PT  - JOURNAL ARTICLE
AU  - H Kong
AU  - K Raynor
AU  - K Yasuda
AU  - G I Bell
AU  - T Reisine
TI  - Mutation of an aspartate at residue 89 in somatostatin receptor subtype 2 prevents Na+ regulation of agonist binding but does not alter receptor-G protein association.
DP  - 1993 Aug 01
TA  - Molecular Pharmacology
PG  - 380--384
VI  - 44
IP  - 2
4099  - http://molpharm.aspetjournals.org/content/44/2/380.short
4100  - http://molpharm.aspetjournals.org/content/44/2/380.full
SO  - Mol Pharmacol1993 Aug 01; 44
AB  - Sodium ions have been shown to reduce the binding of agonists to a number of G protein-linked receptors. They are believed to do so by interacting with aspartate residues in the second membrane-spanning region of these receptors to cause G protein uncoupling, resulting in a diminished affinity of the receptors for agonists. To investigate Na+ regulation of agonist binding to somatostatin receptors, Na+ was tested for its effect on the binding of agonists to cloned somatostatin receptor type 1 (SSTR1) and somatostatin receptor type 2 (SSTR2) stably expressed in Chinese hamster ovary cells. Na+ reduced agonist binding to SSTR2 but not to SSTR1. Because high affinity agonist binding to SSTR1 does not depend on G protein coupling but agonist binding to SSTR2 is reduced by guanosine-5'-(beta, gamma-imido)triphosphate and pertussis toxin treatment, the selective Na+ effect on SSTR2 is consistent with previous findings with other receptors showing that Na+ uncouples receptors from G proteins, thereby reducing the affinity of the receptors for agonists. Conversion of Asp89 to Asn89 in SSTR2 resulted in a mutant receptor whose affinity for agonists was not altered by Na+, indicating that Asp89 is involved in mediating the effects of Na+ on agonist binding to SSTR2. However, the affinities of the mutant and wild-type receptors for somatostatin were the same, and both guanosine-5'-O-(gamma-thio)triphosphate and pertussis toxin treatment reduced agonist binding to the mutant and wild-type receptors. These findings differ from the results of similar mutagenesis studies on other G protein-linked receptors, in that the mutant and wild-type SSTR2 forms associate with G proteins in similar ways. These results indicate that Asp89 acts in a novel manner to regulate agonist binding and G protein interaction with SSTR2.