Biochemical characterization of Aspergillus oryzae recombinant α-L-rhamnosidase expressed in Pichia pastoris

An alpha-L-rhamnosidase-encoding gene from Aspergillus oryzae, which belongs to the glycoside hydrolase family 78, was cloned and expressed in Pichia pastoris. SDS-PAGE of the purified recombinant alpha-L-rhamnosidase protein revealed smeared bands with apparent molecular mass of 90-130 kDa. After N-deglycosylation, the recombinant enzyme showed a molecular mass of 70 kDa. The enzyme exhibited optimal activity at a pH of 5.0 and a temperature of 70 degrees C. Specific activity of the enzyme was higher toward hesperidin than toward naringin, which consist of alpha-1,6 and alpha-1,2 linkages, respectively. The activity was also higher toward hesperidin than toward rutin, which consist of 7-O- and 3-O-glycosyl linkages of flavonoids, respectively. Kinetic analysis of the enzyme showed that the Michaelis constant (K-m) was lowest toward rutin, moderate toward naringin, and higher toward p-nitrophenyl-alpha-L-rhamnopyranoside and hesperidin. Its high catalytic efficiency (k(cat)/K-m) toward rutin was results of its low K-m value while its high catalytic efficiency toward hesperidin was results of a considerably high k(cat) value. (C) 2017, The Society for Biotechnology, Japan. All rights reserved.