Alleviating product inhibition of Trichoderma reesei cellulase complex with a product-activated mushroom endoglucanase

[Display omitted] •The mushroom endoglucanase PaCel3A increases activity of T. reesei cellulase.•The engineered mutant of PaCel3A improved thermostability.•The viscometric CMCase activity was strongly promoted by 20 mM cellobiose.•The saccharification rate of cellulase complex with PaCel3A increased by >50%•PaCel3A relieves the product inhibition of T. reesei cellulase complex. Product inhibition of cellulase is a challenging issue in industrial processes. Here, we introduced a product-activated mushroom cellulase, PaCel3A from Polyporus arcularius, into Trichoderma reesei. The filter paper activity, carboxymethyl cellulase activity, and saccharification efficiency (substrate: pretreated rice straw, PRS) of transformants increased significantly with this enzyme (by 18.4–26.8%, 13.8–22.8%, and 17.0%, respectively). A mutant of PaCel3A, PaCel3AM, obtained based on B-factor analysis, saturated mutagenesis, and residual activity assay, showed improved thermostability. The PRS saccharification efficiency using the cellulase complex from T. reesei transformants overexpressing pacel3am increased by 56.4%–63.0%. In addition, the T. reesei cellulase complex obtained by adding the purified recombinant PaCel3AM from T. reesei (rCel3aM-tr) to hydrolyze PRS resulted in increased reducing sugar yields at all sampling points, outperforming the cellulase complexes without rCel3aM-tr. These results suggest that introducing product-activated cellulase genes is a simple and feasible method to alleviate the product inhibition of cellulase.