Characterization of Kbot21 Reveals Novel Side Chain Interactions of Scorpion Toxins Inhibiting Voltage-Gated Potassium Channels.

Rym Elfessi-Magouri,Najet Srairi-Abid,Houcemeddine Othman,Mohamed Elayeb,Riadh Kharrat,Steve Peigneur,Jan Tytgat,Alexander G Obukhov

doi:10.1371/journal.pone.0137611

Rym Elfessi-Magouri, Najet Srairi-Abid + Show 6 more

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https://doi.org/10.1371/journal.pone.0137611

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Journal: PloS one	Publication Date: Sep 23, 2015
Citations: 7	License type: CC BY 4.0

Affiliation: Institut Pasteur de Tunis, KU Leuven

Abstract

Scorpion toxins are important pharmacological tools for probing the physiological roles of ion channels which are involved in many physiological processes and as such have significant therapeutic potential. The discovery of new scorpion toxins with different specificities and affinities is needed to further characterize the physiology of ion channels. In this regard, a new short polypeptide called Kbot21 has been purified to homogeneity from the venom of Buthus occitanus tunetanus scorpion. Kbot21 is structurally related to BmBKTx1 from the venom of the Asian scorpion Buthus martensii Karsch. These two toxins differ by only two residues at position 13 (R /V) and 24 (D/N).Despite their very similar sequences, Kbot21 and BmBKTx1 differ in their electrophysiological activities. Kbot21 targets KV channel subtypes whereas BmBKTx1 is active on both big conductance (BK) and small conductance (SK) Ca2+-activated K+ channel subtypes, but has no effects on Kv channel subtypes. The docking model of Kbot21 with the Kv1.2 channel shows that the D24 and R13 side-chain of Kbot21 are critical for its interaction with KV channels.

Highlights

IntroductionThe subtypes of K+ channels targeted by scorpion toxins include voltage-gated [4], inward rectifier [5], ether-a-go-go-related gene [6,7,8] and Ca2+-activated channels including large, intermediate and small conductance channels [9,10,11]
Scorpion venom is a source of interesting bioactive compounds, such as neurotoxins which are invaluable tools for studying structure and function of potassium channels [1] and are serving as templates for the development of molecular therapeutics [2,3].The subtypes of K+ channels targeted by scorpion toxins include voltage-gated [4], inward rectifier [5], ether-a-go-go-related gene [6,7,8] and Ca2+-activated channels including large, intermediate and small conductance channels [9,10,11]
The toxic fraction obtained from Sephadex G-50 chromatography of the Buthus occitanus tunetanus scorpion venom was fractionated by a C8 semi preparative reversed-phase HPLC (Fig 1A)

Summary

Introduction

The subtypes of K+ channels targeted by scorpion toxins include voltage-gated [4], inward rectifier [5], ether-a-go-go-related gene [6,7,8] and Ca2+-activated channels including large, intermediate and small conductance channels [9,10,11]. These toxins (KScTxs) are short-chain peptides of 28 to 40 amino acids, with three or four disulfide bridges Their structures exhibit a common minimal motif, named the “Cystein-Stabilized-Helix” (CSH) [15, 16]. Dauplais et al [17] have demonstrated that lysine at position 27 in charybdotoxin from Leiurus quinquestriatus hebraeus physically occludes the pore of KV1 channels, preventing the flow of K+ ions This lysine and an aromatic residue (tyrosine or phenylalanine) separated by 6.6±1.0 Å forms the functional dyad which is essential to target KV channels [17]. The functional residues for KV and BK channels are located on the β-sheets in contrast to these of ERG and SKCa channels which are located at the α-helix [9]

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