Four cellulose-active lytic polysaccharide monooxygenases from Cellulomonas species

Abstract

Background

The discovery of lytic polysaccharide monooxygenases (LPMOs) has fundamentally changed our understanding of microbial lignocellulose degradation. Cellulomonas bacteria have a rich history of study due to their ability to degrade recalcitrant cellulose, yet little is known about the predicted LPMOs that they encode from Auxiliary Activity Family 10 (AA10).

Results

Here, we present the comprehensive biochemical characterization of three AA10 LPMOs from Cellulomonas flavigena (CflaLPMO10A, CflaLPMO10B, and CflaLPMO10C) and one LPMO from Cellulomonas fimi (CfiLPMO10). We demonstrate that these four enzymes oxidize insoluble cellulose with C1 regioselectivity and show a preference for substrates with high surface area. In addition, CflaLPMO10B, CflaLPMO10C, and CfiLPMO10 exhibit limited capacity to perform mixed C1/C4 regioselective oxidative cleavage. Thermostability analysis indicates that these LPMOs can refold spontaneously following denaturation dependent on the presence of copper coordination. Scanning and transmission electron microscopy revealed substrate-specific surface and structural morphological changes following LPMO action on Avicel and phosphoric acid-swollen cellulose (PASC). Further, we demonstrate that the LPMOs encoded by Cellulomonas flavigena exhibit synergy in cellulose degradation, which is due in part to decreased autoinactivation.

Conclusions

Together, these results advance understanding of the cellulose utilization machinery of historically important Cellulomonas species beyond hydrolytic enzymes to include lytic cleavage. This work also contributes to the broader mapping of enzyme activity in Auxiliary Activity Family 10 and provides new biocatalysts for potential applications in biomass modification.