Distinct Mechanisms for K+ Efflux, Intoxication, and Hemolysis by Bordetella pertussis AC Toxin

Adenylate cyclase (AC) toxin from Bordetella pertussis delivers its catalytic domain to the interior of target cells where it converts host ATP to cAMP in a process referred to as intoxication. This toxin also hemolyzes sheep erythrocytes by a mechanism presumed to include pore formation and osmotic lysis. Intoxication and hemolysis appear at strikingly different toxin concentrations and evolve over different time scales, suggesting that different molecular processes may be involved. The present study was designed to test the hypothesis that intoxication and hemolysis occur by distinct mechanisms. Although the hemolytic activity of AC toxin has a lag of >1 h, intoxication starts immediately. Because of this difference, we sought a surrogate or precursor lesion that leads to hemolysis, and potassium efflux has been observed from erythrocytes treated with other pore-forming toxins. AC toxin elicits an increase in K + efflux from sheep erythrocytes and Jurkat cells, a human T-cell leukemia line, that begins within minutes of toxin addition. The toxin concentration dependence along with the analysis of the time course suggest that toxin monomers are sufficient to elicit release of K + and to deliver the catalytic domain to the cell interior. Hemolysis, on the other hand, is a highly cooperative event that likely requires a subsequent oligomerization of these individual units. Although induction of K + efflux shares some structural and environmental requirements with both intoxication and hemolysis, it can occur under conditions in which intoxication is reduced or prevented. The data presented here suggest that the transmembrane pathway by which K + is released is separate and distinct from the structure required for intoxication but may be related to, or a precursor of, that which is ultimately responsible for hemolysis.