Hg1, novel peptide inhibitor specific for Kv1.3 channels from first scorpion Kunitz-type potassium channel toxin family

The monodomain Kunitz protein EgKU-7 from the dog tapeworm Echinococcus granulosus is a high-affinity trypsin inhibitor with two interaction sites

Typical Kunitz proteins (I2 family of the MEROPS database, Kunitz-A family) are metazoan competitive inhibitors of serine peptidases that form tight complexes of 1:1 stoichiometry, mimicking substrates. The cestode Echinococcus granulosus, the dog tapeworm causing cystic echinococcosis in humans and livestock, encodes an expanded family of monodomain Kunitz proteins, some of which are secreted to the dog host interface. The Kunitz protein EgKU-7 contains, in addition to the Kunitz domain with the anti-peptidase loop comprising a critical arginine, a C-terminal extension of ∼20 amino acids. Kinetic, electrophoretic, and mass spectrometry studies using EgKU-7, a C-terminally truncated variant, and a mutant in which the critical arginine was substituted by alanine, show that EgKU-7 is a tight inhibitor of bovine and canine trypsins with the unusual property of possessing two instead of one site of interaction with the peptidases. One site resides in the anti-peptidase loop and is partially hydrolyzed by bovine but not canine trypsins, suggesting specificity for the target enzymes. The other site is located in the C-terminal extension. This extension can be hydrolyzed in a particular arginine by cationic bovine and canine trypsins but not by anionic canine trypsin. This is the first time to our knowledge that a monodomain Kunitz-A protein is reported to have two interaction sites with its target. Considering that putative orthologs of EgKU-7 are present in other cestodes, our finding unveils a novel piece in the repertoire of peptidase-inhibitor interactions and adds new notes to the evolutionary host-parasite concerto.

Proteomic analyses of venom from a Spider Hawk, Pepsis decorata

Background

The composition of the venom from solitary wasps is poorly known, although these animals are considered sources of bioactive substances. Until the present moment, there is only one proteomic characterization of the venom of wasps of the family Pompilidae and this is the first proteomic characterization for the genus Pepsis.

Methods

To elucidate the components of Pepsis decorata venom, the present work sought to identify proteins using four different experimental conditions, namely: (A) crude venom; (B) reduced and alkylated venom; (C) trypsin-digested reduced and alkylated venom, and; (D) chymotrypsin-digested reduced and alkylated venom. Furthermore, three different mass spectrometers were used (Ion Trap-Time of Flight, Quadrupole-Time of Flight, and Linear Triple Quadruple).

Results

Proteomics analysis revealed the existence of different enzymes related to the insect's physiology in the venom composition. Besides toxins, angiotensin-converting enzyme (ACE), hyaluronidase, and Kunitz-type inhibitors were also identified.

Conclusion

The data showed that the venom of Pepsis decorata is mostly composed of proteins involved in the metabolism of arthropods, as occurs in parasitic wasps, although some classical toxins were recorded, and among them, for the first time, ACE was found in the venom of solitary wasps. This integrative approach expanded the range of compounds identified in protein analyses, proving to be efficient in the proteomic characterization of little-known species. It is our understanding that the current work will provide a solid base for future studies dealing with other Hymenoptera venoms.

Autophagy of Candida albicans cells after the action of earthworm Venetin-1 nanoparticle with protease inhibitor activity

The present studies show the effect of the Venetin-1 protein-polysaccharide complex obtained from the coelomic fluid of the earthworm Dendrobaena veneta on Candida albicans cells. They are a continuation of research on the mechanisms of action, cellular targets, and modes of cell death. After the action of Venetin-1, a reduced survival rate of the yeast cells was noted. The cells were observed to be enlarged compared to the controls and deformed. In addition, an increase in the number of cells with clearly enlarged vacuoles was noted. The detected autophagy process was confirmed using differential interference contrast, fluorescence microscopy, and transmission electron microscopy. Autophagic vesicles were best visible after incubation of fungus cells with the Venetin-1 complex at a concentration of 50 and 100 µg mL-1. The changes in the vacuoles were accompanied by changes in the size of mitochondria, which is probably related to the previously documented oxidative stress. The aggregation properties of Venetin-1 were characterized. Based on the results of the zeta potential at the Venetin-1/KCl interface, the pHiep = 4 point was determined, i.e. the zeta potential becomes positive above pH = 4 and is negative below this value, which may affect the electrostatic interactions with other particles surrounding Venetin-1.

Design of ion channel blocking, toxin-like Kunitz inhibitor peptides from the tapeworm, Echinococcus granulosus, with potential anti-cancer activity

Over-expression of K+ channels has been reported in human cancers and is associated with the poor prognosis of several malignancies. EAG1, a particular potassium ion channel, is widely expressed in the brain but poorly expressed in other normal tissues. Kunitz proteins are dominant in metazoan including the dog tapeworm, Echinococcus granulosus. Using computational analyses on one A-type potassium channel, EAG1, and in vitro cellular methods, including major cancer cell biomarkers expression, immunocytochemistry and whole-cell patch clamp, we demonstrated the anti-tumor activity of three synthetic small peptides derived from E. granulosus Kunitz4 protease inhibitors. Experiments showed induced significant apoptosis and inhibition of proliferation in both cancer cell lines via disruption in cell-cycle transition from the G0/G1 to S phase. Western blotting showed that the levels of cell cycle-related proteins including P27 and P53 were altered upon kunitz4-a and kunitz4-c treatment. Patch clamp analysis demonstrated a significant increase in spontaneous firing frequency in Purkinje neurons, and exposure to kunitz4-c was associated with an increase in the number of rebound action potentials after hyperpolarized current. This noteworthy component in nature could act as an ion channel blocker and is a potential candidate for cancer chemotherapy based on potassium channel blockage.

