Structure-activity analysis of the activation of pertussis toxin

Bordetella pertussis, the causative agent of whooping cough, releases pertussis toxin in an inactive form. The toxin consists of an A protomer containing one S1 peptide subunit and a B oligomer containing several other peptide subunits. The toxin binds to cells via the B oligomer, and the S1 subunit is activated and expresses ADP-ribosyltransferase and NAD glycohydrolase activities. Treatment of purified toxin with dithiothreitol (DTT) in vitro increases both activities. ATP and the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) synergistically reduce the A0.5 (activation constant) for DTT from greater than 100 mM to 200 microM. We studied the structure-activity relationships of activators of the toxin. In the presence of CHAPS (1%) and DTT (10 mM) the following compounds increased the NAD glycohydrolase activity of the toxin with the following A0.5's in microM and fraction of the ATP effect in parentheses: ATP, 0.2 (1.0); ADP, 6 (0.8); UTP, 15 (0.7); GTP, 35 (0.6); pyrophosphate, 45 (0.7); triphosphate, 60 (0.6); tetraphosphate, greater than or equal to 170 (greater than or equal to 0.4). Thus, the polyphosphate moiety is sufficient to stimulate the toxin, and the adenosine moiety confers upon ATP its extraordinary affinity for the toxin. Phospholipid and detergents could substitute for CHAPS in the activation of the toxin. Glutathione substituted for DTT with an A0.5 of 2 mM, a concentration within the range found in eucaryotic cells. Thus, membrane lipids and cellular concentrations of glutathione and ATP are sufficient to activate pertussis toxin without the need for a eucaryotic enzymatic process.