A common precursor for a putative hemorrhagic protein and rhodostomin, a platelet aggregation inhibitor of the venom of Calloselasma rhodostoma: molecular cloning and sequence analysis

Identification of antigenic proteins from the venom of Malaysian snakes using immunoprecipitation assay and tandem mass spectrometry (LC-MS/MS)

Snake envenomation poses a significant risk to Malaysians and country visitors. Malaysia witnesses an estimated 650 snake bites per 100,000 population annually. The primary treatment for snake envenomation involves administering antivenom derived from horses, despite its drawbacks, such as anaphylactic reactions and serum sickness. Identifying the venom proteome is crucial for understanding and predicting the clinical implications of envenomation and developing effective treatments targeting specific venom proteins. In this study, we employ an immunoprecipitation assay followed by LC-MS/MS to identify antigenic proteins in five common venomous snakes in Malaysia compassing of two families which are pit vipers, (Calloselasma rhodostoma and Cryptelytrops purpureomaculatus) and cobras (Ophiophagus hannah, Naja kaouthia, and Naja sumatrana). The immunoprecipitation assay utilises a 2 % agarose gel, allowing antigenic proteins to diffuse and bind with antibodies in the antivenom. The antivenom utilised in this research was procured from the Queen Saovabha Memorial Institute (QSMI), Thailand, including king cobra antivenom (KCAV), cobra antivenom (CAV), Malayan pit viper antivenom (MPAV), Russell's viper antivenom (RPAV), hematopolyvalent antivenom (HPAV), neuropolyvalent antivenom (NPAV), banded krait antivenom (BKAV), and Malayan krait antivenom (MKAV). The protein identified through these interactions which are exclusive to the cobras are three-finger toxins (3FTXs) while snake C-type lectins (Snaclecs) are unique to the pit vipers. Common protein that are present in both families are L-amino acid oxidase (LAAO), Phospholipase A2 (PLA2), and snake venom metalloproteinase (SVMP). Identifying these proteins is vital for formulating a broad-spectrum antivenom applicable across multiple species.

Affected inflammation-related signaling pathways in snake envenomation: A recent insight

Snake envenomation is well known to cause grievous pathological signs, including haemorrhagic discharge, necrosis, and respiratory distress. However, inflammatory reactions are also common envenoming manifestations that lead to successive damage, such as oedema, ulceration, lymphadenectasis, systemic inflammatory response syndrome (SIRS) and even multiple organ dysfunction syndrome (MODS). Interference with the inflammatory burst is hence important in the clinical treatment of snake envenomation. Here, we summarize the typical snake toxins (or venoms) that cause inflammatory reactions and the underlying signaling pathways. In brief, inflammatory reactions are usually triggered by snake venom phospholipase A2 (svPLA2), snake venom metalloprotease (SVMP), snake venom serine protease (SVSP) and C-type lectin/snaclec (CTL) as well as disintegrin (DIS) via multiple signaling pathways. They are nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing 3 (NLRP3), nuclear factor kappa-B (NF-κB), mitogen-activated protein kinase (MAPK), janus kinase/signal transducer and activator of transcription (JAK-STAT) and phosphoinositide 3-Kinase/protein kinase B (PI3K/PKB also called PI3K-AKT) signaling pathways. Activation of these pathways promotes the expression of pro-inflammatory molecules such as cytokines, especially interleukin-1β (IL-1β) which causes further inflammatory cascades and manifestations, such as swelling, fever, pain, and severe complications. Remarkably, almost half of introduced snake toxins (or venoms) have anti-inflammatory effects through blocking these pathways and suppressing the expression of pro-inflammatory molecules. Investigation of affected inflammation-related signaling pathways is meaningful to achieve better clinical treatment.

De Novo Venom Gland Transcriptome Assembly and Characterization for Calloselasma rhodostoma (Kuhl, 1824), the Malayan Pit Viper from Malaysia: Unravelling Toxin Gene Diversity in a Medically Important Basal Crotaline

In Southeast Asia, the Malayan Pit Viper (Calloselasma rhodostoma) is a venomous snake species of medical importance and bioprospecting potential. To unveil the diversity of its toxin genes, this study de novo assembled and analyzed the venom gland transcriptome of C. rhodostoma from Malaysia. The expression of toxin genes dominates the gland transcriptome by 53.78% of total transcript abundance (based on overall FPKM, Fragments Per Kilobase Million), in which 92 non-redundant transcripts belonging to 16 toxin families were identified. Snake venom metalloproteinase (SVMP, PI > PII > PIII) is the most dominant family (37.84% of all toxin FPKM), followed by phospholipase A₂ (29.02%), bradykinin/angiotensin-converting enzyme inhibitor-C-type natriuretic peptide (16.30%), C-type lectin (CTL, 10.01%), snake venom serine protease (SVSP, 2.81%), L-amino acid oxidase (2.25%), and others (1.78%). The expressions of SVMP, CTL, and SVSP correlate with hemorrhagic, anti-platelet, and coagulopathic effects in envenoming. The SVMP metalloproteinase domains encode hemorrhagins (kistomin and rhodostoxin), while disintegrin (rhodostomin from P-II) acts by inhibiting platelet aggregation. CTL gene homologues uncovered include rhodocytin (platelet aggregators) and rhodocetin (platelet inhibitors), which contribute to thrombocytopenia and platelet dysfunction. The major SVSP is a thrombin-like enzyme (an ancrod homolog) responsible for defibrination in consumptive coagulopathy. The findings provide insight into the venom complexity of C. rhodostoma and the pathophysiology of envenoming.

