Hadrurid Scorpion Toxins: Evolutionary Conservation and Selective Pressures.
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ABSTRACT:
SUBMITTER: Santibanez-Lopez CE
PROVIDER: S-EPMC6891616 | biostudies-literature | 2019 Nov
REPOSITORIES: biostudies-literature
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Project description:?-Scorpion toxins constitute a family of peptide modulators that induce a prolongation of the action potential of excitable cells by inhibiting voltage-gated sodium channel inactivation. Although they all adopt a conserved structural scaffold, the potency and phylogentic preference of these toxins largely vary, which render them an intriguing model for studying evolutionary diversification among family members. Here, we report molecular characterization of a new multigene family of ?-toxins comprising 13 members (named MeuNaTx?-1 to MeuNaTx?-13) from the scorpion Mesobuthus eupeus. Of them, five native toxins (MeuNaTx?-1 to -5) were purified to homogeneity from the venom and the solution structure of MeuNaTx?-5 was solved by nuclear magnetic resonance. A systematic functional evaluation of MeuNaTx?-1, -2, -4, and -5 was conducted by two-electrode voltage-clamp recordings on seven cloned mammalian voltage-gated sodium channels (Na(v)1.2 to Na(v)1.8) and the insect counterpart DmNa(v)1 expressed in Xenopus oocytes. Results show that all these four peptides slow inactivation of DmNa(v)1 and are inactive on Na(v)1.8 at micromolar concentrations. However, they exhibit differential specificity for the other six channel isoforms (Na(v)1.2 to Na(v)1.7), in which MeuNaTx?-4 shows no activity on these isoforms and thus represents the first Mesobuthus-derived insect-selective ?-toxin identified so far with a half maximal effective concentration of 130 ± 2 nm on DmNa(v)1 and a half maximal lethal dose of about 200 pmol g(-1) on the insect Musca domestica; MeuNaTx?-2 only affects Na(v)1.4; MeuNaTx?-1 and MeuNaTx?-5 have a wider range of channel spectrum, the former active on Na(v)1.2, Na(v)1.3, Na(v)1.6, and Na(v)1.7, whereas the latter acting on Na(v)1.3-Na(v)1.7. Remarkably, MeuNaTx?-4 and MeuNaTx?-5 are two nearly identical peptides differing by only one point mutation at site 50 (A50V) but exhibit rather different channel subtype selectivity, highlighting a switch role of this site in altering the target specificity. By the maximum likelihood models of codon substitution, we detected nine positively selected sites (PSSs) that could be involved in functional diversification of Mesobuthus ?-toxins. The PSSs include site 50 and other seven sites located in functional surfaces of ?-toxins. This work represents the first thorough investigation of evolutionary diversification of ?-toxins derived from a specific scorpion lineage from the perspectives of sequence, structure, function, and evolution.
| S-EPMC3270107 | biostudies-literature
Project description:It is long known that peptide neurotoxins derived from a diversity of venomous animals evolve by positive selection following gene duplication, yet a force that drives their adaptive evolution remains a mystery. By using maximum-likelihood models of codon substitution, we analyzed molecular adaptation in scorpion sodium channel toxins from a specific species and found ten positively selected sites, six of which are located at the core-domain of scorpion ?-toxins, a region known to interact with two adjacent loops in the voltage-sensor domain (DIV) of sodium channels, as validated by our newly constructed computational model of toxin-channel complex. Despite the lack of positive selection signals in these two loops, they accumulated extensive sequence variations by relaxed purifying selection in prey and predators of scorpions. The evolutionary variability in the toxin-bound regions of sodium channels indicates that accelerated substitutions in the multigene family of scorpion toxins is a consequence of dealing with the target diversity. This work presents an example of atypical co-evolution between animal toxins and their molecular targets, in which toxins suffered from more prominent selective pressure from the channels of their competitors. Our discovery helps explain the evolutionary rationality of gene duplication of toxins in a specific venomous species.
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Project description:The botulinum neurotoxins, characterized by their neuromuscular paralytic effects, are the most toxic proteins known to man. Due to their extreme potency, ease of production, and duration of activity, the BoNT proteins have been classified by the Centers for Disease Control as high threat agents for bioterrorism. In an attempt to discover effective BoNT therapeutics, we have pursued a strategy in which we leverage the blockade of K(+) channels that ultimately results in the reversal of neuromuscular paralysis. Towards this end, we utilized peptides derived from scorpion venom that are highly potent K(+) channel blockers. Herein, we report the synthesis of charybdotoxin, a 37 amino acid peptide, and detail its activity, along with iberiotoxin and margatoxin, in a mouse phrenic nerve hemidiaphragm assay in the absence and the presence of BoNT/A.
