Title: Protection against self-oxidation by copper oxygenases

Paul H. Walton

Department of Chemistry, University of York, Heslington, York, UK, YO10 5DD

paul.walton@york.ac.uk

Lytic polysaccharide monooxygenases (LPMOs) are relatively recently discovered enzymes that catalyse the oxidation of polysaccharides, leading to chain cleavage. LPMOs has transformed our understanding of biomass degradation, and—moreover—are now critical components in the enzymatic breakdown of biomass in the second generation bioethanol industry.¹ We and others have also recently shown that LPMOs are key virulence factors in major plant diseases.²

Our recent work on LPMOs has examined the action of oxidizing agents on the enzyme which has been shown to enhance the activity of the enzymes on saccharidic substrates, but also lead to rapid inactivation of the enzyme, presumably through protein oxidation.³

Active site structure of an LPMO and oxidized amino acids (red) following treatment with H₂O₂.

In this talk, in addition to a description of the structure and reactivity of LPMOs, I will show that the use of UV/vis, CD, XAS, EPR, MCD, MS and resonance Raman spectroscopies augmented with DFT calculations, reveals that one of the products of protein oxidation in an AA9 LPMO is a long-lived ground-state singlet Cu(II)-tyrosyl species, which is inactive for the oxidation of saccharidic substrates. I will also show that this state evolves from an intermediate Cu(II)…tyrosyl triplet species via a open-shell singlet Cu(II)…histidyl radical.

Despite its inactive nature, both Cu(II)-tyrosyl and Cu(II)…tyrosyl species give new insight into the mechanisms by which LPMOs protect themselves from oxidative inactivation.

1. K. E. H. Frandsen, P. H. Walton et al, Nature Chem. Biol. 298—303 (2016).
2. F. Sabbadin, P. H. Walton et al, Science, 373, 774-779 (2021).
3. A. Paradisi, P. H. Walton et al, J. Am. Chem. Soc. 18585—18599 (2019).