Effect of amino acids near the RGD sequence on binding activities between αIIbβ3 integrin and fibrinogen in the presence of RGD-containing synthetic peptides from elegantin and angustatin

Elegantin and angustatin, which were isolated from the snake venoms of Protobothrops elegans and Dendroaspis angusticeps, markedly inhibit binding between platelet integrins and fibrinogen via the Arg-Gly-Asp (RGD) sequence. Angustatin, which is a three-finger toxin containing the RGD sequence, inhibits platelet aggregation almost ten times more strongly than disintegrin isolated from the venoms of Viperidae and Crotalidae. The RGD sequences of both polypeptides are located at the top of hairpin loops, and the composition of the RGD loop is very important for binding to integrin. We investigated the effects of synthetic RGD loop peptides from angustatin and elegantin on ADP- or collagen-induced platelet aggregation and αIIbβ3-fibrinogen binding. Synthetic angustatin (PRGDMP)-type peptides inhibited platelet aggregation more strongly than elegantin (ARGDDX)-type peptides. In particular, the cyclic angustatin peptide (CPRGDMPC) inhibited ADP- and collagen-induced platelet aggregation at least 10-50 times more strongly than the other peptides. The cyclic angustatin peptide (CPRGDMPC) was also the strongest inhibitor of binding between αIIbβ3 and fibrinogen, the IC₅₀ of this peptide was approximately 2.58μM. Regarding the inhibition of binding between αIIbβ3 and fibrinogen, CPRGDMPC demonstrated a stronger inhibitory and more stable effect in the presence of Mg²⁺ than in the presence of Ca²⁺.

Venomics of Calloselasma rhodostoma, the Malayan pit viper: A complex toxin arsenal unraveled

The venom of Malayan pit viper (Calloselasma rhodostoma) is highly toxic but also valuable in drug discovery. However, a comprehensive proteome of the venom that details its toxin composition and abundance is lacking. This study aimed to unravel the venom complexity through a multi-step venomic approach. At least 96 distinct proteins (29 basic, 67 acidic) in 11 families were identified from the venom. The venom consists of mainly snake venom metalloproteinases (SVMP, 41.17% of total venom proteins), within which the P-I (kistomin, 20.4%) and P-II (rhodostoxin, 19.8%) classes predominate. This is followed by C-type lectins (snaclec, 26.3%), snake venom serine protease (SVSP, 14.9%), L-amino acid oxidase (7.0%), phospholipase A2 (4.4%), cysteine-rich secretory protein (2.5%), and five minor toxins (nerve growth factor, neurotrophin, phospholipase B, 5' nucleotidase and phosphodiesterase, totaling 2.6%) not reported in the proteome hitherto. Importantly, all principal hemotoxins unveiled correlate with the syndrome: SVSP ancrod causes venom-induced consumptive coagulopathy, aggravated by thrombocytopenia caused by snaclec rhodocytin, a platelet aggregation inducer, while P-II rhodostoxin mediates hemorrhage, exacerbated by P-I kistomin and snaclec rhodocetin that inhibit platelet plug formation. These toxins exist in multiple isoforms and/or complex subunits, deserving further characterization for the development of an effective, polyspecific regional antivenom.

BIOLOGICAL SIGNIFICANCE

Advents in proteomics and bioinformatics have vigorously propelled the scientific discoveries of toxins from various lineages of venomous snakes. The Malayan pit viper, Calloselasma rhodostoma, is a medically important species in Southeast Asia as its bite can cause envenomation, while the venom is also a source of bioactive compounds for drug discovery. Detailed profiling of the venom, however, is inadequate possibly due to the complex nature of the venom and technical limitation in separating the constituents into details. Integrating a multi-step fractionation method, this study successfully revealed a comprehensive and quantitative profile of the composition of the venom of this medically important venomous snake. The relative abundance of the various venom proteins is determined in a global profile, providing useful information for understanding the pathogenic roles of the different toxins in C. rhodostoma envenomation. Notably, the principal hemotoxins were identified in great details, including the variety of toxin subunits and isoforms. The findings indicate that these toxins are the principal targets for effective antivenom neutralization, and should be addressed in the production of a pan-regional polyspecific antivenom. In addition, minor toxin components not reported previously in the venom were also detected in this study, enriching the current toxin database for the venomous snakes.

Snake Venom Disintegrin Inhibits the Activation of Toll-Like Receptors and Alleviates Sepsis through Integrin alphaVbeta3 Blockade

Bacterial infection-induced sepsis is the leading cause of septic inflammatory disease. Rhodostomin (Rn), a snake venom disintegrin, was previously reported to interact with the αVβ3 integrin and the TLR4 on phagocyte in attenuating LPS-induced endotoxemia. In this report, we further evaluated the effects of Rn on TLR2-activated monocytes and its in vivo efficacy. Rn effectively suppressed the adhesion, migration, and cytokine release of Pam3CSK4-activated THP-1 cells. Rn specifically bound to integrin αVβ3 of TLR2-activated THP-1. Integrin αV and Akt siRNA transfection both restrained Pam3CSK4-elicited cytokine release. Rn decreased the Pam3CSK4-induced phosporylation of MAPKs, degradation of IκB and activation of FAK, Akt, c-Src and Syk. The Pam3CSK4-induced translocation of MyD88, a central adaptor of TLR2, to the cell membrane was also inhibited by Rn treatment. In the polymicrobial inflammatory caecal ligation and puncture model, Rn significantly reduced pro-inflammatory cytokine and chemokine release, alleviated tissue injury and elevated survival rate in vivo. Taken together, in addition to inhibiting the activation of TLR4, Rn exhibits anti-inflammatory activity through antagonizing the activation of phagocytes and interrupting the crosstalk between αVβ3 and TLR2-dependent signaling pathways.

Gene expression profiling of the venom gland from the Venezuelan mapanare (Bothrops colombiensis) using expressed sequence tags (ESTs)

BACKGROUND

Bothrops colombiensis is a highly dangerous pit viper and responsible for over 70% of snakebites in Venezuela. Although the composition in B. colombiensis venom has been identified using a proteome analysis, the venom gland transcriptome is currently lacking.

