Conformation of some acetylcholine analogs as solutes in deuterium oxide and other solvents

Conformation of ligands bound to the muscarinic acetylcholine receptor

Many biogenic amines evoke a variety of physiological responses by acting on G protein-coupled receptors. We have determined the conformation of two acetylcholine analogs, (S)-methacholine and (2S,4R,5S)-muscarine, bound to the M(2) muscarinic acetylcholine receptor (M(2) mAChR) by NMR spectroscopy. The analysis of the transferred nuclear Overhauser effect indicated that the receptor selectively recognized the conformers of (S)-methacholine and (2S,4R,5S)-muscarine with the gauche O-C2-C1-N dihedral angle at +60 degrees. This is distinct from the predominant conformations of these ligands in solution with O-C2-C1-N dihedral angle (+80 to approximately 85 degrees ) in the absence of the M(2) mAChR, as assessed by analyses of the coupling constants and nuclear Overhauser effect spectroscopy. We have also built a molecular model of the M(2) mAChR-(S)-methacholine complex, based on the X-ray crystallographic structure of rhodopsin. This model indicated that the conformation with the gauche O-C2-C1-N dihedral angle at +55.5 degrees, which is similar to the one determined by NMR measurement, is energetically favored in the binding of (S)-methacholine to the receptor. We suggest that this conformation represents the binding of the agonist to the M(2) mAChR in the absence of G protein.

Elucidation of the receptor-bound conformation of the enkephalins

The biologically relevant conformers of enkephalin predicted by solid state, solution state, and theoretical energy studies have been compared with the published structure-activity data on these compounds. No conformational technique proposes a model consistent with all the pharmacological data; the shortcomings of each approach are evaluated. An alternative approach, which correlates the structure-activity data of opiate compounds with that of the enkephalins, is described and shown to produce a model consistent with the available structure-activity data.

The characteristics of 'end-plate noise' produced by different depolarizing drugs

1. End-plate depolarization and associated ;membrane noise' due to decamethonium, acetylthiocholine and suberyldicholine have been examined and compared with the effects of acetylcholine and carbachol.2. The transient ionic channels resulting from the action of decamethonium and acetylthiocholine are of much shorter duration than those produced by acetylcholine. They are, therefore, similarly to carbachol channels, less effective in causing membrane depolarization.3. Suberyldicholine, on the other hand, produces ion channels whose duration exceeds that of acetylcholine.4. Lowering the temperature causes an increase in amplitude of the elementary potential change produced by decamethonium and acetylthiocholine.5. The relation between the characteristic features of drug-induced membrane noise and the underlying molecular reaction rates is discussed.

Conformational relationships between analogs of acetylcholine and those of local anesthetics in solution

Conformations of analogs of acetylcholine and of related local anesthetics, in which either of the oxygen atoms had been replaced by other heteroatoms, were studied in solution by nuclear magnetic resonance. Several correlations between structure and conformation could be made.