Functional characterization of a lytic polysaccharide monooxygenase from Schizophyllum commune that degrades non-crystalline substrates

Lytic polysaccharide monooxygenases (LPMOs) are mono-copper enzymes that use O 2 or H 2 O 2 to oxidatively cleave glycosidic bonds. LPMOs are prevalent in nature, and the functional variation among these enzymes is a topic of great interest. We present the functional characterization of one of the 22 putative AA9-type LPMOs from the fungus Schizophyllum commune , Sc LPMO9A. The enzyme, expressed in Escherichia coli , showed C4-oxidative cleavage of amorphous cellulose and soluble cello-oligosaccharides. Activity on xyloglucan, mixed-linkage β-glucan, and glucomannan was also observed, and product profiles differed compared to the well-studied C4-oxidizing Nc LPMO9C from Neurospora crassa . While Nc LPMO9C is also active on more crystalline forms of cellulose, Sc LPMO9A is not. Differences between the two enzymes were also revealed by nuclear magnetic resonance (NMR) titration studies showing that, in contrast to Nc LPMO9C, Sc LPMO9A has higher affinity for linear substrates compared to branched substrates. Studies of H 2 O 2 -fueled degradation of amorphous cellulose showed that Sc LPMO9A catalyzes a fast and specific peroxygenase reaction that is at least two orders of magnitude faster than the apparent monooxygenase reaction. Together, these results show that Sc LPMO9A is an efficient LPMO with a broad substrate range, which, rather than acting on cellulose, has evolved to act on amorphous and soluble glucans.