A model system for understanding cellular signaling of the cannabinoid CB2 receptor via the inhibitory Gi protein

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Jagjeet Singh (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site: http://library.uncg.edu/
Patricia Reggio

Abstract: One key signaling pathway in the cellular signaling involving G protein coupled receptors (GPCR) is via heterotrimeric G proteins. The first step in GPCR/G protein signaling is the activation of a GPCR by the ligand binding and the next step is the activation of the G protein. Understanding the molecular mechanism behind the GPCR/G protein interactions will help in characterizing this important signaling pathway and should ultimately lead to the design of functionally selective ligands for this larger class of receptors. Earlier, the Reggio group used molecular dynamics simulations to study the activation of the cannabinoid CB2 receptor, a class A GPCR, by its endogenous ligand, 2-arachidonoylglycerol (2-AG) via the lipid bilayer. The goal of the current project was to study the next step in the G-protein mediated signal transduction, when an agonist activated CB2 receptor forms a complex with Gi protein and catalyzes the activation of Gi protein, releasing the guanosine diphosphate (GDP) bound between the ras-like (also known as GTPase domain) and helical domains of the Gá protein. To this end, we report here the CB2 / Gái1â1ã2 complex formation using our 2-AG activated CB2 receptor model. For G protein activation (dissociation of GDP), we hypothesized that GDP release from the ras-like and helical domains of Gái would be triggered by the hydration of GDP. We probed the role of the CB2 receptor interactions with the Gái protein and the resultant progression of GDP hydration. We have seen the number of waters surrounding GDP increase from 16 (t= 0 ns) to 28 waters (t=5 ìs). Two important interactions between the receptor and G-protein appear to lead to the increased hydration of GDP. (1) A hydrophobic interaction occurred between CB2 IC2 loop residue P139 and the Gái hydrophobic pocket residues: V34 (N terminus; L194 (â1 sheet); F196 (â2 sheet); and, F336, T340, I343, I344 (á5 helix) multiple times in our 5 ìs long trajectory. Each time this interaction occurred, an increase in GDP hydration was observed in our simulation. 2) We also observed an IC3 loop interaction with the Gái á4 helix between 1.4 to 1.6 ìs, in which the IC3 loop residue R229 reached to interact with E297 and E298. Taken together, our results show that the intracellular loops play a critical role in the hydration of GDP that should lead to G protein activation.

Additional Information

Language: English
Date: 2014
Cellular signaling, Cannabinoid CB2 receptor
G proteins $x Receptors
Cannabinoids $x Receptors

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