A new Kunitz-type plasmin inhibitor from scorpion venom

Exploration of Novel Plasmin Inhibitor from β-Lactoglobulin for Enhancing the Storage Stability of UHT Milk

Plasmin-induced protein hydrolysis significantly compromises the stability of ultrahigh-temperature (UHT) milk. β-Lactoglobulin (β-Lg) was observed to inhibit plasmin activity, suggesting that there were active sites as plasmin inhibitors in β-Lg. Herein, plasmin inhibitory peptides were explored from β-Lg using experimental and computational techniques. The results revealed that increased denaturation of β-Lg enhanced its affinity for plasmin, leading to a stronger inhibition of plasmin activity. Molecular dynamics simulations indicated that electrostatic and van der Waals forces were the primary binding forces in the β-Lg/plasmin complex. Denatured β-Lg increased hydrogen bonding and reduced the binding energy with plasmin. The sites of plasmin bound to β-Lg were His624, Asp667, and Ser762. Four plasmin inhibitory peptides, QTMKGLDI, EKTKIPAV, TDYKKYLL, and CLVRTPEV, were identified from β-Lg based on binding sites. These peptides effectively inhibited plasmin activity and enhanced the UHT milk stability. This study provided new insights into the development of novel plasmin inhibitors to improve the stability of UHT milk.

Unveiling the Protein Components of the Secretory-Venom Gland and Venom of the Scorpion Centruroides possanii (Buthidae) through Omic Technologies

Centruroides possanii is a recently discovered species of "striped scorpion" found in Mexico. Certain species of Centruroides are known to be toxic to mammals, leading to numerous cases of human intoxications in the country. Venom components are thought to possess therapeutic potential and/or biotechnological applications. Hence, obtaining and analyzing the secretory gland transcriptome and venom proteome of C. possanii is relevant, and that is what is described in this communication. Since this is a newly described species, first, its LD50 to mice was determined and estimated to be 659 ng/g mouse weight. Using RNA extracted from this species and preparing their corresponding cDNA fragments, a transcriptome analysis was obtained on a Genome Analyzer (Illumina) using the 76-base pair-end sequencing protocol. Via high-throughput sequencing, 19,158,736 reads were obtained and ensembled in 835,204 sequences. Of them, 28,399 transcripts were annotated with Pfam. A total of 244 complete transcripts were identified in the transcriptome of C. possanii. Of these, 109 sequences showed identity to toxins that act on ion channels, 47 enzymes, 17 protease inhibitors (PINs), 11 defense peptides (HDPs), and 60 in other components. In addition, a sample of the soluble venom obtained from this scorpion was analyzed using an Orbitrap Velos apparatus, which allowed for identification by liquid chromatography followed by mass spectrometry (LC-MS/MS) of 70 peptides and proteins: 23 toxins, 27 enzymes, 6 PINs, 3 HDPs, and 11 other components. Until now, this work has the highest number of scorpion venom components identified through omics technologies. The main novel findings described here were analyzed in comparison with the known data from the literature, and this process permitted some new insights in this field.

Evolution, expression patterns and distribution of novel ribbon worm predatory and defensive toxins

Ribbon worms are active predators that use an eversible proboscis to inject venom into their prey and defend themselves with toxic epidermal secretions. Previous work on nemertean venom has largely focused on just a few species and has not investigated the different predatory and defensive secretions in detail. Consequently, our understanding of the composition and evolution of ribbon worm venoms is still very limited. Here, we present a comparative study of nemertean venom combining RNA-seq differential gene expression analyses of venom-producing tissues, tandem mass spectrometry-based proteomics of toxic secretions, and mass spectrometry imaging of proboscis sections, to shed light onto the composition and evolution of predatory and defensive toxic secretions in Antarctonemertes valida. Our analyses reveal a wide diversity of putative defensive and predatory toxins with tissue-specific gene expression patterns and restricted distributions to the mucus and proboscis proteomes respectively, suggesting that ribbon worms produce distinct toxin cocktails for predation and defense. Our results also highlight the presence of numerous lineage-specific toxins, indicating that venom evolution is highly divergent across nemerteans, producing toxin cocktails that might be finely tuned to subdue different prey. Our data also suggest that the hoplonemertean proboscis is a highly specialized predatory organ that seems to be involved in a variety of biological functions besides predation, including secretion and sensory perception. Overall, our results advance our knowledge into the diversity and evolution of nemertean venoms and highlight the importance of combining different types of data to characterize toxin composition in understudied venomous organisms.

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.

