NMR structural analysis of alpha-bungarotoxin and its complex with the principal alpha-neurotoxin-binding sequence on the alpha 7 subunit of a neuronal nicotinic acetylcholine receptor.
We report a new, higher resolution NMR structure of alpha-bungarotoxin that defines the structure-determining disulfide core and beta-sheet regions. We further report the NMR structure of the stoichiometric complex formed between alpha-bungarotoxin and a recombinantly expressed 19-mer peptide ((178)IPGKRTESFYECCKEPYPD(196)) derived from the alpha7 subunit of the chick neuronal nicotinic acetylcholine receptor. A comparison of these two structures reveals binding-induced stabilization of the flexible tip of finger II in alpha-bungarotoxin. The conformational rearrangements in the toxin create an extensive binding surface involving both sides of the alpha7 19-mer hairpin-like structure. At the contact zone, Ala(7), Ser(9), and Ile(11) in finger I and Arg(36), Lys(38), Val(39), and Val(40) in finger II of alpha-bungarotoxin interface with Phe(186), Tyr(187), Glu(188), and Tyr(194) in the alpha7 19-mer underscoring the importance of receptor aromatic residues as critical neurotoxin-binding determinants. Superimposing the structure of the complex onto that of the acetylcholine-binding protein (1I9B), a soluble homologue of the extracellular domain of the alpha7 receptor, places alpha-bungarotoxin at the peripheral surface of the inter-subunit interface occluding the agonist-binding site. The disulfide-rich core of alpha-bungarotoxin is suggested to be tilted in the direction of the membrane surface with finger II extending into the proposed ligand-binding cavity.
Moise
Leonard
L
Department of Molecular Pharmacology, Brown University, Providence, Rhode Island 02912, USA.
Piserchio
Andrea
A
Basus
Vladimir J
VJ
Hawrot
Edward
E
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D002038:Bungarotoxins / Q000737:chemistry* / Q000378:metabolism; D002645:Chickens; D004220:Disulfides; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D000596:Amino Acids; D002038:Bungarotoxins; D004220:Disulfides; D008024:Ligands; D010455:Peptides; D011978:Receptors, Nicotinic