title: Pairwise interactions between neuronal alpha(7) acetylcholine receptors and alpha-conotoxin PnIB.
abstract: This work uses alpha-conotoxin PnIB to probe the agonist binding site of neuronal alpha(7) acetylcholine receptors. We mutated the 13 non-cysteine residues in CTx PnIB, expressed alpha(7)/5-hydroxytryptamine-3 homomeric receptors in 293 HEK cells, and measured binding of each mutant toxin to the expressed receptors by competition against the initial rate of (125)I-alpha-bungarotoxin binding. The results reveal that residues Ser-4, Leu-5, Pro-6, Pro-7, Ala-9, and Leu-10 endow CTx PnIB with affinity for alpha(7)/5-hydroxytryptamine-3 receptors; side chains of these residues cluster in a localized region within the three-dimensional structure of CTx PnIB. We next mutated key residues in the seven loops of alpha(7) that converge at subunit interfaces to form the agonist binding site. The results reveal predominant contributions by residues Trp-149 and Tyr-93 in alpha(7) and smaller contributions by Ser-34, Arg-186, Tyr-188, and Tyr-195. To identify pairwise interactions that stabilize the receptor-conotoxin complex, we measured binding of receptor and toxin mutations and analyzed the results by double mutant cycles. The results reveal a single dominant interaction between Leu-10 of CTx PnIB and Trp-149 of alpha(7) that anchors the toxin to the binding site. We also find weaker interactions between Pro-6 of CTx PnIB and Trp-149 and between both Pro-6 and Pro-7 and Tyr-93 of alpha(7). The overall results demonstrate that a localized hydrophobic region in CTx PnIB interacts with conserved aromatic residues on one of the two faces of the alpha(7) binding site.
authors.affiliation: Receptor Biology Laboratory, Department of Physiology and Biophysics Mayo Foundation, Rochester, Minnesota 55905, USA.
authors.forename: P A
authors.initials: PA
authors.lastname: Quiram
authors.forename: J M
authors.initials: JM
authors.lastname: McIntosh
authors.forename: S M
authors.initials: SM
authors.lastname: Sine
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002460:Cell Line; D018680:Cholinergic Antagonists / Q000378:metabolism*; D020916:Conotoxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009474:Neurons / Q000378:metabolism*; D011485:Protein Binding; D011950:Receptors, Cholinergic / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D018680:Cholinergic Antagonists; D020916:Conotoxins; D011950:Receptors, Cholinergic; C089039:alpha-conotoxin PnIB