Evidence for Domain-specific Recognition of SK and Kv Channels by MTX and HsTx1 Scorpion Toxins

Abstract

Maurotoxin (MTX) and HsTx1 are two scorpion toxins belonging to the ␣-KTx6 structural family. These 34-residue toxins, cross-linked by four disulfide bridges, share 59% sequence identity and fold along the classical ␣/␤ scaffold. Despite these structural similarities, they fully differ in their pharmacological profiles. MTX is highly active on small (SK) and intermediate (IK) conductance Ca 2؉ -activated (K ؉ ) channels and on voltage-gated Kv1.2 channel, whereas HsTx1 potently blocks voltagegated Kv1.1 and Kv1.3 channels only. Here, we designed and chemically produced MTX-HsTx1, a chimera of both toxins that contains the N-terminal helical region of MTX (sequence 1-16) and the C-terminal ␤-sheet region of HsTx1 (sequence 17-34). The three-dimensional structure of the peptide in solution was solved by 1 H NMR. MTX-HsTx1 displays the activity of MTX on SK channel, whereas it exhibits the pharmacological profile of HsTx1 on Kv1.1, Kv1.2, Kv1.3, and IK channels. These data demonstrate that the helical region of MTX exerts a key role in SK channel recognition, whereas the ␤-sheet region of HsTx1 is crucial for activity on all other channel types tested.

Pharmacological Profiling of Orthochirus scrobiculosus Toxin 1 Analogs with a Trimmed N-Terminal Domain

“…3). However, [⌬ 36-38 ]-AOSK1 low activity in vitro and in vivo was not unexpected because the integrity of the ␤-sheet structure has been reported to be crucial for the recognition of voltage-gated Kv and Ca 2ϩ -activated K Ca 3.1 potassium channels by scorpion toxins (Castle et al, 2003;Rodriguez de la Vega et al, 2003;Jouirou et al, 2004;Regaya et al, 2004). In contrast, the most severe truncation of the N-terminal extended region of AOSK1 (i.e., [⌬ 1-7 ]-AOSK1) produced differential effects depending on the subtype of K ϩ channel (Fig.…”

“…In addition, a C-terminaltruncated AOSK1 analog ([⌬ 36-38 ]-AOSK1) was synthesized to evaluate the importance of this domain. The latter truncates half of the second strand (amino acid sequence 32-38) of the ␤-sheet structure, and we therefore expected it to show a reduced potency because of the reported importance of the ␤-sheet structure for Kv channel blockage (Regaya et al, 2004). All of the peptides were assembled by solid-phase synthesis using stepwise Fmoc/t-butyl chemistry, as described previously (Merrifield, 1986).…”

Structure, Molecular Modeling, and Function of the Novel Potassium Channel Blocker Urotoxin Isolated from the Venom of the Australian Scorpion Urodacus yaschenkoi

“…First, several peptides that inhibit K v 1.2 also block this channel, such as maurotoxin (Regaya et al, 2004;Wulff and Castle, 2010) and charybdotoxin (Grissmer et al, 1994). Second, because urotoxin inhibits hK v 1.3, and the selectivity of a peptide for hK v 1.3 over the other K 1 channel of human T cells, hK Ca 3.1, is of great interest due to the potential therapeutic application of these peptides.…”

Anuroctoxin, a New Scorpion Toxin of the α-KTx 6 Subfamily, Is Highly Selective for Kv1.3 over IKCa1 Ion Channels of Human T Lymphocytes

“…Of the panel of channels studied (Shaker, Kv1.1, Kv1.2, and Kv2.1), anuroctoxin inhibited only Kv1.2 channels significantly with approximately 7-fold lower affinity than Kv1.3 channels. Within subfamily 6 of ␣-KTx, the only high-affinity blocker of Kv1.3 is HsTx1, which also inhibits Kv1.1 channels with nanomolar affinity (K d ϭ 7 nM) and IKCa1 channels with a modest/low affinity (K d ϭ 460 nM) (Regaya et al, 2004). Thus, although phylogenetic analysis classifies anuroctoxin into subfamily 6, its pharmacological profile is similar to that of MgTx (␣-KTx 2.2) and Ntx (␣-KTx 2.1).…”

“…Branch tips are labeled with the systematic numbering of the subfamily. Within subfamily 6, the relative potency on various channels is indicated [data from Pi1 (Peter et al, 2000;Mouhat et al, 2004), Pi4 (M'Barek et al, 2003, MauTx (Regaya et al, 2004), and HsTx1 (Regaya et al, 2004)]. …”