Background: Lytic polysaccharide monooxygenase (LPMO) has recently been discovered to depolymerize cellulose.Results: Dynamic imaging was applied to reveal the effects of LPMO and cellulase activity on solid cellulose surface.Conclusion: Critical features of surface morphology for LPMO synergy with cellulases are recognized.Significance: Direct insights into cellulose deconstruction by LPMO alone and in synergy with cellulases are obtained.

Background: Synergistic interplay of cellulases is key for efficiency of cellulose hydrolysis.Results: In situ observation of individual and synergistic action of endo- and exo-cellulases on a polymorphic cellulose substrate reveals specificity of individual enzyme components for crystalline or amorphous regions.Conclusion: Cellulase synergism is governed by mesoscopic morphological characteristics of the cellulose substrate.Significance: Advanced knowledge basis for rational optimization of cellulose saccharification.

LPMO (lytic polysaccharide monooxygenase) represents a unique paradigm of cellulosic biomass degradation by an oxidative mechanism. Understanding the role of LPMO in deconstructing crystalline cellulose is fundamental to the enzyme’s biological function and will help to specify the use of LPMO in biorefinery applications. Here we show with real-time atomic force microscopy that C1 and C4 oxidizing types of LPMO from Neurospora crassa (NcLPMO9F, NcLPMO9C) bind to nanocrystalline cellulose with high preference for the very same substrate surfaces that are also used by a processive cellulase (Trichoderma reesei CBH I) to move along during hydrolytic cellulose degradation. The bound LPMOs, however, are immobile during their adsorbed residence time ( ~ 1.0 min for NcLPMO9F) on cellulose. Treatment with LPMO resulted in fibrillation of crystalline cellulose and strongly ( ≥ 2-fold) enhanced the cellulase adsorption. It also increased enzyme turnover on the cellulose surface, thus boosting the hydrolytic conversion.