Homology modeling and dynamics of the extracellular domain of rat and human neuronal nicotinic acetylcholine receptor subtypes alpha4beta2 and alpha7.

In recent years, it has become clear that the neuronal nicotinic acetylcholine receptor (nAChR) is a valid target in the treatment of a variety of diseases, including Alzheimer's disease, anxiety, and nicotine addiction. As with most membrane proteins, information on the three-dimensional (3D) structure of nAChR is limited to data from electron microscopy, at a resolution that makes the application of structure-based design approaches to develop specific ligands difficult. Based on a high-resolution crystal structure of AChBP, homology models of the extracellular domain of the neuronal rat and human nAChR subtypes alpha4beta2 and alpha7 (the subtypes most abundant in brain) were built, and their stability assessed with molecular dynamics (MD). All models built showed conformational stability over time, confirming the quality of the starting 3D model. Lipophilicity and electrostatic potential studies performed on the rat and human alpha4beta2 and alpha7 nicotinic models were compared to AChBP, revealing the importance of the hydrophobic aromatic pocket and the critical role of the alpha-subunit Trp-the homolog of AChBP-Trp 143-for ligand binding. The models presented provide a valuable framework for the structure-based design of specific alpha4beta2 nAChR subtype ligands aimed at improving therapeutic and diagnostic applications.