Abstract
Arabinogalactan-proteins (AGPs) are proteoglycans found in plasma membrane and/or cell wall of plants, and involved in various functions such as cell adhesion, morphogenesis, and cell death. The carbohydrate moieties of AGPs account for ~90% of weight and their structures are modified depending on organs or growth stage. Radish AGPs are known to contain Gal, L-Araf, GlcA and 4-O-methyl-GlcA (4-Me-GlcA), however, the glycosidic linkages and physiological functions of (4-Me-)GlcAs remain uncleared.
To elucidate the structure and functions of the carbohydrate moieties of AGPs, we cloned two β-glucuronidases from Aspergillus niger and Neurospora crassa. Radish native AGPs were not hydrolyzed by β-glucuronidases, whereas α-L-arabinosidase-treated AGPs were susceptible to the enzymes. These enzymes released higher amounts of uronic acids from root AGP than L-fucose-containing leaf AGP, suggesting that the L-Araf and L-fucose residues in radish AGPs affect the action of β-glucuronidases.