Peptide Inhibitors of Kv1.5: An Option for the Treatment of Atrial Fibrillation

The human voltage gated potassium channel Kv1.5 that conducts the IKur current is a key determinant of the atrial action potential. Its mutations have been linked to hereditary forms of atrial fibrillation (AF), and the channel is an attractive target for the management of AF. The development of IKur blockers to treat AF resulted in small molecule Kv1.5 inhibitors. The selectivity of the blocker for the target channel plays an important role in the potential therapeutic application of the drug candidate: the higher the selectivity, the lower the risk of side effects. In this respect, small molecule inhibitors of Kv1.5 are compromised due to their limited selectivity. A wide range of peptide toxins from venomous animals are targeting ion channels, including mammalian channels. These peptides usually have a much larger interacting surface with the ion channel compared to small molecule inhibitors and thus, generally confer higher selectivity to the peptide blockers. We found two peptides in the literature, which inhibited IKur: Ts6 and Osu1. Their affinity and selectivity for Kv1.5 can be improved by rational drug design in which their amino acid sequences could be modified in a targeted way guided by in silico docking experiments.

Transcriptomic and proteomic analyses of venom glands from scorpions Liocheles australasiae, Mesobuthus martensii, and Scorpio maurus palmatus

Scorpion venom contains a cocktail of differing peptides and proteins. Previous studies focused on the identification of species-specific components in scorpion venoms, and whether there could be peptides and/or proteins conserved in the venom gland of a scorpion ancestor has been rarely investigated. Here, using a combination of transcriptomic and proteomic approaches, putative conserved toxins from the venom glands of scorpions Liocheles australasiae, Mesobuthus martensii, and Scorpio maurus palmatus were identified and compared. Similar to other studies, more than half of the conserved toxins are predominantly proteins including proteases. On the other hand, unique venom peptides, including ion channel toxins were revealed specifically in the M. martensii. The sodium channel toxin peptides revealed in M. martensii consolidated that scorpions in the Buthidae are able to envenomate their prey wih highly neurotoxic venom. This study suggested that these conserved proteins had already formed part of the arsenal in the venom gland of the common ancestor of scorpions, and likely perform important functional roles in envenomation during scorpion evolution.

Anti-fibrinolytic activity of a metalloprotease inhibitor from bumblebee (Bombus ignitus) venom

Bee venom is a mixture of bioactive components that include proteases and protease inhibitors. A metalloprotease inhibitor has been predicted to be a bumblebee-specific toxin in the venom proteome of Bombus terrestris; however, the identification and functional roles of bee venom metalloprotease inhibitors have not been previously determined. In this study, we identified a bumblebee (B. ignitus) venom metalloprotease inhibitor (BiVMPI) that exhibits anti-fibrinolytic activity. BiVMPI contains a trypsin inhibitor-like cysteine-rich domain that exhibits similarity to inducible metalloprotease inhibitor. Using an anti-BiVMPI antibody raised against a recombinant BiVMPI protein produced in baculovirus-infected insect cells, the presence of BiVMPI in the venom gland and secreted venom of B. ignitus worker bees was confirmed. The recombinant BiVMPI protein demonstrated inhibitory activity against a metalloprotease, trypsin, chymotrypsin, protease K, and plasmin, but not subtilisin A, elastase, or thrombin. Additionally, the recombinant BiVMPI bound to plasmin and inhibited the plasmin-mediated degradation of fibrin, demonstrating an anti-fibrinolytic role for BiVMPI as a bee venom metalloprotease inhibitor. Our results provide the first evidence for the identification and anti-fibrinolytic activity of a metalloprotease inhibitor from bee venom.

An Smp43-Derived Short-Chain α-Helical Peptide Displays a Unique Sequence and Possesses Antimicrobial Activity against Both Gram-Positive and Gram-Negative Bacteria

Scorpion venoms are rich resources of antimicrobial peptides (AMPs). While the short-chain noncysteine-containing AMPs have attracted much attention as templates for drug development, the antimicrobial potential of long-chain noncysteine-containing AMPs has been largely overlooked. Here, by using the online HeliQuest server, we designed and analyzed a series of 14-residue fragments of Smp43, a 43-residue long-chain noncysteine-containing AMP identified from the venom of Scorpio maurus palmatus. We found that Smp43(1-14) shows high antimicrobial activity against both Gram-positive and Gram-negative bacteria and is nontoxic to mammalian cells at the antimicrobial dosage. Sequence alignments showed that the designed Smp43(1-14) displays a unique primary structure that is different from other natural short-chain noncysteine-containing AMPs from scorpions, such as Uy17, Uy192 and IsCT. Moreover, the peptide Smp43(1-14) caused concentration-dependent fluorescence increases in the bacteria for all of the tested dyes, propidium iodide, SYTOX^TM Green and DiSC₃-5, suggesting that the peptide may kill the bacteria through the formation of pore structures in the plasma membrane. Taken together, our work sheds light on a new avenue for the design of novel short-chain noncysteine-containing AMPs and provides a good peptide template with a unique sequence for the development of novel drugs for use against bacterial infectious diseases.

Inhibition of inflammatory cytokine production and proliferation in macrophages by Kunitz-type inhibitors from Echinococcus granulosus

The genus Echinococcus of cestode parasites includes important pathogens of humans and livestock animals. Transcriptomic and genomic studies on E. granulosus and E. multilocularis uncovered striking expansion of monodomain Kunitz proteins. This expansion is accompanied by the specialization of some family members away from the ancestral protease inhibition function to fulfill cation channel blockade functions. Since cation channels are involved in immune processes, we tested the effects on macrophage physiology of two E. granulosus Kunitz-type inhibitors of voltage-activated cation channels (K_v) that are close paralogs. Both inhibitors, EgKU-1 and EgKU-4, inhibited production of the Th1/Th17 cytokine subunit IL-12/23p40 by macrophages stimulated with the TLR4 agonist LPS. In addition, EgKU-4 but not EgKU-1 inhibited production of the inflammatory cytokine IL-6. These activities were not displayed by EgKU-3, a family member that is a protease inhibitor without known activity on cation channels. EgKU-4 potently inhibited macrophage proliferation in response to M-CSF, whereas EgKU-1 displayed similar activity but with much lower potency, similar to EgKU-3. We discuss structural differences, including a heavily cationic C-terminal extension present in EgKU-4 but not in EgKU-1, that may explain the differential activities of the two close paralogs.

