Cloning and characterization of β-galactoside and β-glucoside hydrolysing enzymes of Thermotoga maritima

Abstract

A gene library of the hyperthermophilic bacterium Thermotoga maritima strain MSB8 was constructed in Escherichia coli. Two non-related T. maritima chromosomal DNA fragments were physically characterized. They conferred the synthesis of thermostable X-Gal (5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside)-hydrolysing activity upon the host organism. The biochemical properties of the recombinant enzymes indicated that genes for a β-galactosidase (BgaA) and a broad-specificity β-glucosidase (Bg1A) had been isolated. The genes were desiignted bgaA and bglA, respectively. According to analytical size exclusion chromatography data, BgaA and BglA had native molecular masses of approximately 240 kDa and 95 kDa, respectively. Both enzymes apparently have dimeric subunit structure. An additional β-glucosidase (designated BglB) activity, clearly distinct from BglA in terms of substrate specificity, could be detected in a crude extract of T. maritima. © 1993.