One of the most dramatic examples to date of a GPCR-interacting protein is the ligand-gated ion channel GABAA receptor. The second intracellular loop of the GABAA receptor y2-subunit interacts specifically with the C-terminal tail of the dopamine D5 receptors. When co-expressed, both receptors can be co-immunoprecipitated. Their interactions depend on the presence of agonists for both receptors:
• GABA reduces the capacity of dopamine to stimulate adenylate cyclase without a reduction in the affinity of dopamine for its receptor.
• The presence of the D5 receptor also alters the function of the GABAa receptor: i.e. dopamine reduces GABAA receptor signalling.
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