A new β-galactosidase with a low temperature optimum isolated from the Antarctic Arthrobacter sp. 20B: gene cloning, purification and characterization
- 22 September 2009
- journal article
- Published by Springer Science and Business Media LLC in Archiv für Mikrobiologie
- Vol. 191 (11), 825-835
- https://doi.org/10.1007/s00203-009-0509-4
Abstract
A psychrotrophic bacterium producing a cold-adapted β-galactosidase upon growth at low temperatures was classified as Arthrobacter sp. 20B. A genomic DNA library of strain 20B introduced into Escherichia coli TOP10F′ and screening on X-Gal (5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside)-containing agar plates led to the isolation of β-galactosidase gene. The β-galactosidase gene (bgaS) encoding a protein of 1,053 amino acids, with a calculated molecular mass of 113,695 kDa. Analysis of the amino acid sequence of BgaS protein, deduced from the bgaS ORF, suggested that it is a member of the glycosyl hydrolase family 2. A native cold-adapted β-galactosidase was purified to homogeneity and characterized. It is a homotetrameric enzyme, each subunit being approximately 116 kDa polypeptide as deduced from native and SDS–PAGE, respectively. The β-galactosidase was optimally active at pH 6.0–8.0 and 25°C. P-nitrophenyl-β-d-galactopyranoside (PNPG) is its preferred substrate (three times higher activity than for ONPG—o-nitrophenyl-β-d-galactopyranoside). The Arthrobacter sp. 20B β-galactosidase is activated by thiol compounds (53% rise in activity in the presence of 10 mM 2-mercaptoethanol), some metal ions (activity increased by 50% for Na+, K+ and by 11% for Mn2+) and inactivated by pCMB (4-chloro-mercuribenzoic acid) and heavy metal ions (Pb2+, Zn2+, Cu2+).Keywords
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