Characterization of N-glycans from Arabidopsis. Application to a fucose-deficient mutant

The structures of glycans N-linked to Arabidopsis proteins have been fully identified. From immuno- and affinodetections on blots, chromatography, nuc lear magnetic resonance, and glycosidase sequencing data, we show that Arab idopsis proteins are N-glycosylated by high-mannose-type N-glycans from Man (5)GlcNAc(2) to Man(9)GlcNAc(2), and by xylose- and fucose (Fuc)-containing oligosaccharides. However, complex biantenary structures containing the te rminal Lewis a epitope recently reported in the literature (A.-C. Fitchette -Laine, V. Gomord, M. Cabanes, J.-C. Michalski, M. Saint Macary, B. Foucher , B. Cavalier, C. Hawes, P. Lerouge, and L. Faye [1997] Plant J 12: 1411-14 17) were not detected. A similar study was done on the Arabidopsis mur1 mut ant, which is affected in the biosynthesis of L-Fuc. In this mutant, one-th ird of the Fuc residues of the xyloglucan has been reported to be replaced by L-galactose (Gal) (E. Zablackis, W.S. York, M. Pauly, S. Hantus, W.D. Re iter, C.C.S. Chapple, P. Albersheim, and A. Darvill [1996] Science 272: 180 8-1810). N-linked glycans from the mutant were identified and their structu res were compared with those isolated from the wild-type plants. In about 9 5% of all N-linked glycans from the mur1 plant, L-Fuc residues were absent and were not replaced by another monosaccharide. However, in the remaining 5%, L-Fuc was round to be replaced by a hexose residue. From nuclear magnet ic resonance and mass spectrometry data of the mur1 N-glycans, and by analo gy with data reported on mur1 xyloglucan, this subpopulation of N-linked gl ycans was proposed to be L-Gal-containing N-glycans resulting from the repl acement of L-Fuc by L-Gal.