Isolation, sequence analysis, and cloning of haemadin. An anticoagulant peptide from the Indian leech

Potential Ancestral Conoidean Toxins in the Venom Cocktail of the Carnivorous Snail Raphitoma purpurea (Montagu, 1803) (Neogastropoda: Raphitomidae)

Venomous marine gastropods of the superfamily Conoidea possess a rich arsenal of toxins, including neuroactive toxins. Venom adaptations might have played a fundamental role in the radiation of conoideans; nevertheless, there is still no knowledge about the venom of the most diversified family of the group: Raphitomidae Bellardi, 1875. In this study, transcriptomes were produced from the carcase, salivary glands, and proximal and distal venom ducts of the northeastern Atlantic species Raphitoma purpurea (Montagu, 1803). Using a gut barcoding approach, we were also able to report, for the first time, molecular evidence of a vermivorous diet for the genus. Transcriptomic analyses revealed over a hundred putative venom components (PVC), including 69 neurotoxins. Twenty novel toxin families, including some with high levels of expansion, were discovered. No significant difference was observed between the distal and proximal venom duct secretions. Peptides related to cone snail toxins (Cerm06, Pgam02, and turritoxin) and other venom-related proteins (disulfide isomerase and elevenin) were retrieved from the salivary glands. These salivary venom components may constitute ancestral adaptations for venom production in conoideans. Although often neglected, salivary gland secretions are of extreme importance for understanding the evolutionary history of conoidean venom.

Comparative genomics of two Asian medicinal leeches Hirudo nipponia and Hirudo tianjinensis: With emphasis on antithrombotic genes and their corresponding proteins

Leeches secrete various biologically active substances which have important medical and pharmaceutical values in antithrombotic treatments. Here, we provide a high quality genome of two Asian medicinal leeches Hirudo nipponia and Hirudo tianjinensis, based on which, we identified 22 antithrombotic gene families, including fourteen coagulation inhibitors, four platelet aggregation inhibitors, three fibrinolysis enhancers, and one tissue penetration enhancer. The total numbers of antithrombotic genes were similar between H. nipponia (N = 86) and H. tianjinensis (N = 83). Molecular evolution analysis showed that no significant differences were detected between the two species in any of the three selection indices (dN, dS, and dN/dS), nor in the number of sites under positive/purifying selection. RNA-Seq based gene expression analysis showed that the overall expression patterns of the antithrombotic gene families were not significantly deviated between the two species. Our results indicated that there were rather close similarities between the two leeches on genomic characteristics, especially for the molecular evolution and expression of antithrombotic genes. Our study provides the most comprehensive collection of antithrombotic biomacromolecules from the two Asian medicinal leeches to date. These results will greatly facilitate the research and application of leech derivatives for medical and pharmaceutical purposes of thrombosis.

Quantitative proteomics based bioactive proteins discovery and quality control of medicinal leeches

ETHNOPHARMACOLOGICAL RELEVANCE

Leech, a classical traditional Chinese medicine for promoting blood circulation and removing blood stasis, is mainly used in the clinical treatment of cardiovascular and cerebrovascular diseases. The discovery of activity proteins or peptides in the dead and dried medicinal leech is an important task with great challenges.

AIM OF THE STUDY

The aim of this study was to provide a basic proteome profile and help further discover active proteins and quality control for medicinal leeches, which would also provide insight into the research of animal medicines.

MATERIALS AND METHODS

Seventeen batches of dried medicinal leeches covering three species were collected from medicinal markets, which were authenticated by DNA barcoding. Then the proteome of different species leeches was profiled to reveal the significantly different proteins using label-free proteomics. The characteristic peptides were screened out based on biological pathways analysis, which were further absolutely quantified using the developed stable isotope-labeled based parallel reaction monitoring method.

RESULTS

Seventeen batches of leech materials were Whitmania pigra Whitman (WP), Whitmania laevis Whitman (WL) and Poecilobdella manillensis Lesson (PM), respectively. A total of 1,035 proteins (452 in WP, 425 in WL and 158 in PM) were identified. Among them, 90 overlapping proteins were mainly concentrated in diverse metabolic pathways and primarily localized in the cytoplasm and mitochondrial inner membrane, which mainly related to ATP binding, catalytic activity and structural molecular activity. In total of 51 uniquely expressed proteins (21 in WP, 23 in WL and 7 in PM), associated with multiple key signaling pathways, including Rap1, cGMP-PKG, PI3K-Akt, Wnt and HIF-1, etc., relevant to treating cardiovascular diseases, diabetes, cancer and even a variety of neurodegenerative diseases. Three proteins with potential bioactivities, including Neurohemerythrin, Hirudin and Eglin C, were selected as the quality makers and then quantified based on the characteristic peptides.

CONCLUSIONS

This work profiled the proteome of three species of leeches, and addressed potential active proteins of the medicinal leech, which would help to provide the potential molecular mechanisms involved in disease treatment. The proteomics-based approach developed in this work is not only useful for the discovery of proteins with potential bioactivities but also helpful for the bioactivity relevant quality control of animal medicines.

