Cellulose hydrolysis – the role of monocomponent cellulases in crystalline cellulose degradation

Abstract

Changes in the molecular structure of cellulose during hydrolysis with four recombinant β-1,4-glycanases from the cellulolytic bacterium Cellulomonas fimi were assessed and compared in an attempt to elucidate the mechanism of crystalline cellulose degradation. It was apparent that the two endoglucanases, Cel6A and Cel5A, degraded sigmacell cellulose differently; Cel5A liberated more soluble sugars (cellobiose and cellotriose) and significantly altered the molecular weight distribution, while Cel6A had a limited effect on the polymer size and liberated primarily cellobiose and glucose. Additionally, both endoglucanases slightly increased the crystallinity of cellulose. In contrast, the cellobiohydrolases, Cel6B and Cel48A, had no effect on cellulose molecular weight and liberated only cellobiose and cellotriose. However, Cel48A was shown to be effective at reducing the crystallinity of the cellulosic substrate, while Cel6B increased the crystallinity index. Synergistic hydrolysis using combinations of the different enzymes showed that, although the cellulose was extensively hydrolysed, the molecular structure of the substrate was similar to the original material. This phenomenon suggests that the actions of individual monocomponent enzymes are offset by the concurrent modification by the complementing enzymes during synergistic hydrolysis.