Fungal lytic polysaccharide monooxygenases bind starch and β-cyclodextrin similarly to amylolytic hydrolases

Starch-binding modules of family 20 (CBM20) are present in 60% of lytic polysaccharide monooxygenases (LPMOs) catalyzing the oxidative breakdown of starch, which highlights functional importance in LPMO activity. The substrate-binding properties of starch-active LMPOs, however, are currently unexplored. Affinities and binding-thermodynamics of two recombinant fungal LPMOs toward starch and β-cyclodextrin were shown to be similar to fungal CBM20s. Amplex Red assays showed ascorbate and Cu-dependent activity, which was inhibited in the presence of β-cylodextrin and amylose. Phylogenetically, the clustering of CBM20s from starch-targeting LPMOs and hydrolases was in accord with taxonomy and did not correlate to appended catalytic activity. Altogether, these results demonstrate that the CBM20-binding scaffold is retained in the evolution of hydrolytic and oxidative starch-degrading activities.