RESULTS

We constructed a cDNA library from the venom gland of B. colombiensis, and a set of 729 high quality expressed sequence tags (ESTs) was identified. A total number of 344 ESTs (47.2% of total ESTs) was related to toxins. The most abundant toxin transcripts were metalloproteinases (37.5%), phospholipases A2s (PLA2, 29.7%), and serine proteinases (11.9%). Minor toxin transcripts were linked to waprins (5.5%), C-type lectins (4.1%), ATPases (2.9%), cysteine-rich secretory proteins (CRISP, 2.3%), snake venom vascular endothelium growth factors (svVEGF, 2.3%), L-amino acid oxidases (2%), and other putative toxins (1.7%). While 160 ESTs (22% of total ESTs) coded for translation proteins, regulatory proteins, ribosomal proteins, elongation factors, release factors, metabolic proteins, and immune response proteins. Other proteins detected in the transcriptome (87 ESTs, 11.9% of total ESTs) were undescribed proteins with unknown functions. The remaining 138 (18.9%) cDNAs had no match with known GenBank accessions.

CONCLUSION

This study represents the analysis of transcript expressions and provides a physical resource of unique genes for further study of gene function and the development of novel molecules for medical applications.

Cloning and characterisation of three novel disintegrin precursors from the venoms of three Atheris species: Atheris chlorechis, Atheris nitschei and Atheris squamigera

Snake venom constitutes one of the most complex mixtures of naturally-occurring toxic proteins/polypeptides and a large number of these possess very profound biological activities. Disintegrins, that are commonly found in viper venoms, are low molecular weight proteins that usually contain an -Arg-Gly-Asp- (-RGD-) motif that is known to be involved in cell adhesion ligand recognition, binding specifically to cell surface integrin receptors and also exhibiting platelet anti-aggregation activity. Here, we report for the first time, the successful cloning of three cDNAs encoding disintegrin precursors from lyophilised venom-derived libraries of Atheris chlorechis, Atheris nitschei and Atheris squamigera, respectively. All of these disintegrins belong to the short-coding class and all exhibit high degrees of structural identity, both in their amino acid sequences and in the arrangement of their functional domains. Mass spectrometric analyses of the HPLC-separated/in-gel digested venom proteins was performed to characterise the mature disintegrins as expressed in the venom proteome. Studies on both the structures and conserved sites within these disintegrins are of considerable theoretical interest in the field of biological evolution and in the development of new research tools or novel templates for drug design.

Improvements in endotoxemic syndromes using a disintegrin, rhodostomin, through integrin αvβ3-dependent pathway

BACKGROUND AND OBJECTIVES

Septic shock is a major cause of morbidity and mortality in intensive care units, but there is still no effective therapy for the patients. We evaluated the effects of rhodostomin (Rn), an Arg-Gly-Asp-containing snake venom disintegrin, on lipopolysaccharide (LPS)-activated phagocytes in vitro and LPS-induced endotoxemia in vivo.

METHODS AND RESULTS

Rn inhibited adhesion, migration, cytokine production and mitogen-activated protein kinase (MAPK) activation of macrophage induced by LPS. Flow cytometric analysis revealed that Rn specifically blocked anti-αv mAb binding to RAW264.7. Besides inhibiting MAPK activation of THP-1, Rn bound to LPS-activated THP-1 and specifically blocked anti-αvβ3 mAb binding to THP-1. Binding assays proved that integrin αvβ3 was the binding site for rhodostomin on phagocytes. Rn reversed the enhancement of fibronectin and vitronectin on LPS-induced monocyte adhesion and cytokine release. Transfection of integrin αv siRNA also inhibited LPS-induced activation of monocyte, and Rn exerted no further inhibitory effect. Furthermore, Rn significantly decreased the production of tumor necrosis factor-α (TNF-a), interleukin (IL)-6, -1β and -10 and attenuated cardiovascular dysfunction, including blood pressure and heart pulse, and thrombocytopenia in LPS-induced endotoxemic mice. Rn also protected against tissue inflammation as evidenced by histological examination.

CONCLUSIONS

Rn may interact with αvβ3 integrin of monocytes/macrophages leading to interfere with the activation of phagocytes triggered by LPS. These results suggest that the protective function of Rn in LPS-induced endotoxemia may be attributed to its anti-inflammation activities in vivo.

Snake venom metalloproteases--structure and function of catalytic and disintegrin domains

Snake venoms are relevant sources of toxins that have evolved towards the engineering of highly active compounds. In the last years, research efforts have produced great advance in their understanding and uses. Metalloproteases with disintegrin domains are among the most abundant toxins in many Viperidae snake venoms. This review will focus on the structure, function and possible applications of the metalloprotease and disintegrin domains.

Primary structure of brevilysin L4, an enzymatically active fragment of a disintegrin precursor from Gloydius halys brevicaudus venom

Brevilysin L4 (L4) is a non-hemorrhagic P-I class metalloprotease (MP) isolated from Gloydius halys brevicaudus venom. Its complete amino acid sequence has been determined. L4 is a single-chain polypeptide and highly homologous to those of other snake venom MPs. A zinc-binding motif, HExxHxxGxxH, is located at residues 142-152. A characteristic feature of L4 is the presence of a spacer sequence (LRTDTVS) at the C-terminal that links metalloprotease and disintegrin domains and is usually removed by post-translational proteolysis, suggesting that L4 is expressed together with a spacer region and a disintegrin domain at the C-terminal. The nucleotide sequence of a cDNA clone encoding L4 has revealed that L4 is a disintegrin precursor and produced as a P-II class MP. The disintegrin coded after L4 sequence was brevicaudin 1, a disintegrin previously isolated from the same venom. P-II class MPs have been suspected to undergo autoproteolysis to release disintegrins. Although being P-I class MP, L4 itself autocatalytically degrades with a half-life of 30min at pH 8.5 and 37 degrees C in the absence of Ca(2+). Sequence analysis of several fragment peptides produced during the autolysis of L4 indicated that more than 40 peptide bonds were split, and the cleavages of Ser(60)-Asn(61), Thr(99)-Ala(100), and Phe(103)-Asp(104) bonds may trigger the autoproteolysis. Addition of Ca(2+) completely suppressed the cleavage of these particular bonds, resulting in a marked prevention of autoproteolysis. Thus, L4 provides a good model for the investigation of autolysis of some MPs.

