Revisiting enzyme engineering strategies and reaction mechanisms of lytic polysaccharide monooxygenases (LPMOs)

Lytic polysaccharide monooxygenases (LPMOs) are auxiliary metalloenzymes that play a crucial role in the degradation of polysaccharides through an oxidative mechanism, distinguishing them from the traditional glycoside hydrolases. Although LPMOs were first identified in 1992, their functional identity and unique oxidative activity were not fully understood until the year 2010. These enzymes cleave at the C1 or C4 position of glycosidic bonds in polysaccharides using molecular oxygen and reductants such as ascorbic acid or cellobiose dehydrogenase (CDH). LPMOs exhibit significant sequence diversity across eight known families and operate via complex mechanisms. Structurally, LPMOs have a conserved active site with a copper ion coordinated by two histidine residues, known as the "histidine brace" which is crucial for their oxidative activity Their ability to enhance the efficiency of cellulase enzymes makes them highly valuable in the bio refinery industry. This review focuses on details of: regioselectivity, reaction mechanism, protein engineering strategies, and industrial applications of LPMO. It also emphasizes the building correlation between challenges at the industrial level and their possible solutions through enzyme engineering.