CYAC-MEDIATED ACTIVATION IS IMPORTANT NOT ONLY FOR TOXIC BUT ALSO FORPROTECTIVE ACTIVITIES OF BORDETELLA-PERTUSSIS ADENYLATE CYCLASE-HEMOLYSIN

Bordetella pertussis adenylate cyclase-hemolysin (AC-Hly), encoded by the cyaA gene, belongs to the RTX family of toxins with extensive glyc ine-rich repeats in the carboxy-terminal portion. AC-Hly possesses bot h adenylate cyclase toxic and hemolytic activities that depend on a po sttranslational modification mediated by the product of the cyaC gene. An improved system for AC-Hly synthesis and activation in Escherichia coli was developed. The results show that with purified AC-Hly, (i) i ncreased expression of the cyaC gene leads to a higher proportion of a ctivated AC-Hly, (ii) the increase in protective activity of the activ ated recombinant AC-Hly correlates with the increase in its invasive a nd hemolytic activities, and (iii) the activated recombinant AC-Hly, b ut not the nonactivated recombinant AC-Hly, is a protective antigen ag ainst B. pertussis infection in a murine respiratory model. This sugge sts that possibly an immunodominant epitope required for protective ac tivity is linked to the CyaC-mediated modification. Surprisingly, the protective and hemolytic activities of activated recombinant AC-Hly we re lower than those of AC-Hly produced by B. pertussis, while its inva sive activity was higher. This indicates that the modification of AC-H ly in B. pertussis and that in E. coli may differ.