Yeast systems for the expression of heterologous gene products

Display of Escherichia coli Phytase on the Surface of Bacillus subtilis Spore Using CotG as an Anchor Protein

Escherichia coli phytase (AppA) has been widely used as an exogenous feed enzyme for monogastric animals; however, the production of this enzyme has been examined primarily in E. coli and yeast expression systems. As an alternative to production of soluble phytase, an enzyme immobilization method using the Bacillus subtilis spore outer-coat protein CotG as an anchoring motif for the display of the AppA was attempted. Using this motif, AppA was successfully produced on the spore surface of B. subtilis as verified by Western blot analysis and phytase activity measurements. Analysis of the pH stability indicated that more than 50% activity was retained after incubation at four different pH values (2.0, 4.0, 7.0, and 8.0) for up to 12 h, with maximum activity observed at pH 4.5. The highest enzyme activity seen at 55 °C and thermal stability measurements demonstrated that more than 30% activity remained after 30 min incubation at 60 °C. The spore surface-displayed AppA was resistant to pepsin, and more stable than phytase produced previously using a yeast expression system. Furthermore, we present data indicating that the use of peptide linkers may help improve the bioactivity of displayed enzymes on the spore surface of B. subtilis.

Transgenic animal bioreactors in biotechnology and production of blood proteins

The regulatory elements of genes used to target the tissue-specific expression of heterologous human proteins have been studied in vitro and in transgenic mice. Hybrid genes exhibiting the desired performance have been introduced into large animals. Complex proteins like protein C, factor IX, factor VIII, fibrinogen and hemoglobin, in addition to simpler proteins like alpha 1-antitrypsin, antithrombin III, albumin and tissue plasminogen activator have been produced in transgenic livestock. The amount of functional protein secreted when the transgene is expressed at high levels may be limited by the required posttranslational modifications in host tissues. This can be overcome by engineering the transgenic bioreactor to express the appropriate modifying enzymes. Genetically engineered livestock are thus rapidly becoming a choice for the production of recombinant human blood proteins.

Production of G-protein-coupled receptors in yeast

Yeasts combine the advantages of fast and easy handling with the potential to perform eukaryotic post-translational modifications and are for this reason interesting hosts for heterologous production of G-protein-coupled receptors. The possibility to connect foreign receptors to a yeast internal MAP kinase pathway was used to establish yeast-based systems for high-throughput screening of compound libraries. In addition, yeasts have the potential for high level production of G-protein-coupled receptors. In this field, non-Saccharomyces yeasts seems to be interesting alternatives to S. cerevisiae, as well as to systems based on higher eukaryotic cells.