Identification of an antiviral component from the venom of the scorpion Liocheles australasiae using transcriptomic and mass spectrometric analyses

Scorpion venom contains a variety of biologically active peptides. Among them, neurotoxins are major components in the venom, but it also contains peptides that show antimicrobial activity. Previously, we identified three insecticidal peptides from the venom of the Liocheles australasiae scorpion, but activities and structures of other venom components remained unknown. In this study, we performed a transcriptome analysis of the venom gland of the scorpion L. australasiae to gain a comprehensive understanding of its venom components. The result shows that potassium channel toxin-like peptides were the most diverse, whereas only a limited number of sodium channel toxin-like peptides were observed. In addition to these neurotoxin-like peptides, many non-disulfide-bridged peptides were identified, suggesting that these components have some critical roles in the L. australasiae venom. In this study, we also isolated a component with antiviral activity against hepatitis C virus using a bioassay-guided fractionation approach. By integrating mass spectrometric and transcriptomic data, we successfully identified LaPLA₂-1 as an anti-HCV component. LaPLA₂-1 is a phospholipase A₂ having a heterodimeric structure that is N-glycosylated at the N-terminal region. Since the antiviral activity of LaPLA₂-1 was inhibited by a PLA₂ inhibitor, the enzymatic activity of LaPLA₂-1 is likely to be involved in its antiviral activity.

Kunitz-Type Peptides from the Sea Anemone Heteractis crispa Demonstrate Potassium Channel Blocking and Anti-Inflammatory Activities

The Kunitz/BPTI peptide family includes unique representatives demonstrating various biological activities. Electrophysiological screening of peptides HCRG1 and HCRG2 from the sea anemone Heteractis crispa on six Kv1.x channel isoforms and insect Shaker IR channel expressed in Xenopus laevis oocytes revealed their potassium channels blocking activity. HCRG1 and HCRG2 appear to be the first Kunitz-type peptides from sea anemones blocking Kv1.3 with IC₅₀ of 40.7 and 29.7 nM, respectively. In addition, peptides mainly vary in binding affinity to the Kv1.2 channels. It was established that the single substitution, Ser5Leu, in the TRPV1 channel antagonist, HCRG21, induces weak blocking activity of Kv1.1, Kv1.2, and Kv1.3. Apparently, for the affinity and selectivity of Kunitz-fold toxins to Kv1.x isoforms, the number and distribution along their molecules of charged, hydrophobic, and polar uncharged residues, as well as the nature of the channel residue at position 379 (Tyr, Val or His) are important. Testing the compounds in a model of acute local inflammation induced by the introduction of carrageenan administration into mice paws revealed that HCRG1 at doses of 0.1–1 mg/kg reduced the volume of developing edema during 24 h, similar to the effect of the nonsteroidal anti-inflammatory drug, indomethacin, at a dose of 5 mg/kg. ELISA analysis of the animals blood showed that the peptide reduced the synthesis of TNF-α, a pro-inflammatory mediator playing a leading role in the development of edema in this model.

Identification, Characterization and Synthesis of Walterospermin, a Sperm Motility Activator from the Egyptian Black Snake Walterinnesia aegyptia Venom

Animal venoms are small natural mixtures highly enriched in bioactive components. They are known to target at least two important pharmacological classes of cell surface receptors: ion channels and G protein coupled receptors. Since sperm cells express a wide variety of ion channels and membrane receptors, required for the control of cell motility and acrosome reaction, two functions that are defective in infertility issues, animal venoms should contain interesting compounds capable of modulating these two essential physiological functions. Herein, we screened for bioactive compounds from the venom of the Egyptian black snake Walterinnesia aegyptia (Wa) that possess the property to activate sperm motility in vitro from male mice OF1. Using RP-HPLC and cation exchange chromatography, we identified a new toxin of 6389.89 Da (termed walterospermin) that activates sperm motility. Walterospermin was de novo sequenced using a combination of matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF/TOF MS/MS) and liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF MS/MS) following reduction, alkylation, and enzymatic proteolytic digestion with trypsin, chymotrypsin or V8 protease. The peptide is 57 amino acid residues long and contains three disulfide bridges and was found to be identical to the previously cloned Wa Kunitz-type protease inhibitor II (Wa Kln-II) sequence. Moreover, it has strong homology with several other hitherto cloned Elapidae and Viperidae snake toxins suggesting that it belongs to a family of compounds able to regulate sperm function. The synthetic peptide shows promising activation of sperm motility from a variety of species, including humans. Its fluorescently-labelled analog predominantly marks the flagellum, a localization in agreement with a receptor that controls motility function.

Head-to-Tail Cyclization after Interaction with Trypsin: A Scorpion Venom Peptide that Resembles Plant Cyclotides

Peptidase inhibitors (PIs) have been broadly studied due to their wide therapeutic potential for human diseases. A potent trypsin inhibitor from Tityus obscurus scorpion venom was characterized and named ToPI1, with 33 amino acid residues and three disulfide bonds. The X-ray structure of the ToPI1:trypsin complex, in association with the mass spectrometry data, indicate a sequential set of events: the complex formation with the inhibitor Lys³² in the trypsin S1 pocket, the inhibitor C-terminal residue Ser³³ cleavage, and the cyclization of ToPI1 via a peptide bond between residues Ile¹ and Lys³². Kinetic and thermodynamic characterization of the complex was obtained. ToPI1 shares no sequence similarity with other PIs characterized to date and is the first PI with CS-α/β motif described from animal venoms. In its cyclic form, it shares structural similarities with plant cyclotides that also inhibit trypsin. These results bring new insights for studies with venom compounds, PIs, and drug design.

Revealing the Venomous Secrets of the Spider's Web

Orb-weaving spiders use a highly strong, sticky and elastic web to catch their prey. These web properties alone would be enough for the entrapment of prey; however, these spiders may be hiding venomous secrets in the web, which current research is revealing. Here, we provide strong proteotranscriptomic evidence for the presence of toxin/neurotoxin-like proteins, defensins, and proteolytic enzymes on the web silk from Nephila clavipes spider. The results from quantitative-based transcriptomic and proteomic approaches showed that silk-producing glands produce an extensive repertoire of toxin/neurotoxin-like proteins, similar to those already reported in spider venoms. Meanwhile, the insect toxicity results demonstrated that these toxic components can be lethal and/or paralytic chemical weapons used for prey capture on the web, and the presence of fatty acids in the web may be a responsible mechanism opening the way to the web toxins for accessing the interior of prey's body, as shown here. Comparative phylogenomic-level evolutionary analyses revealed orthologous genes among two spider groups, Araneomorphae and Mygalomorphae, and the findings showed protein sequences similar to toxins found in the taxa Scorpiones and Hymenoptera in addition to Araneae. Overall, these data represent a valuable resource to further investigate other spider web toxin systems and also suggest that N. clavipes web is not a passive mechanical trap for prey capture, but it exerts an active role in prey paralysis/killing using a series of neurotoxins.

