Plant lectins are major tools in studies of the protein-carbohydrate interactions that play a key role in establishing the specificity of a wide variety of biological recognition and communication events. These carbohydrate binding proteins have also been used for a variety of medical purposes, including blood typing, separation of populations of lymphocytes prior to bone marrow transplantation, targeted drug delivery and various diagnostic assays. It is the long term goal of this research to determine the relationship of plant lectin structure to function. Such information should enhance the utilization and versatility of lectins as tools, provide basic information on protein-carbohydrate interactions and help determine the role of such proteins in oligosaccharide signaling and other recognition events in both plants and animals. The present investigation focuses on a new category of lectins, named LNP, with both carbohydrate binding and apyrase activities. Members of this LNP lectin category are present on the surfaces of legume root hairs and have been found to play a role in the oligosaccharide recognition events that initiate the nitrogen-fixing symbiosis that occurs between rhizobia and legumes. Similarities in sequence suggest that other members of this category of lectins may be present in a wide variety of plants and animals and raise the possibility that they may participate in highly conserved oligosaccharide signaling processes.
The specific aims of this proposal are: (1) to determine the range of carbohydrate specificities found among members of this lectin category and the extent of their distribution in the plant and animal kingdoms; (2) to define the structural prerequisites for the carbohydrate binding and enzymatic activities of a representative legume LNP; and (3) to initiate studies to determine the molecular mechanisms by which legume LNPs elicit the activation of downstream events upon binding to their oligosaccharide ligands. This study will employ a variety of methodologies and approaches in studying LNP structure-function relationships, including carbohydrate binding and enzymatic assays, the recombinant expression of individual and combinations of domains and/or regions of this protein, the initiation of X-ray crystallographic studies, the use of site-specific mutations and transgenic analyses of these mutant lectins.
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