Microscopic binding of M5 muscarinic acetylcholine receptor with antagonists by homology modeling, molecular docking, and molecular dynamics simulation.

By performing homology modeling, molecular docking, and molecular dynamics (MD) simulations, we have developed three-dimensional (3D) structural models of the M5 muscarinic acetylcholine receptor (mAChR) and two complexes for M5 mAChR binding with antagonists SVT-40776 and solifenacin in the environment of lipid bilayer and solvent water. According to the simulated results, each of the antagonists is oriented horizontally in the binding pocket formed by transmembrane helices 2, 3, and 5-7. The cationic headgroup of each of the antagonists interacts with a negatively charged residue, Asp110, through electrostatic and hydrogen-bonding interactions. The simulated results also reveal some significant difference between the binding modes of SVT-40776 and solifenacin. In particular, SVT-40776 is persistently hydrogen bonded with the side chain of residue Tyr458, whereas solifenacin cannot form a similar hydrogen bond with residues around its carbonyl group. Such significant difference in the binding structures is consistent with the fact that SVT-40776 has a much higher binding affinity (K(d) = 0.4 nM) to M5 mAChR than that of solifenacin (K(d) = 31 nM) with the same reeptor. The calculated binding free energy change (-2.3 ± 0.3 kcal/mol) from solifenacin to SVT-40776 is in good agreement with the experimentally derived binding free energy change (-2.58 kcal/mol), suggesting that our modeled M5 mAChR structure and its complexes with the antagonists are reliable. The new structural insights obtained from this computational study are expected to stimulate further biochemical and pharmacological studies on the detailed structures of M5 and other subtypes of mAChRs.