Non-RGD-containing snake venom disintegrins, functional and structural relations

Snake venom disintegrins are present in a variety of species and are functionally divided into three families: RGD, MLD and R/KTS. The RGD family of disintegrins, which bind and inhibit the physiological functions of RGD-dependent integrins, constitute the largest and most investigated family. This review will be focused on characterization of two relatively new families of snake venom disintegrins, expressing in their active site MLD and R/KTS motifs. The MLD motif, present only in heterodimeric disintegrins, mediates binding of these disintegrins to α4β1, α4β7 and α9β1 integrins, whereas the presence of a KTS or RTS sequence in the active site selectively directs activity of disintegrins to the collagen receptor α1β1 integrin. Structurally, KTS-disintegrins are short, monomeric molecules containing 41 amino acids in its polypeptide chain. Biological activities of MLD and KTS-disintegrins were investigated in many systems in vitro and in vivo. Purified disintegrins are non-toxic in therapeutic doses in rodent and avian models. Their modulatory properties were observed in investigations of cancer angiogenesis and metastasis, immunosuppression of IDDM (insulin-dependent diabetes mellitus) and asthma, as well as in neurodegenerative assays and cell apoptosis.

Adaptive evolution of the venom-targeted vWF protein in opossums that eat pitvipers

The rapid evolution of venom toxin genes is often explained as the result of a biochemical arms race between venomous animals and their prey. However, it is not clear that an arms race analogy is appropriate in this context because there is no published evidence for rapid evolution in genes that might confer toxin resistance among routinely envenomed species. Here we report such evidence from an unusual predator-prey relationship between opossums (Marsupialia: Didelphidae) and pitvipers (Serpentes: Crotalinae). In particular, we found high ratios of replacement to silent substitutions in the gene encoding von Willebrand Factor (vWF), a venom-targeted hemostatic blood protein, in a clade of opossums known to eat pitvipers and to be resistant to their hemorrhagic venom. Observed amino-acid substitutions in venom-resistant opossums include changes in net charge and hydrophobicity that are hypothesized to weaken the bond between vWF and one of its toxic snake-venom ligands, the C-type lectin-like protein botrocetin. Our results provide the first example of rapid adaptive evolution in any venom-targeted molecule, and they support the notion that an evolutionary arms race might be driving the rapid evolution of snake venoms. However, in the arms race implied by our results, venomous snakes are prey, and their venom has a correspondingly defensive function in addition to its usual trophic role.

Profiling the venom gland transcriptomes of Costa Rican snakes by 454 pyrosequencing

BACKGROUND

A long term research goal of venomics, of applied importance for improving current antivenom therapy, but also for drug discovery, is to understand the pharmacological potential of venoms. Individually or combined, proteomic and transcriptomic studies have demonstrated their feasibility to explore in depth the molecular diversity of venoms. In the absence of genome sequence, transcriptomes represent also valuable searchable databases for proteomic projects.

RESULTS

The venom gland transcriptomes of 8 Costa Rican taxa from 5 genera (Crotalus, Bothrops, Atropoides, Cerrophidion, and Bothriechis) of pitvipers were investigated using high-throughput 454 pyrosequencing. 100,394 out of 330,010 masked reads produced significant hits in the available databases. 5.165,220 nucleotides (8.27%) were masked by RepeatMasker, the vast majority of which corresponding to class I (retroelements) and class II (DNA transposons) mobile elements. BLAST hits included 79,991 matches to entries of the taxonomic suborder Serpentes, of which 62,433 displayed similarity to documented venom proteins. Strong discrepancies between the transcriptome-computed and the proteome-gathered toxin compositions were obvious at first sight. Although the reasons underlaying this discrepancy are elusive, since no clear trend within or between species is apparent, the data indicate that individual mRNA species may be translationally controlled in a species-dependent manner. The minimum number of genes from each toxin family transcribed into the venom gland transcriptome of each species was calculated from multiple alignments of reads matched to a full-length reference sequence of each toxin family. Reads encoding ORF regions of Kazal-type inhibitor-like proteins were uniquely found in Bothriechis schlegelii and B. lateralis transcriptomes, suggesting a genus-specific recruitment event during the early-Middle Miocene. A transcriptome-based cladogram supports the large divergence between A. mexicanus and A. picadoi, and a closer kinship between A. mexicanus and C. godmani.

CONCLUSIONS

Our comparative next-generation sequencing (NGS) analysis reveals taxon-specific trends governing the formulation of the venom arsenal. Knowledge of the venom proteome provides hints on the translation efficiency of toxin-coding transcripts, contributing thereby to a more accurate interpretation of the transcriptome. The application of NGS to the analysis of snake venom transcriptomes, may represent the tool for opening the door to systems venomics.

