Abstract
Talaromyces leycettanus JCM12802 is a great producer of thermophilic glycoside hydrolases (GHs). In this study, two cellulases (TlCel5A and TlCel6A) belonging to GH5 and GH6 respectively were expressed in Pichia pastoris and functionally characterized. The enzymes had acidic and thermophilic properties, showing optimal activities at pH 3.5-4.5 and 75-80°C, and retained stable at temperatures up to 60°C and over a broad pH range of 2.0-8.0. TlCel5A and TlCel6A acted against several cellulose substrates with varied activities (3,101.1 vs. 92.9 U/mg to barley β-glucan, 3,905.6 U/mg vs. 109.0 U/mg to lichenan, and 840.3 and 0.09 U/mg to CMC-Na). When using Avicel, phosphoric acid swollen cellulose (PASC) or steam-exploded corn straw (SECS) as the substrate, combination of TlCel5A and TlCel6A showed significant synergistic action, releasing more reduced sugars (1.08-2.87 mM) than the individual enzymes. These two cellulases may represent potential enzyme additives for the efficient biomass conversion and bioethanol production.
Highlights
Cellulose, the major component of plant cell walls, is composed of repeating D-glucose residues linked by β-1,4-glucosidic bonds
BLAST analysis indicated that TlCel5A is an endoglucanase of GH5 while TlCel6A is a cellobiohydrolase of GH6, respectively
Both enzymes consist of a cellulose-binding module (CBM), a linker region and a catalytic domain
Summary
The major component of plant cell walls, is composed of repeating D-glucose residues linked by β-1,4-glucosidic bonds. It represents the most plentiful sustainable resource on Earth and is widely used for the production of renewable energy [1,2,3]. The complete hydrolysis of cellulose requires the synergy of three types of cellulases: endoglucanase (EG; EC 3.2.1.4) that randomly cleaves the intracellular β-1,4-glucosidic bond of cellulose to release cellooligosaccharides; cellobiohydrolase (CBH; EC 3.2.1.91) that hydrolyzes short cellulose molecules and cellooligosaccharides to cellobiose; and β-glucosidase (BG; EC 3.2.1.21) to degrade cellobiose into glucose [4,5,6].
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