The catalytic cycle of LPMOs is far from elucidated. It requires two electrons to complete the cycle and these electrons may be provided by either a chemical reductant, such as ascorbate, or an enzyme, such as cellobiose dehydrogenase (CDH). Previous studies of LPMO action on lignocellulosic substrates have indicated that lignin may serve as an electron acceptor/donor in the redox cycle of LPMOs. Here, we have studied the interactions among lignin and LPMOs using a purified GH61-type LPMO, as well as LPMO-containing commercial cellulolytic cocktails. We found that lignin (isolated from wheat straw) was able to boost the oxidation of both lignocellulose and phosphoric acid-swollen-cellulose generating a pool of oxidized oligosaccharides. Oxidized products were generated in amounts similar to those obtained with artificial electron donors such as ascorbate.
The presentation shows for the first time the kinetics of LPMOs acting on lignocellulose while boosted by a specific pool of lignin molecules. Moreover, we show how pre-treatment technology, which the biomass undergoes before enzymatic hydrolysis, affects lignin structure and LPMO boosting potential. A range of different pre-treatments were tested to select the one which structurally modifies the lignin in order to gain a typology that is optimally suited to transfer electrons to LPMOs.