Discovery and Expression of Thermostable LPMOs from Thermophilic Fungi for Producing Efficient Lignocellulolytic...

In this study, two novel thermostable lytic polysaccharide monooxygenases (LPMOs) were cloned from thermophilic fungus Scytalidium thermophilum (PMO9D_SCYTH) and Malbranchea cinnamomea (PMO9D_MALCI) and expressed in the methylotrophic yeast Pichia pastoris X33. The purified PMO9D_SCYTH was active at 60 °C (t_1/2 = 60.58 h, pH 7.0), whereas, PMO9D_MALCI was optimally active at 50 °C (t_1/2 = 144 h, pH 7.0). The respective catalytic efficiency (k_cat/K_m) of PMO9D_SCYTH and PMO9D_MALCI determined against avicel in presence of H₂O₂ was (6.58 × 10^-3 and 1.79 × 10^-3 mg^-1 ml min^-1) and carboxy-methylcellulose (CMC) (1.52 × 10^-1 and 2.62 × 10^-2 mg^-1 ml min^-1). The HRMS analysis of products obtained after hydrolysis of avicel and CMC showed the presence of both C₁ and C₄ oxidized oligosaccharides, in addition to phylogenetic tree constructed with other characterized type 1 and 3 LPMOs demonstrated that both LPMOs belongs to type-3 family of AA9s. The release of sugars during saccharification of acid/alkali pretreated sugarcane bagasse and rice straw was enhanced upon replacing one part of commercial enzyme Cellic CTec2 with these LPMOs.