TAT-Modified Martentoxin Displays Intravenous Antiseizure Activities

Epilepsy is a chronic disease of brain dysfunction, which arises from imbalance between excitatory and inhibitory activities in neural circuits. Previously, we reported that peptide Martentoxin (MarTX), from scorpion Buthus martensii Karsch, displayed antiseizure activities by specifically inhibiting BK(α + β4) channel currents. Injection of MarTX into the hippocampal region of mice significantly alleviated convulsive seizures. However, intravenous injection of MarTX had no antiepileptic efficacy due to the blood-brain barrier (BBB). To address this, here, we designed cell-penetrating peptide TAT-modified MarTX, in which the linker containing three glycines was put between TAT and the N-terminus of MarTX (forming MTX-N-TAT) or between TAT and the C-terminus of MarTX (forming MTX-C-TAT), respectively. We prepared them in a large amount through Escherichia coli overexpression system and then probed their antiseizure activities. Our results indicated that intravenous injection of MTX-C-TAT showed significant therapeutic efficacy of antiseizure. It increased seizure latency, reduced the total seizure duration and the number of seizures at stages 3, 4, and 5, inhibited hippocampal neuronal hyperexcitability, and exhibited neuroprotective effects on hippocampal neurons. These studies implied that MTX-C-TAT displayed intravenous antiseizure activities properly through crossing BBB and would be a potential antiepileptic drug in the future.

Homology modeling and molecular docking simulation of martentoxin as a specific inhibitor of the BK channel

Background

Large conductance calcium-activated potassium channel (BK channel) is gated by both voltage and calcium ions and is widely distributed in excitable and nonexcitable cells. BK channel plays an important role in epilepsy and other diseases, but BK channel subtype-specific drugs are still extremely rare. Martentoxin was previously isolated from the venom of members of Scorpionidae and shown to be composed of 37 amino acids. Research has shown that the pharmacological selectivity of martentoxin to the BK channel is higher than that to other potassium channels. Therefore, it is of great significance to study the mechanism of interaction between martentoxin and BK channels.

Methods

The three-dimensional structure of BK channel pore region was constructed by homologous modeling method, and the key amino acid sites of BK channel interaction with martentoxin were analyzed by protein-protein docking, molecular dynamic simulation and virtual alanine mutation.

Results

Based on homologous modeling of BK channel pore structure and protein-protein docking analysis, Phe1, Lys28 and Arg35 of martentoxin were found to be key amino acids in toxin BK channel interaction.

Conclusions

This study reveals the structural basis of martentoxin interaction with BK channel. These results will contribute to the design of BK channel specific blockers based on the structure of martentoxin.

Martentoxin, a large-conductance Ca(2+)-activated K(+) channel inhibitor, attenuated TNF-α-induced nitric oxide release by human umbilical vein endothelial cells

Martentoxin, a 4,046 Da polypeptide toxin purified from the venom of the scorpion Buthus martensii Karsch, has been demonstrated to block large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels; however, its biological roles are still largely unknown. In the present study, we investigated the pharmacological effects of martentoxin on regulating the production of nitric oxide induced by TNF-α in human umbilical vein endothelial cells (HUVECs). We found that, 1, 10 and 100 µmol/L martentoxin decreased nitric oxide production by HUVECs exposed to 10 ng/mL TNF for 6, 12 and 24 hours. We further demonstrated that martentoxin inhibited the activity of iNOS and retarded the down-regulation of eNOS mRNA induced by TNF-α. Therefore, martentoxin could be a potential therapeutic agent for vascular diseases.