Expression and Characterization of a Rice β-Xylosidase with Xylooligosaccharide Hydrolysis and Transglycosylation Activities

Plant β-xylosidases are less well characterized for hemicellulose degradation than their microbial counterparts. To address this, a broadly expressed rice (Oryza sativa) glycoside hydrolase family 3 (GH3) β-xylosidase designated OsXyl1 was expressed in heterologous Pichia pastoris. OsXyl1 showed maximal enzyme activity at pH 4.0 and 60 °C. It was relatively stable at 30–50 °C. It hydrolyzed 4NP-β-d-xylopyranoside (4NPXyl) and β-1,4-linked xylooligosaccharides (XOS) with degrees of polymerization (DP) of 2–6. OsXyl1 hydrolylsis of 4NPXyl was much more rapid and specific than that of other 4NP glycosides with an apparent k_cat/K_m value of 19.0 mM^–1 s^–1. OsXyl1 had similar specificity toward XOS having DP values of 2–5 with apparent k_cat/K_m values of 2.6–4.2 mM^–1 s^–1. OsXyl1 was also efficient at transglycosylating short alcohols with 4NPXyl and XOS xylosyl donors. Therefore, rice OsXyl1 β-xylosidase may function in recycling of xylans in plant cell wall recycling and it may be applied for transglycosylation of alcohol acceptors.