A Novel β-Glucosidase from Humicola insolens with High Potential for Untreated Waste Paper Conversion to Sugars

Abstract

Humicola insolens produced a new β-glucosidase (BglHi2) under solid-state fermentation. The purified enzyme showed apparent molecular masses of 116 kDa (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and 404 kDa (gel-filtration), suggesting that it is a homotetramer. Mass spectrometry analysis showed amino acid sequence similarity with a β-glucosidase from Chaetomium thermophilum. Optima of pH and temperature were 5.0 and 65 °C, respectively, and the enzyme was stable for 60 min at 50 °C, maintaining 71 % residual activity after 60 min at 55 °C. BglHi2 hydrolyzed p-nitrophenyl-β-D-glucopyranoside and cellobiose. Cellobiose hydrolysis occurred with high apparent affinity (K M = 0.24 ± 0.01 mmol L(-1)) and catalytic efficiency (k cat/K M = 1,304.92 ± 53.32 L mmol(-1) s(-1)). The activity was insensitive to Fe(+3), Cr(+2), Mn(+2), Co(+2), and Ni(2+), and 50-60 % residual activities were retained in the presence of Pb(2+), Hg(2+), and Cu(2+). Mixtures of pure BglHi2 or H. insolens crude extract (CE) with crude extracts from Trichoderma reesei fully hydrolyzed Whatman no. 1 paper. Mixtures of H. insolens CE with T. reesei CE or Celluclast 1.5 L fully hydrolyzed untreated printed office paper, napkin, and magazine papers after 24-48 h, and untreated cardboard was hydrolyzed by a H. insolens CE/T. reesei CE mixture with 100 % glucose yield. Data revealed the good potential of BglHi2 for the hydrolysis of waste papers, promising feedstocks for cellulosic ethanol production.