High-efficiency expression of a superior β-mannanase engineered by cooperative substitution method in Pichia pastoris and its application in preparation of prebiotic mannooligosaccharides

β-mannanase with high specific activity is a prerequisite for the industrial preparation of prebiotic mannooligosaccharides. Three mutants, namely MEI, MER, and MEIR, were constructed by cooperative substitution based on three predominant single-point site mutations (K291E, L211I, and Q112R, respectively). Heterologous expression was facilitated in Pichia pastoris and the recombinase was characterized completely. The specific activities of MER (7481.9 U mg−1) and MEIR (9003.1 U mg−1) increased by 1.07- and 1.29-fold from the initial activity of ME (6970.2U mg−1), respectively. MEIR was used for high-cell-density fermentation to further improve enzyme activity, and the expression levels achieved in the 10-L fermenter were significantly high (105,836 U mL−1). The prebiotic mannooligosaccharides (