A novel conotoxin from Conus betulinus, kappa-BtX, unique in cysteine pattern and in function as a specific BK channel modulator.
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.
Fan
Chong-Xu
CX
Research Institute of Pharmaceutical Chemistry, Beijing 102205, China.
Chen
Xiao-Ke
XK
Zhang
Chen
C
Wang
Li-Xiu
LX
Duan
Kai-Lai
KL
He
Lin-Lin
LL
Cao
Ying
Y
Liu
Shang-Yi
SY
Zhong
Ming-Nai
MN
Ulens
Chris
C
Tytgat
Jan
J
Chen
Ji-Sheng
JS
Chi
Cheng-Wu
CW
Zhou
Zhuan
Z
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015220:Calcium Channels / Q000502:physiology; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects / Q000502:physiology; D002850:Chromatography, Gel; D020916:Conotoxins / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008969:Molecular Sequence Data; D008974:Mollusca; D015221:Potassium Channels / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors*; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000502:physiology; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D015220:Calcium Channels; D020916:Conotoxins; D017931:DNA Primers; D018076:DNA, Complementary; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D015222:Sodium Channels; C475056:kappa-conotoxin BtX