Expression optimization and characterization of a novel amylopullulanase from the thermophilic Cohnella sp. A01

Amylopullulanase (EC. 3.2.1.41/1) is an enzyme that hydrolyzes starch and pullulan, capable of breaking (4 → 1)-α and (6 → 1)-α bonds in starch. Here, the Amy1136 gene (2166 base pairs) from the thermophilic bacterium Cohnella sp. A01 was cloned into the expression vector pET-26b(+) and expressed in Escherichia coli BL21. The enzyme was purified using heat shock at 90 °C for 15 min. The expression optimization of Amy1136 was performed using Plackett-Burman and Box-Behnken design as follows: temperature of 26.7 °C, rotational speed of 180 rpm, and bacterial population of 1.25. The Amy1136 displayed the highest activity at a temperature of 50 °C (on pullulan) and a pH of 8.0 (on starch) and, also exhibited stability at high temperatures (90 °C) and over a range of pH values. Ag⁺ significantly increased enzyme activity, while Co²⁺ completely inhibited amylase activity. The enzyme was found to be calcium-independent. The kinetic parameters K_m, V_max, k_cat, and k_cat/K_m for amylase activity were 2.4 mg/mL, 38.650 μmol min^-1 mg^-1, 38.1129 S^-1, and 0.09269 S^-1mg mL^-1, respectively, and for pullulanase activity were 173.1 mg/mL, 59.337 μmol min^-1 mg^-1, 1.586 S^-1, and 1.78338 S^-1mg mL^-1, respectively. The thermodynamic parameters K_in, t_1/2, Ea^#, ΔH^#, ΔG^# and ΔS^# were calculated equal to 0.20 × 10^-2 (m^-1), 462.09 (min), 16.87 (kJ/mol), 14.18 (kJ/mol), 47.34 (kJ/mol) and 102.60 (Jmol K^-1), respectively. The stability of Amy1136 under high temperature, acidic and alkaline pH, surfactants, organic solvents, and calcium independence, suggests its suitability for industrial applications.