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α-Conotoxin SI is a 13-amino-acid disulfide-rich peptide from the venom of Conus striatus. It is a competitive antagonist of muscle-type nicotinic acetylcholine receptors and is widely used to study neuromuscular nAChR pharmacology, receptor-binding-site differences, and α-conotoxin structure–activity relationships.
α-Conotoxin SI contains two native disulfide bonds, Cys2–Cys7 and Cys3–Cys13, together with C-terminal amidation.
α-Conotoxin SI Product Information
| Property | Information |
|---|---|
| Product Name | α-Conotoxin SI |
| CAS No. | 115797-06-3 |
| Sequence | ICCNPACGPKYSC-NH₂ |
| Length | 13 amino acids |
| Molecular Formula | C₅₅H₈₄N₁₆O₁₆S₄ |
| Molecular Weight | 1353.61 Da |
| C-Terminus | Amide |
| Disulfide Bonds | Cys2–Cys7; Cys3–Cys13 |
| Cysteine Framework | CC–C–C |
| Subclass | α3/5 |
| Natural Source | Conus striatus |
| Primary Target | Muscle-type nAChRs |
| Form | Lyophilized peptide |
| Purity | According to selected product specification |
Product Overview
α-Conotoxin SI is structurally related to GI, MI, and SIA but exhibits a distinct receptor-binding profile.
Studies comparing SI, GI, and MI demonstrated that relatively minor sequence differences can alter recognition of the two agonist-binding interfaces within muscle-type nAChRs. In particular, SI behaves differently from GI and MI in its ability to discriminate between receptor-binding sites.
This makes SI useful not only as an nAChR inhibitor but also as a comparative molecular probe for understanding how α-conotoxin loop sequences encode receptor selectivity.
Biological Activity & Target
UniProt identifies α-Conotoxin SI as an inhibitor of muscle nAChRs, with reported activity against both adult and fetal muscle receptor subtypes.
| Research Property | Description |
|---|---|
| Target | Muscle-type nAChRs |
| Mechanism | Competitive antagonist |
| Functional Effect | Inhibition of acetylcholine-mediated receptor activation |
| Research Value | Comparison of nAChR agonist-binding interfaces |
Structural Features
Sequence:
ICCNPACGPKYSC-NH₂
Native disulfide topology:
Cys2–Cys7
Cys3–Cys13
Controlled synthesis studies have shown that the same amino-acid sequence can form multiple possible disulfide regioisomers, while native SI uses the Cys2–Cys7 / Cys3–Cys13 arrangement.
Alan Scientific Technical View: For α-Conotoxin SI, correct disulfide pairing is a structural identity attribute, not merely an optional secondary quality parameter.
Research Applications
| Application | Typical Use |
|---|---|
| Muscle nAChR Research | Functional receptor inhibition |
| Electrophysiology | Measurement of nAChR-mediated currents |
| Binding-Site Studies | Comparison of agonist-binding interfaces |
| Conotoxin SAR | Sequence and loop-residue optimization |
| Disulfide Peptide Research | Folding and regioisomer studies |
Quality Control
Identity and purity are typically evaluated by MS and analytical HPLC. For folded α-Conotoxin SI, the intended oxidation state and native disulfide topology should also be considered when interpreting analytical results.
Storage & Handling
Follow the batch-specific COA or product storage specification. After reconstitution, minimize repeated freeze–thaw cycles and consider solvent, concentration, and pH when evaluating peptide stability.
Selected References
1. Zafaralla GC, et al. Phylogenetic specificity of cholinergic ligands: α-Conotoxin SI. Defines the 13-residue sequence and nAChR activity.
2. Hargittai B, Barany G. Controlled syntheses of natural and disulfide-mispaired regioisomers of α-Conotoxin SI. Journal of Peptide Research. 1999.
3. Solution structure of α-Conotoxin SI. FEBS Letters. 2000.
Related Technical Resources
Peptide Modifications & Applications
Peptide Purification & Quality Control
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