Abstract
IntroductionCellulases are of great interest for application in biomass degradation, yet the molecular details of the mode of action of glycoside hydrolases during degradation of insoluble cellulose remain elusive. To further improve these enzymes for application at industrial conditions, it is critical to gain a better understanding of not only the details of the degradation process, but also the function of accessory modules.MethodWe fused a carbohydrate-binding module (CBM) from family 2a to two thermophilic endoglucanases. We then applied neutron reflectometry to determine the mechanism of the resulting enhancements.ResultsCatalytic activity of the chimeric enzymes was enhanced up to three fold on insoluble cellulose substrates as compared to wild type. Importantly, we demonstrate that the wild type enzymes affect primarily the surface properties of an amorphous cellulose film, while the chimeras containing a CBM alter the bulk properties of the amorphous film.ConclusionOur findings suggest that the CBM improves the efficiency of these cellulases by enabling digestion within the bulk of the film.
Highlights
Cellulases are of great interest for application in biomass degradation, yet the molecular details of the mode of action of glycoside hydrolases during degradation of insoluble cellulose remain elusive
We demonstrate that the wild type enzymes affect primarily the surface properties of an amorphous cellulose film, while the chimeras containing a carbohydrate-binding module (CBM) alter the bulk properties of the amorphous film
A cellulase consists of a catalytic domain (CD) that often is linked to other modular accessory domains, including carbohydrate-binding modules (CBMs) [11], in many possible orientations and combinations [12,13,14]
Summary
Cellulases are of great interest for application in biomass degradation, yet the molecular details of the mode of action of glycoside hydrolases during degradation of insoluble cellulose remain elusive. To further improve these enzymes for application at industrial conditions, it is critical to gain a better understanding of the details of the degradation process, and the function of accessory modules. Some molecular details are still unclear, in relation to how the CBM affects enzyme-substrate interactions and activity on solid substrates
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