Enzymatic activity of adenylate cyclase toxin from Bordetella pertussis is not required for hemolysis

Adenylate cyclase (AC) toxin from Bordetella pertussis enters cells to cause supraphysiologic increases in cAMP. AC toxin is also hemolytic. Substitution of Lys-58 with a methionine residue by site-directed mutagenesis of the structural gene for AC toxin, cyaA, and introduction of this mutation onto the B. pertussis chromosome results in an organism that synthesizes an enzyme-deficient AC toxin molecule. This mutant toxin molecule exhibits 1000-fold reduction in enzymatic activity relative to wild-type and has no toxin activity in J774 cells. The enzyme-deficient toxin molecule is not, however, impaired in its ability to lyse sheep red blood cells. In order to ascertain the importance of these two separate activities of AC toxin in vivo the enzyme-deficient organisms were used to infect infant mice. The hemolytic, enzyme-deficient mutant organisms are reduced in virulence relative to wild-type organisms after intranasal challenge indicating that, although the enzymatic activity of AC toxin does not contribute to hemolysis, it is this property of the toxin which is important for virulence of B. pertussis.