Characterization of Sphingomonas sp. JB13 exo-inulinase: a novel detergent-, salt-, and protease-tolerant exo-inulinase.

A glycoside hydrolase family 32 exo-inulinase gene was cloned from Sphingomonas sp. JB13 and expressed in Escherichia coli BL21 (DE3). The purified recombinant enzyme (rInuAJB13) showed an apparently optimal activity at pH 5.5 and 55 °C and remained activity at 10-70 °C. The addition of most metal ions and chemical reagents showed little or no effect (retaining more than 76.5 % activity) on the enzyme activity, notably the addition of surfactants SDS, CTAB, Tween 80, and Triton X-100. Most local liquid detergents, including Balin, Walch, Ariel, Tide, Tupperware, and Bluemoon, also showed little or no effect (retaining more than 77.8 % activity) on the enzyme activity. rInuAJB13 exhibited 135.3-163.6 % activity at the NaCl concentration of 1.0-4.5 M. After incubation with up to 57.0 mg mL(-1) trypsin and 90.0 mg mL(-1) proteinase K at 37 °C for 60 min (pH 7.2), rInuAJB13 retained more than 80 % of its initial activity. The enzyme presents a high proportion (28.0 %) of amino acid residues G, A, and V. This paper is the first to report a detergent-, salt-, and protease-tolerant exo-inulinase.