MAGNESIUM HOMEOSTASIS IN MICROORGANISMS

Mg 2+是细胞内最丰富的二价阳离子。它的化学性质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特的，或者是现有家庭中非常不寻常的成员。 Mg 2+在原核细胞中也起着重要的调节作用，尤其是在细菌的致病机制中。我们的长期目标是了解Mg 2+转运过程和Mg 2+调控基因表达，以制定Mg 2+稳态的总体情况。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。 它在细菌和酵母菌中普遍存在，在酵母菌中有同源物。系统发育和结构研究表明，该家族的各个成员可能在功能和膜拓扑结构上都有差异。所有的CorA都含有一个大的可溶性N-末端结构域和一个小的C-末端膜结构域，通过将其作为两个可分离的结构域来处理，有利于研究其结构。CorA已被证明是寡聚的，可溶性结构域已被纯化并保留二级结构，并且已确定Mg 2+通过膜移动的部分途径。该更新概述了继续研究以确定CorA的功能结构。 23 kDa MgtC蛋白由两个基因操纵子的第一个基因沿着P型ATP酶Mg 2+转运蛋白MgtB编码。操纵子转录通过PhoPQ双组分调节系统由细胞外Mg 2+浓度控制。PhoPQ是S.鼠伤寒。mgtCB操纵子的插入突变使S.鼠伤寒沙门氏菌基本上是无毒的，其中大部分毒力降低是由于mgtC的丧失。 MgtC表达异常。操纵子的转录在低胞外Mg 2+浓度下增加数千倍，但仅表达MgtB蛋白。相反，如果mgtB基因被插入失活，则MgtC大量表达。MgtC已被纯化至同质，似乎是一种寡聚膜蛋白。初步数据表明，它改变了细胞的Ca 2+稳态。这一更新建议旨在确定其异常表达的基础，并研究其在Ca 2+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.