Integrin inhibitors from snake venom: exploring the relationship between the structure and activity of RGD-peptides

Moojecin: The first disintegrin from Bothrops moojeni venom and its antitumor activity in acute myeloid leukemia

Disintegrins are a class of peptides found in snake venom that inhibit the activity of integrins, which are essential cell adhesion receptors in tumor progression and development. In this work, moojecin, a RGD disintegrin, was isolated from Bothrops moojeni snake venom, and its antitumor potential in acute myeloid leukemia (AML) HL-60 and THP-1 cells was characterized. The isolation was performed using a C18 reverse-phase column in two chromatographic steps, and its molecular mass is 7417.84 Da. N-terminal and de novo sequencing was performed to identify moojecin. Moojecin did not show cytotoxic or antiproliferative activity in THP-1 and HL-60 at tested concentrations, but it exhibited significant antimigratory activity in both cell lines, as well as inhibition of angiogenesis in the tube formation assay on Matrigel in a dose-dependent manner. A stronger interaction with integrin αVβ3 was shown in integrin interaction assays compared to α5β1, and the platelet aggregation assay indicated an IC50 of 5.039 μg/mL. Preliminary evaluation of disintegrin toxicity revealed no incidence of hemolysis or cytotoxic effects on peripheral blood mononuclear cells (PBMCs) across the tested concentrations. Thus, this is the first study to report the isolation, functional and structural characterization of a disintegrin from B. moojeni venom and bring a new perspective to assist in AML treatment.

Expression, Purification and Characterization of Recombinant Disintegrin from Gloydius Brevicaudus Venom in Escherichia Coli

Disintegrins, a family of snake venom protein, which are capable of modulating the activity of integrins that play a fundamental role in the regulation of many physiological and pathological processes. The main purpose of this study is to obtain the recombinant disintegrin (r-DI) and evaluate its biological activity. In this study, we explored a high-level expression prokaryotic system and purification strategy for r-DI. Then, r-DI was treated to assay effects on cell growth, migration, and invasion. The affinity for the interactions of r-DI with integrin was determined using Surface plasmon resonance (SPR) analyses. The r-DI can be expressed in Escherichia coli and purified by one-step chromatography. The r-DI can inhibit B16F10 cells proliferation, migration, and invasion. Also, we found that r-DI could interact with the integrin αIIbβ3 (GPIIb/IIIa). The r-DI can be expressed, purified, characterized through functional assays, and can also maintain strong biological activities. Thus, this study showed potential therapeutic effects of r-DI for further functional and structural studies.

Snake venom disintegrins update: insights about new findings

Snake venom disintegrins are low molecular weight, non-enzymatic proteins rich in cysteine, present in the venom of snakes from the families Viperidae, Crotalidae, Atractaspididae, Elapidae, and Colubridae. This family of proteins originated in venom through the proteolytic processing of metalloproteinases (SVMPs), which, in turn, evolved from a gene encoding an A Disintegrin And Metalloprotease (ADAM) molecule. Disintegrins have a recognition motif for integrins in their structure, allowing interaction with these transmembrane adhesion receptors and preventing their binding to proteins in the extracellular matrix and other cells. This interaction gives disintegrins their wide range of biological functions, including inhibition of platelet aggregation and antitumor activity. As a result, many studies have been conducted in an attempt to use these natural compounds as a basis for developing therapies for the treatment of various diseases. Furthermore, the FDA has approved Tirofiban and Eptifibatide as antiplatelet compounds, and they are synthesized from the structure of echistatin and barbourin, respectively. In this review, we discuss some of the main functional and structural characteristics of this class of proteins and their potential for therapeutic use.

rJararacin, a recombinant disintegrin from Bothrops jararaca venom: Exploring its effects on hemostasis and thrombosis

