Paula Juárez

Evolution of Snake Venom Disintegrins by Positive Darwinian Selection

PII-disintegrins, cysteine-rich polypeptides broadly distributed in the venoms of geographically diverse species of vipers and rattlesnakes, antagonize the adhesive functions of beta(1) and beta(3) integrin receptors. PII-disintegrins evolved in Viperidae by neofunctionalization of disintegrin-like domains of duplicated PIII-snake venom hemorrhagic metalloproteinase (SVMP) genes recruited into the venom proteome before the radiation of the advanced snakes. Minimization of the gene (loss of introns and coding regions) and the protein structures (successive loss of disulfide bonds) underpins the postduplication divergence of disintegrins. However, little is known about the underlying genetic mechanisms that have generated the structural and functional diversity among disintegrins. Phylogenetic inference and maximum likelihood-based codon substitution approaches were used to analyze the evolution of the disintegrin family. The topology of the phylogenetic tree does not parallel that of the species tree. This incongruence is consistent with that expected for a multigene family undergoing a birth-and-death process in which the appearance and disappearance of loci are being driven by selection. Cysteine and buried residues appear to be under strong purifying selection due to their role in maintaining the active conformation of disintegrins. Divergence of disintegrins is strongly influenced by positive Darwinian selection causing accelerated rate of substitution in a substantial proportion of surface-exposed disintegrin residues. Global and lineage-specific sites evolving under diversifying selection were identified. Several sites are located within the integrin-binding loop and the C-terminal tail, two regions that form a conformational functional epitope. Arginine-glycine-aspartic acid (RGD) was inferred to represent the ancestral integrin-recognition motif, which emerged from the subgroup of PIII-SVMPs bearing the RDECD sequence. The most parsimonious nucleotide substitution model required for the emergence of all known disintegrins integrin inhibitory motifs from an ancestral RGD sequence involves a minimum of three mutations. The adaptive advantage of the emergence of motifs targeting beta(1) integrins and the role of positively selected sites located within nonfunctional disintegrin regions appear to be difficult to rationalize in the context of a predator-prey arms race. Perhaps, this represents a consequence of the neofunctionalization potential of the disintegrin domain, a feature that may underlie its recruitment into the venom proteome followed by its successful transformation into a toxin.

Combined snake venomics and venom gland transcriptomic analysis of the ocellated carpet viper, Echis ocellatus

Snakebite in Africa causes thousands of deaths annually and considerable permanent physical disability. The saw-scaled viper, Echis ocellatus, represents the single most medically important snake species in West Africa. To provide a detailed compositional analysis of the venom of E. ocellatus for designing novel toxin-specific immunotherapy and to delineate sequence structure-function relationships of individual toxins, we characterised the venom proteome and the venom gland transcriptome. Whole E. ocellatus venom was fractionated by reverse-phase HPLC, followed by analysis of each chromatographic fraction using a combination of SDS-PAGE, N-terminal sequencing, MALDI-TOF mass fingerprinting, and CID-MS/MS of tryptic peptides. This analysis identified around 35 distinct proteins of molecular masses in the range of 5.5-110 kDa belonging to 8 different toxin families (disintegrin, DC-fragment, phospholipase A(2), cysteine-rich secretory protein, serine proteinase, C-type lectin, l-amino acid oxidase, and Zn(2+)-dependent metalloprotease). Comparison of the toxin composition of E. ocellatus venom determined using a proteomic approach, with the predicted proteome derived from assembly of 1000 EST sequences from a E. ocellatus venom gland cDNA library, shows some differences. Most notably, peptides derived from 26% of the venom proteins could not be ascribed an exact match in the transcriptome. Similarly, 64 (67%) out of the 95 putative toxin clusters reported in the transcriptome did not match to peptides detected in the venom proteome. These data suggest that the final composition of venom is influenced by transcriptional and post-translational mechanisms that may be more complex than previously appreciated. This, in turn, emphasises the value of combining proteomic and transcriptomic approaches to acquire a more complete understanding of the precise composition of snake venom, than would be gleaned from using one analysis alone. From a clinical perspective, the large amount of SVMPs (66.5% of the total venom proteins) is consistent with the haemorrhagic pathology associated with E. ocellatus envenoming. More significantly, whilst the proteomic analysis confirms the majority of these metalloproteinases (58%) belong to the SVMP PIII class, MS/MS derived peptide sequencing also demonstrates a major constituent (32%) of E. ocellatus venom is a PIV-SVMP with a quaternary structure comprising a 48 kDa (Q2UXQ4 or Q2UXQ5) PIII-SVMP subunit, and two 14-16 kDa C-type lectin-like domains [EOC_00087 and EOC_00124] which display similarity to echicetin alpha [P81017] and beta [P81996] subunits.

