title: Dissecting the chemistry of nicotinic receptor-ligand interactions with infrared difference spectroscopy.
abstract: The physical interactions that occur between the nicotinic acetylcholine receptor from Torpedo and the agonists carbamylcholine and tetramethylamine have been studied using both conventional infrared difference spectroscopy and a novel double-ligand difference technique. The latter was developed to isolate vibrational bands from residues in a membrane receptor that interact with individual functional groups on a small molecule ligand. The binding of either agonist leads to an increase in vibrational intensity at frequencies centered near 1663, 1655, 1547, 1430, and 1059 cm(-1) indicating that both induce a conformational change from the resting to the desensitized state. Vibrational shifts near 1580, 1516, 1455, 1334, and between 1300 and 1400 cm(-1) are assigned to structural perturbations of tyrosine and possibly both tryptophan and charged carboxylic acid residues upon the formation of receptor-quaternary amine interactions, with the relatively intense feature near 1516 cm(-1) indicating a key role for tyrosine. Other vibrational bands suggest the involvement of additional side chains in agonist binding. Two side-chain vibrational shifts from 1668 and 1605 cm(-1) to 1690 and 1620 cm(-1), respectively, could reflect the formation of a hydrogen bond between the ester carbonyl of carbamylcholine and an arginine residue. The results demonstrate the potential of the double-ligand difference technique for dissecting the chemistry of membrane receptor-ligand interactions and provide new insight into the nature of nicotinic receptor-agonist interactions.
authors.affiliation: Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Ryan
authors.forename: Danny G
authors.initials: DG
authors.lastname: Hill
authors.forename: John E
authors.initials: JE
authors.lastname: Baenziger
mesh_terms: D000588:Amines / Q000737:chemistry; D000818:Animals; D001120:Arginine; D004952:Esters / Q000737:chemistry; D006860:Hydrogen Bonding; D008024:Ligands; D008956:Models, Chemical; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000378:metabolism*; D014101:Torpedo / Q000235:genetics / Q000378:metabolism; D014867:Water / Q000737:chemistry
chemical_list: D000588:Amines; D004952:Esters; D008024:Ligands; D011978:Receptors, Nicotinic; D014867:Water; D001120:Arginine