Integrins are a family of heterodimeric transmembrane receptors which link the extracellular matrix to the cell cytoskeleton. These receptors play a role in many cellular processes: adhesion, proliferation, migration, apoptosis, and platelet aggregation, thus modulating a wide range of scenarios in health and disease. Therefore, integrins have been the target of new antithrombotic drugs. Disintegrins from snake venoms are recognized by the ability to modulate the activity of integrins, such as integrin αIIbβ3, a fundamental platelet glycoprotein, and αvβ3 expressed on tumor cells. For this reason, disintegrins are unique and potential tools for examining integrin-matrix interaction and the development of novel antithrombotic agents. The present study aims to obtain the recombinant form of jararacin and evaluate the secondary structure and its effects on hemostasis and thrombosis. rJararacin was expressed in the Pichia pastoris (P. pastoris) expression system and purified the recombinant protein with a yield of 40 mg/L of culture. The molecular mass (7722 Da) and internal sequence were confirmed by mass spectrometry. Structure and folding analysis were obtained by Circular Dichroism and ¹H Nuclear Magnetic Resonance spectra. Disintegrin structure reveals properly folded with the presence of β-sheet structure. rJararacin significantly demonstrated inhibition of the adhesion of B16F10 cells and platelets to the fibronectin matrix under static conditions. rJararacin inhibited platelet aggregation induced by ADP (IC₅₀ 95 nM), collagen (IC₅₀ 57 nM), and thrombin (IC₅₀ 22 nM) in a dose-dependent manner. This disintegrin also inhibited 81% and 94% of the adhesion of platelets to fibrinogen and collagen under continuous flow, respectively. In addition, rjararacin efficaciously prevents platelet aggregation in vitro and ex vivo with rat platelets and thrombus occlusion at an effective dose (5 mg/kg). The data here provides evidence that rjararacin possesses the potential as an αIIbβ3 antagonist, capable of preventing arterial thrombosis.

The recombinant disintegrin, jarastatin, inhibits platelet adhesion and endothelial cell migration

Integrins are transmembrane heterodimeric glycoproteins, present in most cell types that act as mechanoreceptors, connecting extracellular matrix proteins to the cytoskeleton of the cell, mediating several physiological and pathological processes. The disintegrins are peptides capable of modulating the activity of integrins, such as αIIbβ3, responsible for the platelet aggregation and αvβ3, related to angiogenesis. The aim of this study was to produce the recombinant disintegrin jarastatin (rJast), to evaluate its secondary structure and biological activity. rJast was expressed in the yeast Komagataella phaffii (earlier Pichia pastoris) purified using molecular exclusion chromatography and the internal sequence and molecular mass were confirmed by mass spectrometry. The yield was approximately 40 mg/L of culture. rJast inhibited platelet aggregation induced by 2-4 μM ADP, 10 nM thrombin, and 1 μg/mL collagen (IC₅₀ of 244.8 nM, 166.3 nM and 223.5 nM, respectively). It also blocked the adhesion of platelets to collagen under continuous flow in approximately 60% when used 1 μM. We also evaluated the effect of rJast on HMEC-1 cells. rJast significantly inhibited the adhesion of these cells to vitronectin, as well as cell migration (IC₅₀ 1.77 μM) without changing the viability. Conclusions: rJast was successfully expressed with activity in human platelets aggregation identical to the native molecule. Also, rJast inhibits adhesion and migration of endothelial cells. Thus, being relevant for the development of anti-thrombotic and anti-angiogenic drugs.

15N, 13C, and 1H resonance assignments of Jarastatin: a disintegrin of Bothrops jararaca

Disintegrins are a group of cysteine-rich proteins found in a wide variety of snake venoms. These proteins selectively bind to integrins, which play a fundamental role in the regulation of many physiological and pathological processes. Here, we report the NMR chemical shift assignments for ¹H, ¹⁵N, and ¹³C nuclei in the backbone and side chains of recombinant disintegrin Jarastatin (rJast), which was further validated by secondary structure prediction using the TALOS-N server. Taken together, these data are essential to perform NMR-based experiments, including structure determination, backbone dynamics, mapping ligand sites and enabling a deeper understanding of the effect of hydrophobic surface clusters, which are important elements to stabilize some 3D proteins structure/folding.