Cloning and identification of a new multifunctional Ascaris-type peptide from the hemolymph of Buthus martensii Karsch

Only a few work have been done for peptides from non-venom gland tissues of venomous animals. Here, with the help of the whole body transcriptomic and the hemolymph proteomic data of the Chinese scorpion Buthus martensii Karsch, we identified the first Ascaris-type peptide BmHDP from scorpion hemolymph. The precursor of BmHDP has 80 residues, including a 16 residue signal peptide and a 64 residue mature peptide. The mature peptide has 10 conserved cysteines and adopts a conserved Ascaris-type fold. Using combined inclusion body refolding and biochemical identification strategies, recombinant BmHDP was obtained successfully. Protease inhibitory assays showed that BmHDP inhibited chymotrypsin apparently at a concentration of 8 nM. Patch-clamp experiments showed that BmHDP inhibited the Kv1.3 potassium channel apparently at a concentration of 1000 nM. Coagulation experiment assays showed that BmHDP inhibited intrinsic coagulation pathway apparently at a concentration of 500 nM. To the best of our knowledge, BmHDP is the first Ascaris-type peptide from scorpion hemolymph. Our work highlighted a functional link between scorpion non-venom gland peptides and venom gland toxin peptides, and suggested that scorpion hemolymph might be a new source of bioactive peptides.

NaStEP, an essential protein for self-incompatibility in Nicotiana, performs a dual activity as a proteinase inhibitor and as a voltage-dependent channel blocker

The S-specific pollen rejection response in Nicotiana depends on the interaction between S-RNase and a suite of SLF proteins. However, the biochemical pathway requires other essential proteins. One of them is the stigmatic protein NaStEP, which belongs to the Kunitz-type protease inhibitor family. Within the pollen tubes, NaStEP is a positive regulator of HT-B stability, likely inhibiting its degradation and, additionally, interacts with NaSIPP, a mitochondrial phosphate carrier. To gain a deeper understanding of the biochemical role of NaStEP in pollen rejection, we evaluated whether the activity of NaStEP as protease inhibitor is specific to a particular type of protease and whether it has the function of a voltage-dependent channel (VDC) blocker. Our findings indicate that, in vitro, NaStEP inhibits a subtilisin-like protease in an irreversible manner, but not other proteases, such as thermolysin and papain. Furthermore, we found that subtilisin processes the native NaStEP (24 kDa) into two lower molecular weight peptides of 21 and 14 kDa. Moreover, when we incubated NaStEP along with Xenopus leavis oocytes expressing the voltage-dependent potassium channel Kv 1.3, the current was blocked, indicating that NaStEP acts as a VDC blocker. These data allow us to propose NaStEP acts as a key molecule with two functions, one protecting HT-B from degradation by inhibiting a subtilisin-like protease and the second one by forming a complex with a mitochondrial VDC that could destabilize the mitochondria to trigger cell death, which would reinforce S-specific pollen rejection in Nicotiana.

Transcriptomic and proteomic analyses of the venom and venom glands of Centruroides hirsutipalpus, a dangerous scorpion from Mexico

Centruroides hirsutipalpus (Scorpiones: Buthidae) is related to the "striped scorpion" group inhabiting the western Pacific region of Mexico. Human accidents caused by this species are medically important due to the great number of people stung and the severity of the resulting intoxication. This communication reports an extensive venom characterization using high-throughput proteomic and Illumina transcriptomic sequencing performed with RNA purified from its venom glands. 2,553,529 reads were assembled into 44,579 transcripts. From these transcripts, 23,880 were successfully annoted using Trinotate. Using specialized databases and by performing bioinformatic searches, it was possible to identify 147 putative venom protein transcripts. These include α- and β-type sodium channel toxins (NaScTx), potassium channel toxins (KScTx) (α-, β-, δ-, γ- and λ-types), enzymes (metalloproteases, hyaluronidases, phospholipases, serine proteases, and monooxygenases), protease inhibitors, host defense peptides (HDPs) such as defensins, non-disulfide bridge peptides (NDBPs), anionic peptides, superfamily CAP proteins, insulin growth factor-binding proteins (IGFBPs), orphan peptides, and other venom components (La1 peptides). De novo tandem mass spectrometric sequencing of digested venom identificatied 50 peptides. The venom of C. hirsutipalpus contains the highest reported number (77) of transcripts encoding NaScTxs, which are the components responsible for human fatalities.

Tick-Borne Encephalitis Virus Infection Alters the Sialome of Ixodes ricinus Ticks During the Earliest Stages of Feeding

Ticks are hematophagous arthropods that transmit a number of pathogens while feeding. Among these is tick-borne encephalitis virus (TBEV), a flavivirus transmitted by Ixodes ricinus ticks in the temperate zone of Europe. The infection results in febrile illness progressing to encephalitis and meningitis with a possibility of fatality or long-term neurological sequelae. The composition of tick saliva plays an essential role in the initial virus transmission during tick feeding. Ticks secrete a diverse range of salivary proteins to modulate the host response, such as lipocalins to control the itch and inflammatory response, and both proteases and protease inhibitors to prevent blood coagulation. Here, the effect of viral infection of adult females of Ixodes ricinus was studied with the goal of determining how the virus alters the tick sialome to modulate host tissue response at the site of infection. Uninfected ticks or those infected with TBEV were fed on mice and removed and dissected one- and 3-h post-attachment. RNA from the salivary glands of these ticks, as well as from unfed ticks, was extracted and subjected to next-generation sequencing to determine the expression of key secreted proteins at each timepoint. Genes showing statistically significant up- or down-regulation between infected and control ticks were selected and compared to published literature to ascertain their function. From this, the effect of tick viral infection on the modulation of the tick-host interface was determined. Infected ticks were found to differentially express a number of uncategorized genes, proteases, Kunitz-type serine protease inhibitors, cytotoxins, and lipocalins at different timepoints. These virus-induced changes to the tick sialome may play a significant role in facilitating virus transmission during the early stages of tick feeding.

