Molecular Determinants of Selectivity in Receptor-G protein Interaction

Helerotrimeric G proteins provide a signal transduction coupling between surface receptors and the effectors that regulate the concentration of the intraccllular second messengers. The specific recognition between G protein and cognate receptor plays a key role in specific cellular responses to environmental stimuli. A number of studies show that ihe C-terminal region of the a subunit of heterotrimeric G proteins is an important site for receptor recognition. However, other studies suggest that other regions in the Ga subunit may be involved in determining the specificity of G protein - receptor recognition Here we lake advantage of the specificity of the 5-hydroxytryptamine, (5-HT,) receptor for G,i and lack of its coupling to (}, to explore specificity in this receptor-G protein coupling mechanism. Gu can bind 5-HTiu receptor and stabilize the high affinity agonist binding state of this receptor, hut G, can not. In addition, the 5-HTis receptor stimulated GTPyS binding to G,i but not G, again showing specificity of coupling, βy subunits from cither retina or brain supported coupling of α but not α, to the 5HT1 receptor. A series of GαGα, chimeric proteins were generated in E. colt. Their functional integrity was reported previously i,Skiba et al. ( 1996) J.Biol.Chem. 271:413-424). We tested the functional coupling abilities of the Gα/Gα, chimeras to 5-HTia receptors by high affinity agonist binding and receptor stimulated GTPyS binding. In the presence of βy subunit, aminoacid residues 299-318 of Gαn increase agonist binding to the 5-HTia receptor and receptor stimulation of GTPyS binding. Moreover the chimeras, containing Go, amino acid sequences homologous to 299-318 Gαi, do not show any coupling ability to the receptors This region is quite different among G proteins, bul is conserved in Gα, Gα,: and Gα which can couple to the 5-H1B receptor. Interestingly, this region also overlaps with the effector binding region (Gα,293-314). These studies suggest that the α4 helix and α4-β6 loop region of Ga's are important region for specific recognition between G proteins and their cognale receptors.

Duke Scholars

Author Nikolai Petrovich Skiba Ophthalmology