Effects of three novel metalloproteinases from the venom of the West African saw-scaled viper, Echis ocellatus on blood coagulation and platelets

Two metalloproteinases, a 24-kDa P-I EoVMP1 and a 56-kDa P-III EoVMP2, have recently been isolated from the venom of the West African saw-scaled viper Echis ocellatus. We now reveal a new 65-kDa haemorrhagic group P-III metalloproteinase which we have designated EoVMP3. The aim of this study was to determine whether these three snake venom metalloproteinases (SVMPs) affect platelets and blood coagulation. EoVMP1 had no effect on the aggregation of washed human platelets, whereas EoVMP2 inhibited collagen-induced platelet aggregation. In contrast, EoVMP3 did not inhibit the aggregation of platelets by collagen but instead activated platelets in the absence of any additional co-factors. All three SVMPs were capable of activating prothrombin to varying degrees and can therefore be described as procoagulants. EoVMP1, EoVMP2 and EoVMP3 share sequence identity with other members of the reprolysin family, but differ greatly in their effects on some of the components that control haemostasis.

Application of Recombinant Rhodostomin in Studying Cell Adhesion

Rhodostomin from venom of Agkistrodon rhodostoma (also called Calloselasma rhodostoma) contains 68 amino acid residues including 6 pairs of disulfide bonds and an arginine-glycine-aspartic acid (RGD) sequence at positions 49-51. It has been known as one of the strongest antagonists to platelet aggregation among the family termed disintegrin. In this review paper, in addition to introducing the characteristics of disintegrin and its related molecules, the advantages of using recombinant DNA technology to produce rhodostomin are described. The recombinant rhodostomin has been demonstrated to facilitate cell adhesion via interaction between the RGD motif of rhodostomin and integrins on the cell surface. This property allowed us to use the recombinant rhodostomin as an extracellular matrix to study cell adhesion and to distinguish attachment efficiency between two melanoma cell lines B16-F1 and B16-F10, the former is a low metastasis cell while the latter is a high metastasis cell. Furthermore, by using the recombinant rhodostomin as a substrate, osteoprogenitor-like cells are able to be selected and enriched within 3 days from rat bone marrow which contains a heterogeneous cell population. Finally, we show that the recombinant rhodostomin can be immobilized on beads and which serve as an affinity column to dissect cell-surface protein(s) binding to the RGD motif of rhodostomin.

Molecular cloning and sequence analysis of cDNA encoding flavoridin, a disintegrin from the venom of Trimeresurus flavoviridis

We isolated a cDNA of 2001bp encoding the full-length precursor of flavoridin, which is one of the four disintegrins in the venom of Trimeresurus flavoviridis, and analyzed the cDNA nucleotide sequence. The deduced amino acid sequence of the open reading frame consisted of a pro-domain (190 residues), a metalloproteinase domain (205 residues), a spacer domain (18 residues) and a disintegrin (flavoridin) domain (70 residues), thus indicating that the flavoridin precursor belongs to the P-II class of snake venom metalloproteinases. The unknown metalloproteinase domain shared strong sequence similarity with HR2a (71.2% identity) and H(2)-proteinase (74.1% identity), a low molecular mass hemorrhagic metalloproteinase and a non-hemorrhagic metalloproteinase in the same snake venom, respectively.

The disintegrin-like domain of the snake venom metalloprotease alternagin inhibits alpha2beta1 integrin-mediated cell adhesion

The alpha2beta1 integrin is a major collagen receptor that plays an essential role in the adhesion of normal and tumor cells to the extracellular matrix. Here we describe the isolation of a novel metalloproteinase/disintegrin, which is a potent inhibitor of the collagen binding to alpha2beta1 integrin. This 55-kDa protein (alternagin) and its disintegrin domain (alternagin-C) were isolated from Bothrops alternatus snake venom. Amino acid sequencing of alternagin-C revealed the disintegrin structure. Alternagin and alternagin-C inhibit collagen I-mediated adhesion of K562-alpha2beta1-transfected cells. The IC50 was 134 and 100 nM for alternagin and alternagin-C, respectively. Neither protein interfered with the adhesion of cells expressing alphaIIbeta3, alpha1beta1, alpha5beta1, alpha4beta1 alphavbeta3, and alpha9beta1 integrins to other ligands such as fibrinogen, fibronectin, and collagen IV. Alternagin and alternagin-C also mediated the adhesion of the K562-alpha2beta1-transfected cells. Our results show that the disintegrin-like domain of alternagin is responsible for its ability to inhibit collagen binding to alpha2beta1 integrin.

alpha 2beta 1 integrin is not recognized by rhodocytin but is the specific, high affinity target of rhodocetin, an RGD-independent disintegrin and potent inhibitor of cell adhesion to collagen

We have recombinantly expressed a soluble form of human alpha(2)beta(1) integrin that lacks the membrane-anchoring transmembrane domains as well as the cytoplasmic tails of both integrin subunits. This soluble alpha(2)beta(1) integrin binds to its collagen ligands the same way as the wild-type alpha(2)beta(1) integrin. Furthermore, like the wild-type form, it can be activated by manganese ions and an integrin-activating antibody. However, it does not bind to rhodocytin, a postulated agonist of alpha(2)beta(1) integrin from the snake venom of Calloselasma rhodostoma, which elicits platelet aggregation. Taking advantage of the recombinantly expressed, soluble alpha(2)beta(1) integrin, an inhibition assay was established in which samples can be tested for their capability to inhibit binding of soluble alpha(2)beta(1) integrin to immobilized collagen. Thus, by scrutinizing the C. rhodostoma snake venom in this protein-protein interaction assay, we found a component of the snake venom that inhibits the interaction of soluble alpha(2)beta(1) integrin to type I collagen efficiently. N-terminal sequences identified this inhibitor as rhodocetin, a recently published antagonist of collagen-induced platelet aggregation. We could demonstrate that its inhibitory effect bases on its strong and specific binding to alpha(2)beta(1) integrin, proving that rhodocetin is a disintegrin. Standing apart from the growing group of RGD-dependent snake venom disintegrins, rhodocetin interacts with alpha(2)beta(1) integrin in an RGD-independent manner. Furthermore, its native conformation, which is stabilized by disulfide bridges, is indispensibly required for its inhibitory activity. Rhodocetin does not contain any major collagenous structure despite its high affinity to alpha(2)beta(1) integrin, which binds to collagenous molecules much more avidly than to noncollagenous ligands, such as laminin. Blocking alpha(2)beta(1) integrin as the major collagen receptor on platelets, rhodocetin is responsible for hampering collagen-induced, alpha(2)beta(1) integrin-mediated platelet activation, leading to hemorrhages and bleeding disorders of the snakebite victim. Moreover, having a widespread tissue distribution, alpha(2)beta(1) integrin also mediates cell adhesion, spreading, and migration. We showed that rhodocetin is able to inhibit alpha(2)beta(1) integrin-mediated adhesion of fibrosarcoma cells to type I collagen completely.

