A novel low-temperature-active exo-inulinase identified based on Molecular-Activity strategy from Sphingobacterium sp. GN25 isolated from feces of Grus nigricollis

• Sphingobacterium sp. GN25 was isolated from feces of Grus nigricollis.
• A novel exo-inulinase gene was cloned from Sphingobacterium sp. GN25.
• Molecular-Activity strategy was proposed to predict activity before experiments.
• The exo-inulinase was predicted and then verified to be low-temperature active.
• Fructose was produced from artichoke by the exo-inulinase at low temperatures.

A novel glycosyl hydrolase family 32 exo-inulinase (InuAGN25) gene was cloned from Sphingobacterium sp. GN25 isolated from feces of Grus nigricollis. InuAGN25 showed the highest identity of 54.3% with a putative levanase recorded in GenBank. Molecular-Activity strategy was proposed to predict InuAGN25 to be a low-temperature-active exo-inulinase before experiments performance. Molecular analyses included progressive sequential, phylogenetic and structural analyses. InuAGN25 was effectively expressed in Escherichia coli. The purified recombinant InuAGN25 showed characteristics of low-temperature-active enzymes: (1) the enzyme retained 55.8% of the maximum activity at 20 °C, 35.8% at 10 °C, and even 8.2% at 0 °C; (2) the enzyme exhibited 75.8, 30.5 and 10.8% of the initial activity after preincubation for 60 min at 45, 50 and 55 °C, respectively; (3) Km values of the enzyme toward inulin were 2.8, 3.0, 3.2 and 5.8 mg ml−1 at 0, 10, 20 and 40 °C, respectively. Fructose was the main product of inulin and Jerusalem artichoke tubers hydrolyzed by the purified recombinant InuAGN25 at room temperature, 10 °C and 0 °C. These results suggested the Molecular-Activity strategy worked efficiently and made InuAGN25 promising for the production of fructose at low temperatures.