Molecular Dynamics Simulations of the Activated Cannabinoid Receptor Subtype 2/Gi Protein Complex

The cannabinoid receptor subtype 2 (CB2) is a class A (rhodopsin-like) G-protein-coupled receptor (GPCR) that is highly expressed in the immune system (Galiegue et al., 1995) and signals via Gi proteins (Glass and Northup, 1999). The GPCR signaling cascade begins with agonist binding to an inactive receptor, causing conformational changes that activate the receptor. In previous work, we used molecular dynamics simulations to study the activation of the CB2 receptor, by the endogenous ligand, 2-arachidonoylglycerol (2-AG) via the lipid bilayer (Hurst et al., 2010). In work described here, we used our 2-AG activated CB2 model to produce an initial 2-AG/CB2/Gαi1β1γ2 assembly based on the crystal structure of β2 adrenoreceptor in complex with Gαsβ1γ2 (Rasmussen et al., 2011). Here, the G protein was located underneath CB2, but not inserted into CB2. The 2-AG/CB2/Gαi1β1γ2 assembly was then immersed in a fully hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer and NPT NAMD (Phillips et al., 2005) molecular dynamics simulations were initiated for four different makes of this system. Initial dynamics (50ns - 150ns) suggests that the C-terminus of Gαi (last 11 residues on α5 helix I344 to F354) inserts itself into the intracellular opening of the CB2 activated receptor at an altered angle compared to the β2 adrenoreceptor/Gαsβ1γ2 complex. The distance between intracellular ends of CB2 TMH3 and TMH6 increases relative to the 2-AG/CB2 complex, suggesting the first step in the formation of the 2-AG/CB2/Gαi1β1γ2 complex. [Support: RO1 DA003934 and KO5 DA021358 (PHR)]