Tacrine modulates Kv2.1 channel gene expression and cell proliferation

Purpose/Aim: Besides as a cholinesterase (ChE) inhibitor, tacrine is able to act on multiple targets such as nicotinic receptors (nAChRs) and voltage-gated K⁺ (Kv) channels. Kv2.1, a Kv channel subunit underlying delayed rectifier currents with slow kinetics of inactivation, is highly expressed in the mammalian brain, especially in the hippocampus. Nevertheless, limited data are available concerning the relationship between tacrine and Kv2.1 channels. In the present study, we explore the possible effects of tacrine on Kv2.1 channels in heterologous expression systems and N2A cells.Materials and methods: The change of expression and currents of Kv2.1 after treatment with tacrine was detected by PCR and whole-cell recordings, respectively. WST-8 experiments were performed to reveal the effects of tacrine on cell proliferation.Results: Incubation with tacrine induced a significant reduction of the mRNA level of Kv2.1 channels in HEK293 cells. The decline of corresponding currents carried by Kv2.1 was also observed. Moreover, the proliferation rates of HEK293 cells with Kv2.1 channel were substantially enhanced after treatment with this chemical for 24 h. Similar results were also detected after exposure to tacrine in N2A cells with native expression of Kv2.1 channels.Conclusion: These lines of evidence indicate that application of tacrine downregulates the expression of Kv2.1 channels and increase cell proliferation. The effect of tacrine on Kv2.1 channels may provide an alternative explanation for its neuroprotective action.

Proteomic-components provide insights into the defensive secretion in termite workers of the soldierless genus Ruptitermes

Termite soldiers constitute the defensive frontline of the colonies, despite workers also perform such tasks, especially within the Neotropical Apicotermitinae, in which all species are soldierless. Workers of the genus Ruptitermes display an extreme form of defense, characterized by body rupture and release of a sticky secretion. Previous observations suggested that such behavior may be advantageous against enemies, but the chemical composition of this secretion has been neglected. Here we firstly provide the proteomic profile of the defensive secretion of Ruptitermes reconditus and Ruptitermes pitan workers. Additionally, the mechanisms of action of this behavior was evaluated through different bioassays. A total of 446 proteins were identified in R. reconditus and 391 proteins in R. pitan, which were classified into: toxins, defensins and proteolytic enzymes; sticky components/ alarm communication; proteins related to detoxification processes; proteins involved in folding/conformation and post-translational modifications; housekeeping proteins; and uncharacterized/hypothetical proteins. According to the bioassays, the self-sacrifice is triggered by a physical stimulus, and the defensive secretion may cause immobility and death of the opponents. Assuming that termites are abundant in the tropics and therefore exposed to predators, suicidal behaviors seem to be advantageous, since the loss of an individual benefit the whole colony. SIGNIFICANCE: Although recent studies have reported the biochemical composition of different weapons in soldiered species of termites, such efforts had not been applied to sordierless taxa up until now. Thus, this is the first report of the defensive mechanisms in soldierless termite species based on proteomic analysis. The diversity of compounds, which included toxin-like and mucin-like proteins, reflect the mechanisms of action of the defensive secretion released by termite workers, which may cause immobility and death of the opponents. Our findings may contribute to the knowledge regarding the development of defensive strategies in termites, especially in groups which lost the soldier caste during the evolution.

Hadrurid Scorpion Toxins: Evolutionary Conservation and Selective Pressures

Scorpion toxins are thought to have originated from ancestral housekeeping genes that underwent diversification and neofunctionalization, as a result of positive selection. Our understanding of the evolutionary origin of these peptides is hindered by the patchiness of existing taxonomic sampling. While recent studies have shown phylogenetic inertia in some scorpion toxins at higher systematic levels, evolutionary dynamics of toxins among closely related taxa remain unexplored. In this study, we used new and previously published transcriptomic resources to assess evolutionary relationships of closely related scorpions from the family Hadruridae and their toxins. In addition, we surveyed the incidence of scorpine-like peptides (SLP, a type of potassium channel toxin), which were previously known from 21 scorpion species. We demonstrate that scorpine-like peptides exhibit gene duplications. Our molecular analyses demonstrate that only eight sites of two SLP copies found in scorpions are evolving under positive selection, with more sites evolving under negative selection, in contrast to previous findings. These results show evolutionary conservation in toxin diversity at shallow taxonomic scale.

Venoms of Iranian Scorpions (Arachnida, Scorpiones) and Their Potential for Drug Discovery

Scorpions, a characteristic group of arthropods, are among the earliest diverging arachnids, dating back almost 440 million years. One of the many interesting aspects of scorpions is that they have venom arsenals for capturing prey and defending against predators, which may play a critical role in their evolutionary success. Unfortunately, however, scorpion envenomation represents a serious health problem in several countries, including Iran. Iran is acknowledged as an area with a high richness of scorpion species and families. The diversity of the scorpion fauna in Iran is the subject of this review, in which we report a total of 78 species and subspecies in 19 genera and four families. We also list some of the toxins or genes studied from five species, including Androctonus crassicauda, Hottentotta zagrosensis, Mesobuthus phillipsi, Odontobuthus doriae, and Hemiscorpius lepturus, in the Buthidae and Hemiscorpiidae families. Lastly, we review the diverse functions of typical toxins from the Iranian scorpion species, including their medical applications.

Diverse Structural Features of Potassium Channels Characterized by Scorpion Toxins as Molecular Probes

Scorpion toxins are well-known as the largest potassium channel peptide blocker family. They have been successfully proven to be valuable molecular probes for structural research on diverse potassium channels. The potassium channel pore region, including the turret and filter regions, is the binding interface for scorpion toxins, and structural features from different potassium channels have been identified using different scorpion toxins. According to the spatial orientation of channel turrets with differential sequence lengths and identities, conformational changes and molecular surface properties, the potassium channel turrets can be divided into the following three states: open state with less hindering effects on toxin binding, half-open state or half-closed state with certain effects on toxin binding, and closed state with remarkable effects on toxin binding. In this review, we summarized the diverse structural features of potassium channels explored using scorpion toxin tools and discuss future work in the field of scorpion toxin-potassium channel interactions.

