Collaborative Research: Structure and Function of the Nodulin 26 Aquaglyceroporin

9904978 Roberts/Mitra在豆类和根瘤菌之间形成固氮共生体的过程中，诱导了一组基因，编码“根瘤蛋白”，这是一种帮助建立和维持共生关系的蛋白质。结节蛋白26是靶向包裹内共生类细菌并与宿主进行代谢物交换的特殊共生体膜的结节蛋白之一。节蛋白26是MIP/水孔蛋白通道家族的成员之一，该家族包括多种负责流动水或不带电荷的溶质的蛋白质。该蛋白已成为一个独特的植物MIP亚家族的原型，该家族具有不同寻常的多功能转运特征，包括与其他水通道蛋白相比，其固有的水分转运速率较低，以及能够流动甘油等不带电荷的溶质。这项合作研究(与Roberts 9904978)的目的是研究结核蛋白26的结构细节，使其成为一种多功能的水甘油疏松蛋白。其目标是：1.合理设计结瘤蛋白26突变体以确定决定单通道速率和运输选择性的残基/结构域(Roberts)；2.用于晶体结构分析的大豆根瘤蛋白26(Roberts)的纯化和膜重组(Roberts)；以及3.从遗传可追踪模式豆科植物莲花(Roberts)中获得一个根瘤蛋白26同源基因的功能分析。最近水通道蛋白的发现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数十个成员组成的多样化的家族，每个成员都有为其生物学角色量身定做的谨慎的功能特性。这些不同功能特性的结构性原因尚未揭开。膜蛋白水囊学家和植物生物化学家的合作项目将提供对根瘤蛋白26的详细结构分析，根瘤蛋白26是一种独特的水孔蛋白，在固氮共生过程中专门表达。这项工作将阐明使根瘤蛋白26成为一种多选择性转运蛋白的结构特征，并将提供关于决定水通道蛋白活性和选择性的结构特征的更基本信息。

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.