The Mg²⁺ transporter, MgtE. The crystal structure of the N-terminal hydrophilic domain has been determined to 2.3 Å resolution (Hattori et al., 2007) (>50% identical to 9.A.19.1.1), while the C-terminal transmembrane domain has been determined at 2.2 Å resolution (Takeda et al. 2014). The structure reveals a homodimer with the channel at the interface of the two subunits.  There is a plug helix connecting the two domains, and the cytoplasmic domain possesses multiple Mg²⁺ binding sites at the cytoplasmic face that can bind Mg²⁺, Mn²⁺ and Ca²⁺. Dissociation of Mg²⁺ ions from the cytoplasmic domain induces structural changes in the cytoplasmic domain, leading to channel opening (Wang et al. 2023). Novel crystal structures of the Mg²⁺-bound MgtE cytoplasmic domains from two different bacterial species, Chryseobacterium hispalense and Clostridiales bacterium allowed identification of multiple Mg²⁺ binding sites, including ones that were not observed in the previous MgtE structure. These structures reveal the conservation and diversity of the cytoplasmic Mg²⁺ binding site in MgtE family proteins (Wang et al. 2023).