Novel β-glucanases along with xylanase identified in Thermomyces lanuginosus secretome for enhanced saccharification of different lignocellulosics

Abstract

The LC/MS-based exo-proteome analysis of thermophilic fungus Thermomyces lanuginosus showed 22.59% (40 proteins) of the total identified proteins (177) as CAZymes (carbohydrate-active enzymes). The CAZymes were primarily represented by glycosyl hydrolases (72.5%) belonging to 21 different GH families. Xylanase (GH11) was found to be the major protein (24.3%) in addition to the β-glucanase and another complex polysaccharide-degrading (carbohydrate-active enzymes) CAZymes in the secretome. FPLC-based fractionation of secretome was employed to identify proteins responsible for enhancing the catalytic efficacy of Cellic Ctec2 during hydrolysis of acid pre-treated lignocellulosics and eventually xylanase (GH11) and β-glucanases (GH64 and GH81) were identified and purified. The purified xylanase when supplemented with Cellic Ctec2 resulted in 2.05-, 1.79-, and 1.60-fold increase in the release of glucose from acid-treated bagasse at 10, 15, and 20% substrate loading rate, respectively when compared with the control. Similarly, enhanced hydrolysis of acid pre-treated corn residue and rice straw was observed upon supplementation with xylanase. Spiking benchmark cellulase with purified GH64 and GH81 also resulted in 1.18- and 1.23-fold enhanced hydrolysis of acid pre-treated sugarcane bagasse. The supplementation of xylanase (1000 units/g substrate) was found to reduce the Cellic Ctec2 loading rate from 36 mg/g substrate by 2.70-, 2.88-, and 2.57-fold required for hydrolysis of acid treated bagasse, corn residue, and rice straw, respectively, at high substrate loading rate (20%) and thus, it is an important candidate for economizing the 2G ethanol process.