A new methodology for the preparation of non-natural oligosaccharides has been developed using various glycosyl fluorides as activated glycosyl donors for enzymatic polycondensation. The reaction proceeds in a complete regio- and stereoselective manner to afford oligosaccharides of well-defined structures. The resulting oligosaccharides are difficult to prepare by conventional chemical methods with use of protecting groups.
A putative gene for a β-glucosyltransferase, celA, was isolated from cotton in 1996. Recently, a homologous gene RSW1 was identified from studies with a cell wall mutant of Arabidopsis. These two independent studies strongly suggest that celA is involved in cellulose synthesis in plants. In addition to the celA multigene family, two other related multigene families of putative β-glycosyltransferases have been identified by the Arabidopsis genome projects. The celA-like superfamily of proteins all share conserved motifs that may be involved in substrate binding and/or catalysis. We discuss proposed reaction mechanisms by which plants make wall polysaccharides including cellulose. While recent advances in cellulose synthesis in vitro have unraveled some aspects involved in the processes, cellulose synthesis in vivo involves additional processes such as translocation of glucan products across the plasma membrane and the deposition of cellulose microfibrils in the cell wall. We discuss generally accepted models in which cellulose synthesizing complexes move in the plasma membrane during cellulose synthesis and deposition, and also describe an alternative model in which β-transglucosylase activity of a hypothetical endo-1, 4-β-D-glucanase is involved in cellulose synthesis in plants.
Starch is the most important source of calories on the planet and a vital storage compound in plants. Despite its importance, we do not fully understand how starch is synthesized, how starch synthesis is initiated and what controls starch structure. Many genes in the starch biosynthesis pathway have been isolated and multiple forms of starch synthase and branching enzyme have been identified. For example, five starch synthase genes and three branching enzyme genes have been cloned from maize. To fully illustrate the mechanism of starch biosynthesis, we need to understand the functions of individual enzyme as well as the concerted actions of multiple forms of enzymes in starch synthesis. Since maize is the number one supply of starch for food and non-food industries and also a good source for genetic and biochemical studies, here we will use maize as a model plant to discuss the mechanism of starch biosynthesis, particularly the initiation of starch synthesis, the functions and interaction of multiple isozymes of starch synthase and branching enzyme.
Investigation of the biological functions of glycoconju-gates based on specific molecular interactions is an emerging area of great potential interest. With the advent of Biomolecular Interaction Analysis (BIA) Technology seven years ago, the BIACORE biosensor instrument has been extensively used to elucidate and characterize many biomolecular interactions which are well documented in the literature. In BIA technology, the biomolecule of interest is immobilized onto a sensor surface and a binding partner can then be passed over it in a mobile aqueous phase. Their interaction on the sensor surface can subsequently be monitored in real time without the use of labels. In this paper, applications of the BIACORE instrument as a research tool for investigating specific interactions of glycoconjugates is introduced, where binding kinetics were determined using Concanavalin A and immobilized asialofetuin in a model system.