Dcu family

Anaerobic c4-dicarboxylate membrane transporter
Identifiers
Symbol DcuA_DcuB
Pfam PF03605
Pfam clan CL0182
InterPro IPR004668
TCDB 2.A.13

The C4-dicarboxylate uptake family or Dcu family (TC# 2.A.13) is a family of transmembrane ion transporters found in bacteria. Their function is to exchange dicarboxylates such as aspartate, malate, fumarate and succinate. A representative list of the proteins belonging to the Dcu family can be found in the Transporter Classification Database.

Structure

Many members of this family are predicted to have 11 or 12 transmembrane regions (TMSs); however, one member of this family (Uncharacterized protein of Encarsia pergandiella; TC# 2.A.13.2.1) is reported to have 10 transmembrane regions, with both the N- and C-termini localized to the periplasm.[1] 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.[2] The fully sequenced proteins are of fairly uniform size, from 434-446 amino acyl residues in length.

There are no crystal structures available for members of the Dcu family.

Function

The two E. coli proteins, DcuA (TC# 2.A.13.1.1) and DcuB (TC# 2.A.13.1.2), of the Dcu family are involved in the transport of aspartate, malate, fumarate and succinate, functioning as antiporters with any two of these substrates.[3][4][5] 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 catalyse aspartate:fumarate and fumarate:malate exchange during the anaerobic utilization of aspartate and fumarate, respectively.[6] The two transporters can apparently substitute for each other under certain physiological conditions.[7]

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

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

Expression

The Escherichia coli DcuA and DcuB proteins have very different expression patterns.[8] DcuA is constitutively expressed; DcuB is strongly induced anaerobically by FNR and C4-dicarboxylates, while it is repressed by nitrate and subject to CRP-mediated catabolite repression. 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.[8][9][10][11] DcuA is expressed constitutively in aerobic and anaerobic growth and can substitute for DcuB.[6][8]

See also

References

  1. ↑ Zientz E, Six S, Unden G (December 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 (24): 7241–7. PMC 178639Freely accessible. PMID 8955408.
  2. ↑ Golby P, Kelly DJ, Guest JR, Andrews SC (September 1998). "Topological analysis of DcuA, an anaerobic C4-dicarboxylate transporter of Escherichia coli". J. Bacteriol. 180 (18): 4821–7. PMC 107505Freely accessible. PMID 9733683.
  3. ↑ Six S, Andrews SC, Roberts RE, Unden G, Guest JR (November 1993). "Construction and properties of Escherichia coli mutants defective in two genes encoding homologous membrane proteins with putative roles in anaerobic C4-dicarboxylic acid transport". Biochem. Soc. Trans. 21 (4): 342S. PMID 8131924.
  4. ↑ Nogrady N, Imre A, Rychlik I, Barrow PA, Nagy B (December 2003). "Genes responsible for anaerobic fumarate and arginine metabolism are involved in growth suppression in Salmonella enterica serovar Typhimurium in vitro, without influencing colonisation inhibition in the chicken in vivo". Vet. Microbiol. 97 (3-4): 191–9. doi:10.1016/j.vetmic.2003.08.011. PMID 14654290.
  5. ↑ Ullmann R, Gross R, Simon J, Unden G, Kroger A (October 2000). "Transport of C(4)-dicarboxylates in Wolinella succinogenes". J. Bacteriol. 182 (20): 5757–64. doi:10.1128/jb.182.20.5757-5764.2000. PMC 94697Freely accessible. PMID 11004174.
  6. 1 2 Six S, Andrews SC, Unden G, Guest JR (November 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 (21): 6470–8. PMC 197000Freely accessible. PMID 7961398.
  7. ↑ Engel, P.; Krämer, R.; Unden, G. (1994-06-01). "Transport of C4-dicarboxylates by anaerobically grown Escherichia coli. Energetics and mechanism of exchange, uptake and efflux". European journal of biochemistry / FEBS. 222 (2): 605–614. doi:10.1111/j.1432-1033.1994.tb18903.x. ISSN 0014-2956. PMID 8020497.
  8. 1 2 3 Golby P, Kelly DJ, Guest JR, Andrews SC (December 1998). "Transcriptional regulation and organization of the dcuA and dcuB genes, encoding homologous anaerobic C4-dicarboxylate transporters in Escherichia coli". J. Bacteriol. 180 (24): 6586–96. PMC 107762Freely accessible. PMID 9852003.
  9. ↑ Engel P, Kramer R, Unden G (September 1992). "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 (17): 5533–9. PMC 206496Freely accessible. PMID 1512189.
  10. ↑ Golby P, Davies S, Kelly DJ, Guest JR, Andrews SC (February 1999). "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 (4): 1238–48. PMC 93502Freely accessible. PMID 9973351.
  11. ↑ Zientz E, Bongaerts J, Unden G (October 1998). "Fumarate regulation of gene expression in Escherichia coli by the DcuSR (dcuSR genes) two-component regulatory system". J. Bacteriol. 180 (20): 5421–5. PMC 107591Freely accessible. PMID 9765574.
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