Magnesium ion (Mg2+) is an essential metal element for life, and has many cellular functions, including ATP utilization, activation of enzymes, and maintenance of genomic stability. The intracellular Mg2+ concentration is regulated by a class of transmembrane proteins, called Mg 2+ transporters. One of the prokaryotic Mg2+ transporters, MgtE, is a 450-residue protein, and functions as a dimer. We previously reported that MgtE exhibits the channel-like electrophysiological property, i.e., it permeates Mg2+ according to the electrochemical potential of Mg2+. The Mg2+-permeation pathway opens in response to the decrease of the intracellular Mg2+ concentration, while it is completely closed at the intracellular Mg2+ concentration of 10 mM. The crystal structures of the MgtE dimer revealed that the Mg 2+-sensing cytoplasmic region consists of the N and CBS domains. The Mg2+-bound state of MgtE adopts a compact, globular conformation, which is stabilized by the coordination of a number of Mg2+ ions between these domains. On the other hand, in the Mg2+-unbound state, these domains are far apart, and fixed by the crystal packing. Therefore, structural analyses in solution were awaited, in order to characterize the Mg2+-dependent alteration of the MgtE structure and dynamics relevant to its gating. In this paper, we report the backbone resonance assignments of the dimer of the cytoplasmic region of the MgtE from Thermus thermophilus with a molecular weight of 60 KDa, in the Mg2+-unbound state.
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