Targeting Trypanosoma evansi with disulphide-rich peptides derived from a phage display library

A phage-display library was generated using a Bus thalamus scorpion toxin (BTK-2) as a peptide scaffold. BTK-2 belongs to the disulfide-rich family of proteins with pronounced structural stability due to the presence of three disulfide bridges that connects antiparallel beta-sheets and one alpha helix. Using BTK-2 as a phage display scaffold, we introduced mutations in five residues located in the alpha-helix and two residues located in the smaller loop, keeping intact the disulfide bridges to create a peptide phage-displayed library with disulfide-rich family properties. The library was subjected to in vivo and in vitro phage display selections against Trypanosoma evansi, the etiological agent of "Surra", a disease that affects a wide range of mammals. The development of T. evansi specific biomarkers is essential to improve diagnostic methods and epidemiological studies leading to a more accurate clinical decision for the treatment of this disease of economic impact for commercial livestock production. In this study, we identified two disulfide-rich peptides targeting T. evansi parasites. Further specificity studies are necessary to investigate the potential of selected peptides as new biomarkers to aid diagnostic and treatment procedures of T. evansi infections.

Identification and Characterization of ShSPI, a Kazal-Type Elastase Inhibitor from the Venom of Scolopendra Hainanum

Elastase is a globular glycoprotein and belongs to the chymotrypsin family. It is involved in several inflammatory cascades on the basis of cleaving the important connective tissue protein elastin, and is strictly regulated to a balance by several endogenous inhibitors. When elastase and its inhibitors are out of balance, severe diseases will develop, especially those involved in the cardiopulmonary system. Much attention has been attracted in seeking innovative elastase inhibitors and various advancements have been taken on clinical trials of these inhibitors. Natural functional peptides from venomous animals have been shown to have anti-protease properties. Here, we identified a kazal-type serine protease inhibitor named ShSPI from the cDNA library of the venom glands of Scolopendra hainanum. ShSPI showed significant inhibitory effects on porcine pancreatic elastase and human neutrophils elastase with Ki values of 225.83 ± 20 nM and 12.61 ± 2 nM, respectively. Together, our results suggest that ShSPI may be an excellent candidate to develop a drug for cardiopulmonary diseases.

Fibrinolysis Inhibitors: Potential Drugs for the Treatment and Prevention of Bleeding

Hyperfibrinolytic situations can lead to life-threatening bleeding, especially during cardiac surgery. The approved antifibrinolytic agents such as tranexamic acid, ε-aminocaproic acid, 4-aminomethylbenzoic acid, and aprotinin were developed in the 1960s without the structural insight of their respective targets. Crystal structures of the main antifibrinolytic targets, the lysine binding sites on plasminogen's kringle domains, and plasmin's serine protease domain greatly contributed to the structure-based drug design of novel inhibitor classes. Two series of ligands targeting the lysine binding sites have been recently described, which are more potent than the most-widely used antifibrinolytic agent, tranexamic acid. Furthermore, four types of promising active site inhibitors of plasmin have been developed: tranexamic acid conjugates targeting the S1 pocket and primed sites, substrate-analogue linear homopiperidylalanine-containing 4-amidinobenzylamide derivatives, macrocyclic inhibitors addressing nonprimed binding regions, and bicyclic 14-mer SFTI-1 analogues blocking both, primed and nonprimed binding sites of plasmin. Furthermore, several allosteric plasmin inhibitors based on heparin mimetics have been developed.

Structural studies of plasmin inhibition

Plasminogen (Plg) is the zymogen form of the serine protease plasmin (Plm), and it plays a crucial role in fibrinolysis as well as wound healing, immunity, tissue remodeling and inflammation. Binding to the targets via the lysine-binding sites allows for Plg activation by plasminogen activators (PAs) present on the same target. Cellular uptake of fibrin degradation products leads to apoptosis, which represents one of the pathways for cross-talk between fibrinolysis and tissue remodeling. Therapeutic manipulation of Plm activity plays a vital role in the treatments of a range of diseases, whereas Plm inhibitors are used in trauma and surgeries as antifibrinolytic agents. Plm inhibitors are also used in conditions such as angioedema, menorrhagia and melasma. Here, we review the rationale for the further development of new Plm inhibitors, with a particular focus on the structural studies of the active site inhibitors of Plm. We compare the binding mode of different classes of inhibitors and comment on how it relates to their efficacy, as well as possible future developments.

