Structure and Function of Bacterial CNNM Magnesium Transporters

细菌CNNM镁转运蛋白的结构和功能

• 批准号: RGPIN-2020-07195
• 负责人: Gehring, Kalle
• 金额: $ 3.29万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=718728
• 关键词: Structure; Function; Bacterial; CNNM; Magnesium

Magnesium (Mg2+) is the most abundant divalent cation inside cells and essential for a wide variety of biochemical activities. Although there is not a large gradient of Mg2+ across the cell membrane, increasing evidence suggests that changes in intracellular Mg2+ modulate cell growth through the requirement of many enzymes and metabolic sensors for Mg2+. The importance of cellular Mg2+ homeostasis is manifest in the large number of Mg2+ transporters both in bacteria and eukaryotes. In humans, hereditary diseases of magnesium uptake or deposition arise from mutations in transient receptor potential melastatin type 6 (TRPM6), Mg2+ transporter 1 (MagT1), solute carrier family 41 members (Slc41a1-3), claudin 16, and CNNMs. In bacteria, crystal structures for the Mg2+ transporters MgtE and CorA have revealed the mechanisms for ion selectivity and gating. The CNNM proteins are of particular interest as they are conserved across both eukaryotes and prokaryotes and play essential roles in Mg2+ homeostasis. The CNNM family is defined by a conserved transmembrane domain (DUF21 -- domain of unknown function 21) and a cytosolic cystathionine beta--synthase (CBS) pair domain. While associated with Mg2+ transport, it is unknown if CNNM proteins are themselves Mg2+ transporters or if they regulate transport by other proteins. In humans, mutations in CNNM proteins cause a variety of diseases related to Mg2+ and Ca2+ uptake or deposition. In lower eukaryotes and bacteria, mutations in CNNM proteins lead to resistance to metal toxicity and defects in Mg2+ transport. Our group has determined multiple structures of CNNM cytosolic domains and shown that they undergo a large conformational change upon Mg2+·ATP binding. Here, we propose to determine the structural basis of bacterial CNNM protein function and regulation. We have two aims: 1. Structural studies. We have cloned and expressed DUF21--containing proteins from over 20 species. Several proteins are well expressed and crystallize under multiple conditions. We have also used negative stain electron microscopy (EM) to study one bacterial protein. We will determine the structure of a CNNM bacterial ortholog by either EM or X--ray crystallography. 2. Functional studies. We will characterize the function and conformational changes of CNNM proteins using biophysical methods and functional assays. These studies will address the question of whether DUF21 domains directly or indirectly mediate ion transport and reveal how their cytosolic domains regulate their function. The DUF21 domain of CNNM proteins is the largest family of domains of unknown function and there are no known structures. There are well over 50,000 CNNM orthologs known in plants, animals and bacteria yet we do not understand their precise biochemical function. The work proposed will advance our understanding of the function of the CNNM proteins in divalent cation transport and their regulation by Mg2+·ATP binding.

镁(Mg2+)是细胞内含量最丰富的二价阳离子，是多种生化活动所必需的。虽然镁离子在细胞膜上的梯度并不大，但越来越多的证据表明，细胞内镁离子的变化是通过许多酶和代谢感受器对镁离子的需求来调节细胞生长的。细菌和真核生物中存在大量的镁离子转运体，细胞内镁离子动态平衡的重要性可见一斑。在人类中，遗传性 镁摄取或沉积疾病由瞬时受体潜力蛋白6(TRPM6)、镁离子转运体1(MagT1)、溶质载体家族41成员(Slc41a1-3)、claudin 16和CNNMs突变引起。在细菌中，镁离子转运体MgtE和Cora的晶体结构揭示了离子选择性和门控的机制。 CNNM蛋白在真核生物和原核生物中都是保守的，在镁离子稳态中起着重要的作用。CNNM家族是由一个保守的跨膜结构域(DUF21--未知功能的结构域)和胞浆中的胱硫醚-β-合成酶(CBS)对结构域定义的。虽然与镁离子转运有关，但目前尚不清楚CNNM蛋白本身是镁离子转运蛋白，还是通过其他蛋白质调节镁离子转运。在人类中，CNNM蛋白的突变会导致与镁和钙摄取或沉积有关的各种疾病。在低等真核生物和细菌中，CNNM蛋白的突变导致对金属毒性的抗性和镁离子转运的缺陷。本课题组已经确定了CNNM胞浆结构域的多种结构，并表明它们在与Mg2+·ATP结合时发生了很大的构象变化。 在这里，我们建议确定细菌CNNM蛋白功能和调控的结构基础。我们有两个目标： 1.结构研究。我们已经克隆并表达了来自20多个物种的含有DUF21-的蛋白。几种蛋白质在多种条件下都能很好地表达和结晶。我们还用负染色电子显微镜(EM)研究了一种细菌蛋白。我们将通过EM或X射线结晶学来确定CNNM细菌同源基因的结构。 2.功能研究。我们将使用生物物理方法和功能分析来表征CNNM蛋白的功能和构象变化。这些研究将解决DUF21结构域是否直接或间接调节离子转运的问题，并揭示它们的胞浆结构域如何调节它们的功能。 CNNM蛋白的DUF21结构域是功能未知、结构未知的最大家族。在植物、动物和细菌中已知的CNNM同源基因有50,000多个，但我们并不了解它们的确切生化功能。这项工作将有助于我们进一步了解CNNM蛋白在二价阳离子转运中的作用及其受镁离子·ATP结合的调节。