COMPARATIVE PRODUCTION AND CHARACTERIZATION OF A CATALYTICALLY INACTIVE BoNT/C1 HOLOPROTEIN IN TWO PRODUCTION STRAINS OF PICHIA PASTORIS

Abstract

Botulinum neurotoxins (BoNTs) are the causative agents of the disease botulism. At present no FDA-licensed vaccine exists for the prevention of BoNT intoxication. Efforts to produce a catalytically inactive BoNT/CI holoprotein (ciBoNT/CI HP) vaccine in Pichia pastoris X-33 by a government contractor were hampered by extensive proteolysis of the recombinant protein. In an effort to reduce proteolysis, the ciBoNT/CI HP was expressed and purified from both X-33 and the protease knockout PichiaPink. By modifying the fermentation method and purification protocol, the level of proteolytic degradation was significantly improved over that obtained by the contractor. However, equivalent levels of ciBoNT/CI HP proteolysis were observed from both X-33 and PichiaPink. The purified vaccine was found to be both safe and protective in mice with a median effective dose of 13.6 ng (X-33) and 14.7 ng (PichiaPink) in a single-dose mouse potency assay involving challenge with 1,000 MLD50 of BoNT/C.