Identification and characterization of a novel family of membrane magnesium transporters, MMgT1 and MMgT2.

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 and 123 amino acids with two predicted transmembrane domains. The two separate gene products comprise the family that we have termed “membrane Mg2+ transporters” (MMgTs), because the proteins reside in the membrane and mediate Mg2+ transport. When expressed in Xenopus laevis oocytes, MMgT1 and MMgT2 mediate Mg2+ transport as determined with two-electrode voltage-clamp analysis and fluorescence measurements. Transport is saturable Mg2+ uptake with Michaelis constants of 1.47 ± 0.17 and 0.58 ± 0.07 mM, respectively. Real-time RT-PCR demonstrated that MMgT mRNAs are present in a wide variety of cells. Subcellular localization with immunohistochemistry determined that the MMgT1-hemagglutinin (HA) and MMgT2-V5 fusion proteins reside in the Golg...