Virtuelle (Nano) Welten: PDB Molecule of the Month 28: Anthrax Toxin

Protective Antigen

The protective antigen is the delivery mechanism of anthrax toxin. The bacteria secrete it as a single chain, as shown on the left from PDB entry 1acc. The protein then finds a cell surface and binds to it. A human protease on the surfaces of cells then clips off a small piece, colored blue here, arming the mechanism. It then combines with six other copies of the protein to form a seven-sided ring (the actual ring is much tighter than shown in this picture--the structure of the ring is not currently available at the PDB). This ring binds firmly to the cell surface and is thought to extend loops into the membrane, forming a pore. The other two parts of the toxin then bind to the ring and are carried into the cell.