Received for publication September 12, 2007.
Revised March 13, 2008.
Accepted for publication March 13, 2008.

A Role for Leu118 of Loop E in Agonist Binding to the 7 Nicotinic Acetylcholine Receptor

Abstract

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels mediating fast cholinergic synaptic transmission in the brain and at neuromuscular junctions. We used the structure of the acetylcholine binding protein (AChBP) from Lymnaea stagnalis, to model the chicken 7 agonist-binding domain. The initial models and a preliminary docking study suggested that position L118 may play an important role in determining agonist actions on 7. A prediction from these in silico studies, that L118E and L118D would retain binding to acetylcholine, but L118K and L118R would not, was confirmed in electrophysiological studies on functional recombinant mutant receptors expressed in Xenopus laevis oocytes. The functional studies also demonstrated that residues at position 118 can have a dramatic effect on the actions of imidacloprid (a partial agonist of wild-type 7 receptors) and its des-nitro derivative. Molecular Dynamics simulations indicate that L118 can strongly influence the behaviour of the binding pocket and that the model is robust in terms of its prediction for acetylcholine binding. Together, the results indicate that L118 is influential on the binding properties and selectivity of nAChR agonists.

Key words: Nicotinic cholinergic, Molecular dynamics, Func. analysis receptor/ion channel mutants, Mutagenesis/Chimeric approaches, Receptor binding studies