Mg 2+ is the most abundant divalent cation in cells and an essential cofactor for many enzymes, nucleotides, and nucleic acids. It plays a critical role in DNA/RNA synthesis and in stabilizing protein complexes. In bacteria, Mg 2+ homeostasis is required for bacterial survival and virulence, and is maintained by channels, transporters, and exchangers. As a result, CorA, the primary bacterial Mg 2+ channel, is an attractive drug target. CorA has been investigated as a drug target in Mycobacterium tuberculosis through channel inhibition using a pyrimidinetrione amide, though its inhibition mechanism is unknown. At the same time, the structure of CorA has only been determined in non-pathogenic bacteria, with no existing full-length structural data from pathogenic bacteria. Thus, our aim was to determine the full-length structure of CorA from the pathogen M. tuberculosis ( Mt CorA). Here, we present a 2.95 Å structure of Mt CorA in the closed Mg 2+ -bound state and a 5.06 Å structure in a Mg 2+ -depleted environment. Both were extracted in native lipid nanodiscs and resolved using single-particle cryo-electron microscopy (cryo-EM). Within the closed state structure, we report Mg 2+ -binding sites and a novel lipid-binding region validated by molecular dynamics (MD) simulations. The dynamics of Mt CorA were also investigated using cryoSPARC’s 3D variability analysis, which showed a transition between different states where Mt CorA breaks symmetry. As antibiotic resistance becomes more common, detailed structural knowledge of drug targets is required to develop novel and effective drugs. Our findings further our understanding of Mg 2+ homeostasis in tuberculosis and inform future efforts to design CorA-targeted antibiotics.
Pathak et al. (Sun,) studied this question.