A Collision Coupling Model Governs the Activation of Neuronal GIRK1/2 Channels by Muscarinic-2 Receptors
The G protein-activated Inwardly Rectifying K + -channel (GIRK) modulates heart rate and neuronal excitability. Following G-Protein Coupled Receptor (GPCR)-mediated activation of heterotrimeric G proteins (Gαβγ), opening of the channel is obtained by direct binding of Gβγ subunits. Interestingly, GI...
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Published in | Frontiers in pharmacology Vol. 11; p. 1216 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Frontiers Media S.A
12.08.2020
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Subjects | |
Online Access | Get full text |
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Summary: | The G protein-activated Inwardly Rectifying K
+
-channel (GIRK) modulates heart rate and neuronal excitability. Following G-Protein Coupled Receptor (GPCR)-mediated activation of heterotrimeric G proteins (Gαβγ), opening of the channel is obtained by direct binding of Gβγ subunits. Interestingly, GIRKs are solely activated by Gβγ subunits released from Gα
i/o
-coupled GPCRs, despite the fact that all receptor types, for instance Gα
q
-coupled, are also able to provide Gβγ subunits. It is proposed that this specificity and fast kinetics of activation stem from pre-coupling (or pre-assembly) of proteins within this signaling cascade. However, many studies, including our own, point towards a diffusion-limited mechanism, namely collision coupling. Here, we set out to address this long-standing question by combining electrophysiology, imaging, and mathematical modeling. Muscarinic-2 receptors (M2R) and neuronal GIRK1/2 channels were coexpressed in
Xenopus laevis
oocytes, where we monitored protein surface expression, current amplitude, and activation kinetics. Densities of expressed M2R were assessed using a fluorescently labeled GIRK channel as a molecular ruler. We then incorporated our results, along with available kinetic data reported for the G-protein cycle and for GIRK1/2 activation, to generate a comprehensive mathematical model for the M2R-G-protein-GIRK1/2 signaling cascade. We find that, without assuming any irreversible interactions, our collision coupling kinetic model faithfully reproduces the rate of channel activation, the changes in agonist-evoked currents and the acceleration of channel activation by increased receptor densities. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Edited by: Rami Yaka, Hebrew University of Jerusalem, Israel This article was submitted to Pharmacology of Ion Channels and Channelopathies, a section of the journal Frontiers in Pharmacology ORCID: Shai Berlin, orcid.org/0000-0002-5153-4876; Reem Handklo-Jamal, orcid.org/0000-0001-6237-5412; Nathan Dascal, orcid.org/0000-0002-5397-4146; Daniel Yakubovich, orcid.org/0000-0003-2871-1026 Reviewed by: Michel Vivaudou, UMR5075 Institut de Biologie Structurale (IBS), France; David J. Adams, University of Wollongong, Australia Present addresses: Etay Artzy, Paragon Ltd., Even Yehuda, Israel; Uri Kahanovitch, Virginia Tech School of Neuroscience, Blacksburg, VA, United States |
ISSN: | 1663-9812 1663-9812 |
DOI: | 10.3389/fphar.2020.01216 |