Dissecting Toxicity: The Venom Gland Transcriptome and the Venom Proteome of the Highly Venomous Scorpion Centruroides limpidus (Karsch, 1879)

Venom glands and soluble venom from the Mexican scorpion Centruroides limpidus (Karsch, 1879) were used for transcriptomic and proteomic analyses, respectively. An RNA-seq was performed by high-throughput sequencing with the Illumina platform. Approximately 80 million reads were obtained and assembled into 198,662 putative transcripts, of which 11,058 were annotated by similarity to sequences from available databases. A total of 192 venom-related sequences were identified, including Na⁺ and K⁺ channel-acting toxins, enzymes, host defense peptides, and other venom components. The most diverse transcripts were those potentially coding for ion channel-acting toxins, mainly those active on Na⁺ channels (NaScTx). Sequences corresponding to β- scorpion toxins active of K⁺ channels (KScTx) and λ-KScTx are here reported for the first time for a scorpion of the genus Centruroides. Mass fingerprint corroborated that NaScTx are the most abundant components in this venom. Liquid chromatography coupled to mass spectometry (LC-MS/MS) allowed the identification of 46 peptides matching sequences encoded in the transcriptome, confirming their expression in the venom. This study corroborates that, in the venom of toxic buthid scorpions, the more abundant and diverse components are ion channel-acting toxins, mainly NaScTx, while they lack the HDP diversity previously demonstrated for the non-buthid scorpions. The highly abundant and diverse antareases explain the pancreatitis observed after envenomation by this species.

Scorpion toxins targeting Kv1.3 channels: insights into immunosuppression

Scorpion venoms are natural sources of molecules that have, in addition to their toxic function, potential therapeutic applications. In this source the neurotoxins can be found especially those that act on potassium channels. Potassium channels are responsible for maintaining the membrane potential in the excitable cells, especially the voltage-dependent potassium channels (Kv), including Kv1.3 channels. These channels (Kv1.3) are expressed by various types of tissues and cells, being part of several physiological processes. However, the major studies of Kv1.3 are performed on T cells due its importance on autoimmune diseases. Scorpion toxins capable of acting on potassium channels (KTx), mainly on Kv1.3 channels, have gained a prominent role for their possible ability to control inflammatory autoimmune diseases. Some of these toxins have already left bench trials and are being evaluated in clinical trials, presenting great therapeutic potential. Thus, scorpion toxins are important natural molecules that should not be overlooked in the treatment of autoimmune and other diseases.

Computational Protein-Protein Docking Reveals the Therapeutic Potential of Kunitz-type Venom against hKv1.2 Binding Sites

BACKGROUND & OBJECTIVE

Kunitz-type venoms are bioactive proteins isolated from a wide variety of venomous animals. These venoms are involved in protease inhibitory activity or potassium channel blocking activity. Therefore, they are reported as an important source for lead drug candidates towards protease or channel associated diseases like neurological, metabolic and cardiovascular disorders.

METHODS

This study aimed to check the inhibitory action of Kunitz-type venoms against potassium channels using computational tools.

RESULTS

Among potassium channels, Human Voltage-Gated Potassium Channel 1.2 (hKv1.2) was used as a receptor whereas Kunitz-type peptides from the venoms of various species were selected as ligand dataset.

CONCLUSION

This study helped in finding the binding interface between the receptor and ligand dataset for their potential therapeutic use in treating potassium channelopathies.

Defensins, a novel type of animal toxin-like potassium channel inhibitor

The classical potassium channel inhibitors are toxin peptides from venomous animals, and whether there are peptide inhibitors from other species is an open question. Due to both the independent and interdependent relationships between the spear (peptide inhibitors) and the shield (potassium channels), human defensins were first identified by our group as endogenous potassium channel inhibitors. Encouraged by the discovery of human defensins as potassium channel inhibitors, defensins from invertebrates and fungi were successively found by our group to be potassium channel inhibitors. In addition, a plant defensin was reported to be a potassium channel inhibitor. Since defensins are widely produced by vertebrate, invertebrate, plant and fungi species, the recent work established a new research field on defensin-potassium channel interactions. Here, we review the current work on defensins from vertebrate, invertebrate, plant and fungi species as inhibitors of potassium channels and discuss future work in this research field.

KV1.2 channel-specific blocker from Mesobuthus eupeus scorpion venom: Structural basis of selectivity

Scorpion venom is an unmatched source of selective high-affinity ligands of potassium channels. There is a high demand for such compounds to identify and manipulate the activity of particular channel isoforms. The objective of this study was to obtain and characterize a specific ligand of voltage-gated potassium channel K_V1.2. As a result, we report the remarkable selectivity of the peptide MeKTx11-1 (α-KTx 1.16) from Mesobuthus eupeus scorpion venom to this channel isoform. MeKTx11-1 is a high-affinity blocker of K_V1.2 (IC₅₀ ∼0.2 nM), while its activity against K_V1.1, K_V1.3, and K_V1.6 is 10 000, 330 and 45 000 fold lower, respectively, as measured using the voltage-clamp technique on mammalian channels expressed in Xenopus oocytes. Two substitutions, G9V and P37S, convert MeKTx11-1 to its natural analog MeKTx11-3 (α-KTx 1.17) having 15 times lower activity and reduced selectivity to K_V1.2. We produced MeKTx11-1 and MeKTx11-3 as well as their mutants MeKTx11-1(G9V) and MeKTx11-1(P37S) recombinantly and demonstrated that point mutations provide an intermediate effect on selectivity. Key structural elements that explain MeKTx11-1 specificity were identified by molecular modeling of the toxin-channel complexes. Confirming our molecular modeling predictions, site-directed transfer of these elements from the pore region of K_V1.2 to K_V1.3 resulted in the enhanced sensitivity of mutant K_V1.3 channels to MeKTx11-1. We conclude that MeKTx11-1 may be used as a selective tool in neurobiology.

Characterization and molecular basis for the block of Kv1.3 channels induced by carvedilol in HEK293 cells

Carvedilol is a non-selective β-adrenoreceptor antagonist and exhibits a wide range of biological activities. The voltage-gated K⁺ (Kv) channel is one of the target ion channels of this compound. The rapidly activating Kv1.3 channel is expressed in several different tissues and plays an important role in the regulation of physiological functions, including cell proliferation and apoptosis. However, little is known about the possible action of carvedilol on Kv1.3 currents. Using the whole-cell configuration of the patch-clamp technique, we have revealed that exposure to carvedilol produced a concentration-dependent blocking of Kv1.3 channels heterologously expressed in HEK293 cells, with an IC₅₀ value of 9.7 μM. This chemical decelerated the deactivation tail current of Kv1.3 currents, resulting in a tail crossover phenomenon. In addition, carvedilol generated a markedly hyperpolarizing shift (20 mV) of the inactivation curve, but failed to affect the activation curve. Mutagenesis experiments of Kv1.3 channels identified G427 and H451, two related sites of TEA block, as important residues for carvedilol-mediated blocking. The present results suggest that carvedilol acts directly on Kv1.3 currents by inducing closed- and open-channel block and helps to elucidate the mechanisms of action of this compound on Kv channels.

