New Binding Site on Common Molecular Scaffold Provides HERG Channel Specificity of Scorpion Toxin BeKm-1

Abstract

The scorpion toxin BeKm-1 is unique among a variety of known short scorpion toxins affecting potassium channels in its selective action on ether-a-go-go-related gene (ERG)-type channels. BeKm-1 shares the common molecular scaffold with other short scorpion toxins. The toxin spatial structure resolved by NMR consists of a short ␣-helix and a triple-stranded antiparallel ␤-sheet. By toxin mutagenesis study we identified the residues that are important for the binding of BeKm-1 to the human ERG K ؉ (HERG) channel. The most critical residues (Tyr-11, Lys-18, Arg-20, Lys-23) are located in the ␣-helix and following loop whereas the "traditional" functional site of other short scorpion toxins is formed by residues from the ␤-sheet. Thus the unique location of the binding site of BeKm-1 provides its specificity toward the HERG channel.

APETx1 from Sea Anemone Anthopleura elegantissima Is a Gating Modifier Peptide Toxin of the Human Ether-a-go-go- Related Potassium Channel

“…The spatial relationship among Lys18, Tyr32, Phe33, and Leu34 on APETx1 bears some resemblance to the relationship among residues on BeKm-1 that are involved in binding to the hERG channel (Lys18, Phe14, and Tyr11) ( Fig. 1) (Korolkova et al, 2002;Tseng et al, 2007). However, the mechanism of APETx1's action and its binding site on the hERG channel have not been investigated.…”

“…Several such peptide toxins have been identified (Gurrola et al, 1999;Korolkova et al, 2001;Corona et al, 2002;Nastainczyk et al, 2002;Huys et al, 2004). Two peptide toxins purified from scorpions, BeKm-1 and CnErg1 (also called ErgTx1), are the best-studied cases (Korolkova et al, 2002;Pardo-López et al, 2002a,b;Zhang et al, 2003;Tseng et al, 2007). Both toxins bind to hERG's outer vestibule to suppress ion conduction through the pore.…”

“…An alanine-scanning mutagenesis study showed that BeKm-1 uses its ␣-helix and the following turn as the interaction surface in binding to the hERG channel ( Fig. 1A) (Korolkova et al, 2002). BeKm-1 does not totally occlude ion flux through the hERG pore (Zhang et al, 2003), probably because it binds above the selectivity filter (Tseng et al, 2007).…”

“…Both toxins bind to hERG's outer vestibule to suppress ion conduction through the pore. Their backbone fold consists of an ␣-helix and a triple-stranded antiparallel ␤-sheet (PDB identification numbers 1J5J and 1PX9, respectively) (Korolkova et al, 2002;Frená l et al, 2004). An alanine-scanning mutagenesis study showed that BeKm-1 uses its ␣-helix and the following turn as the interaction surface in binding to the hERG channel ( Fig.…”

Amino acid sequence determination and chemical synthesis of CllErg1 (gamma-KTx1.5), a K+ channel blocker peptide isolated from the scorpion Centruroides limpidus limpidus

“…29 The first ergtoxin isolated (CnErg1) was recently used in various publications dealing with the possible sites of interaction of ergtoxin-1 (systematic nomenclature -KTx1.1) with the HERG channels. 30,31 More recently yet, the three-dimensional structure of synthetic CnErg1, 32 and native CnErg1, 33 as well as that of BeKm-1, 34 were determined by nuclear magnetic resonance (NMR) and the interactions of these peptides with HERG channels were studied.Furthermore, structural studies on scorpion toxins that potently inhibit HERG are beginning to provide clues as to the structural differences between HERG and other voltage-gated K + channels. 31,35,36 In this paper, we describe the isolation and sequencing of two novel peptides from the venom of scorpion C. l. limpidus.…”