The disulfide bond pattern of catrocollastatin C, a disintegrin-like/cysteine-rich protein isolated from Crotalus atrox venom

The disulfide bond pattern of catrocollastatin-C was determined by N-terminal sequencing and mass spectrometry. The N-terminal disintegrin-like domain is a compact structure including eight disulfide bonds, seven of them in the same pattern as the disintegrin bitistatin. The protein has two extra cysteine residues (XIII and XVI) that form an additional disulfide bond that is characteristically found in the disintegrin-like domains of cellular metalloproteinases (ADAMs) and PIII snake venom Zn-metalloproteinases (SVMPs). The C-terminal cysteine-rich domain of catrocollastatin-C contains five disulfide bonds between nearest-neighbor cysteines and a long range disulfide bridge between CysV and CysX. These results provide structural evidence for a redefinition of the disintegrin-like and cysteine-rich domain boundaries. An evolutionary pathway for ADAMs, PIII, and PII SVMPs based on disulfide bond engineering is also proposed.

Nucleotide sequence of a cDNA encoding a common precursor of disintegrin flavostatin and hemorrhagic factor HR2a from the venom of Trimeresurus flavoviridis

The venom of Trimeresurus flavoviridis has three disintegrins that act as platelet aggregation inhibitors by binding to integrin alphaIIb beta3 on platelets through its Arg-Gly-Asp sequence. We isolated the cDNA encoding the flavostatin precursor that is one of the disintegrins in T. flavoviridis venom. The open reading frame consisted of four regions, a pre-peptide region, a metalloprotease region, a spacer region and a disintegrin region, indicating that the flavostatin precursor belongs to the metalloprotease/disintegrin family. Surprisingly, the deduced amino acid sequence of the metalloprotease region was completely consistent with that of hemorrhagic metalloprotease HR2a, which indicated that this metalloprotease released from the flavostatin precursor functions as a hemorrhagic factor. These observations indicated that a disintegrin and a hemorrhagic metalloprotease were synthesized as a common precursor. Thus, our results support the hypothesis that a disintegrin is synthesized as a metalloprotease/disintegrin precursor and matures by cleavage from the precursor molecule.

Oligosaccharide residues of Loxosceles intermedia (brown spider) venom proteins: dependence on glycosylation for dermonecrotic activity

Loxosceles spp. (brown spider) envenomation has been reported to provoke dermonecrosis and haemorrhage at the bite site (a hallmark of accidents) and, to a lesser extent, thrombocytopenia, hemolysis and disseminated intravascular coagulation in some cases. Using lectin-immunolabeling, lectin-affinity chromatography, glycosidase and proteinase K treatments we were able to identify several venom N-glycosylated proteins with high-mannose oligosaccharide structures, complex-type glycoconjugates such as fucosylated glycans, but no galactose or sialic acid residues as complex sugars or glycosaminoglycan residues. Working with enzymatically or chemically deglycosylated venom we found that platelet aggregation (thrombocytopenic activity) as well as the fibronectinolytic and fibrinogenolytic (haemorrhagic) effects of the venom were sugar-independent when compared to glycosylated venom. Nevertheless, zymograph analysis in co-polymerized gelatin gels showed that enzymatic N-deglycosylation of loxolysin-B, a high-mannose 32-35 kDa glycoprotein of the venom with gelatinolytic metalloproteinase activity, caused a reduction of approximately 2 kDa in its molecular weight and a reduction of the gelatinolytic effect to a residual activity of 28% when compared to the glycosylated molecule, indicating a post-translational glycosylation-dependent gelatinolytic effect. Analysis of the dermonecrotic effect of the chemically or enzymatically N-deglycosylated venom detected only residual activity when compared with the glycosylated control. Thus, the present report suggests that oligosaccharide moieties play a role in the destructive effects of brown spider venom and opens the possibility for a carbohydrate-based therapy.

Full-spreading platelets induced by the recombinant rhodostomin are via binding to integrins and correlated with FAK phosphorylation

We have previously reported that non-activated platelets can be induced by morphological changes from the recombinant fusion protein of GST-rhodostomin [GST-RHO(RGD)], a member of disintegrin with an arginine-glycine-aspartic acid (RGD) motif. In this study, we further characterized the factors involved in platelet shape changes induced by rhodostomin. From less to full-spreading, four cell spreading indexes, p1, p2, s1 and s2, were designated to the platelet shape based on the scanning electron micrographs. Results of peptide competition and antibody blocking confirmed that interaction between the RGD of rhodostomin and the alpha(IIb)beta3 integrins of platelets was required for induction of a higher percentage of s2 cells. When platelets were pretreated with calphostin C, herbimycin A and cytochalasin B, respectively, the percentage of p1 and p2 cells on rhodostomin-coated plates was increased and, concomitantly, the percentage of s1 and s2 cells was decreased. Biochemical analyses indicated that the focal adhesion kinase (FAK or pp125FAK) in platelets that adhered to GST-RHO(RGD) was phosphorylated in contrast to little or no phosphorylation of FAK in cells adhered to fibrinogen or non-activated cells. Furthermore, the degree of FAK phosphorylation was consistently correlated with morphological changes in platelets treated with various drugs. Taking all the results together, we suggested that rhodostomin could directly bind to integrins of platelets and then trigger signal transduction leading to FAK phosphorylation and actin polymerization and finally resulting in platelet full-spreading.

