Characterization of a high performance α-galactosidase from Irpex lacteus and its usage in removal of raffinose family oligosaccharides from soymilk

Abstract

Raffinose family oligosaccharides (RFOs) negatively affect nutritional value of legume-derived food and feed. It has been challenging to develop a high performance α-galactosidase excelled on catalytic efficiency, thermostability, pH stability and protease-resistance that could efficiently hydrolyze RFOs. In this study, the first GH family 27 α-galactosidase gene from Irpex lacteus was cloned. The gene had an open reading frame of 1314 bp interrupted by 12 introns. The recombinant α-galactosidase expressed in Pichia pastoris (rILgalA) had an apparent molecular mass of 64 kDa and was highly N-glycosylated. rILgalA was maximally active at pH 4.8 and 70 °C. It was stable over a broad pH range of 3-11, retained 90% of its activity after incubation at 60 °C for 10 h and exhibited strong resistance to digestive proteases. Unlike many other α-galactosidases, rILgalA was hyperactive on RFOs. Its specific activities toward melibiose, raffinose and stachyose were 644, 755 and 833 U mg^-1, respectively. The corresponding K_cat/K_m values were 120, 130 and 180 mM^-1 s^-1, which were the highest among reported α-galactosidases. rILgalA almost completely hydrolyzed raffinose and stachyose in soymilk at 60 °C in 30 min. These superior properties would make rILgalA an ideal remover of RFOs in food and feed industries.

Keywords: Irpex lacteus; Pichia pastoris; Raffinose family oligosaccharides; Soymilk; α-Galactosidase.