Characterization of .ALPHA.-L-arabinofuranosidase related to the secondary cell walls formation in Arabidopsis thaliana

Abstract

A gene encoding a family 51 α-L-arabinofuranosidase (At3g10740) is specifically expressed at the stage of xylem vessel formation in Arabidopsis thaliana. To investigate the role of the enzyme in the xylem vessel formation, the recombinant protein was expressed in Pichia pastoris and the properties were characterized. The enzyme showed optimal activity at pH 4.5 and 50°C and was stable over the pH range of 4.0–7.0 under 30°C. The enzyme released L-arabinose from p-nitrophenyl-α-L-arabinofuranoside, synthetic arabinofuranobiosides, arabinoxylo-oligosaccharides and arabinose-containing polysaccharides. The enzyme hydrolyzed p-nitrophenyl-α-L-arabinofuranoside but did not hydrolyze any other p-nitrophenyl-glycosides, and the specific activity for p-nitrophenyl-α-L-arabinofuranoside was 1.2 units mg−1. Among the synthetic regioisomers of arabinofuranobiosides, the enzyme hydrolyzed all linkages that can occur between two α-L-arabinofuranosyl residues in the following order: α-1,5-linkage>α-1,2-linkage>α-1,3-linkage. The enzyme hydrolyzed arabinan, gum arabic, corn hull arabinoxylan, and wheat arabinoxylan. The enzyme showed higher activity for oligosaccharides than for polysaccharides. Furthermore, the enzyme preferentially hydrolyzed arabinoxylo-oligosaccharides such as O-α-L-arabinofuranosyl-1,3-O-β-D-xylopyranosyl-1,4-D-xylopyranoside and O-β-D-xylopyranosyl-1,4-[O-α-L-arabinofuranosyl-1,3]-O-β-D-xylopyranosyl-1,4-O-β-D-xylopyranoside, which were the hydrolysis products of xylan generated by a family 10 xylanase, in comparison to its activity for arabinofuranobiosides. These data suggest that the enzyme is involved in the modification of the structure of xylan together with family 10 xylanases during the xylem vessel formation.