| 1.A.67 The Membrane Mg2+ Transporter (MMgT) Family
Magnesium is an essential metal, but few selective transporters have been identified at the molecular level. Microarray analysis was used to identify two similar transcripts that are upregulated with low extracellular Mg2+. The corresponding cDNAs encode proteins of 131 (MMgT1) and 123 (MMgT2) amino acids with two predicted transmembrane domains (TMDs). When expressed in Xenopus oocytes, MMgT1 and MMgT2 mediate Mg2+ transport. Uptake is saturable with Michaelis constants of 1.5mM and 0.6mM, respectively. MMgT1-HA and MMgT2-V5 fusion proteins reside in the Golgi complex and post-Golgi vesicles but in separate populations of post-Golgi vesicles. MMgT1 and MMgT2 mRNA increased in kidney epithelial cells cultured in low magnesium media. With the increase in transcripts there was an apparent increase in MMgT1 and MMgT2 protein in the Golgi and post-Golgi vesicles. Thus, MMgT proteins provide regulated pathways for Mg2+ transport in the Golgi and post-Golgi organelles of epithelial-derived cells (Goytain and Quamme, 2007).
Most homologues are ~100-130aas in length. They have 2 TMSs, and are found in all types of eukaryotes. Because there are only 2TMSs, these proteins are presumed to form oligomeric channels (Saier, 2003).
The transport reaction catalyzed by MMgT homologues is:
Mg 2+ (out)  Mg 2+ (in)
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| References: |
Goytain, A. and G.A. Quamme. (2008). Identification and characterization of a novel family of membrane magnesium transporters, MMgT1 and MMgT2. Am. J. Physiol. Cell Physiol. 294(2): C495-502.
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Guna, A., N. Volkmar, J.C. Christianson, and R.S. Hegde. (2018). The ER membrane protein complex is a transmembrane domain insertase. Science 359: 470-473.
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Saier, M.H., Jr. (2003). Tracing pathways of transport protein evolution. Mol. Microbiol. 48: 1145-1156.
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Schäffers, O.J.M., J.G.J. Hoenderop, R.J.M. Bindels, and J.H.F. de Baaij. (2018). The rise and fall of novel renal magnesium transporters. Am. J. Physiol. Renal Physiol 314: F1027-F1033.
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Wunderlich, J. (2022). Updated List of Transport Proteins in. Front Cell Infect Microbiol 12: 926541.
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.A.67.1.1 | Magnesium transporter-1, MMgT1. As of 2018, the function of this protein as a Mg2+ transporter was under debate (Schäffers et al. 2018). | Animals | MMgT1 of Mus musculus (A7UH87) |
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| 1.A.67.1.10 | Membrane magnesium transporter-domain-containing protein, MMgT, of 110 aas and 2 N-terminal TMSs. | | MMgT of Gongronella butleri |
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| 1.A.67.1.2 | Magnesium transporter-2, MMgT2. As of 2018, the function of this protein as a Mg2+ transporter was under debate (Schäffers et al. 2018). | Animals | MMgT2 of Mus musculus (Q8R3L0) |
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| 1.A.67.1.3 | Uncharacterized protein of 107 aas and 2 TMSs. | | UP of Ustilago hordei (Barley covered smut fungus) |
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| 1.A.67.1.4 | Uncharacterized protein of 487 aas and 2 C-terminal TMSs. | | UP of Brassica rapa (Chinese cabbage) (Brassica pekinensis) |
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| 1.A.67.1.5 | Uncharacterized protein of 137 aas and 2 N-terminal TMSs | | UP of Leptosphaeria maculans (Blackleg fungus) (Phoma lingam) |
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| 1.A.67.1.6 | Uncharacterized protein of 126 aas and 2 N-terminal TMSs. | | UP of Naegleria gruberi (Amoeba) |
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| 1.A.67.1.7 | ER membrane protein complex subunit 5, Emc5 of 141 aas and 2 TMSs. The EMC seems to be required for efficient folding of proteins in the endoplasmic reticulum (ER) and also for insertion of integral membrane proteins into the ER membrane (Guna et al. 2018). | | Emc5 of Saccharomyces cerevisiae (Baker's yeast) |
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| 1.A.67.1.8 | Membrane magnesium transporter, MmgT, of 112 aas and 2 TMSs. | | MmgT of Toxoplasma gondii |
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| 1.A.67.1.9 | Uncharacterized protein of 103 aas and 2 TMSs | | UP of Piriformospora indica |
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.A.67.2.1 | Uncharacterized protein of 132 aas and 2 TMSs. | | UP of Leishmania braziliensis |
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| 1.A.67.2.2 | Uncharacterized protein of 143 aas and 2 TMSs. | | UP of Trypanosoma cruzi |
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| 1.A.67.2.3 | Uncharacterized protein of 133 aas and 2 TMSs | | UP of Strigomonas culicis |
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.A.67.3.1 | ER membrane protein complex subunit 5, EMC5, putative, MMgT of 116 aas and 2 N-terminal TMSs (Wunderlich 2022). | | MMgT of Plasmodium falciparum |
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| 1.A.67.3.2 | ER membrane protein complex subunit 5 of 115 aas and 2 TMSs. | | ER membrane protein of Plasmodium yoelii |
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| 1.A.67.3.3 | ER membrane protein complex subunit 5 of 115 aas and 2 N-terminal TMSs. | | ER membrane protein of Plasmodium berghei |
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