| S-EPMC3869784 | biostudies-literature
Project description:BackgroundTeleost fishes do not have a vomeronasal organ (VNO), and their vomeronasal receptors (V1Rs, V2Rs) are expressed in the main olfactory epithelium (MOE), as are odorant receptors (ORs) and trace amine-associated receptors (TAARs). In this study, to obtain insights into the functional distinction among the four chemosensory receptor families in teleost fishes, their evolutionary patterns were examined in zebrafish, medaka, stickleback, fugu, and spotted green pufferfish.Methodology/principal findingsPhylogenetic analysis revealed that many lineage-specific gene gains and losses occurred in the teleost fish TAARs, whereas only a few gene gains and losses have taken place in the teleost fish vomeronasal receptors. In addition, synonymous and nonsynonymous nucleotide substitution rate ratios (K(A)/K(S)) in TAARs tended to be higher than those in ORs and V2Rs.Conclusions/significanceFrequent gene gains/losses and high K(A)/K(S) in teleost TAARs suggest that receptors in this family are used for detecting some species-specific chemicals such as pheromones. Conversely, conserved repertoires of V1R and V2R families in teleost fishes may imply that receptors in these families perceive common odorants for teleosts, such as amino acids. Teleost ORs showed intermediate evolutionary pattern between TAARs and vomeronasal receptors. Many teleost ORs seem to be used for common odorants, but some ORs may have evolved to recognize lineage-specific odors.
| S-EPMC2605262 | biostudies-literature
Project description:The Kv1.2 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 Kv1.2-targeted scorpion toxins (Margatoxin, Agitoxin-2, OsK-1, and Mesomartoxin) to construct their complexes with Kv1.2 based on the experimental structure of ChTx-Kv1.2. 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 Kv1.2-specific interacting amino acids (D353, Q358, V381, and T383) are identified for the first time. This discovery might help design highly selective Kv1.2-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.
| S-EPMC5705969 | biostudies-literature
Project description:Scorpion toxins affecting K(+) channels (KTxs) represent important pharmacological tools and potential drug candidates. Here, we report molecular characterization of seven new KTxs in the scorpion Mesobuthus eupeus by cDNA cloning combined with biochemical approaches. Comparative modeling supports that all these KTxs share a conserved cysteine-stabilized ?-helix/?-sheet structural motif despite the differences in protein sequence and size. We investigated functional diversification of two orthologous ?-KTxs (MeuTXK?1 from M. eupeus and BmP01 from Mesobuthus martensii) by comparing their K(+) channel-blocking activities. Pharmacologically, MeuTXK?1 selectively blocked Kv1.3 channel with nanomolar affinity (IC(50), 2.36 ± 0.9 nM), whereas only 35% of Kv1.1 currents were inhibited at 3 ?M concentration, showing more than 1271-fold selectivity for Kv1.3 over Kv1.1. This peptide displayed a weak effect on Drosophila Shaker channel and no activity on Kv1.2, Kv1.4, Kv1.5, Kv1.6, and human ether-a-go-go-related gene (hERG) K(+) channels. Although BmB01 and MeuTXK?1 have a similar channel spectrum, their affinity and selectivity for these channels largely varies. In comparison with MeuTXK?1, BmP01 only exhibits a submicromolar affinity (IC(50), 133.72 ± 10.98 nM) for Kv1.3, showing 57-fold less activity than MeuTXK?1. Moreover, it lacks the ability to distinguish between Kv1.1 and Kv1.3. We also found that MeuTXK?1 inhibited the proliferation of activated T cells induced by phorbol myristate acetate and ionomycin at micromolar concentrations. Our results demonstrate that accelerated evolution drives affinity variations of orthologous ?-KTxs on Kv channels and indicate that MeuTXK?1 is a promising candidate to develop an immune modulation agent for human autoimmune diseases.
