Molecular docking and molecular dynamics simulations studies on β-glucosidase and xylanase to predict degradation order of cellulosic components in oil palm leaves for nanocellulose preparation.

Literature has shown that oil palm leaves (OPL) can be transformed into nanocellulose (NC) by fungal lignocellulosic enzymes, particularly those produced by the species. However, mechanism of β-glucosidase and xylanase selectivity to degrade lignin, hemicellulose and cellulose in OPL for NC production remains relatively vague. The study aimed to comprehend this aspect by an approach of molecular docking, molecular dynamics (MD) simulation and Molecular-mechanics Poisson-Boltzmann surface area (MM-PBSA) analysis, to compare interactions between the β-glucosidase- and xylanase from UC1 in complex with each substrate. Molecular docking of the enzyme-substrate complex showed residues Glu165-Asp226-Glu423 and Arg155-Glu210-Ser160 being the likely catalytic residues of β-glucosidase and xylanase, respectively. The binding affinity of β-glucosidase for the substrates are as follows: cellulose (-8.1 kcal mol) > lignin (-7.9 kcal mol) > hemicellulose (-7.8 kcal mol), whereas, xylanase showed a corresponding preference for; hemicellulose (-6.7 kcal mol) > cellulose (-5.8 kcal mol) > lignin (-5.7 kcal mol). Selectivity of both enzymes was reiterated by MD simulations where interactions between β-glucosidase-cellulose and xylanase-hemicellulose were the strongest. Notably low free-binding energy (ΔG) of β-glucosidase and xylanase in complex with cellulose (-207.23 +/- 47.13 kJ/mol) and hemicellulose (-131.48 +/- 24.57 kJ/mol) were observed, respectively. The findings thus successfully identified the cellulose component selectivity of the polymer-acting β-glucosidase and xylanase of UC1.Communicated by Ramaswamy H. Sarma.