Cold-Adapted β-Galactosidase from the Antarctic Psychrophile Pseudoalteromonas haloplanktis

• Published in: Applied and Environmental Microbiology
• Main Authors: Hoyoux, A., Jennes, I., Dubois, P., Genicot, S., Dubail, F., François, J. M., Baise, E., Feller, G., Gerday, C.
• Format: Text
• Language: English
• Published: American Society for Microbiology 2001
• Subjects: Enzymology and Protein Engineering; Antarctic; The Antarctic; Antarc*
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC92765; http://www.ncbi.nlm.nih.gov/pubmed/11282601; https://doi.org/10.1128/AEM.67.4.1529-1535.2001

The β-galactosidase from the Antarctic gram-negative bacterium Pseudoalteromonas haloplanktis TAE 79 was purified to homogeneity. The nucleotide sequence and the NH2-terminal amino acid sequence of the purified enzyme indicate that the β-galactosidase subunit is composed of 1,038 amino acids with a calculated Mr of 118,068. This β-galactosidase shares structural properties with Escherichia coli β-galactosidase (comparable subunit mass, 51% amino sequence identity, conservation of amino acid residues involved in catalysis, similar optimal pH value, and requirement for divalent metal ions) but is characterized by a higher catalytic efficiency on synthetic and natural substrates and by a shift of apparent optimum activity toward low temperatures and lower thermal stability. The enzyme also differs by a higher pI (7.8) and by specific thermodynamic activation parameters. P. haloplanktis β-galactosidase was expressed in E. coli, and the recombinant enzyme displays properties identical to those of the wild-type enzyme. Heat-induced unfolding monitored by intrinsic fluorescence spectroscopy showed lower melting point values for both P. haloplanktis wild-type and recombinant β-galactosidase compared to the mesophilic enzyme. Assays of lactose hydrolysis in milk demonstrate that P. haloplanktis β-galactosidase can outperform the current commercial β-galactosidase from Kluyveromyces marxianus var. lactis, suggesting that the cold-adapted β-galactosidase could be used to hydrolyze lactose in dairy products processed in refrigerated plants.