Xyloglucan, the major hemicellulosic component in

Xyloglucan, the major hemicellulosic component in Arabidopsis thaliana, is biosynthesized in the Golgi apparatus by a series of glycan synthases and glycosyltransferases before export to the wall. The xyloglucan-specific alha2-fucosyltransferase FUT1 catalyzes the transfer of fucose from GDP-fucose to terminal galactosyl residues on xyloglucan side chains.

The article reports the crystal structures of Arabidopsis FUT1 in its apoform and in a ternary complex with GDP and a xylo-oligosaccharide acceptor (named XLLG). FUT1 is contains a variant of the GT-B fold, which includes an extra C-terminal region that is part of the acceptor binding site. The crystal structures support previous findings that FUT1 behaves as a functional dimer. Mutational studies and structure comparison with other fucosyltransferases suggest that FUT1 uses a SN2-like reaction mechanism similar to that of protein-O-fucosyltransferase 2. These results provide new insights into the mechanism of xyloglucan fucosylation in the Golgi.