title: Spatial distribution of cytoplasmic domains of the Mg(2+)-transporter MgtE, in a solution lacking Mg(2+), revealed by paramagnetic relaxation enhancement.
abstract: 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.
authors: Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors: Shunsuke
authors: S
authors: Imai
authors: Tatsuro
authors: T
authors: Maruyama
authors: Masanori
authors: M
authors: Osawa
authors: Motoyuki
authors: M
authors: Hattori
authors: Ryuichiro
authors: R
authors: Ishitani
authors: Osamu
authors: O
authors: Nureki
authors: Ichio
authors: I
authors: Shimada
mesh_terms: D017920:Antiporters / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D003593:Cytoplasm / Q000378:metabolism*; D017136:Ion Transport; D008274:Magnesium / Q000378:metabolism*; D008958:Models, Molecular
chemical_list: D017920:Antiporters; D001426:Bacterial Proteins; C092192:MgtE protein, bacteria; D008274:Magnesium