Magnesium transporter E

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MgtE
2zy9 mgte.png
Crystal structure of magnesium transporter MgtE. PDB 2zy9 [1]
Identifiers
SymbolMgtE
Pfam PF01769
InterPro IPR006667
TCDB 1.A.26
OPM superfamily 180
OPM protein 2yvx

Magnesium transporters E (MgtE) are a family of transmembrane eubacterial MgtE magnesium transporters. Related regions are found also in archaeal and eukaryotic proteins. They have sizes that vary considerably from 311 residues for the Methanococcus thermoautotrophicum protein, 463 residues for a Synechocystis homologue, and 513 residues for the human homologue, SLC41A1. These proteins are capable of transporting Mg2+ and Co2+ but not Ni2+. Multiple alignments contain two highly conserved aspartates that may be involved in cation binding.

Contents

Human transporters from this family are SLC41A1, SLC41A2 and SLC41A3.

Structure and Mechanism

The Bacillus firmus transporter and several homologues examined have strongly charged, hydrophilic N-terminal domains (cytoplasmic) followed by a hydrophobic C-terminal domain with 5 putative transmembrane α-helical spanners. A central 100 residues resembles archaeal inositol monophosphate dehydrogenases. [2]

Kehres and Maguire suggest that the MgtE proteins are secondary carriers with inwardly directed polarity. [2] Hattori et al. have considered MgtE to function by a channel mechanism, providing evidence that the MgtE cytosolic domain acts as a Mg2+ sensor to regulate gating of the pore in response to the intracellular Mg2+ concentration. [1] This produces a mechanism for the maintenance of homeostasis conditions. [1] The cytosolic domain of MgtE undergoes a Mg2+-dependent structural change, which may gate the ion-conducting pore passing through the transmembrane domain.

Maruyama et al. showed that MgtE exhibits the channel-like electrophysiological properties, i.e., Mg2+ transport occurs in accordance to the electrochemical potential of Mg2+. [3] The Mg2+-permeation pathway opens in response to a decrease of the intracellular Mg2+ concentration, while it is completely closed at the intracellular Mg2+ concentration of 10 mM. The crystal structures of the MgtE dimer reveal that the Mg2+-sensing cytoplasmic region consists of the N and CBS domains. The Mg2+-bound state adopts a compact, globular conformation, which is stabilized by the coordination of a number of Mg2+ ions between these domains. On the other hand, in the Mg2+-unbound state, these domains are far apart, and fixed by the crystal packing.

Transport Reaction

The transport reaction catalyzed by MgtE proteins is:

Mg2+ (or Co2+) (out) → Mg2+ (or Co2+) (in)

Related Research Articles

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Sodium-solute symporter group of transport proteins

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The anion exchanger family is a member of the large APC superfamily of secondary carriers. Members of the AE family are generally responsible for the transport of anions across cellular barriers, although their functions may vary. All of them exchange bicarbonate. Characterized protein members of the AE family are found in plants, animals, insects and yeast. Uncharacterized AE homologues may be present in bacteria. Animal AE proteins consist of homodimeric complexes of integral membrane proteins that vary in size from about 900 amino acyl residues to about 1250 residues. Their N-terminal hydrophilic domains may interact with cytoskeletal proteins and therefore play a cell structural role. Some of the currently characterized members of the AE family can be found in the Transporter Classification Database.

The sulfate permease (SulP) family is a member of the large APC superfamily of secondary carriers. The SulP family is a large and ubiquitous family of proteins derived from archaea, bacteria, fungi, plants and animals. Many organisms including Bacillus subtilis, Synechocystis sp, Saccharomyces cerevisiae, Arabidopsis thaliana and Caenorhabditis elegans possess multiple SulP family paralogues. Many of these proteins are functionally characterized, and most are inorganic anion uptake transporters or anion:anion exchange transporters. Some transport their substrate(s) with high affinities, while others transport it or them with relatively low affinities. Others may catalyze SO2−
4
:HCO
3
exchange, or more generally, anion:anion antiport. For example, the mouse homologue, SLC26A6, can transport sulfate, formate, oxalate, chloride and bicarbonate, exchanging any one of these anions for another. A cyanobacterial homologue can transport nitrate. Some members can function as channels. SLC26A3 and SLC26A6 can function as carriers or channels, depending on the transported anion. In these porters, mutating a glutamate, also involved in transport in the CIC family, created a channel out of the carrier. It also changed the stoichiometry from 2Cl/HCO
3
to 1Cl/HCO
3
.

The Ca2+:cation antiporter (CaCA) family (TC# 2.A.19) is a member of the cation diffusion facilitator (CDF) superfamily. This family should not be confused with the Ca2+:H+ Antiporter-2 (CaCA2) Family (TC# 2.A.106) which belongs to the Lysine Exporter (LysE) Superfamily. Proteins of the CaCA family are found ubiquitously, having been identified in animals, plants, yeast, archaea and divergent bacteria. Members of this family facilitate the antiport of calcium ion with another cation.

The Magnesium Transporter 1 (MagT1) Family (TC# 1.A.76) is a group of magnesium transporters that are part of the TOG superfamily. Goytain and Quamme identified a Mg2+--related transporter whose expression or function was affected by an implantation-associated protein precursor. They designated this protein, MagT1. MagT1 is expressed as a 335 amino acid polypeptide which includes five transmembrane helices. The nascent polypeptide possesses a cleavage site after the N-terminal signal sequence helix, rendering a mature MagT1 protein with four transmembrane helices. MagT1 additionally contains a number of phosphorylation sites.

Zinc transporter proteins (Zrt), or simply zinc transporters, are membrane transport proteins of the solute carrier family which control the membrane transport of zinc and regulate its intracellular and cytoplasmic concentrations. They include two major groups: (1) the zinc transporter (ZnT) or solute carrier 30 (SLC30) family, which controls the efflux of zinc from the cytoplasm out of the cell and from the cytoplasm into vesicles; and (2) the zinc importer, Zrt- and Irt-like protein (ZIP), or solute carrier 39A (SLC39A) family, which controls the influx of zinc into the cytoplasm from outside the cell and from vesicles.

Metal transporter CNNM3 is a human transmembrane protein which is made up of 707 amino acids. Although CNNM3 is ubiquitous, it is mostly present in the kidney, brain, lung, spleen, heart and liver.

References

  1. 1 2 3 Hattori M, Iwase N, Furuya N, Tanaka Y, Tsukazaki T, Ishitani R, Maguire ME, Ito K, Maturana A, Nureki O (November 2009). "Mg(2+)-dependent gating of bacterial MgtE channel underlies Mg(2+) homeostasis". The EMBO Journal. 28 (22): 3602–12. doi:10.1038/emboj.2009.288. PMC   2782099 . PMID   19798051.
  2. 1 2 Kehres DG, Maguire ME (September 2002). "Structure, properties and regulation of magnesium transport proteins". Biometals. 15 (3): 261–70. doi:10.1023/A:1016078832697. PMID   12206392. S2CID   30291849.
  3. Maruyama T, Imai S, Osawa M, Hattori M, Ishitani R, Nureki O, Shimada I (April 2013). "Backbone resonance assignments for the cytoplasmic region of the Mg(2+) transporter MgtE in the Mg (2+)-unbound state". Biomolecular NMR Assignments. 7 (1): 93–6. doi:10.1007/s12104-012-9385-y. PMID   22477092. S2CID   11653432.
This article incorporates text from the public domain Pfam and InterPro: IPR006667

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