Chemical Synthesis of L-Fucose Derivatives for Acceptor Specificity Characterisation of Plant Cell Wall Glycosyltransferases

Abstract

Seven derivatives of L-fucose: methyl α-L-fucopyranoside, methyl 2-O-methyl-α-L-fucopyranoside, methyl 3-O-methyl-α-L-fucopyranoside, methyl 4-O-methyl-α-L-fucopyranoside, α-L-fucopyranosyl-(1→4)-α/β-L-rhamnopyranose, methyl α-L-fucopyranosyl-(1→4)-α-L-rhamnopyranoside and methyl α-L-fucopyranosyl-(1→4)-β-L-rhamnopyranoside, were chemically synthesized and characterized. The derivatives of L-fucose were designed to mimic the L-fucose moieties present in the A-chain of pectic rhamnogalacturonan-II and used to investigate the regiospecificity of three heterologously expressed xylosyltransferases from Arabidopsis thaliana. The monosaccharide methyl α-L-fucopyranoside was the most efficient acceptor, 30 fold more effective than methyl 4-O-methyl-α-L-fucopyranoside. O-methylation in position 2 or 3 abolished acceptor function. The efficiencies of the disaccharides as acceptors were methyl α-L-fucopyranosyl-(1→4)-β-L-rhamnopyranoside > α-L-fucopyranosyl-(1→4)-α/β-L-rhamnopyranose > methyl α-L-fucopyranosyl-(1→4)-α-L-rhamnopyranoside. These findings demonstrate the utility of acceptor derivatives as probes of glycosyltransferase regiospecificity.