A Subfamily of Acidic α-K+ Toxins

Abstract

Three homologous acidic peptides have been isolated from the venom of three different Parabuthus scorpion species, P. transvaalicus, P. villosus, and P. granulatus. Analysis of the primary sequences reveals that they structurally belong to subfamily 11 of short chain ␣-K ؉ -blocking peptides (Tytgat, J., Chandy, K. G., Garcia, M. L., Gutman, G. A., Martin-Eauclaire, M. F., van der Walt, J. J., and Possani, L. D. (1999) Trends Pharmacol. Sci. 20, 444 -447). These toxins are 36 -37 amino acids in length and have six aligned cysteine residues, but they differ substantially from the other ␣-K ؉ toxins because of the absence of the critical Lys 27 and their total overall negative charge. Parabutoxin 1 (PBTx1), which has been expressed by recombinant methods, has been submitted to functional characterization. Despite the lack of the Lys 27 , this toxin blocks several Kv1-type channels heterologously expressed in Xenopus oocytes but with low affinities (micromolar range). Because a relationship between the biological activity and the acidic residue substitutions may exist, we set out to elucidate the relative impact of the acidic character of the toxin and the lack of the critical Lys 27 on the weak activity of PBTx1 toward Kv1 channels. To achieve this, a specific mutant named rPBTx1 T24F/V26K was made recombinantly and fully characterized on Kv1-type channels heterologously expressed in Xenopus oocytes. Analysis of rPBTx1 T24F/V26K displaying an affinity toward Kv1.2 and Kv1.3 channels in the nanomolar range shows the importance of the functional dyad above the acidic character of this toxin.

Structural and Functional Diversity of Acidic Scorpion Potassium Channel Toxins

“…Toxins ImKTx104 and HeTx204 effectively blocked the KCNQ1 channel at 10 µM concentration, while LmKTx2 and HeTx203 only weakly inhibited the KCNQ1 channel at the same concentration, and 10 µM StKTx23 did not inhibit KCNQ1 channels. In comparison, the previously studied acidic BmP01, BmP02, and PbTx1 [25], [43] were only weak inhibitors of KCNQ1 channels, with BmP01 having the lowest inhibitory activity at 10 µM.…”

“…Acidic toxin MeuTXKα1 was the first selective Kv1.3 inhibitor with high affinity (nanomolar range) [6]. Many acidic toxins block the Kv1.x channel with low activity (micromolar range), such as BmP01, PbTx1, OmTx1, and OmTx3 [12], [43]. We report that representative toxins of four subfamilies have different effects on the Kv1.3 channel.…”

“…One exception is the toxin MeuTXKα1, which specifically inhibits the Kv1.3 channel with an IC 50 value of 2.36±0.90 nM [6], [12], [43]. We therefore investigated the effects of the newly identified acidic KTxs on the Kv1.3 channel.…”

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

“…The a-KTx is the best studied family; its members are small basic peptides (up to 4 kDa) consisting of 23 to 40 amino acids with the structure stabilized by three to four disulfide bridges. To date, the a-KTx family is classified into 27 subfamilies (http://www.uniprot.org/docs/scorpktx) Goudet et al, 2002;Huys et al, 2004;Rodríguez de la Vega and Possani, 2004;Tan et al, 2006;Zhijian et al, 2006;Gurrola et al, 2012) with K 1 channel affinities varying in the micromolar to picomolar range. The a-KTx toxins target mainly the voltage-gated potassium (K v ) channels, especially the K v 1 family members and some Ca 21 -activated K 1 channels ; Rodríguez de la Vega and .…”

Scorpion toxin peptide action at the ion channel subunit level

“…(Huys et al, 2004b) Inhibit current, Rat, Xenopus oocytes, Kd ¼ 1.0 mM, (Huys et al, 2004b) Inhibit current, Xenopus oocyte, Kd ¼ 0.8 mM (Huys et al, 2004b) PBTx3 a-…”