Biased inhibition by a suramin analogue of A1-adenosine receptor/G protein coupling in fused receptor/G protein tandems: the A1-adenosine receptor is predominantly coupled to Goalpha in human brain

Naunyn Schmiedebergs Arch Pharmacol. 2002 Jan;365(1):8-16. doi: 10.1007/s00210-001-0493-y. Epub 2001 Nov 7.


The interface between receptors and G proteins can be considered as a drug target. Various classes of low molecular weight inhibitors have been identified that block the ability of receptors to interact with G proteins (e.g. peptides, suramin analogues and amphiphilic cations). Here we have tested if there are compounds that differentially affect the interaction of one receptor with two different (related) G protein alpha-subunits. Fusion proteins comprising the human A1-adenosine receptor and Galphai-1 (A1/Galphai-1) or Galphao (A1/Galphao) were expressed in HEK293 cells. Suramin analogues were screened for their ability to differentially affect high affinity binding of the agonist (-) N6-3-[125I](iodo-4-hydroxyphenylisopropyl) adenosine (IHPIA). One compound [NF326 = 8,8'-(carbonylbis-(imino-3,1-phenylenecarbonylimino))bis-(1-naphthol-3,6-disulfonic acid, disodium salt)] was identified that inhibited high affinity agonist binding to the fusion protein A1/Galphai-1 but modestly enhanced binding of IHPIA to A1/Galphao. This action was specific because NF326 did not affect antagonist binding to either fusion protein. In addition, it was unrelated to a difference in affinity of the receptor for the G protein fusion moiety because the stability of ternary complexes formed by IHPIA + A1/Galphai-1 and IHPIA + A1/Galphao) is comparable and because lowering the affinity of the receptor for the G protein (by introducing point mutations at cys351 of Galphai-1) enhanced the uncoupling effect of NF326. Finally, NF326 did not discriminate between a fusion protein comprising the alpha2A-adrenoceptor and Galphai-1 (alpha2A)/Galphai-1) or Galphao-1 (alpha2A)/Galphao-1); binding of the agonist [3H]UK14304 (bromoxidine) to both fusion proteins was inhibited over a comparable concentration range while binding of the antagonist [3H]yohimbine was unaffected. These observations are consistent with the interpretation that the contact sites that are formed between individual receptors and G proteins differ. These differences suffice to allow for selective disruption by G protein inhibitors of different classes. Using NF326 we show that the bulk of the A1-adenosine receptors in human cerebrocortical membranes interacts with Galphao rather than Galphai.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / metabolism
  • Antineoplastic Agents / pharmacology
  • Brain / metabolism*
  • COS Cells
  • Dose-Response Relationship, Drug
  • GTP-Binding Protein alpha Subunits, Gi-Go
  • GTP-Binding Proteins / metabolism*
  • Heterotrimeric GTP-Binding Proteins / metabolism*
  • Humans
  • Purinergic P1 Receptor Antagonists*
  • Receptors, Purinergic P1 / metabolism*
  • Suramin / analogs & derivatives*
  • Suramin / metabolism
  • Suramin / pharmacology*
  • Swine


  • Antineoplastic Agents
  • Purinergic P1 Receptor Antagonists
  • Receptors, Purinergic P1
  • Suramin
  • GTP-Binding Proteins
  • GTP-Binding Protein alpha Subunits, Gi-Go
  • Heterotrimeric GTP-Binding Proteins