Functional expression of the sweet-tasting protein brazzein in transgenic tobacco

Abstract

The sweet-tasting protein, brazzein, has potential as a low-calorie sugar substitute owing to its high sweetness, stability, and water solubility. In this study, the synthetic brazzein gene was expressed in the tobacco plant, Nicotiana tabacum. Three types of expression cassettes containing the brazzein gene were constructed to examine the expression and purification efficiency of the brazzein: pBI-BZ1 containing a signal sequence and His-tag, pBI-BZ2 containing a signal sequence, and pBI-BZ3 containing only the brazzein gene. Brazzein expression confirmed by ELISA was purified using ammonium sulfate precipitation, heat treatment, and CM-sepharose chromatography. The purity and conformational state of the brazzein were confirmed using SDS-PAGE, HPLC, and circular dichroism. The identity of the brazzein was confirmed by N-terminal amino acid analysis, ESI-MS/MS, and sweetness analysis. We successfully generated brazzein overexpression tobacco plants, suggesting that this method could be used as a brazzein production platform to provide an alternative to currently produced sweeteners.

Keywords:
alternative sweetener; brazzein; Agrobacterium-mediated transformation; transgenic tobacco plant; protein purification