Chimeric Galpha(q) mutants harboring the last five carboxy-terminal residues of Galpha(i2) or Galpha(o) are resistant to pertussis toxin-catalyzed ADP-ribosylation.

Three widely-used Galpha(q) chimeras harboring the last five residues of Galpha(i), Galpha(o) and Galpha(z) (qi5, qo5 and qz5) were examined for their ability to serve as substrates for pertussis toxin (PTX)-catalyzed ADP-ribosylation. In COS-7 cells coexpressing one of the three opioid receptors (mu, delta, and kappa) and a Galpha(q) chimera, agonist-induced stimulation of phosphoinositide-specific phospholipase C (PI-PLC) was largely insensitive to PTX treatment. Only the qi5-mediated stimulation of PI-PLC by kappa-opioids was partially inhibited by PTX. In betagamma-release assays, PTX treatment did not affect the ability of opioid receptors to activate these chimeras. [32P]ADP-ribosylation labeled Galpha(i/o) but not qi5 or qo5, although the expression of these chimeras was confirmed by immunodetection. Thus, Galpha(q) chimeras with a Galpha(i/o)-like tail are insensitive to PTX treatment.