Magnesium transporters: Properties, regulation and structure
Magnesium transporters: Properties, regulation and structure
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DOI：
10.2741/2039
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发表时间：
2006-09-01
影响因子：
3.1
通讯作者：
Maguire, Michael E.
中科院分区：
文献类型：
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作者：
Maguire, Michael E.
Mg2+的化学性质在生物阳离子中是独特的，Mg2+输运系统的性质反映了这种化学性质。原核生物携带三种Mg2+转运系统：CorA、MgtA/B和MgtE。CorA和MgtE广泛分布于真细菌和古细菌中，而MgtA/B类主要存在于真细菌中。CorA的真核同源物虽然具有明确的Mg2+转运蛋白功能，但其序列同源性最小，包括真菌的Mrs2p线粒体Mg2+通道和ALR蛋白。MgtE同源物在真核生物中更容易被识别为SLC41类转运蛋白。MgtA/B Mg2+转运体属于p型atp酶超家族，但它介导Mg2+沿其电化学梯度内流，而不是像其他p型atp酶那样沿梯度内流。它们的生理作用尚不清楚。CorA是唯一一个结构已被解决的Mg2+转运体。它是一种均戊体，每个单体具有两个跨膜结构域，其中第一个结构域形成离子传导途径。Mg2+转运首先涉及到完全水合阳离子与连接跨膜结构域的胞外结合环的结合。通过膜不涉及静电相互作用，但两个细胞质结构域，一个携带极高浓度的正电荷，另一个携带极高浓度的负电荷，似乎有助于控制Mg2+的通量，并与每个单体结构域之间的细胞内Mg2+结合相一致。CorA和MgtE似乎都不受转录调控，这意味着它们主要是“管家”基因。尽管如此，肠炎沙门氏菌血清型鼠伤寒沙门氏菌的corA基因突变导致毒力衰减和其他缺陷，即使菌株携带两个额外的Mg2+转运蛋白，并且突变体没有Mg2+依赖性生长缺陷。
The chemistry of Mg2+ is unique amongst biological cations, and the properties of Mg2+ transport systems reflect this chemistry. Prokaryotes carry three classes of Mg2+ transport systems: CorA, MgtA/B and MgtE. CorA and MgtE are widely distributed in both Eubacteria and Archaea, while the MgtA/B class is found primarily in the Eubacteria. Eukaryotic homologs of CorA, although clearly functional as Mg2+ transporters, have minimal sequence homology and include the Mrs2p mitochondrial Mg2+ channel and the ALR proteins of fungi. MgtE homologs are more recognizable in eukaryotes as the SLC41 class of transporters. The MgtA/B Mg2+ transporters belong to the P-type ATPase superfamily, but mediate Mg2+ influx down its electrochemical gradient rather than against the gradient as with other P-type ATPases. Their physiological role is not clear. CorA is the only Mg2+ transporter whose structure has been solved. It is a homopentamer with two transmembrane domains per monomer, the first of which forms the ion conduction pathway. Mg2+ transport involves first the binding of the fully hydrated cation to an extracellular binding loop connecting the transmembrane domains. Passage through the membrane involves no electrostatic interactions, but two cytosolic domains, one carrying ext remely high concentrations of positive charge and the other negative charge appear to help control Mg2+ flux, in concert with an intracellular Mg2+ bound between domains of each monomer. Neither CorA nor MgtE appear to be transcriptionally regulated, implying they are primarily "housekeeping" genes. Nonetheless, mutation of the corA gene in Salmonella enterica serovar Typhimurium leads to attenuation of virulence and other defects, even though the strain carries two additional Mg2+ transporters and the mutant exhibits no Mg2+-dependent growth deficit.