The β6/α5 regions of Gαi2 and GαoA increase the promiscuity of Gα16 but are insufficient for pertussis toxin-catalyzed ADP-ribosylation

Abstract Replacement of β6/α5 region at the C-terminus on Gα 16 with Gα z -specific residues has been shown to broaden the promiscuity of Gα 16 . Here, we substituted the last 44 residues of Gα 16 with the corresponding region from either Gα i2 or Gα oA (16i44 and 16o44). 16i44 and 16o44 chimeras were more effective than Gα 16 at coupling to G i -linked δ-opioid, μ-opioid, and Xenopus melatonin MT 1c receptors when coexpressed in green monkey fibroblast (COS-7) cells. 16i44, but not 16o44, also enhanced the formyl peptide-induced stimulation of phospholipase C activity. Both chimeras were resistant to pertussis toxin-catalyzed [ 32 P]ADP-ribosylation, despite the fact that pertussis toxin partially inhibited the chimera-mediated stimulation of phospholipase Cβ. The use of Gα t1 as a Gβγ scavenger revealed that the pertussis toxin-sensitivity can be attributed to endogenous Gβγ subunits released from G i/o . Although incorporation of a Gα i -like β6/α5 region into the C-terminus of Gα 16 increases its promiscuity, this region is not sufficient to support recognition by pertussis toxin.