Open AccessSynthesis and characterization of Pi4, a scorpion toxin from Pandinus imperator that acts on K + channels
Author(s) -
M'Barek Sarrah,
Mosbah Amor,
Sandoz Guillaume,
Fajloun Ziad,
OlamendiPortugal Timoteo,
Rochat Hervé,
Sampieri François,
Guijarro J. Iñaki,
Mansuelle Pascal,
Delepierre Muriel,
De Waard Michel,
Sabatier JeanMarc
Publication year - 2003
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1033.2003.03743.x
Subject(s) - scorpion toxin , scorpion venoms , biology , venom , toxin , channel blocker , xenopus , biochemistry , stereochemistry , biophysics , chemistry , scorpion , organic chemistry , gene , calcium
Pi4 is a 38‐residue toxin cross‐linked by four disulfide bridges that has been isolated from the venom of the Chactidae scorpion Pandinus imperator . Together with maurotoxin, Pi1, Pi7 and HsTx1, Pi4 belongs to the α KTX6 subfamily of short four‐disulfide‐bridged scorpion toxins acting on K + channels. Due to its very low abundance in venom, Pi4 was chemically synthesized in order to better characterize its pharmacology and structural properties. An enzyme‐based cleavage of synthetic Pi4 (sPi4) indicated half‐cystine pairings between Cys6–Cys27, Cys12–32, Cys16–34 and Cys22–37, which denotes a conventional pattern of scorpion toxin reticulation (Pi1/HsTx1 type). In vivo , sPi4 was lethal after intracerebroventricular injection to mice (LD 50 of 0.2 µg per mouse). In vitro , addition of sPi4 onto Xenopus laevis oocytes heterologously expressing various voltage‐gated K + channel subtypes showed potent inhibition of currents from rat Kv1.2 (IC 50 of 8 p m ) and Shaker B (IC 50 of 3 n m ) channels, whereas no effect was observed on rat Kv1.1 and Kv1.3 channels. The sPi4 was also found to compete with 125 I‐labeled apamin for binding to small‐conductance Ca 2+ ‐activated K + (SK) channels from rat brain synaptosomes (IC 50 value of 0.5 µ m ). sPi4 is a high affinity blocker of the Kv1.2 channel. The toxin was docked ( Bigger program) on the Kv channel using the solution structure of sPi4 and a molecular model of the Kv1.2 channel pore region. The model suggests a key role for residues Arg10, Arg19, Lys26 (dyad), Ile28, Lys30, Lys33 and Tyr35 (dyad) in the interaction and the associated blockage of the Kv1.2 channel.