ABSTRACT
The interaction of protective antigen (PA), a component of the anthrax toxin, with receptors on the Chinese hamster ovary cell line CHO-K1 was characterized. Protective antigen binding at 4 degrees C is highly specific, concentration dependent, saturable (Kd = 0.9 nM), and reversible. Scatchard analysis indicates the presence of a single class of PA binding sites at a concentration of 10,000 +/- 2,000 per cell. Pretreatment of cells with a number of different proteases strongly inhibits PA binding, suggesting that the receptor may be at least partially proteinaceous. Direct chemical cross-linking of radioiodinated PA to the cell surface results in the appearance of a major band exhibiting an apparent molecular mass of 170 kDa, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The appearance of this band is completely inhibited by a 200-fold molar excess of unlabeled PA, indicating a high specificity for this interaction. Our results suggest that a cell surface protein(s) of 85 to 90 kDa is, or constitutes a portion of, a specific receptor for the PA.
