GABAB receptors couple to G proteins Go, Go and G·i1 but not to Gi2

Abstract
We studied the selectivity of GABAB receptors for coupling to G proteins by testing the ability of various purified G proteins to increase GABA binding to N‐ethylmaleimide (NEM)‐treated membranes of bovine brain. The addition of Go, G o or gi1 to NEM‐treated membranes increased GABA binding in a dose‐dependent manner. However, the addition of Gi2 did not elicit a marked increase in GABA binding. When α subunits of G proteins were mixed with various brain βγ subunit complexes composed of different γ subunits, and they were added to the NEM‐treated membranes, Gi2 with any βγ subunits hardly increased GABA binding. On the other hand, Go with any βγ subunits caused a marked increase, though Go with a small γ subunit was more effective than that with a large γ subunit. These data suggest that the selective coupling of the G proteins to GABAB receptors is determined by the α subunit.

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