Cellulose Nanofibrils as Assay Substrates for Cellulases and Lytic Polysaccharide Monooxygenases

A facile method for preparing colloidal cellulose nanofibrils (CNFs) from potato tubers is presented comprising alkaline treatment to remove noncellulosic polysaccharides, followed by hypochlorite oxidation and homogenization. The CNF consisted of similar to 94% cellulose, and carboxyl groups on the surface of CNF prevented their agglomeration. Aqueous suspensions of CNF had up to two times higher optical transparency than phosphoric acid swollen cellulose (PASC). The motivation for preparing CNF was to use it as a substrate for probing cellulose-degrading enzymes. It was shown that a lytic polysaccharide monooxygenase (LPMO) is active on CNF under formation of the same products as with other cellulose substrates. Moreover, CNF responded to cellulase treatment in a similar way to microcrystalline cellulose (Avicel), while PASC was rapidly broken down. Thus, a new assay substrate for these enzymes is presented with a unique combination of naturelike fibrillar structures and high optical transparency, which opens up for new types of analyses.