Modeling subtype-selective agonists binding with alpha 4 beta 2 and alpha 7 nicotinic acetylcholine receptors: Effects of local binding and long-range electrostatic interactions

摘要

The subtype-selective binding of 14 representative agonists with alpha 4 beta 2 and alpha 7 nicotinic acetylcholine receptors (nAChRs) has been studied by performing homology modeling, molecular docking, geometry optimizations, and microscopic and phenomenological binding free energy calculations. All of the computational results demonstrate that the subtype selectivity of the agonists binding with alpha 4 beta 2 and alpha 7 nAChRs is affected by both local binding and long-range electrostatic interactions between the receptors and the protonated structures of the agonists. The effects of the long-range electrostatic interactions are mainly due to the distinct difference in the net charge of the ligand-binding domain between the two nAChR subtypes. For the alpha 4 beta 2-selective agonists examined, the microscopic binding modes with the alpha 4 beta 2 nAChR are very similar to the corresponding modes with the alpha 7 nAChR, and therefore, the subtype selectivity of these agonists binding with alpha 4 beta 2 and alpha 7 nAChRs is dominated by the long-range electrostatic interactions. For the alpha 7-selective agonists, their microscopic binding modes with the alpha 7 nAChR are remarkably different from those with the alpha 4 beta 2 nAChR so that the local binding (including the hydrogen bonding and cation-pi interactions) with the alpha 7 nAChR is much stronger than that with the alpha 4 beta 2 nAChR. The calculated phenomenological binding free energies are in good agreement with available experimental data for the relative binding free energies concerning the subtype selectivity of agonists binding with the two different nAChR subtypes. The fundamental insights obtained in the present study should be valuable for future rational design of potential therapeutic agents targeted to specific nAChR subtypes.