Lytic Polysaccharide MonoOxygenases display great variability towards cellulose ultrastructure while performing oxidative functionalization of the polymers. Aiming at employing AA9-LPMOs for isolation of cellulose nano-crystals (CNCs), the ratio between functionalization/crystalline degradation became a crucial parameter. Here are reported the constraints posed by the substrate ultrastructure on the activity of seven different AA9 LPMOs representative of various regioselectivity and substrate affinity: TtAA9E, TaAA9A, PcAA9D, MtAA9A, MtAA9D, MtAA9I-CBM and MtAA9J. The substrate crystallinity and dry matter loading greatly affected the seven AA9s in an enzyme-specific manner, impacting their efficiency for CNCs functionalization purposes. X-ray diffraction pattern analyses were used to assess the cracking efficacy of the enzymatic treatment to de-crystallize CNCs, revealing that those AA9s with minor efficiency in releasing oligosaccharides resulted instead the most disruptive towards the crystal lattice and in reducing the particle sizes. These non-catalytic effects were found comparable with the one caused by the expansin BsEXLX1 enzyme.
Keywords: CNCs; Cellulose; High dry matter; Lytic polysaccharide MonoOxygenases; Regioselectivity.
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