Type-dependent action modes of TtAA9E and TaAA9A acting on cellulose and differently pretreated lignocellulosic substrates

摘要

BackgroundLytic polysaccharide monooxygenase (LPMO) is a group of recently identified proteins that catalyze oxidative cleavage of the glycosidic linkages of cellulose and other polysaccharides. By utilizing the oxidative mode of action, LPMOs are able to enhance the efficiency of cellulase in the hydrolysis of cellulose. Particularly, auxiliary activity family 9 (AA9) is a group of fungal LPMOs that show a type-dependent regioselectivity on cellulose in which Types 1, 2, and 3 hydroxylate at C1, C4, and C1 and C4 positions, respectively. In this study, we investigated comparative characteristics of Tt AA9E from Thielavia terrestris belonging to Type 1 and Ta AA9A from Thermoascus aurantiacus belonging to Type 3 on cellulose and pretreated lignocellulose. ResultsFrom product analysis, Tt AA9E dominantly generated oligosaccharides with an aldonic acid form, which is an evidence of C1 oxidation, while Ta AA9A generated oligosaccharides with both aldonic acid and 4-ketoaldose forms, which is evidence of C1 and C4 oxidations, respectively. For hydrolysis of cellulose (Avicel) by cellulase, higher synergism was observed for Tt AA9E than for Ta AA9A. For hydrolysis of pretreated lignocellulose using rice straw, synergistic behaviors of Tt AA9E and Ta AA9A were different depending on the pretreatment of rice straw. Specifically, on acid-pretreated rice straw, Tt AA9E showed a higher synergism than Ta AA9A while on alkali-pretreated rice straw, Ta AA9A showed a higher synergism than Tt AA9E. ConclusionsWe show type-dependent action modes of Tt AA9E and Ta AA9A for cellulose oxidation together with substrate-dependent synergistic hydrolysis of cellulosic substrates. The results obtained from this study indicate the different behaviors of AA9s on cellulose and pretreated lignocellulose, suggesting a selection of AA9 proteins specific to substrates is required for industrial utilization.