Fig. 6.

Agonist promotes the activation of Gi protein by inducing opening of the Gαi subunit. Gi protein activation mediated by (A) morphine binding to pre-activated μOR-Gi protein complex, (B) MP1104 binding to pre-activated κOR-Gi protein complex and (C) DPI-287 binding to pre-activated δOR-Gi protein complex. Overall, we performed an aggregate ~1.1 μs metaMD simulations to evaluate the energetics relevant to opening the Gαi subunit from its GDP binding site. For these free energy calculations, the collective variable was the distance between the AH domain (the centre of mass of the Cα atoms for the residues 147–181) and the Ras-like domain (the centre of mass of the Cα atoms for the residues 42–59), which define the GDP binding site. The weighted averages and the standard deviations were calculated for the converged period between the initial configuration before metaMD ‘i’ and the final conformation ‘f’ after metaMD calculations.