Restoring the promoting implications of expansin on enzymatic hydrolysis of lignocellulosic biomass by polyethylene glycol

The recalcitrant structure of lignocellulose greatly hinders its enzymatic digestion. Expansins are non-catalytic proteins that can loosen the crystalline structure of cellulose. In this paper, three expansins, BpEXLX1, BsEXLX1a, and BsEXLX1b were utilized to hydrolyze Avicel-PH101 and corncob residues with commercial cellulases. All of them gave favorable influence on the enzymatic digestion of Avicel-PH101, with BpEXLX1 as the best candidate. However, large fluctuations in enzymatic yield were observed with corncob residues as substrate. Pre-incubation BpEXLX1 with polyethylene glycol (PEG) recovered the synergistic promotion effects of expansins on cellulases and lead to a 17.28 % increase in reducing sugars. This is the first report on the collaboration of expansin with PEG and cellulases, while the underlying mechanism was revealed by comparing the promoting results in microcrystalline cellulose and lignocellulose. These conclusions deepen in the understanding of the synergy of combined expansin and cellulases on enzymatic saccharification of lignocellulosic biomass.