Functional characterisation of a putative rhamnogalacturonan II specific xylosyltransferase

An Arabidopsis thaliana gene, At1g56550, was expressed in Pichia pastoris and the recombinant protein was shown to catalyse transfer of d-xylose from UDP-alpha-d-xylose onto methyl alpha-l-fucoside. The product formed was shown by 1D and 2D (1)H NMR spectroscopy to be Me alpha-d-Xyl-(1,3)-alpha-l-Fuc, which is identical to the proposed target structure in the A-chain of rhamnogalacturonan II. Chemically synthesized methyl l-fucosides derivatized by methyl groups on either the 2-, 3- or 4 position were tested as acceptor substrates but only methyl 4-O-methyl-alpha-l-fucopyranoside acted as an acceptor, although to a lesser extent than methyl alpha-l-fucoside. At1g56550 is suggested to encode a rhamnogalacturonan II specific xylosyltransferase.