MAGNESIUM HOMEOSTASIS IN MICROORGANISMS

镁离子是细胞内含量最丰富的二价阳离子。它的化学成分在生物阳离子中是独一无二的。同样，它的各种交通系统也是独一无二的，或者是现有家庭中非常不寻常的成员。在原核细胞中，尤其是在细菌的致病过程中，镁离子也起着重要的调节作用。我们的长期目标是了解镁离子的转运过程和镁离子对基因表达的调控，以形成镁离子动态平衡的总体图景。CORA代表了一个新的转运蛋白家族，与其他已知蛋白缺乏相似性。它在细菌和古生菌中普遍存在，在酵母中也有同源物。系统发育和结构研究表明，该家族的不同成员在功能和膜拓扑结构上可能有所不同。所有的CORA都含有一个大的可溶的N-末端结构域和一个小的C-末端膜结构域，便于通过将其作为两个可分离的结构域来处理来研究其结构。CORA已经被证明是低聚的，可溶域已经被纯化并保留了二级结构，并且已经确定了镁离子通过膜移动的部分途径。这一更新概述了定义CORA功能结构的持续研究。23 kDa的MGTC蛋白由两个基因操纵子的第一个基因和P型ATPase镁离子转运体MgtB共同编码。操纵子的转录是由细胞外的镁离子浓度通过PhoPQ双组分调控系统控制的。PhoPQ是鼠伤寒沙门氏菌毒力的重要调节因子。MgtCB操纵子的插入突变使鼠伤寒沙门氏菌基本上是无毒的，其中大部分毒力下降是由于MGTC的丢失。MGTC的表达异常。在胞外低浓度的镁离子下，操纵子的转录增加了几千倍，但只表达了镁B蛋白。相反，如果mgtB基因被插入失活，mgtc就会大量表达。MGTC已纯化至均一状态，似乎是一种寡聚膜蛋白。初步数据表明，它改变了细胞内钙的稳态。这一更新建议试图确定其异常表达的基础，并研究其在钙稳态中的可能作用。

Mg2+ is the most abundant intracellular divalent cation. Its chemistry is unique among the biological cations. Likewise, its various transport systems are also unique or are highly unusual members of existing families. Mg2+ also plays a fundamental regulatory role in prokaryotic cells and especially in bacterial pathogenesis. Our long-term goal is to understand both Mg2+ transport processes and Mg2+ regulation of gene expression to formulate an overall picture of Mg2+ homeostasis. CorA represents a new family of transport proteins lacking similarity to other known proteins. It is ubiquitous in the Bacteria and Archaea with homologs in yeast. Phylogenetic and structural studies suggest the various members of the family may differ in both function and membrane topology. All CorA's contain a large soluble N-terminal domain and a small C-terminal membrane domain, facilitating study of its structure through treatment as two separable structural domains. CorA has been shown to be oligomeric, the soluble domain has been purified and retains secondary structure, and a partial pathway for Mg2+ movement through the membrane has been identified. This renewal outlines continuing studies to define the functional structure of CorA. The 23 kDa MgtC protein is encoded by the first gene of a two gene operon along with the P-type ATPase Mg2+ transporter MgtB. Operon transcription is controlled by extracellular Mg2+ concentration through the PhoPQ two component regulatory system. PhoPQ is an essential regulator of virulence in S. typhimurium. Insertional mutagenesis of the mgtCB operon renders S. typhimurium essentially avirulent, with the large majority of this decrease in virulence due to loss of mgtC. Expression of MgtC is unusual. Transcription of the operon is increased several thousand fold at low extracellular Mg2+ concentrations, but only MgtB protein is expressed. In contrast, if the mgtB gene is insertionally inactivated, MgtC is expressed in large amounts. MgtC has been purified to homogeneity and appears to be an oligomeric membrane protein. Preliminary data suggest that it alters cellular Ca2+ homeostasis. This renewal proposal seeks to determine the basis for its unusual expression and to investigate its possible role in Ca2+ homeostasis.