Isolation, sequence analysis, and biological activity of atrolysin E/D, the non-RGD disintegrin domain from Crotalus atrox venom

Crotalid snake venom metalloproteinases often have associated with them nonproteinase domains that may be processed from the mature proteinases. Nascent atrolysin E, from the western diamondback rattlesnake, Crotalus atrox, has a metalloproteinasedomain and a non-RGD disintegrin domain that is lacking in the mature metalloproteinase. In this studywe report on the isolation, sequence analysis, andbiological activity of the 7.4-kDa atrolysin E disintegrin domain (atrolysin E/D). Atrolysin E/D represents approximately 0.2% of the total protein fromthe crude venom. The protein begins with a glycinyl residue found in the latter part of the spacer region. The sequence of atrolysin E/D is identical to thatof the non-RGD disintegrin domain of atrolysin E. The structure is termed a non-RGD disintegrin sincein lieu of the characteristic RGD sequence, a Met-Val-Asp (MVD) is found instead. Nevertheless, the protein is a potent inhibitor of both collagen- and ADP-stimulated platelet aggregation with IC50 values of 4 and 8 nM, respectively. A cyclized synthetic peptide, Ac-CRVSMVDRNDDTC-NH2, which represents the sequence of the atrolysin E/D non-RGD loop, was demonstrated to be an effective inhibitor of platelet aggregation. Therefore, this region of atrolysin E/D's structure, as in the disintegrins proper, is important for the biological activity of the protein. Thus, like the non-RGD disintegrin barbourin from Sistrurus miliarius barbouri, a RGD sequence in the context of the disintegrin protein backbone is not an absolute requirement for platelet aggregation inhibitory activity. These data underscore the biochemical and functional complexity of crotalid snake venoms due to differential proteolytic processing of the precursor metalloproteinases and exemplify how the processed fragments may contribute to the observed pathological effects of the venom.

CD156 (human ADAM8): expression, primary amino acid sequence, and gene location

The murine cell-surface antigen MS2 [ADAM 8; mouse CD156 (mCD156)] is a transmembrane glycoprotein that is highly expressed in monocytic lineages. mCD156 consists of a long exterior region containing domains strikingly similar to those of hemorrhagic snake venom proteins. cDNA for human CD156 was isolated from cDNA libraries from the human macrophage cell line THP-1 and from human granulocytes. The CD156 cDNA detected mRNA from human macrophage cell lines, granulocytes, monocytes, and B cell but not T cell lines. The nucleotide sequence of the CD156 cDNA showed 65.6% homology with that of mCD156, and its amino acid sequence had high homology with hemorrhagic snake venom proteins and other related mammalian proteins. The CD156 gene was mapped to human chromosome 10q26.3.

ADM-1, a protein with metalloprotease- and disintegrin-like domains, is expressed in syncytial organs, sperm, and sheath cells of sensory organs in Caenorhabditis elegans

A search was carried out for homologues of possible fusogenic proteins to study their function in a genetically tractable animal. The isolation, molecular, and cellular characterization of the Caenorhabditis elegans adm-1 gene (a disintegrin and metalloprotease domain) are described. A glycoprotein analogous to viral fusion proteins has been identified on the surface of guinea pig sperm (PH-30/fertilin) and is implicated in sperm-egg fusion. adm-1 is the first reported invertebrate gene related to PH-30 and a family of proteins containing snake venom disintegrin- and metalloprotease-like domains. ADM-1 shows a domain organization identical to PH-30. It contains prepro, metalloprotease, disintegrin, cysteine rich with putative fusion peptide, epidermal growth factor-like repeat, transmembrane, and cytoplasmic domains. Antibodies which recognize ADM-1 protein in immunoblots were generated. Using immunofluorescence and in situ hybridization, the products of adm-1 have been detected in specific cells during different stages of development. The localization of ADM-1 to the plasma membrane of embryonic cells and to the sheath cells of sensory organs suggests a function in cell adhesion. ADM-1 expression in the hypodermis, pharynx, vulva, and mature sperm is consistent with a putative role in somatic and gamete cell fusions.

Are C-type lectin-related proteins derived by proteolysis of metalloproteinase/disintegrin precursor proteins?

Metalloproteinases and disintegrins, non-enzymatic inhibitors of platelet aggregation, are derived by proteolysis from common precursors. A closer examination of the cDNA and amino acid sequences of these precursors indicated that the putative signal peptide may be an internal hydrophobic segment and that the sequences are incomplete at the 5'-region. The studies indicated that C-type lectin-related proteins are also derived from the amino terminal region of these precursors. Based on these findings, a five-domain structure is proposed for the precursors.

KUZ, a conserved metalloprotease-disintegrin protein with two roles in Drosophila neurogenesis

During neurogenesis in Drosophila both neurons and nonneuronal cells are produced from a population of initially equivalent cells. The kuzbanian (kuz) gene described here is essential for the partitioning of neural and nonneuronal cells during development of both the central and peripheral nervous systems in Drosophila. Mosaic analyses indicated that kuz is required for cells to receive signals inhibiting the neural fate. These analyses further revealed that the development of a neuron requires a kuz-mediated positive signal from neighboring cells. The kuz gene encodes a metalloprotease-disintegrin protein with a highly conserved bovine homolog, raising the possibility that kuz homologs may act in similar processes during mammalian neurogenesis.

Analysis of transcripts encoding novel members of the mammalian metalloprotease-like, disintegrin-like, cysteine-rich (MDC) protein family and their expression in reproductive and non-reproductive monkey tissues

A number of sequence-related, cysteine-rich proteins containing metalloprotease-like and disintegrin-like domains (the MDC protein family), at least one of which has been shown to play a role in egg recognition during fertilization, are abundantly expressed in the mammalian male reproductive tract. In this paper we report the cloning and sequence analysis of three closely related isoforms of a novel member of this family which are expressed not only in the testis, but also in the liver, albeit at a lower level. Using a PCR-based approach we also demonstrate the presence of transcripts encoding additional, novel, disintegrin-containing proteins, in the liver and epididymis. We conclude that while some members of the MDC family are specific to the reproductive tract, suggesting functions peculiar to those tissues, others have a broader tissue distribution and may therefore play a more general role in integrin-mediated cell-cell recognition, adhesion or signalling.

