Rational protein engineering of α-L-arabinofuranosidase from Aspergillus niger for improved catalytic hydrolysis efficiency on kenaf hemicellulose

Abstract

Lignocellulosic biomass utilisation as an alternative to fossil resources was hampered due to its recalcitrant to enzymatic hydrolysis. Herein, rational protein engineering strategy has been carried out on Aspergillus niger α-L-arabinofuranosidase (AnabfA) substrate binding pathway to improve its catalytic efficiency towards pre-treated kenaf (Hibiscus cannabinus) hemicellulose hydrolysis. A total of five variants (N246D, L371 V, E449D, W453Y and E449D/W453Y) were constructed based on AnabfA sequence and structure information. Substitutions from bulky to smaller amino acids and hydrophobic to less hydrophobic residues were shown to improve the enzyme catalytic reaction towards insoluble substrate. Variant E449D/W453Y induces the highest hydrolysis of hemicellulose by producing up to 62 % reducing sugar. It is evident that substituting amino acids at the substrate binding site reduces steric hindrance, thus allowing insoluble substrate to easily penetrate and complement the enzyme’s active site.