Abstract:
The conventional endo–exo synergism model has extensively been supported in literature,
which is based on the perception that endoglucanases (EGs) expose or create accessible sites on the
cellulose chain to facilitate the action of processive cellobiohydrolases (CBHs). However, there is
a lack of information on why some bacterial and fungal CBHs and EGs do not exhibit synergism.
Therefore, the present study evaluated and compared the synergistic relationships between cellulases
from different microbial sources and provided insights into how different GH families govern
synergism. The results showed that CmixA2 (a mixture of TlCel7A and CtCel5A) displayed the
highest effect with BaCel5A (degree of synergy for reducing sugars and glucose of 1.47 and 1.41,
respectively) in a protein mass ratio of 75–25%. No synergism was detected between CmixB1/B2
(as well as CmixC1/C2) and any of the EGs, and the combinations did not improve the overall
cellulose hydrolysis. These findings further support the hypothesis that “not all endo-to exo-cellulase
interactions are synergistic”, and that the extent of synergism is dependent on the composition of
cellulase systems from various sources and their compatibility in the cellulase cocktail. This method
of screening for maximal compatibility between exo- and endo-cellulases constitutes a critical step
towards the design of improved synergistic cellulose-degrading cocktails for industrial-scale biomass
degradation.
