Influence of Modification of Cysteine Residues in the Carbohydrate-Binding Domain on Cellulase Activity: Achieving Enhanced Performance and pH-Sensitive Recovery

The conversion of cellulosic biomass into fermentable sugars represents a pivotal stage in the environmentally friendly and sustainable production of clean fuels and chemicals. In this paper, a new strategy to enhance enzyme performance was proposed. This strategy can achieve pH-sensitive recovery of cellulase while improving the catalytic activity and stability of the enzyme. This strategy was achieved by means of a chemical modification of the cysteine residue (−SH) of the carbohydrate-binding domain (CBD) of cellulase with a PEG-based modifier (Mal-PEG-FA). It was shown that chemical modification altered the conformation of cellulase, which significantly improved the efficiency of the CBD of the enzyme, which in turn promoted the activity of the enzyme. In particular, the cellulase that was modified with a molecular weight of 10 k demonstrated the highest level of activity, with an increase of 130.02% in comparison to the native cellulase. Ultimately, the effective recovery of modified cellulase in the aqueous phase system was accomplished by adjusting the pH of the system. After five cycles, the modified cellulase still maintained 81.0% of its initial enzymatic activity. This research is of significant strategic importance for the promotion of efficient biomass utilization.