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Divergent mechanisms for allosteric modulators of adenosine A1 receptors
Author(s) -
May Lauren Therese,
Sexton Patrick M,
Ijzerman Ad P,
Christopoulos Arthur
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1119
Subject(s) - allosteric regulation , chemistry , receptor , g protein coupled receptor , adenosine receptor , agonist , biophysics , allosteric modulator , adenosine a1 receptor , cysteine , allosteric enzyme , stereochemistry , biochemistry , pharmacology , biology , enzyme
Allosteric modulators of adenosine A 1 receptors are potentially novel therapeutic agents; however, their mode of interaction with the receptor remains largely unknown. Two previously‐described A 1 modulators, SCH‐202676 and LUF‐5484, both contain a sulfur atom within their structure, leading to the hypothesis that their mode of binding may involve interaction with one or more cysteine residues within the receptor. In radioligand binding assays, SCH‐202676 significantly reduced the dissociation rate of the antagonist, [ 3 H]DPCPX, from CHO‐A 1 membranes, suggestive of an allosteric change in receptor conformation. A similar effect was noted for LUF‐5484 on the dissociation rate of the agonist, [ 3 H] CCPA. In functional assays, SCH‐202676 acted as an inhibitor of R‐PIA‐mediated ERK1/2 phosphorylation, while LUF‐5484 enhanced the potency of R‐PIA in a manner quantitatively consistent with the predictions of a simple allosteric receptor model. When both binding and functional experiments were repeated in the presence of the disulfide reducing agent, dithiothreitol (10 mM), the effects of SCH‐202676 were abolished, but not those of LUF‐5484. These results support the hypothesis that SCH‐202676 is a non‐specific modulator of GPCRs that interacts with receptor sulfhydryl groups. In contrast, LUF‐5484 is a specific A 1 receptor enhancer that does not necessarily utilize cysteine residues for its interaction with the receptor's allosteric site.