From haemadin to haemanorm: Synthesis and characterization of full-length haemadin from the leech Haemadipsa sylvestris and of a novel bivalent, highly potent thrombin inhibitor (haemanorm)

Hirudin from Hirudo medicinalis is a bivalent α-Thrombin (αT) inhibitor, targeting the enzyme active site and exosite-I, and is currently used in anticoagulant therapy along with its simplified analogue hirulog. Haemadin, a small protein (57 amino acids) isolated from the land-living leech Haemadipsa sylvestris, selectively inhibits αT with a potency identical to that of recombinant hirudin (KI  = 0.2 pM), with which it shares a common disulfide topology and overall fold. At variance with hirudin, haemadin targets exosite-II and therefore (besides the free protease) it also blocks thrombomodulin-bound αT without inhibiting the active intermediate meizothrombin, thus offering potential advantages over hirudin. Here, we produced in reasonably high yields and pharmaceutical purity (>98%) wild-type haemadin and the oxidation resistant Met5 → nor-Leucine analogue, both inhibiting αT with a KI of 0.2 pM. Thereafter, we used site-directed mutagenesis, spectroscopic, ligand-displacement, and Hydrogen/Deuterium Exchange-Mass Spectrometry techniques to map the αT regions relevant for the interaction with full-length haemadin and with the synthetic N- and C-terminal peptides Haem(1-10) and Haem(45-57). Haem(1-10) competitively binds to/inhibits αT active site (KI  = 1.9 μM) and its potency was enhanced by 10-fold after Phe3 → β-Naphthylalanine exchange. Conversely to full-length haemadin, haem(45-57) displays intrinsic affinity for exosite-I (KD  = 1.6 μM). Hence, we synthesized a peptide in which the sequences 1-9 and 45-57 were joined together through a 3-Glycine spacer to yield haemanorm, a highly potent (KI  = 0.8 nM) inhibitor targeting αT active site and exosite-I. Haemanorm can be regarded as a novel class of hirulog-like αT inhibitors with potential pharmacological applications.

Revisiting the Asian Buffalo Leech (Hirudinaria manillensis) Genome: Focus on Antithrombotic Genes and Their Corresponding Proteins

Leeches are well-known annelids due to their obligate blood-feeding habits. Some leech species secrete various biologically active substances which have important medical and pharmaceutical value in antithrombotic treatments. In this study, we provided a high-quality genome of the Asian buffalo leech (Hirudinaria manillensis), based on which we performed a systematic identification of potential antithrombotic genes and their corresponding proteins. Combining automatic and manual prediction, we identified 21 antithrombotic gene families including fourteen coagulation inhibitors, three platelet aggregation inhibitors, three fibrinolysis enhancers, and one tissue penetration enhancer. A total of 72 antithrombotic genes, including two pseudogenes, were identified, including most of their corresponding proteins forming three or more disulfide bonds. Three protein families (LDTI, antistasin, and granulin) had internal tandem repeats containing 6, 10, and 12 conserved cysteines, respectively. We also measured the anticoagulant activities of the five identified hirudins (hirudin_Hman1 ~ hirudin_Hman5). The results showed that three (hirudin_Hman1, hirudin_Hman2, and hirudin_Hman5), but not the remaining two, exhibited anticoagulant activities. Our study provides the most comprehensive collection of antithrombotic biomacromolecules from a leech to date. These results will greatly facilitate the research and application of leech derivatives for medical and pharmaceutical purposes in the treatment of thrombotic diseases.

Prospection of Peptide Inhibitors of Thrombin from Diverse Origins Using a Machine Learning Pipeline

Thrombin is a key enzyme involved in the development and progression of many cardiovascular diseases. Direct thrombin inhibitors (DTIs), with their minimum off-target effects and immediacy of action, have greatly improved the treatment of these diseases. However, the risk of bleeding, pharmacokinetic issues, and thrombotic complications remain major concerns. In an effort to increase the effectiveness of the DTI discovery pipeline, we developed a two-stage machine learning pipeline to identify and rank peptide sequences based on their effective thrombin inhibitory potential. The positive dataset for our model consisted of thrombin inhibitor peptides and their binding affinities (KI) curated from published literature, and the negative dataset consisted of peptides with no known thrombin inhibitory or related activity. The first stage of the model identified thrombin inhibitory sequences with Matthew's Correlation Coefficient (MCC) of 83.6%. The second stage of the model, which covers an eight-order of magnitude range in KI values, predicted the binding affinity of new sequences with a log room mean square error (RMSE) of 1.114. These models also revealed physicochemical and structural characteristics that are hidden but unique to thrombin inhibitor peptides. Using the model, we classified more than 10 million peptides from diverse sources and identified unique short peptide sequences (<15 aa) of interest, based on their predicted KI. Based on the binding energies of the interaction of the peptide with thrombin, we identified a promising set of putative DTI candidates. The prediction pipeline is available on a web server.