Engineering varied serine protease inhibitors by converting P1 site of BF9, a weakly active Kunitz-type animal toxin

Although there were a lot of weakly active animal toxins in the venoms, their values and applications are still mysterious, such as BF9, which is a Kunitz-type toxin isolated from the venom of the elapid snake Bungarus fasciatus. Here, we used BF9 to be a molecular scaffold, and engineered eight BF9-derived peptides by changing P1 site Asn17 of BF9, such as BF9-N17Y and BF9-N17T designed from the polar subfamily, BF9-N17L and BF9-N17G designed from the Non-polar subfamily, BF9-N17D designed from acidic subfamily, and BF9-N17H, BF9-N17K and BF9-N17R designed from basic subfamily. Through enzyme inhibitor experiment assays, we found a potent and selective chymotrypsin inhibitor BF9-N17Y, a potent and selective coagulation factor XIa inhibitor BF9-N17H, and two highly potent coagulation factor XIa inhibitors BF9-N17K and BF9-N17. APTT and PT assays further showed that BF9-N17H, BF9-N17K and BF9-N17R were three novel anticoagulants with selectively intrinsic coagulation pathway inhibitory activity. Considering that natural weakly active animal toxins are also a huge peptide resource, our present work might open a new window about pharmacological applications of weakly active animal toxins, which might be good templates for potent and selective molecular probe and lead drug designs.

The Kv1.3 channel-inhibitory toxin BF9 also displays anticoagulant activity via inhibition of factor XIa

The Kv1.3 channel plays potential roles in immune, inflammation and coagulation system. Many studies showed that Kv1.3 channel inhibitors have immunosuppressive and anti-inflammatory activities, but no Kv1.3 channel inhibitors have been found to have anticoagulation activities. Here, based on our previous work about Kv1.3 channel toxin peptide inhibitors, we first attempt to test anticoagulation activities of four known venom-derived Kv1.3 channel inhibitors with different structural folds: BmKTX with CSα/β structural fold, OmTx3 with CSα/α structural fold, BF9 with Kuntz-type structural fold, and SjAPI-2 with Ascaris-type structural fold. Our results showed that BmKTX and OmTx3 have no activities towards both intrinsic and extrinsic coagulation pathway, SjAPI-2 just has weak activity towards intrinsic coagulation pathway, and BF9 has potent activity towards intrinsic coagulation pathway with no apparent effect on extrinsic coagulation pathway. Enzyme and inhibitor reaction kinetics experiments further showed that BF9 inhibited intrinsic coagulation pathway-associated coagulation factor XIa, but have no apparent effects on common coagulation pathway coagulation factor IIa. Structure-activity relationship showed that Gly14, Asn17, Ala18 and Ile20 of BF9 are main residues involved in the inhibiting effect on factor XIa. To the best of our knowledge, BF9 is the first anticoagulant with Kv1.3 channel inhibitory activity. Together, our present studies found the first dual functional peptides with Kv1.3 channel and coagulation factor XIa inhibitory activities, and provided a new molecular template for the lead drug discovery towards immune and thrombosis-associated human diseases.

Mouse β-Defensin 3, A Defensin Inhibitor of Both Its Endogenous and Exogenous Potassium Channels

The human defensins are recently discovered to inhibit potassium channels, which are classical targets of the animal toxins. Whether other vertebrate defensins are potassium channel inhibitors remains unknown. In this work, we reported that the mouse β-defensin 3 (mBD3) was a novel inhibitor of both endogenous and exogenous potassium channels. The structural analysis showed that mBD3 is the most identical to human Kv1.3 channel-sensitive human β-defensin 2 (hBD2). However, the pharmacological profiles indicated that the recombinant mBD3 (rmBD3) weakly inhibited the mouse and human Kv1.3 channels. Different from the pharmacological features of human β-defensins, mBD3 more selectively inhibited the mouse Kv1.6 and human KCNQ1/KCNE1 channels with IC₅₀ values of 0.6 ± 0.4 μM and 1.2 ± 0.8 μM, respectively. The site directed mutagenesis experiments indicated that the extracellular pore region of mouse Kv1.6 channel was the interaction site of rmBD3. In addition, the minor effect on the channel conductance-voltage relationship curves implied that mBD3 might bind the extracellular transmembrane helices S1-S2 linker and/or S3-S4 linker of mouse Kv1.6 channel. Together, these findings not only revealed mBD3 as a novel inhibitor of both endogenous and exogenous potassium channels, but also provided a clue to investigate the role of mBD3-Kv1.6 channel interaction in the physiological and pathological field in the future.

Microbial production of toxins from the scorpion venom: properties and applications

Scorpion venom are composed mainly of bioactive proteins and peptides that may serve as lead compounds for the design of biotechnological tools and therapeutic drugs. However, exploring the therapeutic potential of scorpion venom components is mainly impaired by the low yield of purified toxins from milked venom. Therefore, production of toxin-derived peptides and proteins by heterologous expression is the strategy of choice for research groups and pharmaceutical industry to overcome this limitation. Recombinant expression in microorganisms is often the first choice, since bacteria and yeast systems combine high level of recombinant protein expression, fast cell growth and multiplication and simple media requirement. Herein, we present a comprehensive revision, which describes the scorpion venom components that were produced in their recombinant forms using microbial systems. In addition, we highlight the pros and cons of performing the heterologous expression of these compounds, regarding the particularities of each microorganism and how these processes can affect the application of these venom components. The most used microbial system in the heterologous expression of scorpion venom components is Escherichia coli (85%), and among all the recombinant venom components produced, 69% were neurotoxins. This review may light up future researchers in the choice of the best expression system to produce scorpion venom components of interest.

