Identification, soluble expression, and characterization of a novel endo-inulinase from Lipomyces starkeyi NRRL Y-11557

Studies on endo-inulinases from yeast are scarce, compared to those from other microbial sources. In this study, a novel endo-inulinase from Lipomyces starkeyi NRRL Y-11557 was identified, expressed in its soluble form, and characterized its physicochemically properties, together with its enzymatic activity and production of fructooligosaccharides (FOSs). A putative endo-inulinase gene inu3 was identified through rational genome mining. Through enzymatic activity and SDS-PAGE analysis, the endo-inulinase putative function of the protein encoded by inu3B gene (INU3B) was confirmed, and its soluble expression was achieved with pET22b (+) in Escherichia coli. INU3B showed effective catalytic activity and high thermostability. To our knowledge, the specific activity of INU3B against inulin reported in this study, 2262.8 ± 82.3 U·mg-1, at 70 °C and pH 5.0-6.0, is the highest reported to date. When the enzyme catalyzed FOSs production, the main products were DP3, DP4 and DP5. Overall, this report describes a novel yeast-derived endo-inulinase with optimal enzymatic properties, and thus, the reported enzyme has great potential for industrial production of FOSs.