Cellobiohydrolase and endoglucanase respond differently to surfactants during the hydrolysis of cellulose

Non-ionic surfactants such as polyethylene glycol (PEG) can increase the glucose yield from enzymatic saccharification of pretreated lignocellulosic substrates. In a hydrolysis study using Avicel and PASC, we have shown that the boosting effect of PEG differs for the individual cellulases. For both substrates during hydrolysis with a monocomponent exo-cellulase CBH1, the presence of PEG led to an increase in the final glucose concentration, while there was no change in hydrolysis yield with an endoglucanase (EG). Also, PEG had no effect on the activity of β-glucosidases. PEG increased the thermal stability of both the CBH1 and the EG, but only the activity of the CBH1 increased in the presence of PEG. We propose that this has to do with either the processive mechanism of CBH1 affecting the k_cat, or a change in the adsorption/desorption rate (k_off) of the CBH1.

We have also observed that the properties of the hydrolysis liquid phase change when PEG is present in solution. Using LF-NMR relaxometry we found that PEG increases the relaxation time of the hydrolysis liquid phase, i.e. water is more active. Thus, CBH1 seems to benefit from water being more active, while this is not the case for EG. Based on these results, the properties of the liquid phase have a direct impact on the hydrolysis yield using commercial cellulase mixtures, as CBHs make up most of the T. reesei secretome from which most cellulolytic enzyme mixtures are produced industrially.