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

BackgroundA 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.ResultsThe 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.ConclusionsOur 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.

Isolation of an acidic phospholipase A2 from the venom of the snake Bothrops asper of Costa Rica: Biochemical and toxicological characterization☆

Phospholipases A(2) (PLA(2)) are major components of snake venoms, exerting a variety of relevant toxic actions such as neurotoxicity and myotoxicity, among others. Since the majority of toxic PLA(2)s are basic proteins, acidic isoforms and their possible roles in venoms are less understood. In this study, an acidic enzyme (BaspPLA(2)-II) was isolated from the venom of Bothrops asper (Pacific region of Costa Rica) and characterized. BaspPLA(2)-II is monomeric, with a mass of 14,212 +/- 6 Da and a pI of 4.9. Its complete sequence of 124 amino acids was deduced through cDNA and protein sequencing, showing that it belongs to the Asp49 group of catalytically active enzymes. In vivo and in vitro assays demonstrated that BaspPLA(2)-II, in contrast to the basic Asp49 counterparts present in the same venom, lacks myotoxic, cytotoxic, and anticoagulant activities. BaspPLA(2)-II also differed from other acidic PLA(2)s described in Bothrops spp. venoms, as it did not show hypotensive and anti-platelet aggregation activities. Furthermore, this enzyme was not lethal to mice at intravenous doses up to 100 microg (5.9 microg/g), indicating its lack of neurotoxic activity. The only toxic effect recorded in vivo was a moderate induction of local edema. Therefore, the toxicological characteristics of BaspPLA(2)-II suggest that it does not play a key role in the pathophysiology of envenomings by B. asper, and that its purpose might be restricted to digestive functions. Immunochemical analyses using antibodies raised against BaspPLA(2)-II revealed that acidic and basic PLA(2)s form two different antigenic groups in B. asper venom.

Molecular cloning of disintegrin-like transcript BA-5A from a Bitis arietans venom gland cDNA library: A putative intermediate in the evolution of the long-chain disintegrin bitistatin

We report the cloning and sequence analysis of BA-5A from a venom gland cDNA library of the puff adder, Bitis arietans, that encodes a novel ECD-disintegrin-like domain. BA-5A is a unique PII disintegrin. It contains the 16 cysteine residues that are conserved in all known disintegrin-like domains of ADAM proteins and snake venom metalloproteinases but lacks the cysteine-rich domain. These features suggest that BA-5A may represent an intermediate in the evolutionary pathway of the long disintegrin bitistatin and that removal of the cysteine-rich domain and loss of the PIII-specific disulfide bond were separate events along the structural diversification pathway of disintegrins, the former predating the latter. The protein family composition of the Bitis arietans venom, as determined by combination of reversed-phase HPLC and proteomic analysis, was as follows: Zn2+-metalloproteinase (38.5%), serine proteinase (19.5%), disintegrin (17.8%), C-type lectin-like (13.2%), PLA2 (4.3%), Kunitz-type inhibitor (4.1%), cystatin (1.7%), and unknown (0.9%). BA-5A could not be detected in the venom proteome of Bitis arietans. The occurrence of this very low-abundance (< 0.05%) or nonexpressed disintegrin transcript indicates a hitherto unrecognized structural diversity of this protein family. Whether BA-5A plays a physiological role or represents an orphan protein which could eventually evolve a role in the adaptation of snakes to changing ecological niches and prey habits deserves further investigation.

