Expression of brazzein, a small sweet-tasting protein in Saccharomyces cerevisiae: an introduction for production of sweet yeasts.

The replacement of carbohydrate sweeteners with protein sweeteners from plants has attracted the interest of researchers because these proteins don't trigger the insulin response and are more nutritive for consumption in food. Brazzein (Braz) is a small and heatstable sweet protein that has been originally derived from African plant Pentadiplandra brazzeana. In the present work the solubility, sweetness and yield of recombinant forms of Braz in two expression hosts, E. coli and S. cerevisiae were comprised.The codon-optimized gene of Braz was cloned in expression vectors pET28a and pET41a and GPD. The resulted vectors pET28a-Braz and pET41a-Braz were transformed to BrazS. cerevisiae and the vector GPD-Braz was transformd to S. cerevisiae. The expression of Braz in different systems was analyzed by SDS-PAGE and western blotting.The results verified the heterologous expression of Braz in S. cerevisiae carrying GPD-Braz. Also the expression of Braz as carboxy-terminal extensions of His-tag and glutathione-S-transferase (GST) were verified in transgenic E. coli containing pET28a-Braz and pET41a-Braz, respectively.Although the yield of GST-Braz was higher than His-Braz and Braz expressed in S. cerevisiae, but the higher solubility, sweetness, safety (GRAS) are important advantages of the use of S. cerevisiae as expression host for production of Braz. Therefore the result of present work opens new insights for providing the new sweet yeasts that can be used as food additives.