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- Title
The ‘allosteric modulator’ SCH-202676 disrupts G protein-coupled receptor function via sulphydryl-sensitive mechanisms.
- Authors
Lewandowicz, Anna M.; Vepsäläinen, Jouko; Laitinen, Jarmo T.
- Abstract
Previous studies suggest that the thiadiazole compound SCH-202676 (N-(2,3-diphenyl-1,2,4-thiadiazol-5-(2H)-ylidene)methanamine) acts as an allosteric modulator of a variety of structurally distinct G protein-coupled receptors (GPCRs). It was postulated that SCH-202676 would directly bind a structural motif in the receptor molecule common to divergent members of the GPCR family. The molecular mechanisms of such a promiscuous action, however, remain obscure.To clarify the mechanism of SCH-202676 action, we used the functional approach of [35S]GTPγS autoradiography with rat brain cryostat sections together with classical membrane [35S]GTPγS binding assays to evaluate how the thiadiazole affects G protein activity mediated by various receptors linked to the Gi-family of G proteins.We found that in the absence of dithiotreitol (DTT), SCH-202676 (10−7–10−5 M) elicits nonspecific effects in the [35S]GTPγS-based G protein activation assays, thereby severely compromising interpretations on the compounds ability to allosterically inhibit receptor-mediated G protein activity. Such a nonspecific behaviour was fully reversed upon addition of DTT (1 mM), revealing thiol-based mechanism of action.In routine incubations containing DTT, SCH-202676 had no effect on receptor-driven G protein activity, as assessed for adenosine A1, α2-adrenergic, cannabinoid CB1, lysophosphatidic acid LPA1, muscarinic M2/M4, purinergic P2Y12 or sphingosine 1-phosphate receptors, suggesting that the thiadiazole does not act as an allosteric modulator of GPCR function.1H NMR analysis indicated that SCH-202676 underwent structural changes after incubation with the reducing agent DTT or with brain tissue.We conclude that SCH-202676 modulates GPCRs via thiol modification rather than via true allosteric mechanisms.British Journal of Pharmacology (2006) 147, 422–429. doi:10.1038/sj.bjp.0706624; published online 9 January 2006
- Subjects
G proteins; RHO GTPases; ALLOSTERIC regulation; THIADIAZOLES; THIOLS; ORGANOSULFUR compounds
- Publication
British Journal of Pharmacology, 2006, Vol 147, Issue 4, p422
- ISSN
0007-1188
- Publication type
Academic Journal
- DOI
10.1038/sj.bjp.0706624