Activation of dioxygen by copper containing enzymes is a widely employed strategy in biology, generally achieved by utilizing bi- or polynuclear Cu active sites. Recently, this motif was expanded to include activation by mononuclear Cu sites with the discovery of the cellulose- and chitin degrading Polysaccharide Monooxygenases (PMOs), classified as Auxiliary Activity (AA) enzymes 9-11 in the CAZY database. Understanding how these enzymes activate dioxygen for catalysis is important both from a fundamental chemical standpoint and because of their involvement in 2nd generation biofuels where they greatly enhance the enzymatic degradation of biomass.Crystal structures have shown that the Cu in PMOs is ligated by the bi-dentate His1, via the terminal amine and side-chain imidazole, and an additional histidine. Here, we present a detailed spectroscopic evaluation, including Cu K-edge X-ray absorption, Circular- and Magnetic Circular Dichrosim, and Electronic Paramagnetic Resonance spectroscopies, of the Cu active site in solution, and determine the structural changes that occur upon reduction of the Cu ion. These results are used to optimize experimentally calibrated Density Functional Theory (DFT) structures of the Cu(II) and (I) site. Further, the reactivity of the reduced enzyme with dioxygen is spectroscopically investigated, indicating an innersphere reaction through a Cu-superoxide intermediate. This reactivity is correlated to the experimentally calibrated DFT calculations to elucidate how the T-shaped Cu(I) in the enzyme is set-up to perform the difficult one-electron activation of dioxygen.

Spectroscopic and computational insight into the activation of O<sub>2</sub> by the mononuclear Cu center in <i>Polysaccharide monooxygenases</i>

248th National Meeting (2014)

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Spectroscopic and computational insight into the activation of O2 by the mononuclear Cu center in Polysaccharide monooxygenases

Spectroscopic and computational insight into the activation of O₂ by the mononuclear Cu center in Polysaccharide monooxygenases