omega-Conotoxin GVIA receptors of Discopyge electric organ. Characterization of omega-conotoxin binding to the nicotinic acetylcholine receptor.
A peptide toxin from a Conus marine snail, omega-conotoxin GVIA (omega-CgTx) has been used extensively as a probe for certain types of neuronal calcium channels. It is often assumed that omega-CgTx interacts with Ca2+ channels exclusively. We have tested this assumption in a study of omega-CgTx-binding sites in the electric organ of Discopyge ommata. Synaptosomal membranes from this tissue contain low affinity omega-CgTx receptor sites (Kd = 0.6 microM) in great abundance (280 pmol/mg of protein), as first reported by Ahmad and Miljanich (Ahmad, S. N., and Miljanich, G.P. (1988) Brain Res. 453, 247-256). However, we find that a large majority of these omega-CgTx-binding sites co-purify with the nicotinic acetylcholine receptor (nAChR) and can be immunoprecipitated by monoclonal antibodies generated against the nAChR of Torpedo. Cross-linking experiments with radiolabeled omega-CgTx show pronounced specific labeling of the alpha-subunit of the nAChR but not other subunits. Specific omega-CgTx binding to the nAChR is reduced by millimolar Ca2+ but not by alpha- or kappa-bungarotoxin, alpha-conotoxin, or carbamylcholine. Cross-linking experiments also reveal omega-CgTx-binding proteins of 170 and 60 kDa. The characteristics of the 170-kDa protein make it a likely candidate for the alpha 1-subunit of an N-type Ca2+ channel.
Horne
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WA
Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Beckman Center, California 94305.
Hawrot
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E
Tsien
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D000345:Affinity Labels; D000818:Animals; D001665:Binding Sites; D015220:Calcium Channels / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004557:Electric Organ / Q000378:metabolism*; D066298:In Vitro Techniques; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000378:metabolism*; D012908:Snails; D013574:Synaptosomes / Q000378:metabolism; D014101:Torpedo; D020866:omega-Conotoxin GVIA
D000345:Affinity Labels; D015220:Calcium Channels; D009419:Nerve Tissue Proteins; D010456:Peptides, Cyclic; D011978:Receptors, Nicotinic; D020866:omega-Conotoxin GVIA