Figure 11. V1, V2, and V4 capacities for anthrax toxin protective antigen (PA, 83 kDa) binding, processing, and internalization. A,

PA binding to normal cells (WTB111). At 4°C, PA83 binds the receptors and is cleaved by furin to yield PA63. At 37°C, PA83 not only binds and is cleaved by furin, but enters cells and forms SDS-resistant oligomers. B, PA binding and processing at 4°C to PR230 expressing V1, V2, or V4. C, PA binding, processing, internalization, and SDS-resistant oligomer formation at 37°C. Two blots of a typical experiment are shown.