Studies on the binding of staphylococcal 125I-labeled alpha-toxin to rabbit erythrocytes.
Staphylococcal alpha-toxin, a hemolytic exotoxin, can be iodinated using the lactoperoxidase method. 125 I-Labeled alpha-toxin binds to rabbit erythrocytes in an apparently irreversible and highly specific manner. The binding of 125 I-labeled alpha-toxin to erythrocytes of rabbit and human reflects the species specificity of native alpha-toxin. Binding of 125I-labeled alpha-toxin is blocked by the presence of native alpha-toxin, 127I-labeled alpha-toxin, or anti-alpha-toxin antibody. Simultaneous assays of 125I-labeled alpha-toxin binding and leakage of intracellular 86Rb+ suggest that toxin binding and membrane damage are separate, sequential functions. Both the rate and extent of binding are temperature dependent. Rabbit erythrocytes possess 5 X 10(3) binding sites/cell, while human erythrocytes possess no detectable binding sites. Treatment of rabbit erythrocytes with 125I-labeled alpha-toxin appears to decrease the number of unoccupied binding sites. Chaotropic ions can inhibit 125I-labeled alpha-toxin binding and cause bound 125I-labeled alpha-toxin to dissociate from rabbit erythrocyte membranes. Treatment of intact rabbit erythrocytes with pronase reduces both the binding capacity  of the cells for 125I-labeled alpha-toxin, and the cells' sensitivity to hemolysis by native alpha-toxin. It is proposed that the primary binding site for alpha-toxin in biomembranes is a surface membrane protein.
D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D006461:Hemolysis / Q000187:drug effects; D007467:Iodoproteins; D007700:Kinetics; D010447:Peptide Hydrolases; D011485:Protein Binding; D011817:Rabbits; D012413:Rubidium / Q000097:blood; D013211:Staphylococcus aureus; D013696:Temperature; D014118:Toxins, Biological / Q000097:blood*
D007467:Iodoproteins; D014118:Toxins, Biological; D010447:Peptide Hydrolases; D012413:Rubidium