Molecular Diversity and Functional Evolution of Scorpion Potassium Channel Toxins

Abstract

Scorpion toxins affecting K؉ channels (KTxs) represent important pharmacological tools and potential drug candidates. Here, we report molecular characterization of seven new KTxs in the scorpion Mesobuthus eupeus by cDNA cloning combined with biochemical approaches. Comparative modeling supports that all these KTxs share a conserved cysteine-stabilized ␣-helix/␤-sheet structural motif despite the differences in protein sequence and size. We investigated functional diversification of two orthologous ␣-KTxs (MeuTXK␣1 from M. eupeus and BmP01 from Mesobuthus martensii) by comparing their K ؉ channel-blocking activities. Pharmacologically, Meu-TXK␣1 selectively blocked Kv1.3 channel with nanomolar affinity (IC 50 , 2.36 ؎ 0.9 nM), whereas only 35% of Kv1.1 currents were inhibited at 3 M concentration, showing more than 1271-fold selectivity for Kv1.3 over Kv1.1. This peptide displayed a weak effect on Drosophila Shaker channel and no activity on Kv1.2, Kv1.4, Kv1.5, Kv1.6, and human ether-a-go-go-related gene (hERG) K ؉ channels. Although BmB01 and MeuTXK␣1 have a similar channel spectrum, their affinity and selectivity for these channels largely varies. In comparison with MeuTXK␣1, BmP01 only exhibits a submicromolar affinity (IC 50 , 133.72 ؎ 10.98 nM) for Kv1.3, showing 57-fold less activity than Meu-TXK␣1. Moreover, it lacks the ability to distinguish between Kv1.1 and Kv1.3. We also found that MeuTXK␣1 inhibited the proliferation of activated T cells induced by phorbol myristate acetate and ionomycin at micromolar concentrations. Our results demonstrate that accelerated evolution drives affinity variations of orthologous ␣-KTxs on Kv channels and indicate that MeuTXK␣1 is a promising candidate to develop an immune modulation agent for human autoimmune diseases.

A bimodal activation mechanism underlies scorpion toxin–induced pain

“…However, it was noticed that TRPV1 activities were observed only when micromolar concentrations of BmP01 were used [median effective concentration (EC 50 ) at 40.4 ± 12.3 μM, n = 10]. Similar properties were previously reported in BmP01-mediated inhibition of voltage-gated Kv channels ( 14 , 16 ). Therefore, given the fact that high concentrations inside the prey are apparently unachievable by a single sting, it appears that BmP01 has evolved to target TRPV1 to produce pain and/or Kv to produce hyperactivity.…”

Structural and Functional Diversity of Acidic Scorpion Potassium Channel Toxins

“…In addition to the known pharmacological effects of acidic KTxs on Kv1.x and SKCa channels [6], [25], our electrophysiological studies demonstrated for the first time that the α-KTx ImKTx104 blocked the KCNQ1 channel with a K d of 11.69 µM. ImKTx104 was found to have a modified cystine-stabilized α-helix-loop-β-sheet (CS-α/β) fold.…”

Hg1, Novel Peptide Inhibitor Specific for Kv1.3 Channels from First Scorpion Kunitz-type Potassium Channel Toxin Family

“…To screen and design the potent and selective peptide inhibitors, efforts to improve peptide specificity are continuing (11)(12)(13). Kunitz-type toxins are a kind of ancient toxin family that has been identified in many animal venoms, such as those of snake, cone snail, spider, sea anemone, and scorpion (14 -18).…”

“…These toxins usually had 30 -40 residues cross-linked by three disulfide bridges, such as Odk2, KTX, OSK1, AOSK1, HsTx1, and ShK (7)(8)(9)(10). Until now, the screening and design of novel potent and selective Kv1.3 inhibitors derived from animal toxins remain an attractive prospect for disease diagnosis and treatment (11)(12)(13).…”