Purification of the Protective Antigen from Bacillus anthracis

Anthrax toxin consists of three separate proteins, protective antigen (PA), edema factor (EF), and lethal factor (LF). PA binds to the receptor on mammalian cells and facilitates translocation of EF or LF into its cytosol. PA is the primary component of anthrax vaccines. In this study we purified PA from culture filtrates of Bacillus anthracis. The purification involved sequential chromatography through hydroxylapatite, DEAE-Sepharose CL-4B, followed by Mono-Q. The purified PA was judged to be homogeneous on SDS-PAGE, and consisted of a single polypeptide chain with a relative molecular weight of 85,000.