Mechanisms of Enzymatic Copper-Oxygen Chemistry

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The ability to use plant dry matter feedstocks for making fuels and chemicals is a critical piece of most renewable energy strategies. Bacteria and fungi release a wide variety of enzymes that decompose fibrous plant matter, such as lignin, cellulose, and chitin. A new class of copper enzymes, known as LPMOs, uses the decomposing capabilities of oxygen and hydrogen peroxide during the oxidative breakdown of fibrous plant matter. Determining the molecular pathways these enzymes use to break down plant matter is a continuing challenge in bioinorganic chemistry. The goal of this research project is to uncover critical new information about the operation of LPMO enzymes. A deeper understanding of how these enzymes function could guide the creation of synthetic catalysts for the conversion of plant dry matter feedstocks into biofuels. The interdisciplinary nature of this research program gives graduate and postdoctoral students the opportunity to gain expertise in a wide variety of laboratory skills.With this award, the Chemistry of Life Processes Program is funding Professor Harry Gray and Professor Jay Winkler of California Institute of Technology to study how lytic polysaccharide monooxygenases (LPMOs) employ reactive oxygen species to break down cellulosic polymers. An ongoing controversy revolves around the oxygen species responsible for catalysis: dioxygen or hydrogen peroxide. Various mechanisms for LPMO catalysis have been proposed, and most implicate a highly oxidized copper center as the critical reactive intermediate. To address these unresolved mechanistic questions, photochemical methods are used to (1) oxidize the resting state of LPMO in the absence of reactive oxygen compounds, (2) characterize the intermediate spectroscopically, and (3) examine its reactivity toward cellulosic substrates. A bacterial lytic polysaccharide monooxygenase enzyme labeled with a ruthenium?]photosensitizer is used to generate the highly oxidized copper active site. The oxidized enzyme is characterized by UV?]visible and X?]ray spectroscopic methods. The reactivity of the oxidized copper center is being evaluated to determine whether it is a likely intermediate in enzymatic catalysis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.