Chimeric G alpha(q) mutants harboring the last five carboxy-terminal residues of G alpha(i2) or G alpha(o) are resistant to pertussis toxin-catalyzedADP-ribosylation

Three widely-used G alpha(q) chimeras harboring the last five residues of G alpha(i), G alpha(o) and G alpha(z) (qi5, qo5 and qz5) were examined for t heir ability to serve as substrates for pertussis toxin (PTX)-catalyzed ADP -ribosylation, In COS-7 cells coexpressing one of the three opioid receptor s (mu, delta, and kappa) and a G alpha(q) chimera, agonist-induced stimulat ion of phosphoinositide-specific phospholipase C (PI-PLC) mas largely insen sitive to PTX treatment. Only the qi5-mediated stimulation of PI-PLC by kap pa-opioids was partially inhibited by PTX. In beta gamma-release assays, PT X treatment did not affect the ability of opioid receptors to activate thes e chimeras. [P-32]ADP-ribosylation labeled G alpha(i/o) but not qi5 or qo5, although the expression of these chimeras was confirmed by immunodetection . Thus, G alpha(q) chimeras with a G alpha(i/o)-like tail are insensitive t o PTX treatment. (C) 1998 Federation of European Biochemical Societies.