Lignin boosts the cellulase performance of a GH-61 enzyme from Sporotrichum thermophile.

An enzyme belonging to the glycoside hydrolase family 61 from the thermophilic fungus Sporotrichum thermophile, was functionally expressed in the methylotrophic yeast Pichia pastoris under the transcriptional control of the alcohol oxidase (AOX1) promoter. The enzyme hydrolyzed barley β-glucan, carboxymethyl cellulose, lichenan, wheat arabinoxylan and birchwood xylan showing optimal activity at pH 8 and 65°C. A 2:1 mixture of Celluclast 1.5L and StCel61a was capable of increasing the degree of spruce conversion by 42%. The use of substrates with varying lignin content permitted the detection of a dependence of the enhancing capacity of StCel61a on the radical scavenging capacity of the different lignocellulosics. In the presence of a reductant, StCel61a boosted the efficiency of a mixture of purified cellulases (EGII, CBHI, β-GLUC) by 20%. The synergistic activity exhibited by StCel61a and its dependence on reducing substances provide guidelines for process design towards the production of economically viable bioethanol.