The Citrate-Mg2+:H+ (CitM) / Citrate-Ca2+:H+ (CitH) Symporter (CitMHS) Family (TC# 2.A.11) is a family of transport proteins belonging to the Ion transporter superfamily.[1] Members of this family are found in Gram-positive and Gram-negative bacteria, archaea and possibly eukaryotes. These proteins all probably arose by an internal gene duplication event. Lensbouer & Doyle (2010) have reviewed these systems, classifying the porters with three superfamilies, according to ion-preference:[2]

1) Mg2+-preferring,

2) Ca2+-preferring, and

3) Fe2+-preferring.

A representative list of proteins belonging to the CitMHS family can be found in the Transporter Classification Database.[3]

CitM and CitH

Two of the characterized members of the CitMHS family, both citrate uptake permeases from Bacillus subtilis, are CitM (TC# 2.A.11.1.1) and CitH (TC# 2.A.11.1.2).

Function

CitM is believed to transport a citrate2−-Mg2+complex in symport with one H+ per Mg2+-citrate while CitH apparently transports a citrate2−-Ca2+ complex in symport with protons.[4][5] The cation specificity of CitM is: Mg2+, Mn2+, Ba2+, Ni2+, Co2+, Ca2+ and Zn2+, in this preferential order. CitM is highly specific for citrate and D-isocitrate and does not transport other di- and tri-carboxylates including succinate, L-isocitrate, cis-aconitate and tricarballylate.[6][7] For CitH, the cation specificity (in order of preference) is: Ca2+, Ba2+ and Sr2+.[5] The two proteins are 60% identical, contain about 400 amino acyl residues and possess twelve putative transmembrane spanners. A CitM homologue in S. mutans transports citrate conjugated to Fe2+ or Mn2+ but not Ca2+, Mg2+ or Ni2+.[8]

The transport reactions catalyzed by (1) CitM and (2) CitH, respectively, are:

(1) Citrate • Mg (out) + nH+ (out) ⇌ Citrate • Mg (in) + nH+ (in)

(2) Citrate (out) + nH+ (out) ⇌ Citrate (in) + nH+ (in)

(3) Citrate • Ca2+ (out) + nH+ (out) ⇌ Citrate • Ca2+ (in) + nH+ (in)

See also

References

  1. ↑ Prakash, Shraddha; Cooper, Garret; Singhi, Soumya; Saier, Milton H. (2003-12-03). "The ion transporter superfamily". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1618 (1): 79–92. doi:10.1016/j.bbamem.2003.10.010. ISSN 0006-3002. PMID 14643936.
  2. ↑ Lensbouer, Joshua J.; Patel, Ami; Sirianni, Joseph P.; Doyle, Robert P. (2008-08-01). "Functional characterization and metal ion specificity of the metal-citrate complex transporter from Streptomyces coelicolor". Journal of Bacteriology. 190 (16): 5616–5623. doi:10.1128/JB.00456-08. ISSN 1098-5530. PMC 2519374. PMID 18556792.
  3. ↑ "2.A.11. The Citrate-Mg2+:H+ (CitM) Citrate-Ca2+:H+ (CitH) Symporter (CitMHS) Family". Transporter Classification Database. Retrieved 2016-03-04.
  4. ↑ Boorsma, A.; van der Rest, M. E.; Lolkema, J. S.; Konings, W. N. (1996-11-01). "Secondary transporters for citrate and the Mg(2+)-citrate complex in Bacillus subtilis are homologous proteins". Journal of Bacteriology. 178 (21): 6216–6222. doi:10.1128/jb.178.21.6216-6222.1996. ISSN 0021-9193. PMC 178492. PMID 8892821.
  5. 1 2 Krom, B. P.; Warner, J. B.; Konings, W. N.; Lolkema, J. S. (2000-11-01). "Complementary metal ion specificity of the metal-citrate transporters CitM and CitH of Bacillus subtilis". Journal of Bacteriology. 182 (22): 6374–6381. doi:10.1128/jb.182.22.6374-6381.2000. ISSN 0021-9193. PMC 94783. PMID 11053381.
  6. ↑ Li, H.; Pajor, A. M. (2002-01-01). "Functional characterization of CitM, the Mg2+-citrate transporter". The Journal of Membrane Biology. 185 (1): 9–16. doi:10.1007/s00232-001-0106-1. ISSN 0022-2631. PMID 11891560. S2CID 8677932.
  7. ↑ Warner, Jessica B.; Lolkema, Juke S. (2002-11-01). "Growth of Bacillus subtilis on citrate and isocitrate is supported by the Mg2+-citrate transporter CitM". Microbiology. 148 (Pt 11): 3405–3412. doi:10.1099/00221287-148-11-3405. ISSN 1350-0872. PMID 12427932.
  8. ↑ Korithoski, Bryan; Krastel, Kirsten; Cvitkovitch, Dennis G. (2005-07-01). "Transport and metabolism of citrate by Streptococcus mutans". Journal of Bacteriology. 187 (13): 4451–4456. doi:10.1128/JB.187.13.4451-4456.2005. ISSN 0021-9193. PMC 1151779. PMID 15968054.

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