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Substrate binding of a copper-dependent fungal lytic polysaccharide monooxigenase

The depolymerisation of complex biomass such as lignocellulose by organisms depends on a network of enzymatic and chemical reactions. Fungi that can grow on lignocellulosic materials are equipped with a complex enzymatic degradation system, including a broad variety of hydrolases and oxidoreductases. In 2010, a new class of enzymes was discovered, which carry out oxidative cleavage of polysaccharides. These enzymes, today known as lytic polysaccharide monooxygenases (LPMOs, CAZy family AA9) are copper-dependent oxidoreductases that can hydroxylate the C1 or C4 positions of glucose and thereby cleave the glycosidic bonds in cellulose. These “cellulase activity boosters” provide hydrolytic enzymes access to crystalline cellulose by introducing chain breaks. LPMOs, despite their importance in biotechnology, are difficult to investigate because of their complex heterogeneous reaction mechanism. An open question is how LPMOs orchestrate the complex reaction between copper reduction, co-substrate activation and substrate binding. It is generally accepted that the first reaction step of LPMO is the reduction of the active-site copper by small molecule reductants or by other enzymes (CDH, GDH). In this work, we address the substrate binding of oxidized and reduced LPMO-02916 from Neurospora crassa to phosphoric acid swollen cellulose (PASC) and microcrystalline cellulose (MC) to investigate the role of the copper centre for substrate binding.

substrate binding ; copper reduction ; LPMO

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