Chapter Ten Glycosyltransferases involved in plant secondary metabolism

Abstract

The glycosyltmnferases of plant secondary metabolism constiaite a superfamily ofmodifying enzymes involved in late steps of the biosynthesis of naaaal products.PtaJfication and characterization revealed several conserved properties of allglycosyltransfemses. These include similar molecular weights and a tendency to bind tohydrophobic and dye ligand malrices, both successfully used in the purification ofindividual enzymes. Heterologous cloning and expression studies of variousglycosyltmnsfemse genes unequivocally defined high subslrate specificities, evenregiospecificities towards the sugar acceptor. This is reflected in a dendrogram deducedfrom amino acid sequence data, which can be interpreted by subsaate similarities, raltaerthan taxonomic classific~on of the corresponding plant source. While pudtication ofglycosyllransferases from A. thaliana is a challenging task due to the limited amount ofplant tissue, functional analysis may start at the nucleotide sequence level by sequencesimilarity search and heterologous expression of the deduced proteins. These functionalstudies will merit fialher investigations, since the complexity of potentialglucosyllramferase targets including xenobiotics, plant and insect hormones, and putative drugs has only been partly realized. 177 With these goals in mind, a refined classification ofthe glucosyltranferase superfamily in plants, similar to the analysis presented forglucuronosyltransferases of animal tissues, 7 might be within reach over the next few years,and probably will enable the design of new erm3anes with defined substrate sqaecificitiesand new properties.