The Magnesium Transporter1 (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+ transporter encoded by an implantation-associated protein precursor, IAP, that is regulated by magnesium. They designated this protein, MagT1. MagT1 is of 335 amino acids and possesses five TMSs with an N-terminal cleavage site and a number of phosphorylation sites.
Contents
Function
When expressed in Xenopus laevis oocytes, MagT1 mediates saturable Mg2+ uptake with a Km of 0.23 mM. Transport of Mg2+ by MagT1 is rheogenic, voltage-dependent, and does not display time-dependent inactivation. Transport is specific to Mg2+, as other divalent cations do not evoke currents. Large external concentrations of some cations inhibited Mg2+ transport (Ni2+, Zn2+, Mn2+) in MagT1-expressing oocytes although Ca2+and Fe2+ were without effect. MagT1 has an N-terminal thioredoxin domain of unknown function.
Zhou and Clapham identified two mammalian genes, MagT1 and TUSC3, catalyzing Mg2+ influx. MagT1 is universally expressed in all human tissues, and its expression level is upregulated in low extracellular Mg2+. Knockdown of either MagT1 or TUSC3 protein lowered the total and free intracellular Mg2+concentrations in mammalian cell lines. Morpholino knockdown of MagT1 and TUSC3 protein expression in zebrafish embryos resulted in early developmental arrest; excess Mg2+ or supplementation with mammalian mRNAs rescued these effects. Thus, MagT1 and TUSC3 are vertebrate plasma membrane Mg2+transport system.
Transport Reaction
The reaction catalyzed by MagT1 is:
Mg2+ (out) → Mg2+ (in)Role in Magnesium Deficiency
MagT1 and its homologues are called tumor suppressor candidate 3 genes and oligosaccharidyl transferase. It was found in various eukaryotes (animals, plants, fungi etc.). The identification of genetic changes and their functional consequences in patients with immunodeficiency revealed that magnesium and MAGT1 are key molecular players for T cell-mediated immune responses. This led to the description of XMEN (X-linked immunodeficiency with magnesium defect, Epstein-Barr Virus infection, and neoplasia) syndrome, for which Mg2+ supplementation has been shown to be beneficial. Similarly, the identification of copy-number variation leading to dysfunctional MAGT1 in a family with atypical ATR-X syndrome and skin abnormalities, suggested that the MAGT1 defect is responsible for the cutaneous problems.