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Crystal structure of the CorA Mg~(2+) transporter

机译：CorA Mg〜（2+）转运蛋白的晶体结构

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摘要

The magnesium ion, Mg~(2+), is essential for myriad biochemical processes and remains the only major biological ion whose transport mechanisms remain unknown. The CorA family of magnesium transporters is the primary Mg~(2+) uptake system of most prokaryotesand a functional homologue of the eukaryotic mitochondrial magnesium transporter. Here we determine crystal structures of the full-length Thermotoga maritima CorA in an apparent closed state and its isolated cytoplasmic domain at 3.9 A and 1.85 A resolution, respectively. The transporter is a funnel-shaped homopentamer with two transmembrane helices per monomer. The channel is formed by an inner group of five helices and putatively gated by bulky hydrophobic residues. The large cytoplasmic domain forms a funnel whose wide mouth points into the cell and whose walls are formed by five long helices that are extensions of the transmembrane helices. The cytoplasmic neck of the pore is surrounded, on the outside of the funnel, by a ring of highly conserved positively charged residues. Two negatively charged helices in the cytoplasmic domain extend back towards the membrane on the outside of the funnel and abut the ring of positive charge. An apparent Mg~(2+) ion was bound between monomers at a conserved site in the cytoplasmic domain, suggesting a mechanism to link gating of the pore to the intra-cellular concentration of Mg~(2+).
机译：镁离子Mg〜（2+）是无数生化过程必不可少的，并且仍然是唯一未知转运机制的主要生物离子。镁转运蛋白的CorA家族是大多数原核生物的主要Mg〜（2+）摄取系统，是真核线粒体镁转运蛋白的功能同源物。在这里，我们确定了在明显的闭合状态下的全长滨海嗜热菌CorA的晶体结构及其分离的胞质结构域，分别为3.9 A和1.85 A分辨率。转运蛋白是漏斗形的均五聚体，每个单体具有两个跨膜螺旋。该通道由五个螺旋的内部基团形成，并被庞大的疏水残基推定为门。大的细胞质结构域形成一个漏斗，其宽口指向细胞，其壁由五个跨膜螺旋的延伸的长螺旋形成。孔的细胞质颈部在漏斗的外部被一圈高度保守的带正电的残基包围。细胞质结构域中的两个带负电的螺旋向着漏斗外侧的膜延伸，并与正电荷环邻接。明显的Mg〜（2+）离子结合在胞质结构域保守位点的单体之间，提示了将孔的门控与Mg〜（2+）的细胞内浓度联系起来的机制。

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