The Nodulin 26 Family of Plant Aquaglyceroporins: Transport Properties and Regulation

主要内在蛋白是一个古老的家族，无处不在的膜通道，作为细胞和组织的“分子管道”，介导水和溶质在生物膜上的快速运输。MIP家族在植物中尤其多样化，反映了水关系在植物生长和发育中的重要性以及适应渗透挑战（干旱和盐度）的需要。在本项目中，将研究植物MIPs的一个独特子集，即结节素样内源性蛋白（NIPs）的结构、功能和调控特性。这个家族的原型是根瘤素26，它是共生体的主要组成部分，共生体是豆科植物根系结瘤时与根瘤菌科的共生固氮细菌形成的细胞器。瘤蛋白26形成一个多选择通道，在共生体膜上运输水和不带电的溶质，并可能参与对共生至关重要的气体交换（固定氨和分子氧）。在发育和水分胁迫信号下，钙调控的磷酸化激活了结节蛋白26的转运。这个项目的目标是调查：1。瘤蛋白26的转运选择性及其介导气体通过共生体膜的能力；2. 钙依赖性磷酸化和其他调控因子在结节蛋白26转运和选择性中的作用3. 3 .利用晶体学和分子动力学技术研究磷酸化和未磷酸化结核蛋白26的结构；NIP同源物在模式植物拟南芥中的转运特性和生物学功能。这项工作将有助于建立这一保守的膜转运蛋白家族的结构和功能概况，并阐明调节其功能的环境和发育因素。除了有助于了解与固氮豆科植物-微生物共生相关的运输过程外，该工作还将利用强大的拟南芥分子遗传模型系统，深入了解NIPs在水关系和胁迫适应中的其他基本作用。更广泛的影响：从基础设施的角度来看，这项工作将影响我们对植物系统中逆境调节和适应的分子基础的理解，并为植物MIP蛋白的研究提供一个结构框架。了解植物逆境响应和固氮共生的分子基础是具有重要农业意义的基础课题。该项目将作为培养田纳西大学本科研究学者、博士候选人和博士后助理的基础。此外，该项目还将为与国际科学家在植物膜生物学和与植物干旱和渗透胁迫信号相关的信号转导过程方面的持续合作奠定基础。分子生物化学和综合植物生物学计划共同资助了这个项目。

Major Intrinsic Proteins are an ancient family of ubiquitous membrane channels that serve as the "molecular plumbing" of cells and tissues, mediating the rapid transport of water and solutes across biological membranes. The MIP family is particularly diverse in plants, reflecting the importance of water relations in plant growth and development and the need to adapt to osmotic challenge (drought and salinity). In this project the structural, functional and regulatory properties of a unique subset of plant MIPs, the Nodulin-like Instrinsic Proteins (NIPs) will be investigated. The archetype of this family is nodulin 26, which is a major component of the symbiosome, an organelle formed during the nodulation of legume roots with symbiotic, nitrogen-fixing bacteria of the Rhizobaceae family. Nodulin 26 forms a multiselective channel that transports water and uncharged solutes across the symbiosome membrane, and may engage in gas exchange (fixed ammonia and molecular oxygen) that is critical to the symbiosis. Nodulin 26 transport is activated by calcium-regulated phosphorylation in response to developmental and water stress signals. The goals of this project are to investigate: 1. the transport selectivity of nodulin 26 and its ability to mediate gas permeability across the symbiosome membrane; 2. the role of calcium-dependent phosphorylation and other regulatory factors on nodulin 26 transport and selectivity; 3. the structures of phosphorylated and unphosphorylated nodulin 26 by crystallography and molecular dynamics techniques, and 4. the transport properties and biological functions of NIP orthologs in the model plant Arabidopsis thaliana. The proposed work will aid in establishing a structural and functional profile for this conserved family of membrane transporters, as well as shedding light on the environmental and developmental factors that regulate their function. Besides contributing to the understanding of transport processes associated with nitrogen-fixing legume-microbe symbiosis, the work will also provide insight into additional fundamental roles of NIPs in water relations and stress adapation by utilizing the powerful Arabidopsis molecular genetic model system.Broader Impact: From the perspective of infrastructure, the work will impact our understanding of the molecular basis of stress regulation and adaptation in plant systems as well as provide a structural framework for plant MIP protein research in general. The understanding of the molecular basis of plant stress responses and nitrogen fixing symbioses are fundamental topics of agricultural importance. The project will serve as a foundation for the training of undergraduate research scholars, as well as Ph.D. candidates and post doctoral associates at the University of Tennessee. In addition, this project will also serve as a foundation for a continuing collaboration with international scientists in plant membrane biology and signal transduction processes related to plant drought and osmotic stress signaling.The Molecular Biochemistry and Integrative Plant Biology Programs jointly fund this project.