Lytic polysaccharide monooxygenases - microbial power tools

Lytic polysaccharide monooxygenases that are found widespread in the microbial world carry out oxidative cleavage of glycosidic bonds in recalcitrant polysaccharides such as cellulose and thereby boost the activity of glycosyl hydrolases. Importantly, several mechanisms for the protection of LPMO-producing organisms against powerful oxidative chemistry have evolved throughout the biosphere. Insect viruses lock the active site of LPMO (fusolin) proteins, which are essential for virulence, in inactive crystals and LPMOs have evolved to become substrate controlled. However, in the absence of cellulose substrate and in the presence of oxygen and a reducing agent, LPMOs may release reactive oxygen species as a product of each redox cycle.

Microbes often produce detoxifying enzymes that reacts with such reactive oxygen species. Among these enzymes Catalase fulfil a crucial role in biology as it terminates chains of radical chemistry by the dismutation of H₂O₂ into water and dioxygen. It has been shown that oxidative inactivation of commercial cellulase mixtures is a significant factor influencing the overall saccharification efficiency and the addition of catalase can be used to protect these mixtures from inactivation. These protective mechanisms reflect the considerable challenges these enzymes must overcome in order to break down highly recalcitrant polysaccharides The recent report of improved catalytic efficiency by the use of photopigments for the essential electron delivery to LPMOs provides a new dimension for the study of the biology of this class of enzymes.