2.A.61 The C₄-dicarboxylate Uptake C (DcuC) Family A single functionally characterized protein comprises the DcuC family. This is an anaerobic C₄-dicarboxylate transporter (DcuC) of E. coli. A paralogue is encoded on the E. coli genome (455 amino acyl residues; 10 putative TMSs; spP45428), and a homologue is probably present in Haemophilus influenzae. The latter is included in the SwissProt database as two distinct but adjacent ORFs, HI0586 (145 aas; 4 putative TMSs; spP44019) and HI0585 (279 aas; 6 putative TMSs; spP44018). These two putative ORFs may be the N- and C-terminal parts of a single protein, respectively. The DcuC protein is induced only under anaerobic conditions and is not repressed by glucose. It 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. The reactions probably catalyzed by the E. coli DcuC protein are: C₄-dicarboxylate (out) + nH+ (out) → C₄-dicarboxylate (in) + nH+ (in) and C₄-dicarboxylate₁ (out) + C₄-dicarboxylate₂ (in) ⇌ C₄-dicarboxylate₁ (in) + C₄-dicarboxylate₂ (out)
This family belongs to the IT Superfamily.
References:
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.
Dzioba, J., E. Ostroumov, A. Winogrodzki, and P. Dibrov. (2002). Cloning, functional expression in Escherichia coli and primary characterization of a new Na⁺/H⁺ antiporter, NhaD, of Vibrio cholerae. Mol. Cell Biochem 229: 119-124.
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.
Habibian, R., J. Dzioba, J. Barrett, M.Y. Galperin, P.C. Loewen, and P. Dibrov. (2005). Functional analysis of conserved polar residues in Vc-NhaD, Na⁺/H⁺ antiporter of Vibrio cholerae. J. Biol. Chem. 280: 39637-39643.
Janausch, I.G. and G. Unden. (1999). The dcuD (former yhcL) gene product of escherichia coli as a member of the DcuC family of C4-dicarboxylate carriers: lack of evident expression. Arch. Microbiol. 172: 219-226.
Ostroumov, E., J. Dzioba, P.C. Loewen, and P. Dibrov. (2002). Asp³⁴⁴ and Thr³⁴⁵ are critical for cation exchange mediated by NhaD, Na⁺/H⁺ antiporter of Vibrio cholerae. Biochim. Biophys. Acta. 1564: 99-106.
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.
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.
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.
Zientz, E., I.G. Janausch, S. Six, and G. Unden. (1999). Functioning of DcuC as the C4-dicarboxylate carrier during glucose fermentation by Escherichia coli. J. Bacteriol. 181: 3716-3720.
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.
Examples:
TC#	Name	Organismal Type	Example
2.A.61.1.1	Anaerobic C₄-dicarboxylate transporter (DcuC) which functions to transport dicarboxylates during glucose fermentation (Zientz et al. 1999). Also facilitates succinate efflux (Chen et al. 2014).	Proteobacteria	*Anaerobic DcuC of E. coli* (P0ABP3)**

2.A.61.1.2	Cryptic C4-dicarboxylate transporter, DcuD (YhcL) (Janausch and Unden 1999).	Proteobacteria	DcuD of Escherichia coli

2.A.61.1.3	Putative uncharacterized transporter HI_0585	Bacteria	HI_0585 of Haemophilus influenzae

2.A.61.1.4	*Dicarboxylate transporter, DcuC, of 463 aas and 11 TMSs. Constitutively synthesized (Wösten et al.* 2017).**		DcuC of Campylobacter jejuni

Examples:
TC#	Name	Organismal Type	Example
2.A.61.2.1	Putative transporter	Bacteria	*Putative transporter of Bacillus halodurans* (gi 15614303)**

2.A.61.2.2	Uncharacterized protein of 457 aas	Firmicutes	UP of Desulfosporosinus orientis (Desulfotomaculum orientis)

2.A.61.2.3	Uncharacterized protein of 429 aas	Proteobacteria	UP of Arcobacter butzleri

2.A.61.2.4	Uncharacterized protein of 419 aas	Proteobacteria	UP of Desulfobacterium autotrophicum