"Weak toxin" from Naja kaouthia is a nontoxic antagonist of alpha 7 and muscle-type nicotinic acetylcholine receptors.
A novel "weak toxin" (WTX) from Naja kaouthia snake venom competes with [(125)I]alpha-bungarotoxin for binding to the membrane-bound Torpedo californica acetylcholine receptor (AChR), with an IC(50) of approximately 2.2 microm. In this respect, it is approximately 300 times less potent than neurotoxin II from Naja oxiana and alpha-cobratoxin from N. kaouthia, representing short-type and long-type alpha-neurotoxins, respectively. WTX and alpha-cobratoxin displaced [(125)I]alpha-bungarotoxin from the Escherichia coli-expressed fusion protein containing the rat alpha7 AChR N-terminal domain 1-208 preceded by glutathione S-transferase with IC(50) values of 4.3 and 9.1 microm, respectively, whereas for neurotoxin II the IC(50) value was >100 microm. Micromolar concentrations of WTX inhibited acetylcholine-activated currents in Xenopus oocyte-expressed rat muscle AChR and human and rat alpha7 AChRs, inhibiting the latter most efficiently (IC(50) of approximately 8.3 microm). Thus, a virtually nontoxic "three-fingered" protein WTX, although differing from alpha-neurotoxins by an additional disulfide in the N-terminal loop, can be classified as a weak alpha-neurotoxin. It differs from the short chain alpha-neurotoxins, which potently block the muscle-type but not the alpha7 AChRs, and is closer to the long alpha-neurotoxins, which have comparable potency against the above-mentioned AChR types.
Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 16/10 Miklukho-Maklaya Str., V-437 Moscow GSP-7, 117997 Russia.
Y N
YN
Utkin
V V
VV
Kukhtina
E V
EV
Kryukova
F
F
Chiodini
D
D
Bertrand
C
C
Methfessel
V I
VI
Tsetlin
D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D002038:Bungarotoxins / Q000493:pharmacokinetics; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D003001:Cloning, Molecular; D003039:Cobra Neurotoxin Proteins / Q000494:pharmacology; D004546:Elapid Venoms / Q000737:chemistry / Q000494:pharmacology*; D017815:Elapidae; D004926:Escherichia coli; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008958:Models, Molecular; D018482:Muscle, Skeletal / Q000502:physiology*; D009498:Neurotoxins / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D011487:Protein Conformation; D051381:Rats; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000502:physiology; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*; D011994:Recombinant Proteins / Q000493:pharmacokinetics; D014101:Torpedo; D014982:Xenopus laevis; D064569:alpha7 Nicotinic Acetylcholine Receptor
D002038:Bungarotoxins; C579167:Chrna7 protein, human; C579165:Chrna7 protein, rat; D003039:Cobra Neurotoxin Proteins; D004546:Elapid Venoms; D009498:Neurotoxins; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic; D011994:Recombinant Proteins; C428174:Weak toxin, Naja; D064569:alpha7 Nicotinic Acetylcholine Receptor; C025154:alpha-cobratoxin