A high-throughput venom-gland transcriptome for the Eastern Diamondback Rattlesnake (Crotalus adamanteus) and evidence for pervasive positive selection across toxin classes

Despite causing considerable human mortality and morbidity, animal toxins represent a valuable source of pharmacologically active macromolecules, a unique system for studying molecular adaptation, and a powerful framework for examining structure-function relationships in proteins. Snake venoms are particularly useful in the latter regard as they consist primarily of a moderate number of proteins and peptides that have been found to belong to just a handful of protein families. As these proteins and peptides are produced in dedicated glands, transcriptome sequencing has proven to be an effective approach to identifying the expressed toxin genes. We generated a venom-gland transcriptome for the Eastern Diamondback Rattlesnake (Crotalus adamanteus) using Roche 454 sequencing technology. In the current work, we focus on transcripts encoding toxins. We identified 40 unique toxin transcripts, 30 of which have full-length coding sequences, and 10 have only partial coding sequences. These toxins account for 24% of the total sequencing reads. We found toxins from 11 previously described families of snake-venom toxins and have discovered two putative, previously undescribed toxin classes. The most diverse and highly expressed toxin classes in the C. adamanteus venom-gland transcriptome are the serine proteinases, metalloproteinases, and C-type lectins. The serine proteinases are the most abundant class, accounting for 35% of the toxin sequencing reads. Metalloproteinases are the most diverse; 11 different forms have been identified. Using our sequences and those available in public databases, we detected positive selection in seven of the eight toxin families for which sufficient sequences were available for the analysis. We find that the vast majority of the genes that contribute directly to this vertebrate trait show evidence for a role for positive selection in their evolutionary history.

Vicrostatin - an anti-invasive multi-integrin targeting chimeric disintegrin with tumor anti-angiogenic and pro-apoptotic activities

Similar to other integrin-targeting strategies, disintegrins have previously shown good efficacy in animal cancer models with favorable pharmacological attributes and translational potential. Nonetheless, these polypeptides are notoriously difficult to produce recombinantly due to their particular structure requiring the correct pairing of multiple disulfide bonds for biological activity. Here, we show that a sequence-engineered disintegrin (called vicrostatin or VCN) can be reliably produced in large scale amounts directly in the oxidative cytoplasm of Origami B E. coli. Through multiple integrin ligation (i.e., alphavbeta3, alphavbeta5, and alpha5beta1), VCN targets both endothelial and cancer cells significantly inhibiting their motility through a reconstituted basement membrane. Interestingly, in a manner distinct from other integrin ligands but reminiscent of some ECM-derived endogenous anti-angiogenic fragments previously described in the literature, VCN profoundly disrupts the actin cytoskeleton of endothelial cells (EC) inducing a rapid disassembly of stress fibers and actin reorganization, ultimately interfering with EC's ability to invade and form tubes (tubulogenesis). Moreover, here we show for the first time that the addition of a disintegrin to tubulogenic EC sandwiched in vitro between two Matrigel layers negatively impacts their survival despite the presence of abundant haptotactic cues. A liposomal formulation of VCN (LVCN) was further evaluated in vivo in two animal cancer models with different growth characteristics. Our data demonstrate that LVCN is well tolerated while exerting a significant delay in tumor growth and an increase in the survival of treated animals. These results can be partially explained by potent tumor anti-angiogenic and pro-apoptotic effects induced by LVCN.

Tenectin is a novel alphaPS2betaPS integrin ligand required for wing morphogenesis and male genital looping in Drosophila

Morphogenesis of the adult structures of holometabolous insects is regulated by ecdysteroids and juvenile hormones and involves cell-cell interactions mediated in part by the cell surface integrin receptors and their extracellular matrix (ECM) ligands. These adhesion molecules and their regulation by hormones are not well characterized. We describe the gene structure of a newly described ECM molecule, tenectin, and demonstrate that it is a hormonally regulated ECM protein required for proper morphogenesis of the adult wing and male genitalia. Tenectin's function as a new ligand of the PS2 integrins is demonstrated by both genetic interactions in the fly and by cell spreading and cell adhesion assays in cultured cells. Its interaction with the PS2 integrins is dependent on RGD and RGD-like motifs. Tenectin's function in looping morphogenesis in the development of the male genitalia led to experiments that demonstrate a role for PS integrins in the execution of left-right asymmetry.

Sensationalistic journalism and tales of snakebite: are rattlesnakes rapidly evolving more toxic venom?

Recent reports in the lay press have suggested that bites by rattlesnakes in the last several years have been more severe than those in the past. The explanation, often citing physicians, is that rattlesnakes are evolving more toxic venom, perhaps in response to anthropogenic causes. We suggest that other explanations are more parsimonious, including factors dependent on the snake and factors associated with the bite victim's response to envenomation. Although bites could become more severe from an increased proportion of bites from larger or more provoked snakes (ie, more venom injected), the venom itself evolves much too slowly to explain the severe symptoms occasionally seen. Increased snakebite severity could also result from a number of demographic changes in the victim profile, including age and body size, behavior toward the snake (provocation), anatomical site of bite, clothing, and general health including asthma prevalence and sensitivity to foreign antigens. Clinical management of bites also changes perpetually, rendering comparisons of snakebite severity over time tenuous. Clearly, careful study taking into consideration many factors will be essential to document temporal changes in snakebite severity or venom toxicity. Presently, no published evidence for these changes exists. The sensationalistic coverage of these atypical bites and accompanying speculation is highly misleading and can produce many detrimental results, such as inappropriate fear of the outdoors and snakes, and distraction from proven snakebite management needs, including a consistent supply of antivenom, adequate health care, and training. We urge healthcare providers to avoid propagating misinformation about snakes and snakebites.

