Purification, characterization of two peptides from Buthus martensi Karch

BmK NSPK, a Potent Potassium Channel Inhibitor from Scorpion Buthus martensii Karsch, Promotes Neurite Outgrowth via NGF/TrkA Signaling Pathway

Scorpion toxins represent a variety of tools to explore molecular mechanisms and cellular signaling pathways of many biological functions. These toxins are also promising lead compounds for developing treatments for many neurological diseases. In the current study, we purified a new scorpion toxin designated as BmK NSPK (Buthus martensii Karsch neurite-stimulating peptide targeting K_v channels) from the BmK venom. The primary structure was determined using Edman degradation. BmK NSPK directly inhibited outward K⁺ current without affecting sodium channel activities, depolarized membrane, and increased spontaneous calcium oscillation in spinal cord neurons (SCNs) at low nanomolar concentrations. BmK NSPK produced a nonmonotonic increase on the neurite extension that peaked at ~10 nM. Mechanistic studies demonstrated that BmK NSPK increased the release of nerve growth factor (NGF). The tyrosine kinases A (TrkA) receptor inhibitor, GW 441756, eliminated the BmK NSPK-induced neurite outgrowth. BmK NSPK also increased phosphorylation levels of protein kinase B (Akt) that is the downstream regulator of TrkA receptors. These data demonstrate that BmK NSPK is a new voltage-gated potassium (K_v) channel inhibitor that augments neurite extension via NGF/TrkA signaling pathway. K_v channels may represent molecular targets to modulate SCN development and regeneration and to develop the treatments for spinal cord injury.

Subtype-selective activation of K(v)7 channels by AaTXKβ₂₋₆₄, a novel toxin variant from the Androctonus australis scorpion venom

K(v)7.4 channel subunits are expressed in central auditory pathways and in inner ear sensory hair cells and skeletal and smooth muscle cells. Openers of K(v)7.4 channels have been suggested to improve hearing loss, systemic or pulmonary arterial hypertension, urinary incontinence, gastrointestinal and neuropsychiatric diseases, and skeletal muscle disorders. Scorpion venoms are a large source of peptides active on K⁺ channels. Therefore, we have optimized a combined purification/screening procedure to identify specific modulator(s) of K(v)7.4 channels from the venom of the North African scorpion Androctonus australis (Aa). We report the isolation and functional characterization of AaTXKβ₂₋₆₄, a novel variant of AaTXKβ₁₋₆₄, in a high-performance liquid chromatography fraction from Aa venom (named P8), which acts as the first peptide activator of K(v)7.4 channels. In particular, in both Xenopus oocytes and mammalian Chinese hamster ovary cells, AaTXKβ₂₋₆₄, but not AaTXKβ₁₋₆₄, hyperpolarized the threshold voltage of current activation and increased the maximal currents of heterologously expressed K(v)7.4 channels. AaTXKβ₂₋₆₄ also activated K(v)7.3, K(v)7.2/3, and K(v)7.5/3 channels, whereas homomeric K(v)1.1, K(v)7.1, and K(v)7.2 channels were unaffected. We anticipate that these results may prove useful in unraveling the novel biologic roles of AaTXKβ₂₋₆₄-sensitive K(v)7 channels and developing novel pharmacologic tools that allow subtype-selective targeting of K(v)7 channels.

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.

Inhibition of martentoxin on neuronal BK channel subtype (alpha+beta4): implications for a novel interaction model

Martentoxin as a 37-residue peptide was capable of blocking large-conductance Ca(2+)-activated K(+) (BK) channels in adrenal medulla chromaffin cells. This study investigated the pharmacological discrimination of martentoxin on BK channel subtypes. The results showed that the iberiotoxin-insensitive neuronal BK channels (alpha+beta4) could be potently blocked by martentoxin (IC(50) = approximately 80 nM). In contrast, the iberiotoxin-sensitive BK channel consisting of only alpha-subunit was less sensitive to martentoxin. Distinctively, martentoxin inhibited neuronal BK channels (alpha+beta4) with a novel interaction mode. Two possible interaction sites of neuronal BK channels (alpha+beta4) might be responsible for the binding with martentoxin: one for trapping and the other located at the pore region for blocking. In addition, the inhibition of martentoxin on neuronal BK channels (alpha+beta4) depended on cytoplasmic Ca(2+) concentration. On the other hand, in vivo experiments from EEG recordings suggested that neuronal BK channels (alpha+beta4) were the primary target of martentoxin. Therefore, this research not only sheds light on a unique ligand for neuronal BK channels (alpha+beta4), but also highlights a novel model approach for the interaction between K(+) channels and specific-ligands.

1H-NMR signal assignments and secondary structure analysis of martentoxin

Martentoxin is a peptide of 37 amino acid residues purified from the venom of the Chinese scorpion Buthus martensi Karch, which has been demonstrated to be an inhibitor of voltage-dependent sodium channel and voltage-dependent delayed rectifier potassium channel. To elucidate the molecular mechanism of this interaction, the structure of martentoxin was studied by 2D-NMR. The secondary structure of martentoxin consists of a triple-stranded beta-sheet connected to a alpha-helical structure. This helix encompasses 10 residues from Ser11 to Lys20. The three strands of beta-sheet probably comprise residues Gly2-Asp5, Q27-N30 and Glu33-Cys36, Cys30-Asn33 with a type I'beta turn centered on Asn31-Asn32. The results indicate that martentoxin possesses the conserved beta alpha beta beta structure of all the potassium channel toxins.