P-type ATPase magnesium transporter MgtA acts as a dimer

Magnesium (Mg2+) uptake systems are present in all domains of life, consistent with the vital role of this ion. P-type ATPase Mg2+ importers are required for bacterial growth when Mg2+ is limiting or during pathogenesis. However, insights into their mechanisms of action are missing. Here we solved the cryo-EM structure of the Mg2+ transporter MgtA from Escherichia coli. We obtained high-resolution structures of both homodimeric (2.9 Å) and monomeric (3.6 Å) forms. The dimer structure is formed by multiple contacts between residues in adjacent soluble N and P subdomains. Our structures revealed an ion, assigned as Mg2+, in the transmembrane segment. Moreover, we detected two cytoplasmic ion-binding sites and determined the structure of the N-terminal tail. Sequence conservation, mutagenesis and ATPase assays indicate dimerization, the ion-binding sites and the N-terminal tail facilitate cation transport or serve regulatory roles. Zeinert et al. provide cryo-EM structures of the E. coli Mg2+ importer MgtA: unexpectedly, this P-type ATPase is a dimer with an uncommon transmembrane ion-binding site and knotted N-terminus, which are functionally important features.