QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Figler, H. Articles by Linden, J. Search for Related Content PubMed PubMed Citation Articles by Figler, H. Articles by Linden, J.

Allosteric Enhancers of A₁ Adenosine Receptors Increase Receptor-G Protein Coupling and Counteract Guanine Nucleotide Effects on Agonist Binding

Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia (H.F., J.L.); and University of South Florida, Tampa, Florida (R.A.O.)

Endogenous ligands of G protein-coupled receptors bind to orthosteric sites that are topologically distinct from allosteric sites. Certain aminothiophenes such as (2-amino-4,5-dimethyl-3-thienyl)-[3-(trifluromethyl)-phenyl]-methanone (PD81,723) and 2-amino-4,5,6,7-tetrahydro-benzo[b]thiophen-3-yl)-biphenyl-4-yl-methanone (ATL525) are positive allosteric regulators, or enhancers, of the human A₁ adenosine receptor (A₁AR). In equilibrium binding assays, ¹²⁵I-N⁶-aminobenzyladenosine (¹²⁵I-ABA) binds to two affinity states of A₁AR with K_D-high (0.33 µM) and K_D-low (10 nM). Enhancers have little effect on K_D-high but convert all A₁AR binding sites to the high-affinity state. Enhancers decrease the potency of guanosine 5'-O-(3-thio)triphosphate (GTPS) as an inhibitor of agonist binding by 100-fold and increase agonist-stimulated guanine nucleotide exchange. The association of ¹²⁵I-ABA to high-affinity receptors on Chinese hamster ovary (CHO)-hA₁ membranes does not follow theoretical single-site association kinetics but is approximated by a bi-exponential equation with t_1/2 values of 1.85 and 12.8 min. Allosteric enhancers selectively increase the number of slow binding sites, possibly by stabilizing newly formed receptor-G protein complexes. A new rapid assay method scores enhancer activity on a scale from 0 to 100 based on their ability to prevent the rapid dissociation of ¹²⁵I-ABA from A₁AR in response to GTPS. Compared with PD81,723, ATL525 (100 µM) scores higher (27 versus 79) and has less antagonist activity. ATL525 functionally enhances A₁ signaling to inhibit cAMP accumulation in CHO-hA1 cells. These data suggest that simultaneously binding orthosteric and allosteric enhancer ligands convert the A₁AR from partly to fully coupled to G proteins and prevents rapid uncoupling upon binding of GTPS.

Address correspondence to: Dr. Joel Linden, MR5 Box 801394, Cardiovascular Research Center, University of Virginia, Charlottesville, VA 22908. E-mail: jlinden{at}virginia.edu

This article has been cited by other articles:

				J. A. Auchampach Adenosine Receptors and Angiogenesis Circ. Res., November 26, 2007; 101(11): 1075 - 1077. [Full Text] [PDF]

				J. M. Mathiesen, T. Ulven, L. Martini, L. O. Gerlach, A. Heinemann, and E. Kostenis Identification of Indole Derivatives Exclusively Interfering with a G Protein-Independent Signaling Pathway of the Prostaglandin D2 Receptor CRTH2 Mol. Pharmacol., August 1, 2005; 68(2): 393 - 402. [Abstract] [Full Text] [PDF]