i1 and Gαi3 Differentially Interact with, and Regulate, the G Protein-activated K+ Channel

Tatiana Ivanina, Dalia Varon, Sagit Peleg, Ida Rishal, Yuri Porozov, Carmen W. Dessauer, Tal Keren-Raifman, Nathan Dascal*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

G protein-activated K+ channels (GIRKs; Kir3) are activated by direct binding of Gβγ subunits released from heterotrimeric G proteins. In native tissues, only pertussis toxin-sensitive G proteins of the Gi/o family, preferably Gαi3 and Gα i2, are donors of Gβγ for GIRK. How this specificity is achieved is not known. Here, using a pulldown method, we confirmed the presence of Gαi3-GDP binding site in the N terminus of GIRK1 and identified novel binding sites in the N terminus of GIRK2 and in the C termini of GIRK1 and GIRK2. The non-hydrolyzable GTP analog, guanosine 5′-3-O-(thio)triphosphate, reduced the binding of Gαi3 by a factor of 2-4 Gαi1-GDp bound to GIRK1 and GIRK2 much weaker than Gαi3-GDp. Titrated expression of components of signaling pathway in Xenopus oocytes and their activation by m2 muscarinic receptors revealed that Gi3 activates GIRK more efficiently than G i1, as indicated by larger and faster agonist-evoked currents. Activation of GIRK by purified Gβγ in excised membrane patches was strongly augmented by coexpression of Gαi3 and less by Gαi1. Differences in physical interactions of GIRK with GDP-bound Gα subunits, or Gαβγ/heterotrimers may dictate different extents of Gαβγ anchoring, influence the efficiency of GIRK activation by Gβγ, and play a role in determining signaling specificity.

Original languageEnglish
Pages (from-to)17260-17268
Number of pages9
JournalJournal of Biological Chemistry
Volume279
Issue number17
DOIs
StatePublished - 23 Apr 2004

Funding

FundersFunder number
National Institute of General Medical SciencesR01GM060419

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