Mechanisms of Maurotoxin Action on Shaker Potassium Channels

Abstract

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 (, Eur. 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.

Mapping of Maurotoxin Binding Sites on hKv1.2, hKv1.3, and hIKCa1 Channels

“…The selection of these amino acids was made based on computer simulations (Fu et al, 2002) or previous reports of the importance in MTX or other peptide toxins binding of the amino acids situated in equivalent positions in other potassium channels. Thus, it has been reported that position 381 from hKv1.2 channels is important in ShakerB channels for MTX binding (Thr 499 ) (Avdonin et al, 2000), whereas in mKv1.3 channels, the corresponding amino acid (His 404 ) is important in the binding of tetraethylammonium (Bretschneider et al, 1999), CTX (Rauer et al, 2000), or KTX (Aiyar et al, 1996). Likewise, position 363 from hKv1.2 channels has been reported as an important position in hIKCa1 channels (Asp 239 ) for CTX binding (Rauer et al, 2000), whereas the corresponding amino acid of position 355 from hKv1.2 channels has been shown to have a small influence in KTX binding to Kv1.1 channels (Glu 353 ) (Wrisch and Grissmer, 2000).…”

“…Despite its different disulfide bridge organization, MTX has the same three-dimensional structure of potassium channels toxin blockers formed by one ␣-helix and two ␤-sheets. Moreover, MTX has been reported to block, in Xenopus laevis oocytes, IKCa1, Kv1.2, and ShakerB channels with an affinity lower than 10 nM, whereas its affinity for other potassium channels, such as Kv1.1 and Kv1.3, was higher than 50 nM (Kharrat et al, 1996;Avdonin et al, 2000;Lecomte et al, 2000;Castle et al, 2003).hKv1.2 and hIKCa1 channels are distributed differently in different tissues. hKv1.2 channels are found predominantly in the brain, where they are most likely to be associated with Kv1.1 and Kv1.6 channel subunits accomplishing crucial roles in neuronal signal transmission (Coleman et al, 1999;Monaghan et al, 2001;Dodson et al, 2003).…”

“…Despite its different disulfide bridge organization, MTX has the same three-dimensional structure of potassium channels toxin blockers formed by one ␣-helix and two ␤-sheets. Moreover, MTX has been reported to block, in Xenopus laevis oocytes, IKCa1, Kv1.2, and ShakerB channels with an affinity lower than 10 nM, whereas its affinity for other potassium channels, such as Kv1.1 and Kv1.3, was higher than 50 nM (Kharrat et al, 1996;Avdonin et al, 2000;Lecomte et al, 2000;Castle et al, 2003).…”

Maurotoxin: A Potent Inhibitor of Intermediate Conductance Ca2+-Activated Potassium Channels

“…It is a basic, C-terminal amidated, 34-mer peptide cross-linked by four disulfide bridges. At nanomolar concentrations, maurotoxin has been reported to display a variety of pharmacological activities, including inhibition of radiolabeled apamin binding to rat brain synaptosomes (Kharrat et al, 1996 and blocking insect (Shaker B) or mammalian (Kv1.2, Kv1.1, and Kv1.3) voltage-gated Kv channels heterologously expressed in Xenopus laevis oocytes (Kharrat et al, 1996Avdonin et al, 2000;Carlier et al, 2000).…”

Targeting ion channels for the treatment of gastrointestinal motility disorders

“…While the block by these molecules is a physical obstruction of the water-filled inner vestibule, its structure in the Na V , Ca V and K V is different enough that blockers generally do not cross react across families [Hille, 2001]. On the other side of the filter, the best known drugs that target the extracellular face of the pore are toxins such as TTX for Na V [Hille, 2001] and a-KTx for K V [Avdonin et al 2000]. An alternative idea to affect permeation and the selectivity filter is through C-type (slow) inactivation, which requires restructuring of the selectivity filter such that ion flow is interrupted (green in Figure 2) [Cuello et al 2010].…”