ACTIVATION OF PERTUSSIS TOXIN BY ATP: STRUCTURE AND BIOLOGY. Bart Hazes and Randy J. Read, University of Alberta, Dept. of Medical Microbiology & Immunology, 1-41 Med. Sci. Bldg. Edmonton, AB T6G 2H7 Canada; Stephen A. Cockle, Connaught Centre for Biotechnology Research, 1755 Steeles Ave, West Willowdale, ON M2R 3T4 Canada.

Pertussis toxin is a virulence factor of Bordetella pertussis, the etiologic agent of whooping cough. ATP activates this toxin by destabilizing the quaternary structure of the holotoxin. The molecular basis for this effect has now been revealed by the pertussis toxin-ATP complex structure which we will present. In short, ATP binds at the heart of the hexameric toxin where it destabilizes the C-terminus of the toxic subunit through unfavorable steric and electrostatic interactions with the triphosphate moiety.

A more general consequence of our work is that the structural results contribute to our understanding of how pertussis toxin and other important protein toxins may enter the cytosol of eukaryotic cells. Several lines of evidence now converge on a mechanism in which these toxins undergo retrograde transport from the cell surface via the Golgi to the ER. In the ER the toxic subunit then dissociates from the holotoxin prior to membrane translocation. Proteolytic cleavage and disulfide bond reduction seem to be the preferred mechanisms for dissociation of the toxic subunit. However, for pertussis toxin we now propose that ATP, which is first encountered in the ER, triggers the dissociation of the holotoxin.

This work was supported by the MRC and PENCE