Structure-Function Relationship of the Disintegrin Family: Sequence Signature and Integrin Interaction

Disintegrins are small cysteine-rich proteins found in a variety of snake venom. These proteins selectively modulate integrin function, heterodimeric receptors involved in cell-cell and cell-matrix interaction that are widely studied as therapeutic targets. Snake venom disintegrins emerged from the snake venom metalloproteinase and are classified according to the sequence size and number of disulfide bonds. Evolutive structure and function diversification of disintegrin family involves a stepwise decrease in the polypeptide chain, loss of cysteine residues, and selectivity. Since the structure elucidation of echistatin, the description of the structural properties of disintegrins has allowed the investigation of the mechanisms involved in integrin-cell-extracellular matrix interaction. This review provides an analysis of the structures of all family groups enabling the description of an expanded classification of the disintegrin family in seven groups. Each group presents a particular disulfide pattern and sequence signatures, facilitating the identification of new disintegrins. The classification was based on the disintegrin-like domain of the human metalloproteinase (ADAM-10). We also present the sequence and structural signatures important for disintegrin-integrin interaction, unveiling the relationship between the structure and function of these proteins.

Novel disintegrin-like peptides derived from an amphibian skin cDNA sequence of Hypsiboas punctatus

Disintegrins comprise a family of small proteins that bind to and alter the physiological function of integrins, especially integrins that mediate platelet aggregation in blood. Here, we report a lysine-glycine-aspartic acid (KGD) disintegrin-like motif present in a 15-amino acid residue peptide identified in a cDNA library of the amphibian Hypsiboas punctatus skin. The original peptide sequence was used as a template from which five new analogs were designed, chemically synthesized by solid phase, and tested for disintegrin activity and tridimensional structural studies using NMR spectroscopy. The original amphibian peptide had no effect on integrin-mediated responses. Nevertheless, derived peptide analogs inhibited integrin-mediated platelet function, including platelet spreading on fibrinogen.

Bioactive Molecules Derived from Snake Venoms with Therapeutic Potential for the Treatment of Thrombo-Cardiovascular Disorders Associated with COVID-19

As expected, several new variants of Severe Acute Respiratory Syndrome-CoronaVirus-2 (SARS-CoV-2) emerged and have been detected around the world throughout this Coronavirus Disease of 2019 (COVID-19) pandemic. Currently, there is no specific developed drug against COVID-19 and the challenge of developing effective antiviral strategies based on natural agents with different mechanisms of action becomes an urgent need and requires identification of genetic differences among variants. Such data is used to improve therapeutics to combat SARS-CoV-2 variants. Nature is known to offer many biotherapeutics from animal venoms, algae and plant that have been historically used in traditional medicine. Among these bioresources, snake venom displays many bioactivities of interest such as antiviral, antiplatelet, antithrombotic, anti-inflammatory, antimicrobial and antitumoral. COVID-19 is a viral respiratory sickness due to SARS-CoV-2 which induces thrombotic disorders due to cytokine storm, platelet hyperactivation and endothelial dysfunction. This review aims to: (1) present an overview on the infection, the developed thrombo-inflammatory responses and mechanisms of induced thrombosis of COVID-19 compared to other similar pathogenesis; (2) underline the role of natural compounds such as anticoagulant, antiplatelet and thrombolytic agents; (3) investigate the management of coagulopathy related to COVID-19 and provide insight on therapeutic such as venom compounds. We also summarize the updated advances on antiviral proteins and peptides derived from snake venoms that could weaken coagulopathy characterizing COVID-19.

