Characterization of a heat-active archaeal β-glucosidase from a hydrothermal spring metagenome.

Thermostable enzymes are required for application in a wide range of harsh industrial processes. High stability and activity at elevated temperatures, as well as high tolerances toward various reagents and solvents, are needed. In this work, a glycoside hydrolase family 1 β-glucosidase (Bgl1) of archaeal origin was isolated from a hydrothermal spring metagenome. The enzyme showed a broad substrate spectrum with activity toward cellobiose, cellotriose and lactose. Compared to most enzymes, extremely high specific activity with 3195U/mg was observed at 90°C and pH 6.5. Bgl1 was completely stable at pH 4.5-9.5 for 48 h at 4 °C. More than 40% of activity was measured at 105 °C. A thermal activation was observed at 90 °C after 30 min. Enzyme stability was enhanced (5- and 7-fold) after applying pressure of 100 and 200 bar at 90 °C for 2h, respectively. The affinity of the β-glucosidase to its substrate was significantly increased in the presence of AlCl₃. The K(i) value for glucose was 150 mM. These distinctive characteristics distinguish Bgl1 from other enzymes described so far and make this enzyme suitable for application in numerous processes that run at high temperatures.