Regulation of the avidity of ternary complexes containing the human 5‐HT 1A receptor by mutation of a receptor contact site on the interacting G protein α subunit

Fusion proteins were constructed between the human 5‐HT 1A receptor and pertussis toxin‐resistant forms of both G i1 α and G o1 α mutated at residue 351 from cysteine to either glycine or isoleucine. Each of these was expressed stably in HEK293 cells. Increasing concentrations of GDP inhibited binding of the agonist [ 3 H]‐8‐OH‐DPAT but not the antagonist [ 3 H]‐MPPF to each construct. The IC 50 for GDP was greater for constructs containing isoleucine at residue 351 of the G proteins compared to those with glycine at this position. The G protein antagonist suramin had similar effects to GDP on the binding of [ 3 H]‐8‐OH‐DPAT. The proportion of 5‐HT 1A receptor binding sites detected by [ 3 H]‐MPPF that displayed high affinity for 8‐OH‐DPAT was significantly greater when the interacting G protein contained isoleucine rather than glycine at residue 351 . The 5‐HT 1A receptor displayed similar avidity of interaction with G i1 α and G o1 α. These results indicate that a higher avidity ternary complex is formed between 8‐OH‐DPAT, the 5‐HT 1A receptor and G proteins when isoleucine rather than glycine is located at residue 351 of the interacting G protein. British Journal of Pharmacology (2002) 137 , 345–352. doi: 10.1038/sj.bjp.0704880