Collaborative Research: Structure and Function of the Nodulin 26 Aquaglyceroporin

在豆科植物和根瘤菌之间形成固氮共生关系的过程中，一组基因被诱导编码“结核蛋白”，这是一种有助于建立和维持共生关系的蛋白质。结节素26是针对特殊的共生体膜的结节素之一，该膜包裹着内共生类细菌并介导与宿主的代谢物交换。根瘤蛋白26是MIP/水通道蛋白家族的一员，该家族包括多种传输水或不带电溶质的蛋白质。该蛋白是一种独特的植物MIP亚家族的原型，具有不同寻常的多功能运输特征，包括与其他水通道蛋白相比，其固有的水运输速率较低，以及输送不带电溶质（如甘油）的能力。这项合作研究（与Roberts 9904978）的目的是研究结节素26的结构细节，使其能够作为多功能的水甘油oporin发挥作用。目标是1。合理设计结核蛋白26突变体，以确定决定单通道速率和转运选择性的残基/结构域（Roberts）；2. 大豆根瘤蛋白26 （Roberts）的纯化和膜重构用于晶体结构分析（Mitra）和3。遗传可驯化模式豆科植物日本莲花（lotusjaponicus）中结核素26同源物的功能分析。最近发现的水通道蛋白膜蛋白已经彻底改变了我们对生物膜如何促进水和中性溶质运输的理解。水通道蛋白是一个由几十个成员组成的多样化的家族，每个成员都具有为其生物学作用量身定制的谨慎的功能特性。这些不同功能特性的结构原因尚未被揭示。这个由膜蛋白晶体学家和植物生化学家合作的项目将提供对结核蛋白26的详细结构分析，结核蛋白26是一种在固氮共生过程中特异性表达的独特水通道蛋白。这项工作将阐明使结节蛋白26成为多选择性转运体的结构特征，并将提供有关决定水通道蛋白活性和选择性的结构特征的更多基本信息。

9904978Roberts/MitraDuring the formation of nitrogen-fixing symbioses between legumes and rhizobia bacteria, a set of genes is induced that encode "nodulins", proteins that aid in the establishment and maintenance of the symbiosis. Nodulin 26 is among the nodulins that are targeted to the specialized symbiosome membrane that encloses the endosymbiotic bacteroid and mediates metabolite exchange with the host. Nodulin 26 is a member of the MIP/aquaporin channel family, which includes a variety of proteins that flux water or uncharged solutes. The protein has emerged as the prototype of a unique plant MIP subfamily that has an unusual multifunctional transport profile, including a low intrinsic water transport rate compared to other aquaporins, as well as the ability to flux uncharged solutes such as glycerol. The purpose of this collaborative research (with Roberts 9904978) is to investigate the structural details of nodulin 26 that allow it to function as a multifunctional aquaglyceroporin. The goals are 1. The rational design of nodulin 26 mutants to identify residues/domains that determine the single channel rate and selectivity of transport (Roberts); 2. The purification and membrane reconstitution of soybean nodulin 26 (Roberts) for crystallographic structural analyses (Mitra); and 3. The functional analysis of a nodulin 26 ortholog from the genetically tractable model legume Lotus japonicus (Roberts). The recent discovery of aquaporin membrane proteins has revolutionized our understanding of how biological membranes facilitate water and neutral solute transport. Aquaporins are a diverse family comprised of dozens of members, each with discreet functional properties tailored for its biological role. The structural reasons for these diverse functional properties have yet to be unraveled. This collaborative project between a membrane protein cystallographer and a plant biochemist will provide a detailed structural analysis of nodulin 26, a unique aquaporin specifically expressed during nitrogen fixing symbioses. This work will shed light on the structural features that enable nodulin 26 to be a multiselective transporter, and also will provide more fundamental information on the structural features that determine aquaporin activity and selectivity.