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Formation of a copper(II)-tyrosyl complex at the active site of lytic polysaccharide monooxygenases following oxidation by H2O2

DOI: 10.1021/jacs.9b09833 DOI Help

Authors: Alessandro Paradisi (University of York) , Esther M. Johnston (University of York) , Morten Tovborg (Novozymes A/S) , Callum R. Nicoll (University of York) , Luisa Ciano (University of York) , Adam Dowle (University of York) , Jonathan Mcmaster (University of Nottingham) , Y. Hancock (University of York) , Gideon J. Davies (University of York) , Paul H. Walton (University of York)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: November 2019
Diamond Proposal Number(s): 17052

Abstract: Hydrogen peroxide is a co-substrate for the oxidative cleavage of saccharidic substrates by copper-containing lytic poly-saccharide monooxygenases (LPMOs). The rate of reaction of LPMOs with hydrogen peroxide is high but it is accompa-nied by rapid inactivation of the enzymes, presumably through protein oxidation. Herein, we use UV/vis, CD, XAS, EPR, VT/VH-MCD and resonance Raman spectroscopies, augmented with mass spectrometry and DFT calculations, to show that the product of reaction of an AA9 LPMO with H2O2 at higher pHs is a singlet Cu(II)-tyrosyl radical species, which is inactive for the oxidation of saccharidic substrates. The Cu(II)-tyrosyl radical center entails the formation of significant Cu(II)-(●OTyr) overlap, which in turn requires that the plane of the d(x2-y2) SOMO of the Cu(II) is orientated towards the tyrosyl radical. We propose from the Marcus cross-relation that the active site tyrosine is part of a ‘hole-hopping’ charge-transfer mechanism formed of a pathway of conserved tyrosine and tryptophan residues, which can protect the protein active site from inactivation during uncoupled turnover.

Subject Areas: Chemistry

Instruments: B18-Core EXAFS