生物谷报道：日本科学家报告说，他们通过分析镁转运体的立体结构，解开了机体维持镁元素平衡的机制，这将有助于治疗心肌梗塞等心脏疾病。
日本科学技术振兴机构和东京工业大学日前发表联合公报说，镁对所有生命体来说都是不可缺少的元素，缺镁是引发心肌梗塞等缺血性心脏病的原因之一，但是过度摄取镁对机体反而有害。机体如何维持镁平衡，是科学界长期没有解决的一个问题。
在此次研究中，研究人员利用Ｘ射线结晶构造分析方法，确定了在镁存在的条件下，细胞膜上的镁转运体ＭｇｔＥ的立体结构。镁转运体ＭｇｔＥ可以把细胞外的镁离子运送到细胞内。
分析显示，ＭｇｔＥ转运体上存在镁进出细胞的通道。ＭｇｔＥ能够感知细胞内镁浓度的变化，然后根据情况关闭或打开通道，从而维持机体的镁平衡。
相关论文已刊登于最新一期英国《自然》杂志网络版上。（新华网）
原始出处:
Nature advance online publication 15 August 2007 | doi:10.1038/nature06093; Received 18 April 2007; Accepted 16 July 2007; Published online 15 August 2007
Crystal structure of the MgtE Mg2+ transporter
Motoyuki Hattori1, Yoshiki Tanaka1, Shuya Fukai2, Ryuichiro Ishitani1 & Osamu Nureki1,3
Department of Biological Information, Graduate School of Bioscience and Biotechnology,
Center for Biological Resources and Informatics, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama-shi, Kanagawa 226-8501, Japan
SORST, JST, Honcho, Kawaguchi-shi, Saitama 332-0012, Japan
Correspondence to: Osamu Nureki1,3 Correspondence and requests for materials should be addressed to O.N. (Email: nureki@bio.titech.ac.jp).
The magnesium ion Mg2+ is a vital element involved in numerous physiological processes. Mg2+ has the largest hydrated radius among all cations, whereas its ionic radius is the smallest. It remains obscure how Mg2+ transporters selectively recognize and dehydrate the large, fully hydrated Mg2+ cation for transport1. Recently the crystal structures of the CorA Mg2+ transporter2, 3, 4, 5 were reported6, 7, 8. The MgtE family of Mg2+ transporters is ubiquitously distributed in all phylogenetic domains9, 10, 11, and human homologues have been functionally characterized and suggested to be involved in magnesium homeostasis12, 13, 14. However, the MgtE transporters have not been thoroughly characterized. Here we determine the crystal structures of the full-length Thermus thermophilus MgtE at 3.5 Å resolution, and of the cytosolic domain in the presence and absence of Mg2+ at 2.3 Å and 3.9 Å resolutions, respectively. The transporter adopts a homodimeric architecture, consisting of the carboxy-terminal five transmembrane domains and the amino-terminal cytosolic domains, which are composed of the superhelical N domain and tandemly repeated cystathionine--synthase domains. A solvent-accessible pore nearly traverses the transmembrane domains, with one potential Mg2+ bound to the conserved Asp 432 within the pore. The transmembrane (TM)5 helices from both subunits close the pore through interactions with the 'connecting helices', which connect the cystathionine--synthase and transmembrane domains. Four putative Mg2+ ions are bound at the interface between the connecting helices and the other domains, and this may lock the closed conformation of the pore. A structural comparison of the two states of the cytosolic domains showed the Mg2+-dependent movement of the connecting helices, which might reorganize the transmembrane helices to open the pore. These findings suggest a homeostasis mechanism, in which Mg2+ bound between cytosolic domains regulates Mg2+ flux by sensing the intracellular Mg2+ concentration. Whether this presumed regulation controls gating of an ion channel or opening of a secondary active transporter remains to be determined.
