Dynamics and orientation of N+(CD3)(3)-bromoacetylcholine bound to its binding site on the nicotinic acetylcholine receptor

Dynamic and structural information has been obtained for an analogue of ace tylcholine while bound to the agonist binding site on the nicotinic acetylc holine receptor (nAcChoR), using wide-line deuterium solid-state NMR, Analy sis of the deuterium lineshape obtained at various temperatures from unorie nted nAcChoR membranes labeled with deuterated bromoacetylcholine (BAC) sho wed that the quaternary ammonium group of the ligand is well constrained wi thin the agonist binding site when compared with the dynamics observed in t he crystalline solids. This motional restriction would suggest that a high degree of complementarity exists between the quaternary ammonium group of t he ligand and the protein within the agonist binding site. nAcChoR membrane s were uniaxially oriented by isopotential centrifugation as determined by phosphorous NMR of the membrane phospholipids. Analysis of the deuterium NM R lineshape of these oriented membranes enriched with the nAcChoR labeled w ith N+(CD3)(3)-BAC has enabled us to determine that the angle formed betwee n the quaternary ammonium group of the BAC and the membrane normal is 42 de grees in the desensitized form of the receptor. This measurement allows us to orient in part the bound ligand within the proposed receptor binding sit e.