Exogenous Integrin αIIbβ3 Inhibitors Revisited: Past, Present and Future Applications

The integrin αIIbβ3 is the most abundant integrin on platelets. Upon platelet activation, the integrin changes its conformation (inside-out signalling) and outside-in signalling takes place leading to platelet spreading, platelet aggregation and thrombus formation. Bloodsucking parasites such as mosquitoes, leeches and ticks express anticoagulant and antiplatelet proteins, which represent major sources of lead compounds for the development of useful therapeutic agents for the treatment of haemostatic disorders or cardiovascular diseases. In addition to hematophagous parasites, snakes also possess anticoagulant and antiplatelet proteins in their salivary glands. Two snake venom proteins have been developed into two antiplatelet drugs that are currently used in the clinic. The group of proteins discussed in this review are disintegrins, low molecular weight integrin-binding cysteine-rich proteins, found in snakes, ticks, leeches, worms and horseflies. Finally, we highlight various oral antagonists, which have been tested in clinical trials but were discontinued due to an increase in mortality. No new αIIbβ3 inhibitors are developed since the approval of current platelet antagonists, and structure-function analysis of exogenous disintegrins could help find platelet antagonists with fewer adverse side effects.

A rhamnose-binding lectin from Rhodnius prolixus and the impact of its silencing on gut bacterial microbiota and Trypanosoma cruzi

Lectins are ubiquitous proteins involved in the immune defenses of different organisms and mainly responsible for non-self-recognition and agglutination reactions. This work describes molecular and biological characterization of a rhamnose-binding lectin (RBL) from Rhodnius prolixus, which possesses a 21 amino acid signal peptide and a mature protein of 34.6 kDa. The in-silico analysis of the primary and secondary structures of RpLec revealed a lectin domain fully conserved among previous insects studied. The three-dimensional homology model of RpLec was similar to other RBL-lectins. Docking predictions with the monosaccharides showed rhamnose and galactose-binding sites comparable to Latrophilin-1 and N-Acetylgalactosamine-binding in a different site. The effects of RpLec gene silencing on levels of infecting Trypanosoma cruzi Dm 28c and intestinal bacterial populations in the R. prolixus midgut were studied by injecting RpLec dsRNA into the R. prolixus hemocoel. Whereas T. cruzi numbers remained unchanged compared with the controls, numbers of bacteria increased significantly. The silencing also induced the up regulation of the R. prolixus defC (defensin) expression gene. These results with RpLec reveal the potential importance of this little studied molecule in the insect vector immune response and homeostasis of the gut bacterial microbiota.

Isolation and Functional Identification of an Antiplatelet RGD-Containing Disintegrin from Cerastes cerastes Venom

The current report focuses on purification, structural and functional characterization of Cerastategrin from Cerastes cerastes venom, a novel basic disintegrin (pI 8.36) with 128 amino acid residues and a molecular weight of 13 835.25 Da measured by MALDI-MSMS. The 3D structure of Cerastategrin is organized as α-helix (13%), β-strand (15%) and disordered structure (30%) and presents homologies with several snake venom disintegrins. Structural modeling shows that Cerastategrin presents an RGD motif that connects specifically to integrin receptors. Cerastategrin exhibits the inhibition of ADP induced platelets with an IC₅₀ of 0.88 µg/mL and shows in vivo long stable anticoagulation effect 24 h post-injection of increasing doses ranging from 0.2 to 1 mg/kg, therefore, Cerastategrin maintained irreversibly the blood incoagulable. Moreover, Cerastategrin decreases the amount of bounded αIIbβ3 and reduced significantly the quantity of externalized P-Selectin. Cerastategrin acts as a molecule targeting specifically the receptor α_IIbβ₃; therefore, it behaves as a potent platelet activation inhibitor. As a new peptide with promising pharmacological properties, Cerastategrin could have a potential therapeutical effect in the vascular pathologies and may be a new effective treatment approach.

