Hydrophobic Ligand Entry and Exit Pathways of the CB1 Cannabinoid Receptor.
It has been reported that some hydrophobic ligands of G-protein-coupled receptors access the receptors binding site from the membrane rather than from bulk water. In order to identify the most probable ligand entrance pathway into the CB1 receptor, we performed several steered molecular dynamics (SMD) simulations of two CB1 agonists, THC and anandamide, pulling them from the receptors binding site with constant velocity. The four main directions of ligand pulling were probed between helices TM4 and TM5, between TM5 and TM6, between TM7 and TM1TM2, and toward the bulk water. The smallest forces were measured during pulling between TM7 and TM1TM2. We also performed supervised molecular dynamics (SuMD) simulations for both anandamide and THC entering the CB1 receptors binding site and found the same pathway as in the pulling simulations. The residues F174