragment) is from Wolenella succinogens. The fully sequenced proteins are of fairly uniform size (434-446 residues). They possess 12 putative transmembrane α-helical spanners, but DcuA has 10 experimentally determined TMSs with both the N- and C-termini localized to the periplasm. For DcuA, the 'positive inside' rule is obeyed, and two putative TMSs are localized to a cytoplasmic loop between TMSs 5 and 6 and in the C-terminal periplasmic region.

The two E. coli proteins, DcuA and DcuB, transport aspartate, malate, fumarate and succinate and function as antiporters with any two of these substrates. They exhibit 36% identity with 63% similarity, and both transport fumarate in exchange for succinate with the same affinity (30 μM). Since DcuA is encoded in an operon with the gene for aspartase, and DcuB is encoded in an operon with the gene for fumarase, their physiological functions may be to catalyze aspartate:fumarate and fumarate:malate exchange during the anaerobic utilization of aspartate and fumarate, respectively. However, the electroneutral antiport of fumarate for succinate during anaerobic fumarate respiration has been demonstrated, and both permeases are induced under anaerobic conditions and are subject to catabolite repression. The two transporters can apparently substitute for each other under certain physiological conditions (Engel et al., 1994; Six et al., 1994; Unden and Bongaerts, 1997).

The generalized transport reaction catalyzed by the proteins of the Dcu family is:

Dicarboxylate1 (out) + Dicarboxylate2 (in) ⇌ Dicarboxylate1 (in) + Dicarboxylate2 (out)

This family belongs to the: IT Superfamily.

References associated with 2.A.13 family:

Bauer, J., M.J. Fritsch, T. Palmer, and G. Unden. (2011). Topology and accessibility of the transmembrane helices and the sensory site in the bifunctional transporter DcuB of Escherichia coli. Biochemistry 50: 5925-5938. 21634397
Chen, J., X. Zhu, Z. Tan, H. Xu, J. Tang, D. Xiao, and X. Zhang. (2014). Activating C4-dicarboxylate transporters DcuB and DcuC for improving succinate production. Appl. Microbiol. Biotechnol. 98: 2197-2205. 24323285
Engel, P., R. Krämer, and G. Unden. (1994). Transport of C4-dicarboxylates by anaerobically grown Escherichia coli: energetics and mechanism of exchange, uptake and efflux. Eur. J. Biochem. 222: 605-614. 8020497
Golby, P., D.J. Kelly, J.R. Guest, and S.C. Andrews. (1998). Topological analysis of DcuA, an anaerobic C4-dicarboxylate transporter of Escherichia coli. J. Bacteriol. 180: 4821-4827. 9733683
Kim, O.B., S. Lux, and G. Unden. (2007). Anaerobic growth of Escherichia coli on D-tartrate depends on the fumarate carrier DcuB and fumarase, rather than the L-tartrate carrier TtdT and L-tartrate dehydratase. Arch. Microbiol. 188: 583-589. 17643228
Kleefeld, A., B. Ackermann, J. Bauer, J. Krämer, and G. Unden. (2009). The fumarate/succinate antiporter DcuB of Escherichia coli is a bifunctional protein with sites for regulation of DcuS-dependent gene expression. J. Biol. Chem. 284: 265-275. 18957436
Saier, M.H., Jr., B.H. Eng, S. Fard, J. Garg, D.A. Haggerty, W.J. Hutchinson, D.L. Jack, E.C. Lai, H.J. Liu, D.P. Nusinew, A.M. Omar, S.S. Pao, I.T. Paulsen, J.A. Quan, M. Sliwinski, T.-T. Tseng, S. Wachi, and G.B. Young. (1999). Phylogenetic characterization of novel transport protein families revealed by genome analyses. Biochim. Biophys. Acta 1422: 1-56. 10082980
Six, S., S.C. Andrews, G. Unden, and J.R. Guest. (1994). Escherichia coli possesses two homologous anaerobic C4-dicarboxylate membrane transporters (DcuA and DcuB) distinct from the aerobic dicarboxylate transport system (Dct). J. Bacteriol. 176: 6470-6478. 7961398
Stopp, M., C. Schubert, and G. Unden. (2021). Conversion of the Sensor Kinase DcuS to the Fumarate Sensitive State by Interaction of the Bifunctional Transporter DctA at the TM2/PAS-Linker Region. Microorganisms 9:. 34203512
Unden, G. and J. Bongaerts. (1997). Alternative respiratory pathways of Escherichia coli: energetics and transcriptional regulation in response to electron acceptors. Biochim. Biophys. Acta 1320: 217-234. 9230919
Unden, G., S. Wörner, and C. Monzel. (2016). Cooperation of Secondary Transporters and Sensor Kinases in Transmembrane Signalling: The DctA/DcuS and DcuB/DcuS Sensor Complexes of Escherichia coli. Adv Microb Physiol 68: 139-167. 27134023
Wörner, S., K. Surmann, A. Ebert-Jung, U. Völker, E. Hammer, and G. Unden. (2018). Cellular Concentrations of the Transporters DctA and DcuB and the Sensor DcuS of Escherichia coli and the Contributions of Free and Complexed DcuS to Transcriptional Regulation by DcuR. J. Bacteriol. 200:. 29203472
Wösten, M.M., C.H. van de Lest, L. van Dijk, and J.P. van Putten. (2017). Function and Regulation of the C4-Dicarboxylate Transporters in Campylobacter jejuni. Front Microbiol 8: 174. 28223978
Zaharik M.L., S.S. Lamb, K.E. Baker, N.J. Krogan, J. Neuhard, R.A. Kelln. (2007). Mutations in yhiT enable utilization of exogenous pyrimidine intermediates in Salmonella enterica serovar Typhimurium. Microbiology.153: 2472-2482. 17660412
Zientz, E., S. Six, and G. Unden. (1996). 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: 7241-7247. 8955408