Monovalent cation:Proton antiporter-3

The Monovalent Cation (K+ or Na+):Proton Antiporter-3 (CPA3) Family (TC# 2.A.63) is a member of the Na+ Transporting Mrp Superfamily. The CPA3 family consist of bacterial multicomponent K+:H+ and Na+:H+ antiporters. The best characterized systems are the PhaABCDEFG system of Sinorhizobium meliloti (TC# 2.A.63.1.1) that functions in pH adaptation and as a K+ efflux system, and the MnhABCDEFG system of Staphylococcus aureus (TC# 2.A.63.1.3) that functions as a Na+ efflux Na+:H+ antiporter.[1]

Homology

A homologous, but only partially sequenced, system was earlier reported to catalyze Na+:H+ antiport in an alkalophilic Bacillus strain. PhaA and PhaD are respectively homologous to the ND5 and ND4 subunits of the H+-pumping NADH:ubiquinone oxidoreductase (TC #3.D.1). Homologous protein subunits from E. coli NADH:quinone oxidoreductase can functionally replace MrpA and MrpD in Bacillus subtilis.[2]

Homologues of PhaA, B, C and D and Nha1, 2, 3 and 4 of an alkalophilic Bacillus strain are the Yuf(Mrp)T, U, V and D genes of Bacillus subtilis. In this system, YufT is believed to be responsible for Na+:H+ antiporter activity, but it does not have activity in the absence of other constituents of the operon.[3]

Structure

The seven Pha proteins are of the following sizes (in #aas) and exhibit the following putative numbers of transmembrane α-helical spanners (TMSs):

All are predicted to be integral membrane proteins.

Corresponding values for the S. aureus Mnh system are:[4]

In view of the complexity of the system, large variation in subunit structure, and the homology with NDH family protein constituents, a complicated energy coupling mechanism, possibly involving a redox reaction, cannot be ruled out.

Function

Na+ or Li+ does, but K+, Ca2+, and Mg2+ do not, support significant antiport by the Gram-positive bacterial systems (TC# 2.A.6.3.1.2 and TC# 2.A.6.3.1.3).[5] Na+(Li+)/H+ antiporters have alkaline pH optima and apparent Km values for Na+ that are among the lowest reported for bacterial Na+/H+ antiporters. Na+/H+antiport consumes the pmf and therefore is probably electrogenic.[5]

YufF (MrpF) appears to catalyze cholate efflux, possibly by a Na+ symport mechanism.[6] It plays a major role in Na+ extrusion and is required for initiation of sporulation.[3][7][8] Additionally, another component of the operon, MrpF (equivalent to PhaF of R. meliloti) has been implicated in choline and Na+ efflux.[8] The MrpA-G proteins of B. subtilis have been shown to be present in a single multicomponent complex.[9] They provide Na+/H+ antiport activity and function in multiple compound resistance and pH homeostasis.[3]

Transport Reaction

The generalized reaction believed to be catalyzed by CPA3 family members is:

[K+ or Na+] (in) + H+ (out) ⇌ [K+ or Na+] (out) + H+ (in).

See also

References

  1. ↑ "2.A.63 The Monovalent Cation (K+ or Na+):Proton Antiporter-3 (CPA3) Family". Transporter Classification Databse. Retrieved 2016-03-16.
  2. ↑ Moparthi, Vamsi K.; Kumar, Brijesh; Mathiesen, Cecilie; Hägerhäll, Cecilia (2011-04-01). "Homologous protein subunits from Escherichia coli NADH:quinone oxidoreductase can functionally replace MrpA and MrpD in Bacillus subtilis". Biochimica Et Biophysica Acta 1807 (4): 427–436. doi:10.1016/j.bbabio.2011.01.005. ISSN 0006-3002. PMID 21236240.
  3. 1 2 3 Kosono, S.; Morotomi, S.; Kitada, M.; Kudo, T. (1999-01-05). "Analyses of a Bacillus subtilis homologue of the Na+/H+ antiporter gene which is important for pH homeostasis of alkaliphilic Bacillus sp. C-125". Biochimica Et Biophysica Acta 1409 (3): 171–175. ISSN 0006-3002. PMID 9878723.
  4. ↑ Hiramatsu, T.; Kodama, K.; Kuroda, T.; Mizushima, T.; Tsuchiya, T. (1998-12-01). "A putative multisubunit Na+/H+ antiporter from Staphylococcus aureus". Journal of Bacteriology 180 (24): 6642–6648. ISSN 0021-9193. PMC 107768. PMID 9852009.
  5. 1 2 Swartz, Talia H.; Ito, Masahiro; Ohira, Takayuki; Natsui, Shinsuke; Hicks, David B.; Krulwich, Terry A. (2007-04-01). "Catalytic properties of Staphylococcus aureus and Bacillus members of the secondary cation/proton antiporter-3 (Mrp) family are revealed by an optimized assay in an Escherichia coli host". Journal of Bacteriology 189 (8): 3081–3090. doi:10.1128/JB.00021-07. ISSN 0021-9193. PMC 1855852. PMID 17293423.
  6. ↑ Ito, M.; Guffanti, A. A.; Wang, W.; Krulwich, T. A. (2000-10-01). "Effects of nonpolar mutations in each of the seven Bacillus subtilis mrp genes suggest complex interactions among the gene products in support of Na(+) and alkali but not cholate resistance". Journal of Bacteriology 182 (20): 5663–5670. ISSN 0021-9193. PMC 94685. PMID 11004162.
  7. ↑ Kosono, S.; Ohashi, Y.; Kawamura, F.; Kitada, M.; Kudo, T. (2000-02-01). "Function of a principal Na(+)/H(+) antiporter, ShaA, is required for initiation of sporulation in Bacillus subtilis". Journal of Bacteriology 182 (4): 898–904. ISSN 0021-9193. PMC 94362. PMID 10648512.
  8. 1 2 Ito, M.; Guffanti, A. A.; Oudega, B.; Krulwich, T. A. (1999-04-01). "mrp, a multigene, multifunctional locus in Bacillus subtilis with roles in resistance to cholate and to Na+ and in pH homeostasis". Journal of Bacteriology 181 (8): 2394–2402. ISSN 0021-9193. PMC 93663. PMID 10198001.
  9. ↑ Kajiyama, Yusuke; Otagiri, Masato; Sekiguchi, Junichi; Kosono, Saori; Kudo, Toshiaki (2007-10-01). "Complex formation by the mrpABCDEFG gene products, which constitute a principal Na+/H+ antiporter in Bacillus subtilis". Journal of Bacteriology 189 (20): 7511–7514. doi:10.1128/JB.00968-07. ISSN 0021-9193. PMC 2168430. PMID 17693497.

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