Construction of new thermostable MtLPMO9V in synergism with cellulases for efficient lignocellulosic hydrolysis.

Lytic polysaccharide monooxygenases (LPMOs) can promote cellulose hydrolysis by disrupting its crystalline zone. This study focused on an uncharacterized thermophilic Myceliophthora thermophila LPMO (MtLPMO9V) in synergism with cellulases for efficient ligocellulosic hydrolysis. After MtLPMO9V was successfully expressed in P. pastoris GS115, the oxidative depolymerization of it was characterized by HPLC, HPAEC-PAD, and MALDI-TOF MS, indicating C4 oxidative cleavage activity. With combination of computer-aided design and MD simulation, MtLPMO9V was improved for a higher catalytic activity and thermostability by introduction of disulfide bonds, followed by point mutation. The mutant, A170C/A175C/Q120Y (M3), exhibited a remarkable enzymatic activity, increasing by 88 % as compared to the wild-type MtLPMO9V (WT), in which the catalytic efficiency (k/K) was roughly 1.90 folds that of the WT. The M3 demonstrated broad applicability, not only showing synergism with the thermostable endoglucanase DtCelA for efficient high-temperature saccharification of cellulosic substrates, but also enhancing the saccharification of lignocellulosic substrates when combined with the commercial cellulase blend Celluclast 1.5L, where LPMO accounts for only 2-4 % of the cellulase mixture. This study provides valuable insights into engineering of new extreme LPMOs and also exhibits their potential applicability in development of cellulase-mediated lignocellulosic biorefinery industry.