Pretreating cellulases with hydrophobins for improving bioconversion of cellulose: an experimental and computational study
Lignocellulosic biomass sugars bring benefits to both the economy and the environment, but their application is limited by their high process cost. In the present contribution, the class II hydrophobin (HFBII) was first reported to be used as an additive to pretreat cellulases prior to hydrolysis, leading to a remarkable improvement of the biodegradation of corn stover and microcrystalline cellulose. 2 mg g−1 HFBII resulted in 37.1% and 55.4% conversion of the substrates, increased by 32.5% and 40.6%, respectively, compared with the control. In particular, HFBII was shown to have a better effect than polyethylene glycol 6000 on the conversion of corn stover, increasing the degradation by 24.5%. 73.1% enzymatic activity was retained after 48 h, whereas the control was 65.3%. Furthermore, the binding of HFBII to cellulase was investigated by molecular dynamics simulations and free-energy calculations. The tunnel-forming loops of the cellulase exhibit a high binding affinity for HFBII. In the formed complex, about 70% hydrophobic patches of the HFBII were found to be exposed, which could compete with the cellulase for hydrophobic adsorption sites of lignin residues. The decrease of the adsorption between the latter two would benefit the enzymatic hydrolysis. Structural analysis indicates that the flexibility of enzymatic tunnel loops was significantly enhanced, and the active area was enlarged, thereby promoting the enzymatic activity. The experimental results and the underlying mechanism provided herein are envisioned to help understand the potential application of HFBII in the practical green hydrolysis of cellulose by reducing the enzyme load.