Transcriptomic Analysis of Pseudoscorpion Venom Reveals a Unique Cocktail Dominated by Enzymes and Protease Inhibitors

Transcriptomic and genomic analyses have illuminated the diversity of venoms in three of the four venomous arachnid orders (scorpions, spiders, and ticks). To date, no venom gland transcriptome analysis has been available for pseudoscorpions, the fourth venomous arachnid lineage. To redress this gap, we sequenced an mRNA library generated from the venom glands of the species Synsphyronus apimelus (Garypidae). High-throughput sequencing by the Illumina protocol, followed by de novo assembly, resulted in a total of 238,331 transcripts. From those, we annotated 131 transcripts, which code for putative peptides/proteins with similar sequences to previously reported venom components available from different arachnid species in protein databases. Transcripts putatively coding for enzymes showed the richest diversity, followed by other venom components such as peptidase inhibitors, cysteine-rich peptides, and thyroglobulin 1-like peptides. Only 11 transcripts were found that code for putatively low molecular mass spider toxins. This study constitutes the first report of the diversity of components within pseudoscorpion venom.

Novel Kunitz-like Peptides Discovered in the Zoanthid Palythoa caribaeorum through Transcriptome Sequencing

Palythoa caribaeorum (class Anthozoa) is a zoanthid that together jellyfishes, hydra, and sea anemones, which are venomous and predatory, belongs to the Phyllum Cnidaria. The distinguished feature in these marine animals is the cnidocytes in the body tissues, responsible for toxin production and injection that are used majorly for prey capture and defense. With exception for other anthozoans, the toxin cocktails of zoanthids have been scarcely studied and are poorly known. Here, on the basis of the analysis of P. caribaeorum transcriptome, numerous predicted venom-featured polypeptides were identified including allergens, neurotoxins, membrane-active, and Kunitz-like peptides (PcKuz). The three predicted PcKuz isotoxins (1-3) were selected for functional studies. Through computational processing comprising structural phylogenetic analysis, molecular docking, and dynamics simulation, PcKuz3 was shown to be a potential voltage gated potassium-channel inhibitor. PcKuz3 fitted well as new functional Kunitz-type toxins with strong antilocomotor activity as in vivo assessed in zebrafish larvae, with weak inhibitory effect toward proteases, as evaluated in vitro. Notably, PcKuz3 can suppress, at low concentration, the 6-OHDA-induced neurotoxicity on the locomotive behavior of zebrafish, which indicated PcKuz3 may have a neuroprotective effect. Taken together, PcKuz3 figures as a novel neurotoxin structure, which differs from known homologous peptides expressed in sea anemone. Moreover, the novel PcKuz3 provides an insightful hint for biodrug development for prospective neurodegenerative disease treatment.

Expanding the pharmacological profile of κ-hefutoxin 1 and analogues: A focus on the inhibitory effect on the oncogenic channel Kv10.1

Peptide toxins, such as scorpion peptides, are interesting lead compounds in the search for novel drugs. In this paper, the focus is on the scorpion peptide κ-hefutoxin 1. This peptide displays a cysteine-stabilized helix-loop-helix fold (CSα/α) and is known to be a weak K_v1.x inhibitor. Due to the low affinity of κ-hefutoxin 1 for these channels, it is assumed that the main target(s) of κ-hefutoxin 1 remain(s) unknown. In order to identify novel targets, electrophysiological measurements and antifungal assays were performed. The effect of κ-hefutoxin 1 was previously evaluated on a panel of 11 different voltage-gated potassium channels. Here, we extended this target screening with the oncogenic potassium channel K_v10.1. κ-Hefutoxin 1 was able to inhibit this channel in a dose-dependent manner (IC₅₀∼26μM). Although the affinity is rather low, this is the first peptide toxin ever described to be a K_v10.1 inhibitor. The structure-activity relationship of κ-hefutoxin 1 on K_v10.1 was investigated by testing eight κ-hefutoxin 1 variants using the two-electrode voltage clamp technique. Several important amino acid residues were identified; the functional dyad residues (Tyr⁵ and Lys¹⁹), N-terminal residues (Gly¹ and His²) and the amidated C-terminal residue (Cys²²). Since the CSα/α fold is also found in a class of antifungal plant peptides, the α-hairpinines, we investigated the antifungal activity of κ-hefutoxin 1. κ-Hefutoxin 1 showed low activity against the plant pathogen Fusarium culmorum and no activity against three other yeast and fungal species, even at high concentrations (∼100μM).

Molecular Dynamics Simulation Reveals Specific Interaction Sites between Scorpion Toxins and Kv1.2 Channel: Implications for Design of Highly Selective Drugs

The K_v1.2 channel plays an important role in the maintenance of resting membrane potential and the regulation of the cellular excitability of neurons, whose silencing or mutations can elicit neuropathic pain or neurological diseases (e.g., epilepsy and ataxia). Scorpion venom contains a variety of peptide toxins targeting the pore region of this channel. Despite a large amount of structural and functional data currently available, their detailed interaction modes are poorly understood. In this work, we choose four K_v1.2-targeted scorpion toxins (Margatoxin, Agitoxin-2, OsK-1, and Mesomartoxin) to construct their complexes with K_v1.2 based on the experimental structure of ChTx-K_v1.2. Molecular dynamics simulation of these complexes lead to the identification of hydrophobic patches, hydrogen-bonds, and salt bridges as three essential forces mediating the interactions between this channel and the toxins, in which four K_v1.2-specific interacting amino acids (D353, Q358, V381, and T383) are identified for the first time. This discovery might help design highly selective K_v1.2-channel inhibitors by altering amino acids of these toxins binding to the four channel residues. Finally, our results provide new evidence in favor of an induced fit model between scorpion toxins and K⁺ channel interactions.

Arthropod toxins acting on neuronal potassium channels

Arthropod venoms are a rich mixture of biologically active compounds exerting different physiological actions across diverse phyla and affecting multiple organ systems including the central nervous system. Venom compounds can inhibit or activate ion channels, receptors and transporters with high specificity and affinity providing essential insights into ion channel function. In this review, we focus on arthropod toxins (scorpions, spiders, bees and centipedes) acting on neuronal potassium channels. A brief description of the K⁺ channels classification and structure is included and a compendium of neuronal K⁺ channels and the arthropod toxins that modify them have been listed. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'