Synergy between processive cellulases in Ruminoccocus albus

Abstract

Endoglucanases (EGs), cellobiohydrolases (CBHs), and β-glucosidases are essential components in enzymatic degradation of cellulose. We analyzed the glycosyl hydrolases from families GH5 and GH48 from Ruminococcus albus 8 (RalCel5G and RalCel48A). Both enzymes feature a catalytic motif and a carbohydrate binding domain from family 37 (CBM37). RalCel5G also exhibited a second CBM37 with lower similarity. As a result, RalCel5G showed higher binding affinity toward insoluble substrates and broader recognition capacity. Kinetic characterization using different cellulosic substrates and reaction product analysis confirmed RalCel5G as a processive EG while RalCel48A is a CBH. Interestingly, we found a synergistic effect on their activity at a low EG to CBH ratio, despite the processive activity of RalCel5G. Furthermore, the lignocellulose degradation capacity was improved by supplementing the cellulases with hemicellulase RalXyn10A. These results provide valuable information about the interaction between processive EG and conventional CBH, necessary for the rational design of enzyme cocktails for optimized biomass processing.