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A novel conotoxin from Conus betulinus, kappa-BtX, unique in cysteine pattern and in function as a specific BK
Chong-Xu Fan1, Xiao-Ke Chen, Chen Zhang
1Research Institute of Pharmaceutical Chemistry, Beijing 102205, China.
Abstract:
A novel conotoxin, kappa-conotoxin (kappa-BtX), has been purified and characterized from the venom of a worm-hunting cone snail, Conus betulinus. The toxin, with four disulfide bonds, shares no sequence homology with any other conotoxins. Based on a partial amino acid sequence, its cDNA was cloned and sequenced. The deduced sequence consists of a 26-residue putative signal peptide, a 31-residue mature toxin, and a 13-residue extra peptide at the C terminus. The extra peptide is cleaved off by proteinase post-processing. All three Glu residues are gamma-carboxylated, one of the two Pro residues is hydroxylated at position 27, and its C-terminal residue is Pro-amidated. The monoisotopic mass of the toxin is 3569.0 Da. Electrophysiological experiments show that: 1) among voltage-gated channels, kappa-BtX is a specific modulator of K(+) channels; 2) among the K channels, kappa-BtX specifically up-modulates the Ca(2+)- and voltage-sensitive BK channels (252 +/- 47%); 3) its EC(50) is 0.7 nm with a single binding site (Hill = 0.88); 4) the time constant of wash-out is 8.3 s; and 5) kappa-BtX has no effect on single channel conductance, but increases the open probability of BK channels. It is concluded that kappa-BtX is a novel specific biotoxin against BK channels.
Insights
A novel toxin, kappa-conotoxin (kappa-BtX), from Conus betulinus snail venom specifically up-modulates BK channels. This unique conotoxin increases BK channel open probability, offering a new tool for studying these important ion channels.
Area of Science:
- Marine Biology
- Neuroscience
- Biochemistry
Background:
- Cone snail venom contains diverse bioactive peptides, including conotoxins targeting ion channels.
- The specific molecular targets and mechanisms of many conotoxins remain incompletely understood.
- Identifying novel conotoxins with unique pharmacological profiles is crucial for drug discovery and biological research.
Purpose of the Study:
- To purify and characterize a novel conotoxin from Conus betulinus venom.
- To elucidate the molecular target and mechanism of action of this new toxin.
- To investigate its potential as a specific modulator of ion channels.
Main Methods:
- Purification and characterization of kappa-conotoxin (kappa-BtX) from Conus betulinus venom.
- cDNA cloning and sequencing to determine the toxin's primary structure.
- Electrophysiological recordings to assess the toxin's effects on various voltage-gated ion channels, particularly K(+) channels.
- Detailed analysis of BK channel modulation, including EC50, binding site, and single-channel kinetics.
Main Results:
- A novel conotoxin, kappa-BtX, was isolated and structurally characterized, showing no sequence homology to known conotoxins.
- kappa-BtX specifically up-modulates calcium- and voltage-sensitive BK channels with high potency (EC50 = 0.7 nM).
- The toxin increases the open probability of BK channels without affecting single-channel conductance, indicating a specific allosteric modulation.
Conclusions:
- kappa-BtX represents a novel class of conotoxins with a unique structure and function.
- This toxin is a highly specific and potent biotoxin that targets BK channels.
- kappa-BtX serves as a valuable pharmacological tool for investigating BK channel physiology and pathophysiology.