Previously, we showed the activation of a Class A GPCR (Cannabinoid CB2 receptor) by its endogenous ligand, 2-arachidonoylglycerol (2-AG) via the lipid bilayer using all-atom molecular dynamics simulations (Hurst et al., 2010). Agonist binding to an inactive receptor results in GPCR activation and begins the signaling cascade via the G protein pathway. To understand the next step in this signaling cascade, we studied G protein activation by an activated GPCR. In this step, GDP is released via the separation of the Gai1 ras-like and helical domains of (Van Eps et al., 2011). To this end, we used our 2-AG activated CB2 model to produce an initial 2-AG/CB2/Gai1�1?2 complex based on the crystal structure of �2 adrenoreceptor in complex with Gas�1?2 (Rasmussen et al., 2011). The complex was immersed in a fully hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer and NPT NAMD (Phillips et al., 2005) molecular dynamics (MD) simulations were initiated for four different trajectories of this system. Results from our 3.5�s long MD simulation suggest that the C terminal a5 helix of Gai prefers a different orientation in the CB2 activated receptor relative to the orientation seen in the empty state (GDP-GTP less) �2 adrenoreceptor/Gas�1?2 complex. During the first 0.5�s of our simulation, hydrophobic interactions between intracellular loop 2 (IC-2 loop) on CB2 (P139) and a hydrophobic pocket on Gai consisting of residues on the N terminus (V34); C terminus (F336, T340, I343 and I344); �1-sheet (L194); and �2-sheet (F196) stabilize the receptor / Gai1 protein interface and the electrostatic interactions between intracellular loop 3 (IC-3 loop) on CB2 (R229) and the a4 helix on Gai1 (Q304/E308) facilitate hydration of GDP later, between 1.4 - 1.6 �s. [Support: RO1 DA003934 and KO5 DA021358 (PHR)]

Molecular dynamics simulations of the activated cannabinoid CB2 receptor in complex with the inhibitory Gai1�1?2 protein

247th National Meeting (2014)

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