Thermodynamic and saccharification analysis of cloned GH12 endo-1,4-β-glucanase from Thermotoga petrophila in a mesophilic host

The thermotolerant endo-1,4-β-glucanase gene, of Thermotoga petrophila RKU-1, was cloned and over-expressed in E. coli strain BL21 CodonPlus. Enzyme was purified to homogeneity, producing a single band on SDS-PAGE corresponding to 38 kDa, by purification steps of heat treatment combined with ion-exchange column chromatography. The purified enzyme was optimally active, with specific activity of 530 Umg-1 against carboxymethyl cellulose (CMC), at pH 6.0 and 95°C and was also stable upto 8 h at 80°C. The enzyme also showed activity against β-glucan barley: 303 %, laminarin: 13.7 %, Whatman filter paper: 0.017 % with no activity against starch and Avicel. The recombinant enzyme exhibited Km, Vmax and Kcat of 12.5 mM, 735 µmol mg-1min-1 and 2351.23 s-1, respectively against CMC as a substrate. The stable recombinant enzyme manifested half life (t1/2) of 6.6 min even at temperature as high as 97°C, with free energy of denaturation (ΔG*D), enthalpy of denaturation (ΔH*D), and entropy of denaturation (ΔS*D) of 98.2 kJ mol-1, 528.9 kJ mol-1, and 1.17 kJ mol-1K-1, respectively at 97°C. In addition, the enthalpy (ΔH*), Gibbs free energy (ΔG*) and entropy (ΔS*) for hydrolysis of CMC substrate by endo-1,4-β-glucanase were calculated at 95°C as 48.2 kJ mol-1, 54.6 kJ mol-1 and -17.4 J mol-1 K-1, respectively. The recombinant enzyme saccharified pre-treated wheat straw and bagasse to 3.32 % and 3.2 %, respectively after 6 h incubation at 85°C. Its thermostability, resistance to heavy metal ions and specific activity make this enzyme an interesting candidate for industrial applications.