A Pseudoscorpion's Promising Pinch: The venom of Chelifer cancroides contains a rich source of novel compounds

New Frontiers in Fighting Mycobacterial Infections: Venom-Derived Peptides

Notwithstanding the indefatigable endeavors to develop effective anti-mycobacterial therapies, mycobacterial infections still present a tough problem for medicine today. The problem is further complicated by the disquieting surge of drug-resistant mycobacterial pathogens, which considerably narrows the existing therapeutic options. Thus, there is a genuine need to discover novel anti-mycobacterial drugs. Animal venoms are considered a treasure trove of structurally variable and biologically active peptides, which may hold promise for therapeutic applications. Over the past two decades, abundant evidence has been amassed regarding anti-mycobacterial effects of various peptides derived from the venoms of honeybees, wasps, scorpions, pseudoscorpions, cone snails, and snakes. This review intends to consolidate the state-of-the-art knowledge on the anti-mycobacterial peptides of animal venoms and to sketch potentially fruitful directions for future investigations. The available data indicate that micromolar concentrations of particular venom-derived peptides can effectively inhibit the in vitro growth of Mycobacterium tuberculosis and non-tuberculous mycobacteria. The proposed mechanisms of action of venom-derived peptides include reduced activity of plasma membrane ATPase, depolarization of the cell membrane, disruption of the cell wall, and increased generation of reactive oxygen species. Interestingly, administering certain peptides (≤ 2 mg/kg body weight) through daily intraperitoneal injections to mice for 8 consecutive days resulted in lower levels of mycobacterial infections and inflammation, hitting two targets with one arrow. Indubitably, such peptides can usher in new possibilities for the prevention and treatment of recalcitrant mycobacterial infections.

Toxins under a Rock: Proteo-transcriptomic analysis reveals the venom composition of the Pseudoscorpion Ammogarypus lawrencei (Pseudoscorpiones: Garypidae)

Pseudoscorpions represent one of the venomous animal groups least investigated with respect to their venom composition. So far, the venom of only a few species of these tiny arachnids has been analyzed, among which only the cosmopolitan species Chelifer cancroides and the Australian Synsphyronus apimelus have been investigated in more detail. Here, we advance the current understanding on pseudoscorpion toxins by unveiling the venom composition of the African species Ammogarypus lawrencei via proteo-transcriptomics-guided venomics. Belonging to the same family as S. apimelus whose venom was analyzed solely by a transcriptomic approach, we found the highest similarities between putative venom compounds in these species. Instead of an enzyme-rich venom predicted for S. apimelus, we found the venom of A. lawrencei to be dominated by Cysteine-rich peptides (CRPs). Many of these peptides show moderate similarity to neurotoxins found primarily in other arachnids, although a large proportion could not be annotated in more detail due to their high sequence disparity. Enzymes are a minor component in the venom of A. lawrencei and classified mostly as peptidases and triacylglycerol lipases, likely fulfilling a predigestive function or acting as spreading factors. Lastly, we identified a range of linear and putatively antimicrobial peptides in the A. lawrencei venom, which seem to be unrelated to the previously identified checacin-type linear peptides identified in the venom of C. cancroides. Our study provides valuable insights into the molecular diversity encoded in pseudoscorpion venom glands and identifies a range of novel biomolecules with putative translational potential.

Determining the pharmacological potential and biological role of linear pseudoscorpion toxins via functional profiling

Arthropod venoms contain bioactive molecules attractive for biomedical applications. However, few of these have been isolated, and only a tiny number has been characterized. Pseudoscorpions are small arachnids whose venom has been largely overlooked. Here, we present the first structural and functional assessment of the checacin toxin family, discovered in the venom of the house pseudoscorpion (Chelifer cancroides). We combined in silico and in vitro analyses to establish their bioactivity profile against microbes and various cell lines. This revealed inhibitory effects against bacteria and fungi. We observed cytotoxicity against specific cell types and effects involving second messengers. Our work provides insight into the biomedical potential and evolution of pseudoscorpion venoms. We propose that plesiotypic checacins evolved to defend the venom gland against infection, whereas apotypic descendants evolved additional functions. Our work highlights the importance of considering small and neglected species in biodiscovery programs.

