Xylanase and β-xylosidase from Penicillium janczewskii : Purification, characterization and hydrolysis of substrates

Abstract

Xylanases and β-d-xylosidases are the most important enzymes responsible for the degradation of xylan, the second main constituent of plant cell walls. In this study, the main extracellular xylanase (XYL I) and β-xylosidase (BXYL I) from the fungus Penicillium janczewskii were purified, characterized and applied for the hydrolysis of different substrates. Their molecular weights under denaturing and non-denaturing conditions were, respectively, 30.4 and 23.6 kDa for XYL I, and 100 and 200 kDa for BXYL I, indicating that the latter is homodimeric. XYL I is highly glycosylated (78%) with optimal activity in pH 6.0 at 65°C, while BXYL I presented lower sugar content (10.5%) and optimal activity in pH 5.0 at 75°C. The half-lives of XYL I at 55, 60 and 65°C were 125, 16 and 6 min, respectively. At 60°C, BXYL I retained almost 100% of the activity after 6 h. NH4+, Na+, DTT and β-mercaptoethanol stimulated XYL I, while activation of BXYL I was not observed. Interestingly, XYL I was only partially inhibited by Hg2 +, while BXYL I was completely inhibited. Xylobiose, xylotriose and larger xylooligosaccharides were the main products from xylan hydrolysis by XYL I. BXYL I hydrolyzed xylobiose and larger xylooligosaccharides with no activity against xylans. The enzymes act synergistically in the degradation of xylans, and present industrial characteristics especially in relation to optimal activity at high temperatures, prolonged stability of BXYL I at 60°C, and stability of XYL I in wide pH range.