title: A structural model of the acetylcholine receptor channel based on partition energy and helix packing calculations.
abstract: A structural model of the transmembrane portion of the acetylcholine receptor was developed from sequences of all its subunits by using transfer energy calculations to locate transmembrane alpha-helices and to calculate which helical side chains should be in contact with water inside the channel, with portions of other transmembrane helices, or with lipid hydrocarbon chains. "Knobs-into-holes" side chain packing calculations were used with other factors to stack the transmembrane alpha-helices together. In the model each subunit has the following structures in order along the sequence from the NH2 terminus: a large extracellular domain of undetermined structure, a short apolar alpha-helix that lies on the extracellular lipid surface of the membrane; three apolar transmembrane alpha-helices (I, II, and III), a cytoplasmic domain of undetermined structure, an amphipathic transmembrane alpha-helix (L) that forms the channel lining, a short extracellular alpha-helix, another apolar transmembrane alpha-helix (IV), and a small cytoplasmic domain formed by the COOH-terminal end of the chain. Three concentric layers form the pore. A bundle of five amphipathic L helices forms the channel lining. This bundle is surrounded by a bundle of 10 alternating II and III helices. Helices I and IV cover portions of the outer surface of the bundle formed by helices II and III. Positions of disulfide bridges are predicted and a mechanism for opening and closing conformational changes is proposed that requires tilting transmembrane helices and possibly a thiol-disulfide interchange reaction.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D007473:Ion Channels / Q000502:physiology*; D046911:Macromolecular Substances; D008958:Models, Molecular; D008961:Models, Structural; D011487:Protein Conformation; D011978:Receptors, Nicotinic / Q000502:physiology*
chemical_list: D007473:Ion Channels; D046911:Macromolecular Substances; D011978:Receptors, Nicotinic