Mechanisms of maurotoxin action on shaker potassium channels

Maurotoxin (alpha-KTx6.2) is a toxin derived from the Tunisian chactoid scorpion Scorpio maurus palmatus, and it is a member of a new family of toxins that contain four disulfide bridges (Selisko et ai,, 1998, fur. J, Biochem. 254:468-479), We investigated the mechanism of the maurotoxin action on voltage-gated K+ channels expressed in Xenopus oocytes, Maurotoxin blocks the channels in a voltage-dependent manner, with its efficacy increasing with greater hyperpolarization, We show that an amino acid residue in the external mouth of the channel pore segment that is known to be involved in the actions of other peptide toxins is also involved in maurotoxin's interaction with the channel. We conclude that, despite the unusual disulfide bridge pattern, the mechanism of the maurotoxin action is similar to those of other K+ channel toxins with only three disulfide bridges.