A stereochemical test of a proposed structural feature of the nicotinic acetylcholine receptor.

Understanding the gating mechanism of the nicotinic acetylcholine receptor (nAChR) and similar channels constitutes a significant challenge in chemical neurobiology. In the present work, we use a stereochemical probe to evaluate a proposed pin-into-hydrophobic socket mechanism for the alphaVal46 side chain of the nAChR. Utilizing nonsense suppression methodology we incorporated isoleucine (Ile), O-methyl threonine (Omt) and threonine (Thr) as well as their side chain epimers (the allo counterparts). Surprisingly, our results indicate that only the pro-S methyl group of the alphaVal46 side chain is sensitive to changes in hydrophobicity, consistent with the precise geometrical requirements of the pin-into-socket mechanism.