Cold-Adapted Beta-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, Jean-Marie, Baise, Etienne, Feller, Georges, Gerday, Charles
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 2001
• Subjects: Life sciences; Biochemistry; biophysics & molecular biology; Sciences du vivant; Biochimie; biophysique & biologie moléculaire; Antarc*; Antarctic
• Online Access: https://orbi.uliege.be/handle/2268/9845; https://orbi.uliege.be/bitstream/2268/9845/1/AEM_2001_betagal.pdf; https://doi.org/10.1128/AEM.67.4.1529-1535.2001

peer reviewed The beta-galactosidase from the Antarctic gram-negative bacterium Pseudoalteromonas haloplanktis TAE 79 was purified to homogeneity. The nucleotide sequence and the NH(2)-terminal amino acid sequence of the purified enzyme indicate that the beta-galactosidase subunit is composed of 1,038 amino acids with a calculated M(r) of 118,068. This beta-galactosidase shares structural properties with Escherichia coli beta-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 beta-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 beta-galactosidase compared to the mesophilic enzyme. Assays of lactose hydrolysis in milk demonstrate that P. haloplanktis beta-galactosidase can outperform the current commercial beta-galactosidase from Kluyveromyces marxianus var. lactis, suggesting that the cold-adapted beta-galactosidase could be used to hydrolyze lactose in dairy products processed in refrigerated plants.