Collaborative Research: Structure and Function of the Nodulin 26 Aquaglyceroporin

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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.