Abstract
The Bordetella pertussis cyaA gene encodes a virulence factor which is a bifunctional protein exhibiting calmodulin-sensitive adenylate cyclase and hemolytic activities (P. Glaser, H. Sakamoto, J. Bellahov, A. Ullmann, and A. Danchin, EMBO J. 7:3997-4004, 1988). We characterized the hemolytic and toxin activities of the 200-kilodalton (kDa) bifunctional (CyaA) protein and showed that, whether cell associated or secreted, the 200-kDa CyaA protein carries hemolytic and toxin functions. The catalytically active 45-kDa form of adenylate cyclase released by proteolytic digestion of the 200-kDa CyaA protein displayed neither hemolytic nor toxin activities. We constructed in-phase deletions in the 3' region of the cyaA gene, which presumably carries the hemolytic determinant, and showed that the resulting proteins exhibited wild-type adenylate cyclase activity and were secreted without processing into culture supernatants. The hemolytic activities of these mutant CyaA proteins were severely reduced, and their toxin activities were abolished. These results suggest that the structural integrity of the 200-kDa CyaA protein is necessary for toxin activity and that distinct structural determinants within the CyaA protein are involved in secretion, pore formation, and entry into target cells.