Characterisation of a thermostable family 42 β-galactosidase from Thermotoga maritima

A β-galactosidase gene (TM_0310) of Thermotoga maritima MSB8 was expressed in Escherichia coli. The recombinant β-galactosidase (designated BgalB) was purified to homogeneity by heat treatment and Ni-NTA affinity chromatography. BgalB belongs to the glycoside hydrolase family 42. Its molecular mass was estimated to be 78 kDa and 76 kDa by SDS–PAGE and gel filtration, respectively. The enzyme was optimum at pH 5.5, and it was quite stable over the pH range 5.0–11.4 at 70 °C. It was optimally active at 80 °C and was stable up to 75 °C. Besides, BgalB exhibited broad substrate specificity with a preference for p-nitrophenyl-β-galactopyranoside (pNPGal). Km values of the purified enzyme for pNPGal, o-nitrophenyl-β-galactopyranoside (oNPGal) and pNP-β-fucopyranoside were 2.7 mM, 12.5 mM and 1.4 mM, respectively. These properties make this enzyme an interesting candidate for biotechnological applications. This is the first report of the family 42 β-galactosidases from T. maritima.