Magnesium transport in prokaryotes
Magnesium transport in prokaryotes
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DOI：
10.1007/s007750050374
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发表时间：
1999-10-01
影响因子：
3
通讯作者：
Maguire, ME
中科院分区：
文献类型：
--
作者：
Moncrief, MBC;Maguire, ME
在生物相关阳离子中，Mg2+具有最大的水合半径、最小的离子半径和最高的电荷密度，这为Mg2+进入活细胞提供了一个有趣的问题。Mg2+的转运系统主要在鼠伤寒沙门菌中进行了表征，因为革兰氏阴性菌的良好遗传学使克隆和研究转运体成为可行的建议。CorA转运系统是组成性表达的，是真细菌和古细菌中主要的Mg2+转运体。它有三个跨膜结构域，一个独特的大的外质结构域，与其他蛋白质没有序列同源性。MgtE Mg2+转运蛋白也缺乏与其他蛋白的序列同源性，目前尚不清楚Mg2+转运是否是其主要功能。MgtA和MgtB Mg2+转运体与p型atp酶具有序列同源性。它们与哺乳动物Ca2+- atp酶的关系比与原核生物p型atp酶的关系更密切。MgtA和MgtB通过Mg2+电化学梯度介导Mg2+内流，而不是相反。与corA和mgtE不同，mgtA和mgtC/mgtB位点受到双组分调控系统PhoP/PhoQ的调控。PhoQ是一种Mg2+膜传感器激酶，在Mg2+限制条件下磷酸化转录因子PhoP。然后该因子诱导mgtA和mgtCB的转录。MgtC由mgtCB操纵子的第一个基因编码，与任何已知蛋白没有序列同源性，是鼠伤寒沙门氏菌在小鼠和巨噬细胞中的毒力所必需的，但似乎是一种Mg2+转运体。这些Mg2+转运体的生理作用及其机制尚不完全清楚，但初步数据表明，Mg2+转运体是一种独特的转运系统，具有介导Mg2+通过膜运动的不寻常机制。
Possessing the largest hydrated radius, the smallest ionic radius, and the highest charge density among the biologically relevant cations, Mg2+ provides an interesting problem for transport into living cells. Transport systems for Mg2+ have been characterized primarily in Salmonella typhimurium because the well-developed genetics of Gram-negative bacteria make cloning and studying the transporters a viable proposition. The CorA transport system is expressed constitutively and is the major Mg2+ transporter in Eubacteria and Archaea. It has three transmembrane domains, a uniquely large periplasmic domain, and no sequence homology to other proteins. The MgtE Mg2+ transporter also lacks sequence homology to other proteins, and it is unclear if Mg2+ transport is its primary function. The MgtA and MgtB Mg2+ transporters have sequence homology to P-type ATPases. They are more closely related to the mammalian Ca2+-ATPases than to the prokaryotic P-type ATPases. MgtA and MgtB mediate Mg2+ influx with, rather than against, the Mg2+ electrochemical gradient. Unlike corA and mgtE, the mgtA and mgtC/mgtB loci are regulated, being induced by the two-component regulatory system PhoP/PhoQ. PhoQ is a Mg2+ membrane sensor kinase that phosphorylates the transcription factor PhoP under Mg2+-limiting conditions. This factor then induces transcription of mgtA and mgtCB. MgtC, which is encoded by the first gene in the mgtCB operon, has no sequence homology to any known protein and is essential for S. typhimurium virulence in mice and macrophages, but does appear to be a Mg2+ transporter. The physiological roles of these Mg2+ transporters and their mechanisms are not yet completely clear, but initial data indicate that Mg2+ transporters are unique transport systems with unusual mechanisms for mediating Mg2+ movement through the membrane.