Regulation of bacterial manganese metabolism

描述（由申请人提供）：锰及其获取和随后代谢的调节对于正常细胞功能很重要，有助于细菌成功适应它们所处的不同环境。锰可能是一种限制性营养素，因此依赖锰的过程必须与金属的可用性相协调。我们有兴趣了解慢生根瘤菌如何感知和获得锰，维持体内平衡，并协调锰依赖的活动与细胞水平。初步的证据使我们能够检验这个假设，即B。japonicum通过与E.大肠杆菌和其他模式生物。B。japonicum属于α-变形菌门（α-Proteobacteria），这是一个多样的分类学类群，包括许多在共生或致病环境中与真核宿主形成紧密或细胞内关联的成员。B。日本血吸虫是研究实验分析难以解决的相关病原体的模式生物。 提出了三个具体目标。(1)阐明维持锰稳态的机制。我们确定了一个高亲和力的外膜通道Mn 2+摄取所必需的。外膜的二价离子的选择性是前所未有的，并揭示了细菌的营养收购策略，以前没有认识到。我们将阐明这一通道在锰稳态中的作用。此外，B.日本根瘤菌耐受对其它细菌有毒的异常高的外部锰浓度。我们将确定这种耐受性的基础，以了解这种生物体如何维持体内平衡。(2)阐明通过B的锰响应转录控制。japonicum Mur蛋白。B。Japonicum已经将全局细菌铁响应性转录阻遏物调整为作为Mn 2+响应性调节物起作用。我们发现了Mur蛋白的新方面。首先，它在与Fur家族蛋白的假定金属结合位点不同的位点结合Mn 2+，解决这个问题应该可以深入了解它如何适应成为Mn 2+传感器。其次，Mur的脱金属形式是有活性的，并且控制与Mn 2+负载蛋白不同的调节子。我们将分析这个新功能。(3)确定铁锰代谢整合的分子基础。初步证据显示，B.日本根瘤菌在转录水平上感知并响应铁和锰的同时缺乏，这与每种金属的单独缺乏在性质上不同。我们将首先集中在两个操纵子参与支链氨基酸降解，以深入了解这一全球性的反应。

DESCRIPTION (provided by applicant): Manganese and the regulation of its acquisition and subsequent metabolism are important for normal cell function, and contribute to the success of bacteria in adapting to the diverse environments in which they occupy. Manganese can be a limiting nutrient, and thus manganese-dependent processes must be coordinated with availability of the metal. We are interested in understanding how Bradyrhizobium japonicum senses and acquires manganese, maintains homeostasis, and coordinates manganese-dependent activities with cellular levels. Preliminary evidence lead us to test the hypothesis that B. japonicum adapts to cellular manganese levels by novel mechanisms that differ substantially from that found in E. coli and other model organisms. B. japonicum belongs to the alpha-Proteobacteria, a diverse taxonomic group that includes numerous members that form close or intracellular associations with eukaryotic hosts in a symbiotic or pathogenic context. B. japonicum serves as a model organism to study related pathogens that are refractory to experimental analysis. Three specific aims are proposed. (1) Elucidate the mechanisms that maintain manganese homeostasis. We identified a high affinity outer membrane channel necessary for Mn2+ uptake. Outer membrane selectivity for a divalent ion is unprecedented and reveals a bacterial strategy for nutrient acquisition not previously appreciated. We will elucidate the role of this channel in manganese homeostasis. Moreover, B. japonicum tolerates an unusually high external manganese concentration that is toxic to other bacteria. We will determine the basis of this tolerance towards the goal of understanding how this organism maintains homeostasis. (2) Elucidate manganese-responsive transcriptional control via the B. japonicum Mur protein. B. japonicum has adapted a global bacterial iron-responsive transcriptional repressor to function as a Mn2+ responsive regulator. We uncovered novel aspects of the Mur protein. Firstly, it binds Mn2+ at a site dissimilar to the presumed metal binding sites of Fur family proteins, and resolving this issue should give insight as to how it has adapted to be a Mn2+ sensor. Secondly, the demetallated form of Mur is active and controls a different regulon than the Mn2+-loaded protein. We will analyze this novel function. (3) Determine the molecular basis for the integration of iron and manganese metabolism. Preliminary evidence shows that B. japonicum senses and responds to a simultaneous deficiency in both iron and manganese at the level of transcription that is qualitatively different from individual deficiencies in each metal. We will focus initially on two operons involved in branched chain amino acid degradation to gain insight into this global response.