Experimentally based model of a complex between a snake toxin and the alpha 7 nicotinic receptor.
To understand how snake neurotoxins interact with nicotinic acetylcholine receptors, we have elaborated an experimentally based model of the alpha-cobratoxin-alpha7 receptor complex. This model was achieved by using (i) a three-dimensional model of the alpha7 extracellular domain derived from the crystallographic structure of the homologous acetylcholine-binding protein, (ii) the previously solved x-ray structure of the toxin, and (iii) nine pairs of residues identified by cycle-mutant experiments to make contacts between the alpha-cobratoxin and alpha7 receptor. Because the receptor loop F occludes entrance of the toxin binding pocket, we submitted this loop to a dynamics simulation and selected a conformation that allowed the toxin to reach its binding site. The three-dimensional structure of the toxin-receptor complex model was validated a posteriori by an additional double-mutant experiment. The model shows that the toxin interacts perpendicularly to the receptor axis, in an equatorial position of the extracellular domain. The tip of the toxin central loop plugs into the receptor between two subunits, just below the functional receptor loop C, the C-terminal tail of the toxin making adjacent additional interactions at the receptor surface. The receptor establishes major contacts with the toxin by its loop C, which is assisted by principal (loops A and B) and complementary (loops D, F, and 1) functional regions. This model explains the antagonistic properties of the toxin toward the neuronal receptor and opens the way to the design of new antagonists.
Fruchart-Gaillard
Carole
C
Commissariat à l'Energie Atomique, Département d'Ingénierie et d'Etudes des Protéines, 91191 Gif-sur-Yvette Cedex, France.
Gilquin
Bernard
B
Antil-Delbeke
Stephanie
S
Le Novère
Nicolas
N
Tamiya
Toru
T
Corringer
Pierre-Jean
PJ
Changeux
Jean-Pierre
JP
Ménez
André
A
Servent
Denis
D
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D003039:Cobra Neurotoxin Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003198:Computer Simulation; D017815:Elapidae; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017434:Protein Structure, Tertiary; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000378:metabolism; D064569:alpha7 Nicotinic Acetylcholine Receptor
C579167:Chrna7 protein, human; D003039:Cobra Neurotoxin Proteins; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C025154:alpha-cobratoxin