Most eukaryotic organisms assemble heterooligomeric oligosaccharyltransferase (OST) complexes that consist of a catalytic subunit (an STT3 protein) plus several accessory subunits. Metazoan organisms express two STT3 proteins (STT3A and STT3B) [].Magnesium transporter protein 1 (MagT1) is involved in N-glycosylation through its association with oligosaccharyltransferase, and could also be involved in Mg2+ transport in epithelial cells [, ]. It is a subunit of the STT3B isoform of OST [].