The archaeal highly thermostable GH35 family β‐galactosidase DaβGal has a unique seven domain protein fold

The most extensively studied β‐ d ‐galactosidases ( EC3.2.1.23 ) belonging to four glycoside hydrolase (GH) families 1, 2, 35, and 42 are widely distributed among Bacteria, Archaea and Eukaryotes. Here, we report a novel GH35 family β‐galactosidase from the hyperthermophilic Thermoprotei archaeon Desulfurococcus amylolyticus (DaβGal). Unlike fungal monomeric six‐domain β‐galactosidases, the DaβGal enzyme is a dimer; it has an extra jelly roll domain D7 and three composite domains (D4, D5, and D6) that are formed by the distantly located polypeptide chain regions. The enzyme possesses a high specificity for β‐ d ‐galactopyranosides, and its distinguishing feature is the ability to cleave pNP‐β‐ d ‐fucopyranoside. DaβGal efficiently catalyzes the hydrolysis of lactose at high temperatures, remains stable and active at 65 °С, and retains activity at 95 °С with a half‐life time value equal to 73 min. These properties make archaeal DaβGal a more attractive candidate for biotechnology than the widely used fungal β‐galactosidases.