Expression and Characterization of Glycosyl Hydrolase Family 115 α-Glucuronidase from Scheffersomyces stipitis

Abstract

The gene encoding glycosyl hydrolase family 115 α-glucuronidase from Scheffersomyces stipitis (ssagu115) was cloned and expressed in Pichia pastoris strain X33. The recombinant enzyme was purified to homogeneity by Ni-chelation affinity chromatography. The apparent molecular weight of the secreted recombinant enzyme was about 150 kDa as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The recombinant α-glucuronidase was able to remove 4-O-methylglucuronic acid groups from several polymeric xylans (beech, birch, and oat spelt xylan) as well as xylooligosaccharides (aldotetraouronic acid and aldopentaouronic acid). The enzyme was more active towards xylooligosaccharides than xylans. Substrate inhibition was observed with aldouronic acids at concentrations above 23 mM. The K_m values of the enzyme towards aldotetraouronic and aldopentaouronic acids were 8.2 mM (5 mg/mL) and 9 mM (6.5 mg/mL), respectively. For beech and birch xylan, the K_m values were 9.5 mg/mL and 35 mg/mL, respectively. The enzyme was active over the pH range of 3.0–8.5, with maximal activity at pH 4.0. The optimum temperature for activity of the enzyme was 50°C. The enzyme exhibited synergy with endoxylanases from the GH10 and GH11 families on hydrolysis of beech xylan, birch xylan, and oat spelt xylan, with the greatest synergistic effect being shown with the GH10 endoxylanase. Treatment of polymeric xylan with SsAgu115 led to reduced solubility and increased precipitation from solution. Insoluble xylans have the potential to form hydrogels, which may have pharmaceutical and biomedical applications.