How to Overcome a Snail? Identification of Putative Neurotoxins of Snail-Feeding Firefly Larvae (Coleoptera: Lampyridae, Lampyris noctiluca)

The larvae of some lampyrid beetles are highly specialized predators of snails. They have been observed to climb on the shells of their prey and use this exposed position to bite and inject secretions potentially originating from the midgut. Besides serving the purpose of extra-oral digestion (EOD), injected compounds also seem to have a paralyzing effect. Up to now, the toxins causing this paralyzing activity have not been identified. In the current study, we provide a first compositional analysis of the midgut secretion from lampyrid larvae, with a focus on identifying putative neurotoxins causing the observed paralyzing effect. For this purpose, we utilized a combined proteo-transcriptomic approach to characterize the compounds present in the midgut secretion of larval stages of Lampyris noctiluca. In terms of the absolute numbers of identified compounds, the midgut secretion is dominated by hydrolyzing enzymes comprising peptidases, carboxylesterases, and glycosidases. However, when considering expression levels, a few rather short cysteine-rich peptides exceed all other compounds. Some of these compounds show moderate similarity to putative neurotoxins identified in the venom of other arthropods and could be responsible for paralyzing effects. In addition to these potential toxins, we provide a list of peptides typical of the midgut secretion of L. noctiluca, supplemented by the corresponding precursor sequences.

Equipped for Sexual Stings? Male-Specific Venom Peptides in Euscorpius italicus

In the animal kingdom, intraspecific variation occurs, for example, between populations, different life stages, and sexes. For venomous animals, this can involve differences in their venom composition. In cases where venom is utilized in the context of mating, the differences in composition might be driven by sexual selection. In this regard, the genus Euscorpius is a promising group for further research, as some of these scorpions exhibit a distinct sexual dimorphism and are known to perform a sexual sting during mating. However, the venom composition of this genus remains largely unexplored. Here, we demonstrate that Euscorpius italicus exhibits a male-specific venom composition, and we identify a large fraction of the substances involved. The sex specificity of venom peptides was first determined by analyzing the presence/absence patterns of ion signals in MALDI-TOF mass spectra of venom samples from both sexes and juveniles. Subsequently, a proteo-transcriptomic analysis provided sequence information on the relevant venom peptides and their corresponding precursors. As a result, we show that several potential toxin precursors are down-regulated in male venom glands, possibly to reduce toxic effects caused to females during the sexual sting. We have identified the precursor of one of the most prominent male-specific venom peptides, which may be an ideal candidate for activity tests in future studies. In addition to the description of male-specific features in the venom of E. italicus, this study also includes a general survey of venom precursors in this species.

Antimicrobial, Insecticidal and Cytotoxic Activity of Linear Venom Peptides from the Pseudoscorpion Chelifer cancroides

Linear cationic venom peptides are antimicrobial peptides (AMPs) that exert their effects by damaging cell membranes. These peptides can be highly specific, and for some, a significant therapeutic value was proposed, in particular for treatment of bacterial infections. A prolific source of novel AMPs are arthropod venoms, especially those of hitherto neglected groups such as pseudoscorpions. In this study, we describe for the first time pharmacological effects of AMPs discovered in pseudoscorpion venom. We examined the antimicrobial, cytotoxic, and insecticidal activity of full-length Checacin1, a major component of the Chelifer cancroides venom, and three truncated forms of this peptide. The antimicrobial tests revealed a potent inhibitory activity of Checacin1 against several bacteria and fungi, including methicillin resistant Staphylococcus aureus (MRSA) and even Gram-negative pathogens. All peptides reduced survival rates of aphids, with Checacin1 and the C-terminally truncated Checacin11-21 exhibiting effects comparable to Spinosad, a commercially used pesticide. Cytotoxic effects on mammalian cells were observed mainly for the full-length Checacin1. All tested peptides might be potential candidates for developing lead structures for aphid pest treatment. However, as these peptides were not yet tested on other insects, aphid specificity has not been proven. The N- and C-terminal fragments of Checacin1 are less potent against aphids but exhibit no cytotoxicity on mammalian cells at the tested concentration of 100 µM.