German-Israel Foundation: Functional and structural analysis of natural product branch-forming glycosyltransferases in plants

Secondary metabolites fulfill a variety of physiological roles in plants, and are valuable for numerous commercial and pharmacological applications. Modifications, such as glycosylation catalyzed by subfamily-1 glycosyltransferases (GTs), play a major part in the biological roles of secondary metabolites. The biological function of sugar-residue attachment often depends on the type and position of glycosylation, which varies between different natural product substrates and between plant species.Furthermore, most glycosylated natural products have more than one sugar attached in tandem (ie. branched sugar), which are essential for their function/characteristics. This proposal brings together a multidisciplinary team to provide the structural basis for branched-sugar formation in plant natural products. Based on the functional characterization of previously cloned branch-forming GT encoding genes from our labs, structural modeling and directed mutagenesis of the catalytic binding site residues responsible for substrate, position and sugar transferase specificity will be deciphered. Domain swapping between branch-forming GT encoding genes will be employed to develop enzymes with novel specificity combinations. Sequence similarity screens will target additional candidate genes, putatively encoding branchforming GTs from various plant species, to enrich and validate the database of genes and proteins encoding novel branch-forming transferase specificities for potential applications in agriculture, chemoenzymatics and molecular farming.