Heterologous expression of lytic polysaccharide monooxygenases (LPMOs)

Lytic polysaccharide monooxygenases (LPMOs) are relatively new enzymes that have been discovered 10 years ago. LPMOs comprise a diverse group of enzymes which play a pivotal role in the depolymerization of sugar-based biopolymers including cellulose, hemicellulose, chitin, and starch. Their mechanism of action relies on the correct coordination of a copper ion in the active site, which is partly composed of the N-terminal histidine. Therefore, correct secretion and folding of these copper-enzymes is fundamental for obtaining a catalytic activity. LPMOs occur in all kingdoms of life; they have been found in viruses, bacteria and eukaryotes, including fungi, plants and animals. In many cases, using homologous expression of these proteins is not feasible and an alternative organism, which can be cultured and is able to heterologously express the protein of interest, is required for studying enzyme properties. Therefore, we made an extensive compilation of expression techniques used for LPMOs the expression and characterization of which have been reported to date. In the current review, we provide a summary of the different techniques, including expression hosts and vectors, secretion methods, and culturing conditions, that have been used for the overexpression and production of this important class of enzymes at laboratory scale. Herein, we compare these techniques and assess their advantages and disadvantages.