Islet-activating protein Pertussis toxin consists of an A protomer subunit (S1) which possesses both NAD+ glycohydrolase and ADP-ribosyltransferase activities, and B oligomer subunits (S2, S3, S4, and S5) which are responsible for attachment of the native toxin to eukaryotic cell surfaces. Pertussis toxin uncouples G proteins from receptors by ADP ribosylating a cysteine residue near the carboxyl terminus of the α subunit.
