A thermophilic fungal GH36 α-galactosidase from Lichtheimia ramosa and its synergistic hydrolysis of locust bean gum

Abstract A novel GH36 α-galactosidase gene (LrAgal36A) from Lichtheimia ramosa was synthesized and highly expressed in Pichia pastoris. The enzyme titer and protein yield for high-density fermentation in a 5 L fermentor were up to 953.6 U mL−1 and 4.36 g L−1. Purified recombinant LrAgal36A showed the maximum activity at pH 6.0 and 65 °C and was thermostable with a half-life of 70 min at 60 °C. LrAgal36A displayed the highest specific activity (353.17 ± 4.19 U mg−1) toward p-nitrophenyl-α- d -galactopyranoside (pNPGal) followed by galacto-oligosaccharides and could act slightly on galactomannans. The Km and catalytic efficiency (kcat/Km) of LrAgal36A for pNPGal were 0.33 mM and 1569.50 mM−1 s−1, respectively. LrAgal36A and GH5 β-mannanase from L. ramosa showed a significant synergistic effect on the degradation of locust bean gum (LBG), resulting in release more reducing sugars (1.56 folds) and galactose (7.6 folds) by simultaneous or sequential reactions. Due to its hydrolysis properties, LrAgal36A might have potential applications in in the area of pulp biobleaching, feed and food processing.