Lytic polysaccharides monooxygenase (LPMO) enzymes are recently discovered fungal enzymes possessing a type II copper active center coordinated by a histidine brace. Their interest arises from their observed “boosting effect” on the enzymatic polysaccharide degradation. LPMOs are classified into the auxiliary activity (AA) family from the CAZy database; and they have demonstrated to disrupt cellulose by an oxidative cleavage, which could be an entry point for further degradation or hydrolysis. In this work, we studied the action of a LPMO enzyme from the coprophilic ascomycete Podospora anserina (PaLPMO9H) that was produced heterologously. The enzyme PaLPMO9H is known to introduce an oxidized group on C4 and eventually on C1. In an attempt to get more insight into the mechanism of action of LPMOs, kraft pulp fibers were treated with both PaLPMO9H. Ascorbate was used as electron donor, and different reaction times and enzyme/substrate ratios (1:50-1000) were tested. After the enzymatic step, a soft mechanical treatment was applied to the fibers to facilitate their fractionation. After 48 h of enzymatic treatment and mechanical dispersion, LPMO-treated fibers showed intense defibrillation whereas control samples remained intact. Optical microscopy showed cellulose defibrillation occurred even at low enzyme/substrate ratios (1:500) for PaLPMO9H. Cellulose structure modifications were investigated by several techniques including FTIR, SEC, 13C CP-MASS solid state NMR and analysis of solubilized fractions. AFM and TEM were also used to characterize fibers and high degree of defibrillation was observed. Therefore, LPMOs can be viewed as promising candidates for enzymatic modification or degradation of cellulose fibers including the preparation of nanocelluloses.

Disruption of cellulose fibers structure by Lytic Polysaccharide Monooxygenase (LPMO) enzymes

253rd National Meeting (2017)

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