Synergistic suppression of a disintegrin acurhagin-C in combination with AZD4547 and reparixin on terminating development for human osteosarcoma MG-63 cell

Current therapies available for the treatment of human osteosarcoma, an aggressive bone tumor, are insufficient. To examine an alternative approach of integrin-based anti-osteosacoma strategy, acurhagin-C, a Glu-Cys-Asp (ECD)-disintegrin, was isolated and evaluated for its application in combination with two potent inhibitors of basic fibroblast growth factor (bFGF) and interleukin-8 (IL-8). The investigation of human osteosarcoma MG-63 cells pre-incubated with a FGF receptor-1 (FGFR-1) blocker AZD4547, a CXC-chemokine receptor-1/-2 (CXCR1/2) antagonist reparixin, and acurhagin-C via two given modes of separation and combination was executed. Detected by flow cytometry, integrins-α2/-α5/-αv/-β1, FGFR-1, CXCR1 and CXCR2 constitutively express on the resting membrane. However, bFGF/IL-8-activated MG-63 cells only statistically enhanced the surface exposure of integrins-α5/-β1, FGFR-1 and CXCR2. In activated MG-63 cells, acurhagin-C targeting integrin-α5 not only might potentiate the inhibitory effect of AZD4547 and reparixin on the surface expression of integrin-α5, FGFR-1 and CXCR2, but also acurhagin-C used alone remained effectively to diminish the surface exposure of those targeted receptors. Hence, a complicated crosstalk mechanism should be involved in the membrane interactions. Furthermore, co-administration of acurhagin-C with AZD4547 and reparixin also showed to have the synergistic suppression toward cell proliferation and the gene expression of matrix metalloproteinase-2. Also, the administration of three-in-one mode could nearly abrogate the cellular attachment onto collagen-IV- and fibronectin-coated wells, as well as penetration into Matrigel-barrier. These data supported an ECD-disintegrin acurhagin-C targeting integrin-α5 upon combined used with AZD4547 and reparixin may become a promising therapeutic approach for attenuating osteosarcoma development.

Cardamonin, a schistosomicidal chalcone from Piper aduncum L. (Piperaceae) that inhibits Schistosoma mansoni ATP diphosphohydrolase

BACKGROUND

Schistosomiasis is one of the world's major public health problems, and praziquantel (PZQ) is the only available drug to treat this neglected disease with an urgent demand for new drugs. Recent studies indicated that extracts from Piper aduncum L. (Piperaceae) are active against adult worms of Schistosoma mansoni, the major etiological agent of human schistosomiasis.

PURPOSE

We investigated the in vitro schistosomicidal activity of cardamonin, a chalcone isolated from the crude extract of P. aduncum. Also, this present work describes, for the first time, the S. mansoni ATP diphosphohydrolase inhibitory activity of cardamonin, as well as, its molecular docking with S. mansoni ATPDase1, in order to investigate its mode of inhibition.

METHODS

In vitro schistosomicidal assays and confocal laser scanning microscopy were used to evaluate the effects of cardamonin on adult schistosomes. Cell viability was measured by MTT assay, and the S. mansoni ATPase activity was determined spectrophotometrically. Identification of the cardamonin binding site and its interactions on S. mansoni ATPDase1 were made by molecular docking experiments.

RESULTS

A bioguided fractionation of the crude extract of P. aduncum was carried out, leading to identification of cardamonin as the active compound, along with pinocembrin and uvangoletin. Cardamonin (25, 50, and 100 µM) caused 100% mortality, tegumental alterations, and reduction of oviposition and motor activity of all adult worms of S. mansoni, without affecting mammalian cells. Confocal laser scanning microscopy showed tegumental morphological alterations and changes on the numbers of tubercles of S. mansoni worms in a dose-dependent manner. Cardamonin also inhibited S. mansoni ATP diphosphohydrolase (IC50 of 23.54 µM). Molecular docking studies revealed that cardamonin interacts with the Nucleotide-Binding of SmATPDase 1. The nature of SmATPDase 1-cardamonin interactions is mainly hydrophobic and hydrogen bonding.

CONCLUSION

This report provides evidence for the in vitro schistosomicidal activity of cardamonin and demonstrated, for the first time, that this chalcone is highly effective in inhibiting S. mansoni ATP diphosphohydrolase, opening the route to further studies of chalcones as prototypes for new S. mansoni ATP diphosphohydrolase inhibitors.

