Modularity impacts cellulose surface oxidation by a lytic polysaccharide monooxygenase from Streptomyces coelicolor

Abstract

Lytic polysaccharide monooxygenases (LPMOs) catalyze the oxidation of β-(1,4)-linked polysaccharides, such as cellulose, in a reaction that requires an electron donor and H2O2 as co-substrate. Several LPMOs include a carbohydrate-binding module (CBM), which promotes action on insoluble substrates. Herein, a fluorescent labeling technique was used to track LPMO action on microcrystalline cellulose and evaluate the impact of CBMs on the distribution of LPMO activity across the fiber surface. Confocal microscopic images revealed that the distribution of oxidized positions on the cellulose surface was CBM-dependent: fluorescent spots were concentrated in reactions with a CBM-containing LPMO whereas they were more dispersed for a CBM-deficient LPMO variant. The more dispersed oxidation pattern for the CBM-free LPMO coincided with the release of fewer soluble reaction products.