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Neutron diffraction augmented with hydrogen isotope substitution has been used to examine the water structure around the acetylcholine molecular ion in aqueous solution. It is shown that the nearest-neighbor water molecules in the region around the trimethylammonium headgroup are located either in a ring around the central nitrogen atom or between the carbon atoms, forming a sheath around the onium group. Moreover the water molecules in this cavity do not bond to the onium group but rather form hydrogen bonds with water molecules in the surrounding aqueous environment. Given that in the bound state the onium headgroup must be completely desolvated, the absence of bonding between the onium headgroup and the surrounding water solvent may be selectively favorable to acetylcholine-binding in the receptor site. Away from the headgroup, pronounced hydrogen-bonding of water to the carbonyl oxygen is observed, but not to the ether oxygen in the acetylcholine chain.

Original publication

DOI

10.1529/biophysj.106.089185

Type

Journal article

Journal

Biophys J

Publication Date

15/09/2006

Volume

91

Pages

2371 - 2380

Keywords

Acetylcholine, Computer Simulation, Hydrogen Bonding, Models, Molecular, Neutron Diffraction, Onium Compounds, Protein Conformation, Solutions, Water