Isolation and characterization of four medium-size disintegrins from the venoms of Central American viperid snakes of the genera Atropoides, Bothrops, Cerrophidion and Crotalus

Four disintegrins were isolated from the venoms of the Central American viperid snakes Atropoides mexicanus (atropoimin), Bothrops asper (bothrasperin), Cerrophidion sasai (sasaimin), and Crotalus simus (simusmin). Purifications were performed by reverse-phase HPLC. The four disintegrins have biochemical characteristics, i.e. molecular mass and location of Cys, which allow their classification within the group of medium-size disintegrins. All of them present the canonical RGD sequence, which determines their interaction with integrins in cell membranes. The disintegrins inhibited ADP and collagen-induced human platelet aggregation, with similar IC50s in the nM range. In addition, disintegrins inhibited the adhesion of an endothelial cell line and a melanoma cell line to the extracellular matrix proteins type I collagen, laminin, fibronectin, and vitronectin, albeit showing variable ability to exert this activity. This study expands the inventory of this family of viperid venom proteins, and reports, for the first time, disintegrins from the venoms of species of the genera Atropoides and Cerrophidion.

rAdinbitor, a disintegrin from Agkistrodon halys brevicaudus stejneger, inhibits tumorigenicity of hepatocarcinoma via enhanced anti-angiogenesis and immunocompetence

Adinbitor is a disintegrin previously obtained from Agkistrodon halys brevicaudus stejneger by our group. Here, we investigated the in vitro and in vivo anti-tumor activities of recombinant Adinbitor (rAdinbitor). rAdinbitor stimulation can inhibit the in vitro proliferation, migration and invasion capacities of murine hepatocarcinoma H22 and Hca-F cells. The administrations of rAdinbitor either by gavage or intraperitoneal injection suppress the tumor malignancy and prolong the survival rate and time of H22-transplanted mice. The number and size of formed blood vessels decreased dramatically in tumorous tissues in that the expression levels of vascular endothelial growth factor (VEGF) and cluster of differentiation 34 (CD34) were significantly decreased in responding to rAdinbitor treatment. The protein levels of IL-18 and IgG increased significantly in the serum of H22-transplanted tumor mice with rAdinbitor treatment. rAdinbitor shows in vitro and in vivo anti-tumor effects as an angiogenesis inhibitor and immunocompetence enhancer.

The structure of hookworm platelet inhibitor (HPI), a CAP superfamily member from Ancylostoma caninum

Secreted protein components of hookworm species include a number of representatives of the cysteine-rich/antigen 5/pathogenesis-related 1 (CAP) protein family known as Ancylostoma-secreted proteins (ASPs). Some of these have been considered as candidate antigens for the development of vaccines against hookworms. The functions of most CAP superfamily members are poorly understood, but one form, the hookworm platelet inhibitor (HPI), has been isolated as a putative antagonist of the platelet integrins αIIbβ3 and α2β1. Here, the crystal structure of HPI is described and its structural features are examined in relation to its possible function. The HPI structure is similar to those of other ASPs and shows incomplete conservation of the sequence motifs CAP1 and CAP2 that are considered to be diagnostic of CAP superfamily members. The asymmetric unit of the HPI crystal contains a dimer with an extensive interaction interface, but chromatographic measurements indicate that it is primarily monomeric in solution. In the dimeric structure, the putative active-site cleft areas from both monomers are united into a single negatively charged depression. A potential Lys-Gly-Asp disintegrin-like motif was identified in the sequence of HPI, but is not positioned at the apex of a tight turn, making it unlikely that it interacts with the integrin. Recombinant HPI produced in Escherichia coli was found not to inhibit the adhesion of human platelets to collagen or fibrinogen, despite having a native structure as shown by X-ray diffraction. This result corroborates previous analyses of recombinant HPI and suggests that it might require post-translational modification or have a different biological function.

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.