Leberagin-C, A disintegrin-like/cysteine-rich protein from Macrovipera lebetina transmediterranea venom, inhibits alphavbeta3 integrin-mediated cell adhesion

Leberagin-C, a new member of the disintegrin-like/cysteine-rich (D/C) family, was purified to homogeneity from the venom of Tunisian snake Macrovipera lebetina transmediterranea. It is a monomeric protein with a molecular mass of 25,787 Da. Its complete sequence of 205 amino acid residues was established by cDNA cloning. The leberagin-C shows many conserved sequences with other known D/C proteins, like the SECD binding sites and a pattern of 28 cysteines. It is the first purified protein from M. lebetina transmediterranea with only two disintegrin-like/cysteine-rich domains. Leberagin-C is able to inhibit platelet aggregation induced by thrombin and arachidonic acid with IC(50) of 40 and 50 nM respectively. It was also able to inhibit the adhesion of melanoma tumour cells on fibrinogen and fibronectin, by interfering with the function of alphavbeta3 and, to a lesser extent, with alphavbeta6 and alpha5beta1 integrins. To our knowledge, leberagin-C is the sole described D/C protein that does not specifically interact with the alpha2beta1 integrin. Structure-activity relationship study of leberagin-C suggested that there are some important amino acid differences with jararhagin, the most studied PIII metalloprotease from Bothrops jararaca, notably around the SECD motif in its disintegrin-like domain. Other regions implicated in leberagin-C specificities could not be excluded.

Exploring the venom proteome of the western diamondback rattlesnake, Crotalus atrox, via snake venomics and combinatorial peptide ligand library approaches

We report the proteomic characterization of the venom of the medically important North American western diamondback rattlesnake, Crotalus atrox, using two complementary approaches: snake venomics (to gain an insight of the overall venom proteome), and two solid-phase combinatorial peptide ligand libraries (CPLL), followed by 2D electrophoresis and mass spectrometric characterization of in-gel digested protein bands (to capture and "amplify" low-abundance proteins). The venomics approach revealed approximately 24 distinct proteins belonging to 2 major protein families (snake venom metalloproteinases, SVMP, and serine proteinases), which represent 69.5% of the total venom proteins, 4 medium abundance families (medium-size disintegrin, PLA(2), cysteine-rich secretory protein, and l-amino acid oxidase) amounting to 25.8% of the venom proteins, and 3 minor protein families (vasoactive peptides, endogenous inhibitor of SVMP, and C-type lectin-like). This toxin profile potentially explains the cytotoxic, myotoxic, hemotoxic, and hemorrhagic effects evoked by C. atrox envenomation. Further, our results showing that C. atrox exhibits a similar level of venom variation as Sistrurus miliarius points to a "diversity gain" scenario in the lineage leading to the Sistrurus catenatus taxa. On the other hand, the two combinatorial hexapeptide libraries captured distinct sets of proteins. Although the CPLL-treated samples did not retain a representative venom proteome, protein spots barely, or not at all, detectable in the whole venom were enriched in the two CPLL-treated samples. The amplified low copy number C. atrox venom proteins comprised a C-type lectin-like protein, several PLA(2) molecules, PIII-SVMP isoforms, glutaminyl cyclase isoforms, and a 2-cys peroxiredoxin highly conserved across the animal kingdom. Peroxiredoxin and glutaminyl cyclase may participate, respectively, in redox processes leading to the structural/functional diversification of toxins, and in the N-terminal pyrrolidone carboxylic acid formation required in the maturation of bioactive peptides such as bradykinin-potentiating peptides and endogenous inhibitors of metalloproteases. Our findings underscore the usefulness of combinatorial peptide libraries as powerful tools for mining below the tip of the iceberg, complementing thereby the data gained using the snake venomics protocol toward a complete visualization of the venom proteome.

Venoms, venomics, antivenomics

Venoms comprise mixtures of peptides and proteins tailored by Natural Selection to act on vital systems of the prey or victim. Here we review our proteomic protocols for uncoiling the composition, immunological profile, and evolution of snake venoms. Our long-term goal is to gain a deep insight of all viperid venom proteomes. Knowledge of the inter- and intraspecies ontogenetic, individual, and geographic venom variability has applied importance for the design of immunization protocols aimed at producing more effective polyspecific antivenoms. A practical consequence of assessing the cross-reactivity of heterologous antivenoms is the possibility of circumventing the restricted availability of species-specific antivenoms in some regions. Further, the high degree of target specificity makes toxins valuable scaffolds for drug development.