Toward a fundamental understanding of cellulase-lignin interactions in the whole slurry enzymatic saccharification process

This bioconversion process is preferentially carried out through the whole slurry enzymatic saccharification of the pre-treated lignocellulosic substrates. However, dissolved lignin, residual lignin, and lignin-derived phenolic molecules in the pre-treated biomass slurry can all trigger the decrease in activity and stability of cellulases, as well as the unfavorable enzyme recyclability. The hydrolyzing efficiencies can be considerably hindered by the lignin-induced non-productive binding of cellulases through various mechanisms. Three major non-covalent forces, i.e., hydrophobic, electrostatic, and hydrogen bonds interactions, can occur between the amino acid residues in cellulases and the functional groups in lignin. Various strategies such as enzyme engineering, substrate modification, additive blocking have been intensively developed to minimize the cellulase-lignin interactions. To investigate the impacts and benefits of different mechanisms and processes, this paper provides a systematic overview of the current opinions about the non-productive binding of cellulase to lignin. Through better understanding of their interactions it is our hope that the enzyme binding groups in lignin could be properly quenched by using new pre-treatment methods and/or biochemical processing strategies to increase the efficiency of cellulose bioconversion.