Zhou, Z (reprint author), Res Inst Pharmaceut Chem, Beijing 102205, Peoples R China,
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;, K-BtX is a specific modulator of K+ channels; 2) among the K channels, kappa-BtX specifically up-modulates the Ca2+- and voltage-sensitive BK channels (252 47%); 3) its EC50 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.
Fan, CX; Chen, XK; Zhang, C; Wang, LX; Duan, KL; He, LL; Cao, Y; Liu, SY; Zhong, MN; Ulens, C; Tytgat, J; Chen, JS; Chi, CW; Zhou, Z.A novel conotoxin from Conus betulinus, kappa-BtX, unique in cysteine pattern and in function as a specific BK channel modulator,JOURNAL OF BIOLOGICAL CHEMISTRY,2003,278(15):12624-12633