| S-EPMC3033675 | biostudies-literature
Project description:BACKGROUND: Although the basic scorpion K(+) channel toxins (KTxs) are well-known pharmacological tools and potential drug candidates, characterization the acidic KTxs still has the great significance for their potential selectivity towards different K(+) channel subtypes. Unfortunately, research on the acidic KTxs has been ignored for several years and progressed slowly. PRINCIPAL FINDINGS: Here, we describe the identification of nine new acidic KTxs by cDNA cloning and bioinformatic analyses. Seven of these toxins belong to three new ?-KTx subfamilies (?-KTx28, ?-KTx29, and ?-KTx30), and two are new members of the known ?-KTx2 subfamily. ImKTx104 containing three disulfide bridges, the first member of the ?-KTx28 subfamily, has a low sequence homology with other known KTxs, and its NMR structure suggests ImKTx104 adopts a modified cystine-stabilized ?-helix-loop-?-sheet (CS-?/?) fold motif that has no apparent ?-helixs and ?-sheets, but still stabilized by three disulfide bridges. These newly described acidic KTxs exhibit differential pharmacological effects on potassium channels. Acidic scorpion toxin ImKTx104 was the first peptide inhibitor found to affect KCNQ1 channel, which is insensitive to the basic KTxs and is strongly associated with human cardiac abnormalities. ImKTx104 selectively inhibited KCNQ1 channel with a K(d) of 11.69 µM, but was less effective against the basic KTxs-sensitive potassium channels. In addition to the ImKTx104 toxin, HeTx204 peptide, containing a cystine-stabilized ?-helix-loop-helix (CS-?/?) fold scaffold motif, blocked both Kv1.3 and KCNQ1 channels. StKTx23 toxin, with a cystine-stabilized ?-helix-loop-?-sheet (CS-?/?) fold motif, could inhibit Kv1.3 channel, but not the KCNQ1 channel. CONCLUSIONS/SIGNIFICANCE: These findings characterize the structural and functional diversity of acidic KTxs, and could accelerate the development and clinical use of acidic KTxs as pharmacological tools and potential drugs.
| S-EPMC3325286 | biostudies-literature
Project description:Apoptosis, a genetically directed process of cell death, has been studied for many years, and the biochemical mechanisms that surround it are well known and described. There are at least three pathways by which apoptosis occurs, and each pathway depends on extra or intracellular processes for activation. Apoptosis is a vital process, but disturbances in proliferation and cell death rates can lead to the development of diseases like cancer. Several compounds, isolated from scorpion venoms, exhibit inhibitory effects on different cancer cells. Indeed, some of these compounds can differentiate between healthy and cancer cells within the same tissue. During the carcinogenic process, morphological, biochemical, and biological changes occur that enable these compounds to modulate cancer but not healthy cells. This review highlights cancer cell features that enable modulation by scorpion neurotoxins. The properties of the isolated scorpion neurotoxins in cancer cells and the potential uses of these compounds as alternative treatments for cancer are discussed.
| S-EPMC7290751 | biostudies-literature
Project description:The rate of change in selective pressures is one of the main factors that determines the likelihood that populations can adapt to stress conditions. Generally, the reduction in the population size that accompanies abrupt environmental changes makes it difficult to generate and select adaptive mutations. However, in systems with high genetic diversity, as happens in RNA viruses, mutations with beneficial effects under new conditions can already be present in the population, facilitating adaptation. In this work, we have propagated an RNA bacteriophage (Q?) at temperatures higher than the optimum, following different patterns of change. We have determined the fitness values and the consensus sequences of all lineages throughout the evolutionary process in order to establish correspondences between fitness variations and adaptive pathways. Our results show that populations subjected to a sudden temperature change gain fitness and fix mutations faster than those subjected to gradual changes, differing also in the particular selected mutations. The life-history of populations prior to the environmental change has great importance in the dynamics of adaptation. The conclusion is that in the bacteriophage Q?, the standing genetic diversity together with the rate of temperature change determine both the rapidity of adaptation and the followed evolutionary pathways.
| S-EPMC6631425 | biostudies-literature
Project description:BackgroundVenom has evolved in parallel in multiple animals for the purpose of self-defense, prey capture or both. These venoms typically consist of highly complex mixtures of toxins: diverse bioactive peptides and/or proteins each with a specific pharmacological activity. Because of their specificity, they can be used as experimental tools to study cell mechanisms and develop novel medicines and drugs. It is therefore potentially valuable to explore the venoms of various animals to characterize their toxins and identify novel toxin-families. This study focuses on the annotation and exploration of the transcriptomes of six scorpion species from three different families. The transcriptomes were annotated with a custom-built automated pipeline, primarily consisting of Basic Local Alignment Search Tool searches against UniProt databases and filter steps based on transcript coverage.ResultsWe annotated the transcriptomes of four scorpions from the family Buthidae, one from Iuridae and one from Diplocentridae using our annotation pipeline. We found that the four buthid scorpions primarily produce disulfide-bridged ion-channel targeting toxins, while the non-buthid scorpions have a higher abundance of non-disulfide-bridged toxins. Furthermore, analysis of the "unidentified" transcripts resulted in the discovery of six novel putative toxin families containing a total of 37 novel putative toxins. Additionally, 33 novel toxins in existing toxin-families were found. Lastly, 19 novel putative secreted proteins without toxin-like disulfide bonds were found.ConclusionsWe were able to assign most transcripts to a toxin family and classify the venom composition for all six scorpions. In addition to advancing our fundamental knowledge of scorpion venomics, this study may serve as a starting point for future research by facilitating the identification of the venom composition of scorpions and identifying novel putative toxin families.
| S-EPMC6693263 | biostudies-literature