A novel conotoxin from Conus betulinus, kappa-BtX, unique in cysteine pattern and in function as a specific BK channel modulator

• Published in: The Journal of biological chemistry 2003-04, Vol.278 (15), p.12624-12633
• Main Authors: Fan, Chong-Xu, Chen, Xiao-Ke, Zhang, Chen, Wang, Li-Xiu, Duan, Kai-Lai, He, Lin-Lin, Cao, Ying, Liu, Shang-Yi, Zhong, Ming-Nai, Ulens, Chris, Tytgat, Jan, Chen, Ji-Sheng, Chi, Cheng-Wu, Zhou, Zhuan
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Calcium Channels - physiology; Cells, Cultured; Chromaffin Cells - drug effects; Chromaffin Cells - physiology; Chromatography, Gel; Conotoxins; Conotoxins - chemistry; Conotoxins - isolation & purification; Conotoxins - pharmacology; Conus betulinus; DNA Primers; DNA, Complementary - genetics; double prime BK channels; Large-Conductance Calcium-Activated Potassium Channels; Marine; Molecular Sequence Data; Mollusca; Potassium Channels - physiology; Potassium Channels, Calcium-Activated - antagonists & inhibitors; Rats; Rats, Wistar; Sodium Channels - physiology; Spectrometry, Mass, Electrospray Ionization; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
• ISSN: 0021-9258
• DOI: 10.1074/jbc.M210200200

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.