cDNA Cloning and Functional Expression of Jerdostatin, a Novel RTS-disintegrin from Trimeresurus jerdonii and a Specific Antagonist of the α1β1 Integrin

Jerdostatin represents a novel RTS-containing short disintegrin cloned by reverse transcriptase-PCR from the venom gland mRNA of the Chinese Jerdons pit viper Trimeresurus jerdonii. The jerdostatins precursor cDNA contained a 333-bp open reading frame encoding a signal peptide, a pre-peptide, and a 43-amino acid disintegrin domain, whose amino acid sequence displayed 80% identity with that of the KTS-disintegrins obtustatin and viperistatin. The jerdostatin cDNA structure represents the first complete open reading frame of a short disintegrin and points to the emergence of jerdostatin from a short-coding gene. The different residues between jerdostatin and obtustatin/viperistatin are segregated within the integrin-recognition loop and the C-terminal tail. Native jerdostatin (r-jerdostatin-R21) and a R21K mutant (r-jerdostatin-K21) were produced in Escherichia coli. In each case, two conformers were isolated. One-dimensional 1H NMR showed that conformers 1 and 2 of r-jerdostatin-R21 represent, respectively, well folded and unfolded proteins. The two conformers of the wild-type and the R21K mutant inhibited the adhesion of α1-K562 cells to collagen IV with IC50 values of 180 and 703 nm, respectively. The IC50 values of conformers 2 of r-jerdostatin-R21 and r-jerdostatin-K21 were, respectively, 5.95 and 12.5 μm. Neither r-jerdostatin-R21 nor r-jerdostatin-K21 showed inhibitory activity toward other integrins, including αIIbβ3, αvβ3, α2β1, α5β1, α4β1, α6β1, and α9β1 up to a concentration of 24 μm. Although the RTS motif appears to be more potent than KTS inhibiting the α1β1 integrin, r-jerdostatin-R21 is less active than the KTS-disintegrins, strongly suggesting that substitutions outside the integrin-binding motif and/or C-terminal proteolytic processing are responsible for the decreased inhibitory activity.

Loss of Introns Along the Evolutionary Diversification Pathway of Snake Venom Disintegrins Evidenced by Sequence Analysis of Genomic DNA from Macrovipera lebetina transmediterranea and Echis ocellatus

Analysis of cDNAs from Macrovipera lebetina transmediterranea (Mlt) and Echis ocellatus (Eo) venom gland libraries encoding disintegrins argued strongly for a common ancestry of the messengers of short disintegrins and those for precursors of dimeric disintegrin chains. We now report the sequence analysis of disintegrin-coding genes from these two vipers. Genomic DNAs for dimeric disintegrin subunits Ml_G1 and Ml_G2 (Mlt) and Eo_D3 (Eo) contain single 1-kb introns exhibiting the 5′-GTAAG (donor)/3′-AG (acceptor) consensus intron splicing signature. On the other hand, the short RTS-disintegrins Ml_G3 (Mlt) and Eo_RTS (Eo) and the short RGD-disintegrin ocellatusin (Eo) are transcribed from intronless genomic DNA sequences, indicating that the evolutionary pathway leading to the emergence of short disintegrins involved the removal of all intronic sequences. The insertion position of the intron within Ml_G1, Ml_G2, and Eo_D3 is conserved in the genes for vertebrate ADAM (Adisintegrin and metalloproteinase) protein disintegrin-like domains and within the gene for the medium-size snake disintegrins halystatins 2 and 3. However, a comparative analysis of currently available disintegrin(-like) genes outlines the view that a minimization of both the gene organization and the protein structure underlies the evolution of the snake venom disintegrin family.

