Abstract
Gβγ dimers containing the γ11 or γ1 subunits are often less potent and effective in their ability to regulate effectors compared with dimers containing the γ subunit. To explore the regions of the γ2 subunit that affect the activity of the βγ dimer, we constructed eight chimeric γ subunits from the γ1 and γ2 subunits. Two chimeras were made in which the N-terminal regions of γ1 and γ2 were exchanged and two in which the C-terminal regions were transposed. Another set of chimeras was made in which the CAAX motifs of the chimeras were altered to direct modification with different prenyl groups. All eight γ chimeras were expressed in Sf9 cells with the β1 subunit, Gβγ dimers were purified, and then they were assayed in vitro for their ability to bind to the Gαi1 subunit, to couple Gαi1 to the A1 adenosine receptor, to stimulate phospholipase C-β, and to regulate type I or type II adenyl cyclases. Dimers containing the C-terminal sequence of the γ2 subunit modified with the geranylgeranyl lipid had the highest affinity for Gi1α (range, 0.5-1.2 nM) and were most effective at coupling the Gi1α subunit to receptor. These dimers were most effective at stimulating the phosphatidylinositol-specific phospholipase C-β isoform and inhibiting type I adenyl cyclase. In contrast, βγ dimers containing the N-terminal sequence of the γ2 subunit and a geranylgeranyl group are most effective at activating type II adenyl cyclase. The results indicate that both the N- and C-terminal regions of the γ subunit impart specificity to receptor and effector interactions.
- Received September 15, 2005.
- Accepted November 30, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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