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Characterization of the omega-conotoxin target. Evidence for tissue-specific heterogeneity in calcium channel types
Abstract:
omega-Conotoxin GVIA (omega-CgTx-VIA) is a 27 amino acid peptide from the venom of the fish-hunting snail, Conus geographus, that blocks voltage-activated Ca channels. The characterization of a biologically active, homogeneous 125I-labeled monoiodinated Tyr22 derivative of omega-conotoxin GVIA and its use in binding and cross-linking studies are described. The 125I-labeled toxin is specifically cross-linked to a receptor protein with an apparent Mr of 135,000. The stoichiometry between omega-conotoxin and nitrendipine binding sites in different chick tissues was determined. Skeletal muscle has a high concentration of [3H]nitrendipine binding sites (greater than 1000 fmol/mg) but no detectable omega-conotoxin sites (less than 7 fmol/mg). Brain microsomes have both binding sites, but omega-conotoxin targets are in excess. These results, combined with recent electrophysiological studies (E. W. McCleskey, A. P. Fox, D. Feldman, L. J. Cruz, B. M. Olivera, R. W. Tsien, and D. Yoshikami, unpublished results), define four types of Ca channels in chick tissues, N, T, Ln (omega sensitive), and Lm (omega insensitive), and are consistent with the hypothesis that the alpha-subunits of certain neuronal Ca2+ channels (Ln, N) are the molecular targets of omega-conotoxin GVIA.
Insights
Omega-conotoxin GVIA (omega-CgTx-VIA), a snail venom peptide, blocks specific calcium channels. This study identifies its receptor and characterizes distinct calcium channel types in chick tissues.
Area of Science:
- Neuropharmacology
- Molecular Biology
- Biochemistry
Background:
- Omega-conotoxin GVIA (omega-CgTx-VIA) is a peptide from Conus geographus venom.
- It is known to block voltage-activated calcium (Ca) channels.
Purpose of the Study:
- To characterize a labeled omega-CgTx-VIA derivative for binding and cross-linking studies.
- To investigate the molecular targets and distribution of omega-CgTx-VIA binding sites in chick tissues.
- To define different types of Ca channels based on omega-CgTx-VIA sensitivity.
Main Methods:
- Preparation and characterization of 125I-labeled monoiodinated Tyr22 derivative of omega-CgTx-VIA.
- Binding assays using [3H]nitrendipine.
- Cross-linking studies to identify receptor proteins.
- Quantification of binding sites in different chick tissues (skeletal muscle, brain microsomes).
Main Results:
- A biologically active, homogeneous 125I-labeled omega-CgTx-VIA derivative was prepared.
- The toxin specifically cross-linked to a 135,000 Mr receptor protein.
- Skeletal muscle showed high nitrendipine binding but no detectable omega-CgTx-VIA sites.
- Brain microsomes had both binding sites, with omega-conotoxin targets in excess.
- Four Ca channel types (N, T, Ln, Lm) were defined in chick tissues.
- Results support omega-CgTx-VIA targeting alpha-subunits of neuronal Ca2+ channels (Ln, N).
Conclusions:
- Omega-conotoxin GVIA targets specific neuronal calcium channels.
- Distinct distributions of omega-conotoxin and nitrendipine binding sites suggest differential Ca channel expression.
- The study provides molecular insights into Ca channel subtypes and their interaction with omega-conotoxin GVIA.