Molecular Cloning of Echis ocellatus Disintegrins Reveals Non-Venom-Secreted Proteins and a Pathway for the Evolution of Ocellatusin

We report the cloning and sequence analysis of Echis ocellatus cDNAs coding for dimeric disintegrin subunits and for the short disintegrin ocellatusin. All the dimeric disintegrin subunit messengers belong to the short-coding class, indicating that short messengers may be more widely distributed than previously thought. Mass spectrometric analysis of the HPLC-separated venom proteins was performed to characterize the dimeric disintegrins expressed in the venom proteome. In addition to previously reported EO4 and EO5 heterodimers, a novel dimeric disintegrin containing RGD- and KGD-bearing subunits was identified. However, a WGD-containing polypeptide encoded by clone Eo1-1 was not detected in the venom, suggesting the occurrence of larger genomic than proteomic diversity, which could represent part of a non-venom-secreted reservoir of disintegrin that may eventually acquire physiological relevance for the snake upon changes of ecological niches and prey habits. On the other hand, the realization of the existence of two distinct messengers coding for the short disintegrin ocellatusin reveals key events of the evolutionary emergence of the short disintegrin ocellatusin from a short-coding dimeric disintegrin precursor by two nucleotide mutations.

Neural and Molecular Features on Charcot-Marie-Tooth Disease Plasticity and Therapy

In the peripheral nervous system disorders plasticity is related to changes on the axon and Schwann cell biology, and the synaptic formations and connections, which could be also a focus for therapeutic research. Charcot-Marie-Tooth disease (CMT) represents a large group of inherited peripheral neuropathies that involve mainly both motor and sensory nerves and induce muscular atrophy and weakness. Genetic analysis has identified several pathways and molecular mechanisms involving myelin structure and proper nerve myelination, transcriptional regulation, protein turnover, vesicle trafficking, axonal transport and mitochondrial dynamics. These pathogenic mechanisms affect the continuous signaling and dialogue between the Schwann cell and the axon, having as final result the loss of myelin and nerve maintenance; however, some late onset axonal CMT neuropathies are a consequence of Schwann cell specific changes not affecting myelin. Comprehension of molecular pathways involved in Schwann cell-axonal interactions is likely not only to increase the understanding of nerve biology but also to identify the molecular targets and cell pathways to design novel therapeutic approaches for inherited neuropathies but also for most common peripheral neuropathies. These approaches should improve the plasticity of the synaptic connections at the neuromuscular junction and regenerate cell viability based on improving myelin and axon interaction.

Recombinant expression of mutants of the Frankenstein disintegrin, RTS-ocellatusin. Evidence for the independent origin of RGD and KTS/RTS disintegrins.

The requirements to transform a short disintegrin of the RGD clade into an RTS disintegrin, were investigated through the generation of recombinant mutants of ocellatusin in which the RGD tripeptide was substituted for RTS in different positions along the integrin-specificity loop. Any attempt to create an active integrin α(1)β(1) inhibitory motif within the specificity loop of ocellatusin was unsuccessful. Replacing the whole RGD-loop of ocellatusin by the RTS-loop of jerdostatin was neither sufficient for confering α(1)β(1) binding specificity to this ocellatusin-RTS Frankenstein(2) mutant. Factors other than the integrin-binding loop sequence per se are thus required to transform a disintegrin scaffold from the RGD clade into another scaffold from the RTS/KTS clade. Moreover, our results provide evidences, that the RTS/KTS short disintegrins have potentially been recruited into the venom gland of Eurasian vipers independently from the canonical neofunctionalization pathway of the RGD disintegrins. PCR-amplifications of jerdostatin-like sequences from a number of taxa across reptiles, including snakes (Crotalinae, Viperinae, and Elapidae taxa) and lizards (Lacertidae and Iguanidae) clearly showed that genes coding for RTS/KTS disintegrins existed long before the split of Lacertidae and Iguania, thus predating the recruitment of the SVMP precursors of disintegrins, providing strong support for the view of an independent evolutionary history of the RTS/KTS and the RGD clades of short disintegrins.