Journal of Biological Chemistry
Volume 272, Issue 51, 19 December 1997, Pages 32071-32077
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PROTEIN CHEMISTRY AND STRUCTURE
Molecular Determinants of Selectivity in 5-Hydroxytryptamine1B Receptor-G Protein Interactions*

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The recognition between G protein and cognate receptor plays a key role in specific cellular responses to environmental stimuli. Here we explore specificity in receptor-G protein coupling by taking advantage of the ability of the 5-hydroxytryptamine1B (5-HT1B) receptor to discriminate between G protein heterotrimers containing Gαi1 or Gαt. Gi1 can interact with the 5-HT1B receptor and stabilize a high affinity agonist binding state of this receptor, but Gt cannot. A series of Gαt/Gαi1 chimeric proteins have been generated in Escherichia coli, and their functional integrity has been reported previously (Skiba, N. P., Bae, H., and Hamm, H. E. (1996) J. Biol. Chem. 271, 413–424). We have tested the functional coupling abilities of the Gαt/Gαi1 chimeras to 5-HT1Breceptors using high affinity agonist binding and receptor-stimulated guanosine 5′-3-O-(thio)triphosphate (GTPγS) binding. In the presence of βγ subunits, amino acid residues 299–318 of Gαi1 increase agonist binding to the 5-HT1Breceptor and receptor stimulation of GTPγS binding. Moreover, Gαi1 containing only Gαt amino acid sequences from this region does not show any coupling ability to 5-HT1B receptors. Our studies suggest that the α4 helix and α4-β6 loop region of Gαs are an important region for specific recognition between receptors and Gi family members.

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*

This work was supported by National Institutes of Health Grant EY10291 (to H. E. H.), American Heart Association Grant MC 11547 (to N. P. S.), an American Heart Association Ohio-West Virginia Affiliate Grant-In-Aid (to S. G. G.), and a Howard Hughes Medical Institute Undergraduate Research Fellowship (to K. A.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.