Lytic polysaccharide monooxygenases (LPMOs) form a copper-dependent family of enzymes classified under the auxiliary activity (AA) superfamily, spanning members AA9-AA17 (with AA12 exempted). The LPMOs are known for their ability to boost polysaccharide degradation by oxidizing the glycosidic bonds that link the monosaccharide subunits. This oxidation is unique among polysaccharide-degrading enzymes and has the potential to significantly contribute to the efficiency of sustainable biofuel production from lignocellulosic sources. Additionally, their biotechnological potential continues to expand, with recent identifications of LPMOs as virulence factors in agricultural pests and disease vectors. The catalytic activity of LPMOs is ascribed to a strictly conserved, solvent-exposed active site in which three nitrogen donor atoms ligate a copper ion, forming a histidine brace. This brace comprises one histidine ligand, coordinating with the imidazole N !2 atom, and the terminal histidine residue that coordinates bidentately with the imidazole N δ1 as well as the back-bone NH 2 group (see Fig. ).