The enzymatic degradation of biomass is a key challenge for the production of economically viable biofuels. The family of Lytic polysaccharide monooxygenases (LPMOs), including GH61 (Glycoside Hydrolase Family 61) or CBM33 (Carbohydrate Binding Module Family 33) enzymes, are a recently discovered class of copper-dependent enzymes able to selectively cleave glycosidic linkages via an oxidative mechanism. X-ray crystallography and various biophysical measurements have demonstrated LPMO activity is dependent upon a mononuclear copper active site, molecular oxygen, and reducing agent (e.g., ascorbic acid). Structures solved to date demonstrate that a copper ion is coordinated by a conserved 'histidine brace'. Beyond the active site, the binding surface is decorated with aromatic and polar residues that are likely related to regioselectivity. Via molecular dynamics, we studied several conformational changes in Phanerochaete chrysosporium GH61D LPMO, the first LPMO obtained from a model basidiomycete fungus. These changes affect binding to the surface of cellulose and help to explain the diversity of LPMO structures and their structure-function relationships. We also performed quantum mechanical calculations of an active site model for both the oxidized and reduced states of an LPMO, obtained from a novel X-ray diffraction method. The structural evolution of the LPMO proceeds from a trigonal bipyramidal geometry in the initial Cu(II)-oxidized form to a T-shaped geometry in the reduced Cu(I) form. We fully characterize the molecular and electronic structure of the active site, offering unprecedented insight into how LPMO catalytic centers are activated for oxygen binding and subsequent catalytic processes.

Quantum mechanical study of a copper-dependent lytic polysaccharide monooxygenase active site

247th National Meeting (2014)

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