Type-dependent action modes of Tt AA9E and Ta AA9A acting on cellulose and differently pretreated lignocellulosic substrates

In Jung Kim; Nari Seo; Hyun Joo An; Jae-Han Kim; Paul V Harris; Kyoung Heon Kim

doi:10.1186/s13068-017-0721-4

Type-dependent action modes of Tt AA9E and Ta AA9A acting on cellulose and differently pretreated lignocellulosic substrates

Biotechnol Biofuels. 2017 Feb 22:10:46. doi: 10.1186/s13068-017-0721-4. eCollection 2017.

Authors

In Jung Kim¹, Nari Seo², Hyun Joo An², Jae-Han Kim³, Paul V Harris⁴, Kyoung Heon Kim¹

Affiliations

¹ Department of Biotechnology, Korea University, Graduate School, Seoul, 02841 South Korea.
² Graduate School of Analytical Science & Technology and Asia-Pacific Glycomics Reference Site, Chungnam National University, Daejeon, 34134 South Korea.
³ Department of Food and Nutrition, Chungnam National University, Daejeon, 34134 South Korea.
⁴ Novozymes, Davis, CA 95618 USA.

Abstract

Background: Lytic 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 TtAA9E from Thielavia terrestris belonging to Type 1 and TaAA9A from Thermoascus aurantiacus belonging to Type 3 on cellulose and pretreated lignocellulose.

Results: From product analysis, TtAA9E dominantly generated oligosaccharides with an aldonic acid form, which is an evidence of C1 oxidation, while TaAA9A 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 TtAA9E than for TaAA9A. For hydrolysis of pretreated lignocellulose using rice straw, synergistic behaviors of TtAA9E and TaAA9A were different depending on the pretreatment of rice straw. Specifically, on acid-pretreated rice straw, TtAA9E showed a higher synergism than TaAA9A while on alkali-pretreated rice straw, TaAA9A showed a higher synergism than TtAA9E.

Conclusions: We show type-dependent action modes of TtAA9E and TaAA9A 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.

Keywords: Auxiliary activity family 9; Cellulose hydrolysis; Cellulose oxidation; Glycoside hydrolase family 61; Lytic polysaccharide monooxygenase; Synergism.