PT  - JOURNAL ARTICLE
AU  - Stephen R. Marsh
AU  - Galina Grishina
AU  - Paul T. Wilson
AU  - Catherine H. Berlot
TI  - Receptor-Mediated Activation of G<sub>sα</sub>: Evidence for Intramolecular Signal Transduction
DP  - 1998 Jun 01
TA  - Molecular Pharmacology
PG  - 981--990
VI  - 53
IP  - 6
4099  - http://molpharm.aspetjournals.org/content/53/6/981.short
4100  - http://molpharm.aspetjournals.org/content/53/6/981.full
SO  - Mol Pharmacol1998 Jun 01; 53
AB  - To investigate the mechanism by which cell surface receptors activate heterotrimeric G proteins, we applied a scanning mutagenesis approach to the carboxyl-terminal 40% of αs (residues 236–394) to identify residues that play a role in receptor-mediated activation. We identified four regions of sequence in which mutations significantly impaired receptor-dependent stimulation of cAMP synthesis in transiently transfected cyc− S49 lymphoma cells, which lack endogenous αs. Residues at the carboxyl terminus are likely to be receptor contact sites. Buried residues near the bound GDP are connected to the carboxyl terminus by an α helix and may regulate GDP affinity. Residues in two adjacent loops of the GTPase domain at the interface with the helical domain, one of which includes a region, switch III, that changes conformation on GTP binding, are positioned to relay the receptor-initiated signal across the domain interface to facilitate GDP release. Consistent with this hypothesis, replacing the helical domain of αs with that of αi2 in an αs/αi2/αs chimera corrects the defect in receptor-mediated activation caused by αi2substitutions on the GTPase side of the interface. Thus, complementary interactions between residues across the domain interface seem to play a role in receptor-catalyzed activation. The American Society for Pharmacology and Experimental Therapeutics