Purified cholera toxin B subunit from transgenic tobacco plants possesses authentic antigenicity

Cholera toxin B subunit (CTB) mature protein was stably expressed in transg enic tobacco plants under the control of the CaMV 35S promoter and TMV Omeg a fragment Fusion of the PR1b signal peptide coding sequence to the CTB mat ure protein gene increased the expression level by 24-fold. The tobacco-syn thesized CTB (tCTB) was purified to homogeneity by a single step of immunoa ffinity chromatography. The purified tCTB is predominantly in the form of p entamers with molecular weight identical to the native pentameric CTB, indi cating that the PR1b-CTB fusion protein has been properly processed in toba cco cells. Furthermore, by immunodiffusion and immunoelectrophoresis, we ha ve shown that the antigenicity of the purified tCTB is indistinguishable fr om that of the native CTB protein. (C) 2001 John Wiley & Sons, Inc.