Light-driven enzymatic degradation of lignocellulose by pigments and metalloenzymes

Light is the basic input for the buildup of organic carbon, but it may also be important for the turnover of organic carbon. In this presentation we describe a new light-driven enzymatic pathway for oxidation of organic carbon. A simple photosystem consisting of an electron donating pigment and an electron-accepting enzyme is capable of oxidizing cellulose and hemicellulose to levels never seen before. The system has a common enzyme as its functional protein, the powerful and widely distributed oxidative enzymes lytic polysaccharide monooxygenases (LPMOs). These enzymes require an external electron donor, and we use excited photosynthetic pigments thylakoids or chlorophyllin for what we have named light-induced-electron-transfer (LIET). LPMOs combined with pigments are exposed to light, results in a never before seen 100-fold increase in catalytic activity. Both reaction rates and product levels increase substantially, just as the substrate specificity is broadened to include both cellulose and hemicellulose. The basic driving force for the LPMO reaction is the transfer of light energy via the photosynthetic pigments.

Thus LPMO enzymes and pigment derivatives common in the environment of plant-degrading organisms form a highly reactive and stable light-driven system increasing the turnover rate and versatility of LPMOs. In the presentation we describe the basic components of the system and their reactions, discuss the electron pathways and outline the potential impact and role of LIET for enzymatic catalysis in both ecosystems and industrial applications.