Structural Basis for Modulation of Gating Property of G Protein-gated Inwardly Rectifying Potassium Ion Channel (GIRK) by i/o-family G Protein α Subunit (Gαi/o)

Abstract

Background: Although G␤␥ is known to activate GIRK, G␣ i/o also modulates GIRK gating. Results: The ␣2/␣3 helices of G␣ i3 in the GTP-bound state directly bind to the ␣A helix of GIRK. Conclusion:The complex model explains how G␣ i/o sequesters G␤␥ efficiently from GIRK upon GTP hydrolysis. Significance: The structural basis for the rapid closure of GIRK by G␣ i/o is provided.

Conformational Dynamics of Kir3.1/Kir3.2 Channel Activation Via δ-Opioid Receptors

“…Previous studies had similarly reported that inactive Ga did not directly interact with Kir3.1/3.2 subunits (Fowler et al, 2007;Berlin et al, 2011) and had proposed that this subunit associates with Kir3 channels via the Gbg dimer (Berlin et al, 2011). On the other hand, NMR studies have revealed a direct interaction between the switch 2 region of GTP-bound Gai3 and the aA helix of Kir3.1 subunits (Mase et al, 2012), suggesting that Ga and the channel may come into direct contact on G protein activation. We did not find evidence for this type of reorganization since DOR stimulation by highly efficacious agonists failed to show BRET at the GaoA/Kir3.1 interface.…”

“…DOR-Evoked Changes at the Gbg/Kir3 Subunit Interface are Concomitant with Conformational Rearrangements Among GaoA/Gbg Subunits and Predictive of Ligand Ability to Induce Channel Currents. Ga subunits are thought to modulate channel activity both through direct interaction with Kir3 subunits and by making Gbg readily available in the proximity of channel subunits (Peleg et al, 2002;Clancy et al, 2005;Rubinstein et al, 2009;Mase et al, 2012). We were therefore interested in characterizing whether DOR activation modified Ga interactions with different complex components.…”

“…Gai/o is also thought to be part of the Kir3-G protein complex, but the way in which this subunit interacts with other complex components, particularly the channel, remains to be fully elucidated. Indeed, biochemical and biophysical studies show that Ga-GTP may interact directly with channel subunits (Berlin et al, 2010;Mase et al, 2012), whereas Ga-GDP would associate with the complex via the Gbg dimer (Clancy et al, 2005;Berlin et al, 2011). Functional studies indicate that Ga actively participates in channel modulation in both its GDP-and GTP-bound states (Berlin et al, 2010;Berlin et al, 2011) and have identified Gbg interactions with Kir3 subunits as the mediator of channel activation (Logothetis et al, 1987;Riven et al, 2006).…”

The Expanding Roles of GβγSubunits in G Protein–Coupled Receptor Signaling and Drug Action

“…5, A and B). The Gbg binding sites on Kir3 channels have also been investigated by NMR (Yokogawa et al, 2011;Mase et al, 2012). By mapping the residues affected by Gbg binding to the structure, the authors proposed that Gbg binds at the interface between adjacent subunits allowing for contacts with the N terminus of one subunit and the C terminus of an adjacent subunit.…”

A Mechanism Regulating G Protein-coupled Receptor Signaling That Requires Cycles of Protein Palmitoylation and Depalmitoylation

“…GIRK channels are opened by G␤␥ subunits and closed by channelbound G i/o ␣ subunits that have hydrolyzed GTP to GDP and reformed G␣␤␥ heterotrimers (37,38). By accelerating G i/o ␣- Palmitate Turnover Regulates GPCR-GIRK Signaling FEBRUARY 28, 2014 • VOLUME 289 • NUMBER 9 mediated GTP hydrolysis, R7 RGS-G␤5 complexes recruited to GIRK channels by R7BP facilitate channel closure (26).…”