PURIFIED CHOLERA TOXIN B SUBUNIT FROM TRANSGENIC TOBACCO PLANTS POSSESSES AUTHENTIC ANTIGENICITY

Cholera toxin B subunit (CTB) mature protein was stably expressed in transgenic tobacco plants under the control of CaMV 35S promoter and TMV Ω fragment. Fusion of the PR1b signal peptide coding sequence to the CTB mature protein gene increased the expression level by 24-fold. The tobacco-synthesized CTB (tCTB) was purified to homogeneity by a single step of immunoaffinity chromatography. The purified tCTB is predominantly in the form of pentamers with molecular weight identical to the native pentameric CTB, indicating the PR1b-CTB fusion protein has been properly processed in tobacco cells. Futhermore, we have shown that the antigenicity of the purified tCTB is indistinguishable from that of the native CTB protein by immunodiffusion and immunoelectrophoresis.