title: Probing the effects of residues located outside the agonist binding site on drug-receptor selectivity in the nicotinic receptor.
abstract: The nicotinic acetylcholine receptors (nAChRs) are a family of closely related but pharmacologically distinct neurotransmitter-gated ion channels. They are therapeutic targets for a wide range of neurological disorders, and a key issue in drug development is selective targeting among the more than 20 subtypes of nAChRs that are known. The present work evaluates a proposed hydrogen bonding interaction involving a residue known as the "loop B glycine" that distinguishes receptors that are highly responsive to ACh and nicotine from those that are much less so. We have performed structure-function studies on the loop B site, including unnatural amino acid mutagenesis, in three different nAChR subtypes and found that the correlation between agonist potency and this residue is strong. Low potency receptor subtypes have a glycine at this key site, and mutation to a residue with a side chain converts a low potency receptor to a high potency receptor. Innately high potency receptors have a lysine at the loop B site and show a decrease in potency for the reverse mutation (i.e., introducing a glycine). This residue lies outside of the agonist binding site, and studies of other residues at the agonist binding site show that the details of how changes at the loop B glycine site impact agonist potency vary for differing receptor subtypes. This suggests a model in which the loop B residue influences the global shape of the agonist binding site rather than modulating any specific interaction.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, 164-30, Pasadena, CA 91125, USA.
authors.forename: Nyssa L
authors.initials: NL
authors.lastname: Puskar
authors.forename: Henry A
authors.initials: HA
authors.lastname: Lester
authors.forename: Dennis A
authors.initials: DA
authors.lastname: Dougherty
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D005998:Glycine / Q000737:chemistry; D006860:Hydrogen Bonding; D008195:Lymnaea / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018722:Nicotinic Agonists / Q000737:chemistry* / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D005998:Glycine