Bldesin, the first functionally characterized pathogenic fungus defensin with Kv1.3 channel and chymotrypsin inhibitory activities

Fungus defensin is a kind of important natural peptide resource, such as plectasin from the soil fungus Pseudoplectania nigrella with potential application in the antimicrobial peptide lead drug discovery. Here, a fungus defensin named Bldesin with Kv1.3 channel and serine protease inhibitory activities was first explored. By GST-Bldesin fusion expression and enterokinase cleaving strategy, recombinant Bldesin was obtained successfully. Antimicrobial assays showed that Bldesin had potent activity against Gram-positive Staphylococcus aureus, but had no effect on Gram-negative Escherichia coli. Electrophysiological experiments showed that Bldesin had Kv1.3 channel inhibitory activity. Serine protease inhibitory associated experiments showed that Bldesin had unique chymotrypsin protease inhibitory, elastase protease inhibitory, and serine protease-associated coagulation inhibitory activities. To the best of our knowledge, Bldesin is the first functionally characterized pathogenic fungus defensin with Kv1.3 channel and chymotrypsin inhibitory activities and highlighted novel pharmacological effects of fungus-derived defensin peptides.

Transcriptomic and Proteomic Analyses Reveal the Diversity of Venom Components from the Vaejovid Scorpion Serradigitus gertschi

To understand the diversity of scorpion venom, RNA from venomous glands from a sawfinger scorpion, Serradigitus gertschi, of the family Vaejovidae, was extracted and used for transcriptomic analysis. A total of 84,835 transcripts were assembled after Illumina sequencing. From those, 119 transcripts were annotated and found to putatively code for peptides or proteins that share sequence similarities with the previously reported venom components of other species. In accordance with sequence similarity, the transcripts were classified as potentially coding for 37 ion channel toxins; 17 host defense peptides; 28 enzymes, including phospholipases, hyaluronidases, metalloproteases, and serine proteases; nine protease inhibitor-like peptides; 10 peptides of the cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 protein superfamily; seven La1-like peptides; and 11 sequences classified as "other venom components". A mass fingerprint performed by mass spectrometry identified 204 components with molecular masses varying from 444.26 Da to 12,432.80 Da, plus several higher molecular weight proteins whose precise masses were not determined. The LC-MS/MS analysis of a tryptic digestion of the soluble venom resulted in the de novo determination of 16,840 peptide sequences, 24 of which matched sequences predicted from the translated transcriptome. The database presented here increases our general knowledge of the biodiversity of venom components from neglected non-buthid scorpions.

Are Fireworms Venomous? Evidence for the Convergent Evolution of Toxin Homologs in Three Species of Fireworms (Annelida, Amphinomidae)

Amphinomids, more commonly known as fireworms, are a basal lineage of marine annelids characterized by the presence of defensive dorsal calcareous chaetae, which break off upon contact. It has long been hypothesized that amphinomids are venomous and use the chaetae to inject a toxic substance. However, studies investigating fireworm venom from a morphological or molecular perspective are scarce and no venom gland has been identified to date, nor any toxin characterized at the molecular level. To investigate this question, we analyzed the transcriptomes of three species of fireworms-Eurythoe complanata, Hermodice carunculata, and Paramphinome jeffreysii-following a venomics approach to identify putative venom compounds. Our venomics pipeline involved de novo transcriptome assembly, open reading frame, and signal sequence prediction, followed by three different homology search strategies: BLAST, HMMER sequence, and HMMER domain. Following this pipeline, we identified 34 clusters of orthologous genes, representing 13 known toxin classes that have been repeatedly recruited into animal venoms. Specifically, the three species share a similar toxin profile with C-type lectins, peptidases, metalloproteinases, spider toxins, and CAP proteins found among the most highly expressed toxin homologs. Despite their great diversity, the putative toxins identified are predominantly involved in three major biological processes: hemostasis, inflammatory response, and allergic reactions, all of which are commonly disrupted after fireworm stings. Although the putative fireworm toxins identified here need to be further validated, our results strongly suggest that fireworms are venomous animals that use a complex mixture of toxins for defense against predators.

Adaptive evolution of insect selective excitatory β-type sodium channel neurotoxins from scorpion venom

Insect selective excitatory β-type sodium channel neurotoxins from scorpion venom (β-NaScTxs) are composed of about 70-76 amino acid residues and share a common scaffold stabilized by four unique disulfide bonds. The phylogenetic analysis of these toxins was hindered by limited sequence data. In our recent study, two new insect selective excitatory β-NaScTxs, LmIT and ImIT, were isolated from Lychas mucronatus and Isometrus maculatus, respectively. With the sequences previously reported, we examined the adaptive molecular evolution of insect selective excitatory β-NaScTxs by estimating the nonsynonymous-to-synonymous rate ratio (ω=d_N/d_S). The results revealed 12 positively selected sites in the genes of insect selective excitatory β-NaScTxs. Moreover, these positively selected sites match well with the sites important for interacting with sodium channels, as demonstrated in previous mutagenesis study. These results reveal that adaptive evolution after gene duplication is one of the most important genetic mechanisms of scorpion neurotoxin diversification.