L- Galactose replaces L-fucose in the pectic polysaccharide rhamnogalacturonan II synthesized by the L-fucose-deficient mur1 Arabidopsis mutant
2004
Reuhs, Bradley L. | Glenn, Joshua | Stephens, Samuel B. | Kim, John S. | Christie, D Benjamin | Glushka, John G. | Zablackis, Earl | Albersheim, Peter | Darvill, Alan G. | O’Neill, Malcolm A.
Arabidopsis thaliana mur1 is a dwarf mutant with altered cell-wall properties, in which L-fucose is partially replaced by L-galactose in the xyloglucan and glycoproteins. We found that the mur1 mutation also affects the primary structure of the pectic polysaccharide rhamnogalacturonan II (RG-II). In mur1 RG-II a non-reducing terminal 2-O-methyl L-galactosyl residue and a 3,4-linked L-galactosyl residue replace the non-reducing terminal 2-O-methyl L-fucosyl residue and the 3,4-linked L-fucosyl residue, respectively, that are present in wild-type RG-II. Furthermore, we found that a terminal non-reducing L-galactosyl residue, rather than the previously reported D-galactosyl residue, is present on the 2-O-methyl xylose-containing side chain of RG-II in both wild type and mur1 plants. Approximately 95% of the RG-II from wild type and mur1 plants is solubilized as a high-molecular-weight (>100 kDa) complex, by treating walls with aqueous potassium phosphate. The molecular mass of RG-II in this complex was reduced to 5–10 kDa by treatment with endopolygalacturonase, providing additional evidence that RG-II is covalently linked to homogalacturonan. The results of this study provide additional information on the structure of RG-II and the role of this pectic polysaccharide in the plant cell wall.
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