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The impact of reductants on the catalytic efficiency of a lytic polysaccharide monooxygenase and the special role of dehydroascorbic acid
Author(s) -
Stepnov Anton A.,
Christensen Idd A.,
Forsberg Zarah,
Aachmann Finn L.,
Courtade Gaston,
Eijsink Vincent G. H.
Publication year - 2022
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1002/1873-3468.14246
Subject(s) - chemistry , monooxygenase , dehydroascorbic acid , ascorbic acid , redox , catalysis , polysaccharide , glycosidic bond , hydrogen peroxide , formic acid , combinatorial chemistry , biochemistry , organic chemistry , enzyme , food science , cytochrome p450
Monocopper lytic polysaccharide monooxygenases (LPMOs) catalyse oxidative cleavage of glycosidic bonds in a reductant‐dependent reaction. Recent studies indicate that LPMOs, rather than being O 2 ‐dependent monooxygenases, are H 2 O 2 ‐dependent peroxygenases. Here, we describe Ssc LPMO10B, a novel LPMO from the phytopathogenic bacterium Streptomyces scabies and address links between this enzyme’s catalytic rate and in situ hydrogen peroxide production in the presence of ascorbic acid, gallic acid and l ‐cysteine. Studies of Avicel degradation showed a clear correlation between the catalytic rate of Ssc LPMO10B and the rate of H 2 O 2 generation in the reaction mixture. We also assessed the impact of oxidised ascorbic acid, dehydroascorbic acid (DHA), on LPMO activity, since DHA, which is not considered a reductant, was recently reported to drive LPMO reactions. Kinetic studies, combined with NMR analysis, showed that DHA is unstable and converts into multiple derivatives, some of which are redox active and can fuel the LPMO reaction by reducing the active site copper and promoting H 2 O 2 production. These results show that the apparent monooxygenase activity observed in Ssc LPMO10B reactions without exogenously added H 2 O 2 reflects a peroxygenase reaction.