A metalloprotease-disintegrin participating in myoblast fusion

Skeletal muscle development involves the formation of multi-nucleated myotubes. This is thought to proceed by the induction of differentiation (acquisition of fusion competence) of myoblast cells, their aggregation, and union of their plasma membranes. Various membrane proteins including N- and M-cadherins, N- and V-CAMs and integrins participate in myotube formation, but the molecular mechanisms of muscle cell fusion are poorly understood. Here we report the identification of three new, myoblast-expressed gene products, meltrin-alpha, beta and gamma, with homology to both viper haemorrhagic factors and fertilin (PH-30), a membrane protein involved in egg-sperm fusion. Meltrin-alpha, a member of the metalloproteinase/disintegrin protein family, appears to be required for myotube formation. Involvement of a fertilin-related protein in myogenesis suggests that there are common mechanisms in gamete and myoblast fusion.

Sequence analysis of fibrolase, a fibrinolytic metalloproteinase from Agkistrodon contortrix contortrix

Fibrolase is a small (203 amino acids), nonhemorrhagic, fibrinolytic enzyme from the venom of Agkistrodon contortrix contortrix (southern copperhead). While the chemical and physical properties of the protein have been extensively studied, its overall globular structure is unknown. By comparison with homologous metalloproteinases and snake toxins, the catalytic zinc binding site of fibrolase has been identified, as well as a potential binding site for calcium, which has not been recognized before. The positions of the major secondary structural features are predicted, and found to be similar to other structurally characterized metalloproteinases, while the positions of the three intramolecular disulfide bonds are also postulated. Finally, fibrolase is reported to be nonhemorrhagic and earlier work on hemorrhagic enzymes from snake venoms identified six amino acids which might be responsible for hemorrhagic activity. It is shown here that most of these residues occur in fibrolase, and yet it is nonhemorrhagic in its activity. Altogether, this work demonstrates the utility of sequence analysis methods in the characterization of the structure of venom-derived proteins.

Do we know the complete sequence of metalloproteinase and nonenzymatic platelet aggregation inhibitor (disintegrin) precursor proteins?

Recent evidence indicates that metalloproteinases and disintegrins, nonenzymatic inhibitors of platelet aggregation, are derived by proteolysis from common precursors. Although proteins and polypeptides with various domain structures have been identified, proteins containing proprotein domains or the complete mature precursors have not yet been isolated. This prompted a closer examination of the putative start codon, signal peptide and the segment upstream of these regions. A critical evaluation of sequence information of these precursors indicates that the putative signal peptide identified in these precursors may be an internal hydrophobic segment within the precursor. There is also evidence to indicate that C-type lectin-related proteins are also derived from these precursors. Thus the available sequence data of the precursors appear to be incomplete.

The primary structure of a hemorrhagic factor, HR2b, from the venom of Okinawa habu (Trimeresurus flavoviridis)

The complete amino acid sequence of a hemorrhagic factor, HR2b, from the venom of Okinawa habu was determined. The hemorrhagic factor was fragmented by CNBr cleavage, trypsin, staphylococcal protease V8 and lysyl endopeptidase digestions. The resulting peptides were purified on high performance chromatography, and sequenced by Edman degradation. HR2b was composed of 204 amino acids with pyroglutamyl residue at the amino terminus, and the calculated mol. wt based on the amino acid composition was 23,335. There are three disulfide linkages in the primary structure. The consensus sequence (His-Glu-Xaa-Xaa-His) for zinc-binding site of zinc-requiring metalloproteinases was found in the structure. The primary structure of HR2b shows a significant similarity with that of HR2a of Amami habu venom; 98.5% identity.

Action of Calloselasma rhodostoma (Malayan pit viper) venom on human blood coagulation and fibrinolysis using computerized thromboelastography (CTEG)

The effects of Malayan pit viper (Calloselasma rhodostoma) venom on human blood coagulation and fibrinolysis were studied in vitro using computerized thromboelastography. At low concentrations the venom had a coagulant effect shown by faster onset of the coagulation process (shortened SP and R), faster progress of the clot (increased angle and shortened K), and increased coagulation (TEG) index. The maximum amplitude (MA) was not affected, suggesting that the venom had no apparent effect on platelet function; and clot lysis was similar to that in the controls, suggesting that there was no primary fibrinolytic activity. At higher concentrations the venom had anticoagulant effects, SP and R were progressively shortened, but there was poor/no progress in the clot formed, evident from prolonged or absent K, diminished MA and reduced angle. These results show that C. rhodostoma venom has both coagulant and anticoagulant actions. The coagulant action may be due to Factor X activator predominance at low concentrations, while the anticoagulant action could be due to ancrod action. TEG is able to demonstrate the dual effect of this venom, previously described as a paradox, and may be a useful tool in the diagnosis and monitoring of envenomation patients.

Cloning of metalloprotease genes in the carpet viper (Echis pyramidum leakeyi). Further members of the metalloprotease/disintegrin gene family

The genes coding for two metalloproteases, EcH-I and EcH-II, have been cloned from an Echis pyramidum leakeyi venom gland cDNA library. The cDNA sequences predict two zymogen molecules with strong amino acid sequence similarity and the same domain structure present in other members of the viper metalloprotease/disintegrin gene family. EcH-I and EcH-II contain pro-protein, enzyme and disintegrin domains. Analysis of the cDNAs coding for EcH-I, EcH-II, jararhagin, trigramin and Ht-e reveals a strong similarity, particularly in the untranslated regions and regions coding for the pro-peptide. Comparison of EcH-I and EcH-II with venom metalloproteases, mammalian matrix-degrading metalloproteases, sperm proteins, and a potential tumour suppressor gene highlights the presence of a number of motifs with potential functional significance.

