Overexpression of a Cellobiose-Glucose-Halotolerant Endoglucanase from Scytalidium thermophilum.

Abstract

Enzyme reaction products and by-products from pretreatment steps can inhibit endoglucanases and are major factors limiting the efficiency of enzymatic lignocellulosic biomass hydrolysis. The gene encoding the endoglucanase from Scytalidium thermophilum (egst) was cloned and expressed as a soluble protein in Pichia pastoris GS115. The recombinant enzyme (Egst) was monomeric (66kDa) and showed an estimated carbohydrate content of 53.3% (w/w). The optimum temperature and pH of catalysis were 60-70°C and pH of 5.5, respectively. The enzyme was highly stable at pH3.0-8.0 with a half-life in water of 100min at 65°C. The Egst presented good halotolerance, retaining 84.1 and 71.4% of the control activity in the presence of 0.5 and 2.0molL-1 NaCl, respectively. Hydrolysis of medium viscosity carboxymethylcellulose (CMC) by Egst was stimulated 1.77-, 1.84-, 1.64-, and 1.8-fold by dithiothreitol, β-mercaptoethanol, cysteine, and manganese at 10, 10, 10, and 5mmolL-1 concentration, respectively. The enzyme hydrolyzed CMC with maximal velocity and an apparent affinity constant of 432.10 ± 16.76 and 10.5 ± 2.53mgmL-1, respectively. Furthermore, the Egst was tolerant to reaction products and able to act on pretreated fractions sugarcane bagasse demonstrating excellent properties for application in the hydrolysis of lignocellulosic biomass.