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 SscLPMO10B, 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 SscLPMO10B 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 SscLPMO10B reactions without exogenously added H 2 O 2 reflects a peroxygenase reaction.

To fully utilize carbohydrates from seaweed biomass, the degradation of the family of polysaccharides known as alginates must be understood. A step in the degradation of alginate is the conversion of 4,5-unsaturated monouronates to 4-deoxy-L-erythro-5-hexoseulose catalysed by the enzyme KdgF. In this study BeKdgF from Bacteroides eggerthii from the human gut microbiota has been produced isotopically labelled in Escherichia coli. Here the 1H, 13C, and 15N NMR chemical shift assignment for BeKdgF is reported.

Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that catalyze oxidative cleavage of polysaccharides, such as cellulose and chitin. LPMO action is key to the efficient varlorization of biomass, but the instability of LPMOs in turnover conditions limits their efficiency. LPMO catalysis requires the presence of a reductant, such as ascorbic acid, and hydrogen peroxide, which can be generated in situ in the presence of molecular oxygen and various electron donors. While it is known that reduced LPMOs are prone to auto-catalytic oxidative damage due to off-pathway reactions with the oxygen co-substrate, little is known about the structural consequences of such damage. Here, we present atomic-level insight into how the structure of the chitin-activeSmLPMO10A is affected by oxidative damage, using NMR and CD spectroscopy. Incubation with ascorbic acid, led to rearrangements of aromatic residues, followed by more profound structural changes near the copper active site and loss of activity. Longer incubation times induced changes in larger parts of the structure, indicative of progressing oxidative damage. Incubation with ascorbic acid in the presence of chitin led to similar changes in the observable (i.e., not substrate-bound) fraction of the enzyme. Upon subsequent addition of H2O2, which drastically speeds up chitin hydrolysis, NMR signals corresponding to seemingly intactSmLPMO10A reappeared, indicating dissociation of catalytically competent LPMO. Activity assays confirmed thatSmLPMO10A retained catalytic activity when pre-incubated with chitin before being subjected to conditions that induce oxidative damage. Overall, this study provides structural insights into the process of oxidative damage ofSmLPMO10A and demonstrates the protective effect of the substrate. The impact of turnover conditions on aromatic residues in the core of the enzyme suggests a role for these residues in dealing with redox-active species generated in the copper center.

The lytic polysaccharide monooxygenase JdLPMO10A is the N-terminal domain of the multimodular protein Jd1381. The isolated JdLPMO10A domain is one of the smallest chitinactive lytic polysaccharide monooxygenases known to date with a size of only 15.5 kDa. JdLPMO10A is a copper-dependent oxidative enzyme that depolymerizes chitin by hydroxylating the C1 carbon in the glycosidic bond. JdLPMO10A has been isotopically labeled and recombinantly expressed. Here, we report the 1 H, 13 C, 15 N resonance assignment of JdLPMO10A. Secondary structural elements predicted based on the NMR assignment are in excellent agreement with the crystal structure of JdLPMO10A.

Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that catalyze oxidative cleavage of polysaccharides, such as cellulose and chitin. LPMO catalysis requires a reductant, such as ascorbic acid, and hydrogen peroxide, which can be generated in situ in the presence of molecular oxygen and various electron donors. While it is known that reduced LPMOs are prone to autocatalytic oxidative damage due to offpathway reactions with the oxygen co-substrate, little is known about the structural consequences of such damage. Here, we present atomic-level insights into how the structure of the chitinactive SmLPMO10A is affected by oxidative damage using NMR and circular dichroism spectroscopy. Incubation with ascorbic acid could lead to rearrangements of aromatic residues, followed by more profound structural changes near the copper-active site and loss of activity. Longer incubation times induced changes in larger parts of the structure, indicative of progressing oxidative damage. Incubation with ascorbic acid in the presence of chitin led to similar changes in the observable (i.e., not substrate-bound) fraction of the enzyme. Upon subsequent addition of H 2 O 2 , which drastically speeds up chitin hydrolysis, NMR signals corresponding to seemingly intact SmLPMO10A reappeared, indicating dissociation of catalytically competent LPMO. Activity assays confirmed that SmLPMO10A retained catalytic activity when preincubated with chitin before being subjected to conditions that induce oxidative damage. Overall, this study provides structural insights into the process of oxidative damage of SmLPMO10A and demonstrates the protective effect of the substrate.