A family of cellular proteins related to snake venom disintegrins

Disintegrins are short soluble integrin ligands that were initially identified in snake venom. A previously recognized cellular protein with a disintegrin domain was the guinea pig sperm protein PH-30, a protein implicated in sperm-egg membrane binding and fusion. Here we present peptide sequences that are characteristic for several cellular disintegrin-domain proteins. These peptide sequences were deduced from cDNA sequence tags that were generated by polymerase chain reaction from various mouse tissue and a mouse muscle cell line. Northern blot analysis with four sequence tags revealed distinct mRNA expression patterns. Evidently, cellular proteins containing a disintegrin domain define a superfamily of potential integrin ligands that are likely to function in important cell-cell and cell-matrix interactions.

Activation of snake venom metalloproteinases by a cysteine switch-like mechanism

The cDNAs of several snake venom zinc endopeptidases code for a putative propeptide, which includes the conserved cysteine-containing sequence PKMCGVT. It has been suggested that binding of the cysteine thiol function to the active-site zinc, resulting in inactivation of the catalytic domain, occurs in a mode similar to the 'cysteine switch' mechanism proposed for matrix metalloproteinases. In order to confirm this hypothesis, inhibition kinetics have been performed on the metalloproteinase adamalysin II of the venom of the snake Crotalus adamanteus using several cysteine peptides. Among these the synthetic hexapeptide PKMCGV-NH2, corresponding to the conserved sequence portion of the known propeptides, was found to be by far the strongest inhibitor of this proteinase with a Ki of 3.4 microM. The inhibitory potencies of an equivalent peptide with the L-Cys replaced by a D-Cys or by an L-Ser as well as of reduced glutathione, cysteine and two unrelated cysteine peptides were by one to two orders of magnitudes lower. These findings strongly support a cysteine switch-like mechanism even for activation of the snake venom metalloproteinases.

Molecular cloning and sequence analysis of the cDNA for ancrod, a thrombin-like enzyme from the venom of Calloselasma rhodostoma

The 1.54 kb cDNA for ancrod, a thrombin-like enzyme, was cloned from a lambda ZAP cDNA library derived from the venom glands of Calloselasma (Agkistrodon) rhodostoma. The cDNA sequence reveals that ancrod is synthesized as a pre-zymogen of 258 amino acids, including a putative secretory peptide of 18 amino acids and a proposed zymogen peptide of 6 amino-acid residues. The amino-acid sequence of the predicted active form of the enzyme exhibits a high degree of sequence similarity to those of mammalian serine proteases (trypsin and pancreatic kallikrein) and other thrombin-like enzymes (batroxobin and flavoxobin). Key amino-acid residues (His43, Asp88, Ser182 and Asp176) that are thought to be involved in the substrate cleavage and in the substrate-binding reaction are conserved. Ancrod contains 13 cysteine residues. Based on alignment with the amino-acid sequences of trypsin and batroxobin, six disulphide bridges can be predicted to be present in the ancrod protein. The existence of a free cysteine, which changes the common sequence surrounding the Ser182 active site from Gly-Asp-Ser-Gly-Gly-Pro to Cys-Asp-Ser-Gly-Gly-Pro, is unusual for a serine protease.

Isolation and characterization of a hemorrhagin from the venom of Calloselasma rhodostoma (Malayan pit viper)

The major hemorrhagin (termed rhodostoxin) of the venom of Calloselasma rhodostoma (Malayan pit viper) was purified to electrophoretic homogeneity by Sephadex G-200 gel filtration followed by high performance ion exchange chromatography. The purified hemorrhagin also yielded a single peak in reversed-phase HPLC. It had an isoelectric point of 5.3 and a mol. wt of 34,000. Rhodostoxin exhibited potent proteolytic, hemorrhagic and edema-inducing activities but was not lethal to mice at a dose of 6 microgram/g (i.v.). Treatment of rhodostoxin with EDTA eliminated both the proteolytic and hemorrhagic activities completely. The N-terminal sequence of rhodostoxin was determined to be NHEIKRHVDIVVVXDSRFCTK.

Nucleotide sequence of a full-length cDNA encoding a common precursor of platelet aggregation inhibitor and hemorrhagic protein from Calloselasma rhodostoma venom

The nucleotide sequence of a full-length cDNA encoding the common precursor of a platelet aggregation inhibitor, rhodostomin and a hemorrhagic protein from Calloselasma rhodostoma snake venom is presented. The 1.98-kb cDNA contains an open reading frame encoding 478 amino acid residues. The complete structure of the precursor protein encoded by the cDNA is elucidated.

Binding interactions of kistrin with platelet glycoprotein IIb-IIIa: analysis by site-directed mutagenesis

The binding interactions between platelet fibrinogen receptor, glycoprotein (GP) IIb-IIIa, and kistrin, a snake venom disintegrin protein that contains the adhesion site recognition sequence Arg-Gly-Asp (RGD) and potently inhibits platelet aggregation, have been investigated by site-directed mutagenesis of a synthetic kistrin gene. Kistrin was expressed as a fusion protein in Escherichia coli under control of the alkaline phosphatase promoter. This construction included the stII signal sequence to direct secretion to the periplasmic space and one synthetic (Z) domain of Staphylococcal protein A to allow affinity purification using IgG Sepharose. Kistrin was cleaved from the Z-domain by site-specific proteolysis using a mutant subtilisin BPN' and purified by reverse-phase HPLC. This approach facilitated the rapid purification of a set of 43 alanine replacement mutants whose relative affinity for GP IIb-IIIa was measured by competition with immobilized kistrin and by inhibition of platelet aggregation in human platelet-rich plasma. Alanine replacements at R49, G50, and D51 led to weaker inhibitors of platelet aggregation by 90-fold, 2-fold, and > 200-fold, respectively. The conservative D51E mutant was still > 100-fold less potent whereas R49K had a minor effect (1.8-fold), implying the critical nature of the aspartate for high affinity binding. However, mutations outside of the RGD region led to proteins indistinguishable from kistrin, suggesting no substantial secondary binding interactions. Furthermore, reduced kistrin is not active. We therefore propose that a favorable conformation of the RGD region alone is responsible for the high affinity binding of kistrin to GP IIb-IIIa.