MOLECULAR DETERMINANTS OF SELECTIVITY IN 5-HYDROXYTRYPTAMINE(1B) RECEPTOR-G PROTEIN INTERACTIONS

The recognition between G protein and cognate receptor plays a key rol e in specific cellular responses to environmental stimuli, Here we exp lore specificity in receptor-G protein coupling by taking advantage of the ability of the 5-hydroxytryptamine(1B) (5-HT1B) receptor to discr iminate between G protein heterotrimers containing G alpha(i1) or G al pha(t). G(i1) can interact with the 5-HT1B receptor and stabilize a hi gh affinity agonist binding state of this receptor, but G(t) cannot. A series of G alpha(t)/G alpha(i1) chimeric proteins have been generate d in Escherichia coli, and their functional integrity has been reporte d previously (Skiba, N. P., Bae, H., and Hamm, H. E. (1996) J. Biol. C hem. 271, 413-424), We have tested the functional coupling abilities o f the G alpha(t)/G alpha(i1) chimeras to 5-HT1B receptors using high a ffinity agonist binding and receptor-stimulated guanosine 5'-3-0-(thio )triphosphate (GTP gamma S) binding, In the presence of beta gamma sub units, amino acid residues 299-318 of G alpha(i1) increase agonist bin ding to the 5-HT1B receptor and receptor stimulation of GTP gamma S bi nding, Moreover, G alpha(i1) containing only G alpha(t) amino acid seq uences from this region does not show any coupling ability to 5-HT1B r eceptors, Our studies suggest that the alpha 4 helix and alpha 4-beta 6 loop region of G alpha s are an important region for specific recogn ition between receptors and G(i) family members.