A G-PROTEIN MUTANT THAT INHIBITS THROMBIN AND PURINERGIC RECEPTOR ACTIVATION OF PHOSPHOLIPASE-A2

The stimulation of phospholipase A2 by thrombin and type 2 (P2)-purinergic receptor agonists in Chinese hamster ovary cells is mediated by the G protein Gi. To delineate α chain regulatory regions responsible for control of phospholipase A2, chimeric cDNAs were constructed in which different lengths of the α subunit of G s (αs) were replaced with the corresponding sequence of the Gi α subunit (αi2). When a carboxyl-terminal chimera αs-i(38), which has the last 38 amino acids of αs substituted with the last 36 residues of αi2, was expressed in Chinese hamster ovary cells, the receptor-stimulated phospholipase A2 activity was inhibited, although the chimera could still activate adenylyl cyclase. Thus, α s-i(38) is an active αs, but also a dominant negative αi molecule, indicating that the last 36 amino acids of αi2 are a critical domain for G protein regulation of phospholipase A2 activity.