TY - JOUR

T1 - Scission of Glucosidic Bonds by a Lentinus similis Lytic Polysaccharide Monooxygenases Is Strictly Dependent on H2O2while the Oxidation of Saccharide Products Depends on O2

AU - Brander, Søren

AU - Tokin, Radina

AU - Ipsen, Johan

AU - Jensen, Poul Erik

AU - Hernández-Rollán, Cristina

AU - Nørholm, Morten H.H.

AU - Lo Leggio, Leila

AU - Dupree, Paul

AU - Johansen, Katja S.

N1 - Funding Information: This work was supported by a grant from Novo Nordisk Fonden (no. NNF17SA0027704 to KSJ). The authors gratefully acknowledge the sample of LsAA9A kindly provided by Novozymes A/S. Malene Billeskov Keller is thanked for a sample of C1-oxidized cellooligosaccharide standards. Stine Lausten is thanked for her technical support and Prof. Bernard Henrissat is thanked for helpful suggestions regarding the presentation of our findings. Publisher Copyright: ©

PY - 2021

Y1 - 2021

N2 - Lytic polysaccharide monooxygenases (LPMOs) are mononuclear copper enzymes that act in synergy with glycoside hydrolases to saccharify the most abundant polysaccharides in nature. Both O2 and H2O2 can be cosubstrates for LPMOs. The Lentinus similis LPMO (LsAA9A) has previously been shown to oxidatively cleave oligosaccharides when supplied with ascorbate as a reductant. This study demonstrates that LsAA9A is unable to complete the catalytic cycle and cleave cellulose without H2O2. Instead, cellooligomers efficiently prevent the slow continuous oxidation of ascorbate taking place under ambient conditions in the absence of a substrate. LsAA9A specifically cleaves cellooligomers in a fast and stoichiometric reaction with H2O2 as a cosubstrate. However, the product profile contains more non-oxidized saccharides than anticipated by the generally accepted LPMO reaction scheme. The scission of glucosidic bonds and oxidation of the saccharide therefore appear not to be directly coupled. This was confirmed by the complete absence of oxidized products under anoxic conditions. A mechanism is proposed involving the hydrolysis of a cellulosic radical formed by a H2O2-derived caged hydroxyl radical. In addition, LsAA9A catalyzes another stoichiometric reaction with excess H2O2 to oxidize ascorbate in the absence of cellulose. Ascorbate is not a cosubstrate for the reaction leading to the scission of glucosidic bonds by LsAA9A.

AB - Lytic polysaccharide monooxygenases (LPMOs) are mononuclear copper enzymes that act in synergy with glycoside hydrolases to saccharify the most abundant polysaccharides in nature. Both O2 and H2O2 can be cosubstrates for LPMOs. The Lentinus similis LPMO (LsAA9A) has previously been shown to oxidatively cleave oligosaccharides when supplied with ascorbate as a reductant. This study demonstrates that LsAA9A is unable to complete the catalytic cycle and cleave cellulose without H2O2. Instead, cellooligomers efficiently prevent the slow continuous oxidation of ascorbate taking place under ambient conditions in the absence of a substrate. LsAA9A specifically cleaves cellooligomers in a fast and stoichiometric reaction with H2O2 as a cosubstrate. However, the product profile contains more non-oxidized saccharides than anticipated by the generally accepted LPMO reaction scheme. The scission of glucosidic bonds and oxidation of the saccharide therefore appear not to be directly coupled. This was confirmed by the complete absence of oxidized products under anoxic conditions. A mechanism is proposed involving the hydrolysis of a cellulosic radical formed by a H2O2-derived caged hydroxyl radical. In addition, LsAA9A catalyzes another stoichiometric reaction with excess H2O2 to oxidize ascorbate in the absence of cellulose. Ascorbate is not a cosubstrate for the reaction leading to the scission of glucosidic bonds by LsAA9A.

KW - cellulose

KW - hydrolysis

KW - lytic polysaccharide monooxygenase

KW - mononuclear copper enzyme

KW - saccharide radical

U2 - 10.1021/acscatal.1c04248

DO - 10.1021/acscatal.1c04248

M3 - Journal article

AN - SCOPUS:85118874746

VL - 11

SP - 13848

EP - 13859

JO - ACS Catalysis

JF - ACS Catalysis

SN - 2155-5435

IS - 22

ER -