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Updated: Jun 18, 2026

Mutagenesis and Functional Analysis of Ion Channels Heterologously Expressed in Mammalian Cells
Published on: October 1, 2010
Live-cell quantitative monitoring reveals distinct, high-affinity Gβγ regulations of GIRK2 and GIRK1/2 channels
Reem Handklo-Jamal1, Tal Keren Raifman1, Boris Shalomov1
1Department of Physiology and Pharmacology, Faculty of Health and Medical Sciences, Tel Aviv University, Tel Aviv, Israel.
Abstract:
Gi/o protein-coupled receptors (GPCRs) inhibit cardiac and neuronal excitability via G protein-activated K+ channels (GIRK), assembled by combinations of GIRK1 - GIRK4 subunits. GIRKs are activated by direct binding of the Gβγ dimer of inhibitory Gi/o proteins. However, key aspects of this textbook signaling pathway remain debated. Recent studies suggested no Gi/o-GIRK precoupling and low (>250 μM) Gβγ-GIRK interaction affinity, contradicting earlier sub-μM estimates and implying low signaling efficiency. We show that Gγ prenylation, which mediates Gβγ membrane attachment required for GIRK activation, also contributes to the Gβγ-GIRK interaction, explaining the poor affinity obtained with non-prenylated Gβγ. Using quantitative protein titration and electrophysiology in live Xenopus oocytes, Gβγ affinity for homotetrameric GIRK2 ranged from 4-30 μM. Heterotetrameric GIRK1/2 showed a higher Gβγ apparent affinity due to unique Gβγ-docking site (anchor) in GIRK1, which enriches Gβγ at the channel. Biochemical approaches and molecular dynamic simulations revealed that the Gβγ anchor is formed by interacting N-terminal and distal C-terminal domains of the GIRK1 subunits, distinct from the Gβγ-binding "activation" site(s) underlying channel opening. Thus, the affinity of Gβγ-GIRK interaction is within the expected physiological range, while dynamic pre-coupling of Gβγ to GIRK1-containing channels through high-affinity interactions further enhances the GPCR-Gi/o-GIRK signaling efficiency.
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