Drugs from slugs. Part II--conopeptide bioengineering

The biological transformation of toxins as research probes, or as pharmaceutical drug leads, is an onerous and drawn out process. Issues regarding changes to pharmacological specificity, desired potency, and bioavailability are compounded naturally by their inherent toxicity. These often scuttle their progress as they move up the narrowing drug development pipeline. Yet one class of peptide toxins, from the genus Conus, has in many ways spearheaded the expansion of new peptide bioengineering techniques to aid peptide toxin pharmaceutical development. What has now emerged is the sequential bioengineering of new research probes and drug leads that owe their lineage to these highly potent and isoform specific peptides. Here we discuss the progressive bioengineering steps that many conopeptides have transitioned through, and specifically illustrate some of the biochemical approaches that have been established to maximize their biological research potential and pharmaceutical worth.

Disintegrins from hematophagous sources

Bloodsucking arthropods are a rich source of salivary molecules (sialogenins) which inhibit platelet aggregation, neutrophil function and angiogenesis. Here we review the literature on salivary disintegrins and their targets. Disintegrins were first discovered in snake venoms, and were instrumental in our understanding of integrin function and also for the development of anti-thrombotic drugs. In hematophagous animals, most disintegrins described so far have been discovered in the salivary gland of ticks and leeches. A limited number have also been found in hookworms and horseflies, and none identified in mosquitoes or sand flies. The vast majority of salivary disintegrins reported display a RGD motif and were described as platelet aggregation inhibitors, and few others as negative modulator of neutrophil or endothelial cell functions. This notably low number of reported disintegrins is certainly an underestimation of the actual complexity of this family of proteins in hematophagous secretions. Therefore an algorithm was created in order to identify the tripeptide motifs RGD, KGD, VGD, MLD, KTS, RTS, WGD, or RED (flanked by cysteines) in sialogenins deposited in GenBank database. The search included sequences from various blood-sucking animals such as ticks (e.g., Ixodes sp., Argas sp., Rhipicephalus sp., Amblyommasp.), tabanids (e.g., Tabanus sp.), bugs (e.g., Triatoma sp., Rhodnius prolixus), mosquitoes (e.g., Anopheles sp., Aedes sp., Culex sp.), sand flies (e.g., Lutzomyia sp., Phlebotomus sp.), leeches (e.g., Macrobdella sp., Placobdella sp.) and worms (e.g., Ancylostoma sp.). This approach allowed the identification of a remarkably high number of novel putative sialogenins with tripeptide motifs typical of disintegrins (>450 sequences) whose biological activity remains to be verified. This database is accessible online as a hyperlinked worksheet and displays biochemical, taxonomic, and gene ontology aspects for each putative disintegrin. It is also freely available for download (right click with the mouse) at links http://exon.niaid.nih.gov/transcriptome/RGD/RGD-Peps-WEB.xlsx (web version) and http://exon.niaid.nih.gov/transcriptome/RGD/RGD-sialogenins.zip (stand alone version).

Structure of protein having inhibitory disintegrin and leukotriene scavenging functions contained in single domain

The antihemostatic/antiangiogenic protein tablysin-15 is a member of the CAP (cysteine-rich secretory, antigen 5, and pathogenesis-related 1 protein) superfamily and has been shown to bind the integrins α(IIb)β(3) and α(V)β(3) by means of an Arg-Gly-Asp (RGD) tripeptide sequence. Here we describe the x-ray crystal structure of tablysin-15 and show that the RGD motif is located in a novel structural context. The motif itself is contained in a type II β-turn structure that is similar in its conformation to the RGD sequence of the cyclic pentapeptide cilengitide when bound to integrin α(V)β(3). The CAP domain also contains a hydrophobic channel that appears to bind a fatty acid molecule in the crystal structure after purification from Escherichia coli. After delipidation of the protein, tablysin-15 was found to bind proinflammatory cysteinyl leukotrienes with submicromolar affinities. The structure of the leukotriene E(4)-tablysin-15 complex shows that the ligand binds with the nonfunctionalized end of the fatty acid chain buried in the hydrophobic pocket, whereas the carboxylate end of the ligand binds forms hydrogen bond/salt bridge interactions with polar side chains at the channel entrance. Therefore, tablysin-15 functions as an inhibitor of integrin function and as an anti-inflammatory scavenger of eicosanoids.

