MgtE is a prokaryotic Mg 2+ transporter that controls cellular Mg 2+ concentrations. We previously reported crystal structures of the cytoplasmic region of MgtE, consisting of 2 domains, that is, N and CBS, in the Mg 2+-free and Mg 2+-bound forms. The Mg 2+-binding sites lay at the interface of the 2 domains, making the Mg 2+-bound form compact and globular. In the Mg 2+-free structure, however, the domains are far apart, and the Mg 2+-binding sites are destroyed. Therefore, it is unclear how Mg 2+-free MgtE changes its conformation to accommodate Mg 2+ ions. Here, we used paramagnetic relaxation enhancement (PRE) to characterize the relative orientation of the N and CBS domains in the absence of Mg 2+ in solution. When the residues on the surface of the CBS domain were labeled with nitroxide tags, significant PRE effects were observed for the residues in the N domain. No single structure satisfied the PRE profiles, suggesting that the N and CBS domains are not fixed in a particular orientation in solution. We then conducted ensemble simulated annealing calculations in order to obtain the atomic probability density and visualize the spatial distribution of the N domain in solution. The results indicate that the N domain tends to occupy the space near its position in the Mg 2+-bound crystal structure, facilitating efficient capture of Mg 2+ with increased intracellular Mg 2+ concentration, which is necessary to close the gate.
|ジャーナル||Biochimica et Biophysica Acta - Proteins and Proteomics|
|出版ステータス||Published - 2012 10|
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