Fig 1. Cryo-EM of magnesium transporter MgtA reveals a high-resolution dimer and a monomeric structure.

a, Schematic representation of MgtA/B based on P-type ATPase structural homology showing ten conserved transmembrane helices colored in purple (1-10), the actuator (A) domain in orchid, the phosphorylation (P) subdomain in light blue, the nucleotide (N) binding or CAP subdomain in light green, and the predicted unstructured N-terminal tail in orange. The A domain is split into two regions a/b. The b segment of the A domain is comprised of a Double Stranded beta-Helix fold (DSβH). The soluble P subdomain is a noncontiguous segment comprised of two regions a/b that house the key catalytic residues required for phosphorylation. The N subdomain binds the nucleotide and aids in catalysis. The P and N subdomains together comprise the Haloacid dehalogenase (HAD) domain, b, Representative micrograph of purified Escherichia coli MgtA. c-d, Representative final 2D class averages for the ~200 kDa dimer (c) and the ~100 kDa monomer (d), respectively, with a box size of 384 pixels (approximately 319 Å). e-f, Cryo-EM reconstruction of the MgtA dimer (e, also see Extended Data Fig. 9a and Extended Data Movie 1) and of the monomer (f, also see Extended Data Fig. 9b and Extended Data Movie 2). Cryo-EM maps in e-f are colored as in a. A transparent gray map at a much lower threshold indicates the detergent micelle and the density for the more flexible loops and the A domain in the monomer map.