STUDIES ON THE STRUCTURE AND FUNCTION OF PERTUSSIS TOXIN

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Studies have been initiated to examine the mechanism of entry of pertussis toxin (PT) into the eukaryotic cell. The interaction of pertussis toxin with cells and model membranes was investigated by examining PT-induced intoxication of Chinese hamster ovary (CHO) cells and by studying the binding of PT and its subunits to phospholipid vesicles. Since certain bacterial toxins require an acidic environment for efficient interaction with membranes and subsequent entry into the cell, the requirement for an acidic environment for PT action was examined. PT, unlike bacterial toxins such as diphtheria toxin, did not require an acidic environment for efficient intoxication of Chinese hamster ovary cells. Potential modes by which PT might interact with biological membranes were studied by examining the binding of PT to model membrane system. PT was found to be capable of interacting with phospholipid vesicles, however efficient binding of the toxin to the vesicles, however, efficient binding of the toxin to the vesicles occurred only in the presence of both ATP and reducing agent. The A subunit portion of the toxin bound preferentially to the vesicles while little binding of the B oligomer portion of PT to the model membranes was observed. Isolated A subunit, in the absence of the B oligomer, also bound to the vesicles with optimal binding occurring in the presence of reducing agent. After cleavage of the A subunit by trypsin, probably at Arg181, Arg182 and/or Arg193, large fragments which lacked the C-terminal portion of PTA no longer associated with the lipid vesicles. These results suggest that the A subunit of PT can interact directly with a lipid matrix and, if freed from the constraints imposed by the B oligomer, may be capable of interacting with cellular membranes. The binding of PT and its B oligomer to lipid vesicles containing glycosphingolipids was also also studied.