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

摘要

Seven derivatives of L-fucose: methyl a-L-fucopyranoside, methyl 2-O-methyl-a-L-fucopyranoside, methyl 3-O-methyl-a-Lfucopyranoside, methyl 4-O-methyl-a-L-fucopyranoside, a-Lfucopyranosyl-( 1!4)-a/b-L-rhamnopyranose, methyl a-L-fucopyranosyl-( 1!4)-a-L-rhamnopyranoside and methyl a-L-fucopyranosyl-( 1!4)-b-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 a-L-fucopyranoside was the most efficient acceptor, 30 fold more effective than methyl 4-O-methyl-a-L-fucopyranoside. Omethylation in position 2 or 3 abolished acceptor function. The efficiencies of the disaccharides as acceptors were methyl a-Lfucopyranosyl-( 1!4)-b-L-rhamnopyranoside > a-L-fucopyranosyl-( 1!4)-a/b-L-rhamnopyranose > methyl a-L-fucopyranosyl- (1!4)-a-L-rhamnopyranoside. These findings demonstrate the utility of acceptor derivatives as probes of glycosyltransferase regiospecificity.