Integrin targeted delivery of gene therapeutics

Integrins have become key targets for molecular imaging and for selective delivery of anti-cancer agents. Here we review recent work concerning the targeted delivery of antisense and siRNA oligonucleotides via integrins. A variety of approaches have been used to link oligonucleotides to ligands capable of binding integrins with high specificity and affinity. This includes direct chemical conjugation, incorporating oligonucleotides into lipoplexes, and use of various polymeric nanocarriers including dendrimers. The ligand-oligonucleotide conjugate or complex associates selectively with the integrin, followed by internalization into endosomes and trafficking through subcellular compartments. Escape of antisense or siRNA from the endosome to the cytosol and nucleus may come about through endogenous trafficking mechanisms, or because of membrane disrupting capabilities built into the conjugate or complex. Thus a variety of useful strategies are available for using integrins to enhance the pharmacological efficacy of therapeutic oligonucleotides.

"Insularin, a disintegrin from Bothrops insularis venom: inhibition of platelet aggregation and endothelial cell adhesion by the native and recombinant GST-insularin proteins"

Insularin (INS) was obtained from Bothrops insularis venom by reversed-phase high-performance liquid chromatography using a C(18) column and characterized as a disintegrin by peptide mass fingerprint and inhibition of ADP-induced platelet aggregation. A cDNA coding for P-II a metalloproteinase/disintegrin was cloned from a cDNA library from B. insularis venom glands. The deduced protein sequence possesses 73 amino acid residues, including the N-terminal, internal peptides of native insularin, the ARGDNP-sequence and 12 cysteines in a conserved alignment. This cDNA fragment was subcloned in the pGEX-4T-1 vector and expressed in a prokaryotic expression system as a fusion protein with glutathione S-transferase (GST-INS). Both native and recombinant insularin inhibited ADP-induced platelet aggregation and endothelial cells (HUVEC) adhesion with similar activities indicating that GST-INS folded correctly and preserved the integrin-binding loop. Insularin may be a tool in studies that involve platelets and endothelial cell adhesion dependent on alphaIIbeta3 and alphavbeta3 integrins.

The mojastin mutant Moj-DM induces apoptosis of the human melanoma SK-Mel-28, but not the mutant Moj-NN nor the non-mutated recombinant Moj-WN

In this study, three recombinant mojastin peptides (Moj-WN, Moj-NN, and Moj-DM) were produced and compared functionally. Recombinant Moj peptides were purified as GST-fusions. GST-Moj-WN and GST-Moj-NN inhibited ADP-induced platelet aggregation in platelet rich plasma. The GST-Moj-WN had an IC(50) of 160nM, while the GST-Moj-NN had an IC(50) of 493nM. The GST-Moj-DM did not inhibit platelet aggregation. All three GST-Moj peptides inhibited SK-Mel-28 cell adhesion to fibronectin. The GST-Moj-WN inhibited the binding of SK-Mel-28 cells to fibronectin with an IC(50) of 11nM, followed by the GST-Moj-NN (IC(50) of 28nM), and the GST-Moj-DM (IC(50) of 46nM). The GST-Moj peptides' ability to induce apoptosis on SK-Mel-28 cells was determined using Annexin-V-FITC and nuclear fragmentation assays. Cells were incubated with 5muM GST-Moj peptides for 24h. At 5microM GST-Moj-DM peptide, 13.56%+/-2.08 of treated SK-Mel-28 cells were in early apoptosis. The GST-Moj-DM peptide also caused nuclear fragmentation as determined by fluorescent microscopy and Hoechst staining. The GST-Moj-WN and GST-Moj-NN peptides failed to induce apoptosis. We characterized the SK-Mel-28 integrin expression, as the first step in determining r-Moj binding specificity. Our results indicate that SK-Mel-28 cells express alphavbeta3, alphav, alpha6, beta1, and beta3 integrin receptors.