Abstract
A powerful tool in enzyme engineering is directed evolution. The design of a suitable screening system to identify enzyme variants with the feature desired is one of the most important points in directed evolution experiments. In this article, we developed and validated a four-step activity-based screening system with a high throughput rate to identify a variant of the metagenome β-galactosidase, called M1, with improved specific activity. An Escherichia coli host–vector system was chosen to realize a high production of the recombinant enzyme in microtiter plate format. Industrial-like conditions of milk processing in dairy industry (substrate lactose, solved in synthetic milk buffer, pH 6.75, and 8 °C) were used for the activity screening. With a coefficient of variance of 15.6 % and a Z′ factor value of 0.53, the assay was reproducible and suitable to identify enzyme variants with the requirement desired. A first-generation library of β-galactosidase variants, constructed by error-prone PCR, was analyzed using the high-throughput screening developed, and one variant, called M1′K2, was identified as having a distinctly improved specific activity. Therefore, this variant was produced in shaking flasks, and after purification via metal affinity chromatography, the improved specific activity was confirmed. In detail, the variant M1′K2 showed a more than twofold enhanced specific activity toward lactose at 8 °C compared to the parental β-galactosidase M1.
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Many thanks go to Claudia Glück and Manuel Krewinkel (Institute of Food Science and Biotechnology) for their good collaboration.
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Rentschler, E., Schwarz, T., Stressler, T. et al. Development and validation of a screening system for a β-galactosidase with increased specific activity produced by directed evolution. Eur Food Res Technol 242, 2129–2138 (2016). https://doi.org/10.1007/s00217-016-2709-x
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DOI: https://doi.org/10.1007/s00217-016-2709-x