An insight into the functional genomics and species classification of Eudiplozoon nipponicum (Monogenea, Diplozoidae), a haematophagous parasite of the common carp Cyprinus carpio

BACKGROUND

Monogenea (Platyhelminthes, Neodermata) are the most species-rich class within the Neodermata superclass of primarily fish parasites. Despite their economic and ecological importance, monogenean research tends to focus on their morphological, phylogenetic, and population characteristics, while comprehensive omics analyses aimed at describing functionally important molecules are few and far between. We present a molecular characterisation of monogenean representative Eudiplozoon nipponicum, an obligate haematophagous parasite infecting the gills of the common carp. We report its nuclear and mitochondrial genomes, present a functional annotation of protein molecules relevant to the molecular and biochemical aspect of physiological processes involved in interactions with the fish hosts, and re-examinate the taxonomic position of Eudiplozoon species within the Diplozoidae family.

RESULTS

We have generated 50.81 Gbp of raw sequencing data (Illumina and Oxford Nanopore reads), bioinformatically processed, and de novo assembled them into a genome draft 0.94 Gbp long, consisting of 21,044 contigs (N50 = 87 kbp). The final assembly represents 57% of the estimated total genome size (~ 1.64 Gbp), whereby repetitive and low-complexity regions account for ~ 64% of the assembled length. In total, 36,626 predicted genes encode 33,031 proteins and homology-based annotation of protein-coding genes (PCGs) and proteins characterises 14,785 (44.76%) molecules. We have detected significant representation of functional proteins and known molecular functions. The numbers of peptidases and inhibitors (579 proteins), characterised GO terms (16,016 unique assigned GO terms), and identified KEGG Orthology (4,315 proteins) acting in 378 KEGG pathways demonstrate the variety of mechanisms by which the parasite interacts with hosts on a macromolecular level (immunomodulation, feeding, and development). Comparison between the newly assembled E. nipponicum mitochondrial genome (length of 17,038 bp) and other diplozoid monogeneans confirms the existence of two distinct Eudiplozoon species infecting different fish hosts: Cyprinus carpio and Carassius spp.

CONCLUSIONS

Although the amount of sequencing data and characterised molecules of monogenean parasites has recently increased, a better insight into their molecular biology is needed. The E. nipponicum nuclear genome presented here, currently the largest described genome of any monogenean parasite, represents a milestone in the study of monogeneans and their molecules but further omics research is needed to understand these parasites' biological nature.

Make it double: identification and characterization of a Tandem-Hirudin from the Asian medicinal leech Hirudinaria manillensis

Haematophagous leeches express a broad variety of secretory proteins in their salivary glands, among them are hirudins and hirudin-like factors. Here, we describe the identification, molecular and initial functional characterization of Tandem-Hirudin (TH), a novel salivary gland derived factor identified in the Asian medicinal leech, Hirudinaria manillensis. In contrast to the typical structure of hirudins, TH comprises two globular domains arranged in a tandem-like orientation and lacks the elongated C-terminal tail. Similar structures of thrombin inhibitors have so far been identified only in kissing bugs and ticks. Expression of TH was performed in both cell-based and cell-free bacterial systems. A subsequent functional characterization revealed no evidence for a thrombin-inhibitory potency of TH.

Screening of the Promising Direct Thrombin Inhibitors from Haematophagous Organisms. Part I: Recombinant Analogues and Their Antithrombotic Activity In Vitro

The success in treatment of venous thromboembolism and acute coronary syndromes using direct thrombin inhibitors has stimulated research aimed at finding a new anticoagulant from haematophagous organisms. This study deals with the comparison between hirudin-1 from Hirudomedicinalis(desirudin), being the first-known and most well-studied natural anticoagulant, along with recombinant analogs of haemadin from the leech Haemadipsa sylvestris, variegin from the tick Amblyomma variegatum, and anophelin from Anopheles albimanus. These polypeptides were chosen due to their high specificity and affinity for thrombin, as well as their distinctive inhibitory mechanisms. We have developed a universal scheme for the biotechnological production of these recombinant peptides as pharmaceutical substances. The anticoagulant activities of these peptides were compared using the thrombin amidolytic activity assay and prolongation of coagulation time (thrombin time, prothrombin time, and activated partial thromboplastin time) in mouse and human plasma. The preliminary results obtained suggest haemadin as the closest analog of recombinant hirudin-1, the active substance of the medicinal product Iprivask (Aventis Pharmaceuticals, USA) for the prevention of deep venous thrombosis in patients undergoing elective hip or knee replacement surgery. In contrast, variegin can be regarded as a natural analog of bivalirudin (Angiomax, The Medicines Company), a synthetic hirudin-1 derivative certified for the treatment of patients undergoing percutaneous coronary intervention and of patients with unstable angina pectoris after percutaneous transluminal coronary angioplasty.

WPK5, a Novel Kunitz-Type Peptide from the Leech Whitmania pigra Inhibiting Factor XIa, and Its Loop-Replaced Mutant to Improve Potency

Kunitz-type proteins or peptides have been found in many blood-sucking animals, but the identity of them in leeches remained elusive. In the present study, five Kunitz-type peptides named WPK1-WPK5 were identified from the leech Whitmania pigra. Recombinant WPK1-WPK5 were expressed in Pichia pastoris GS115, and their inhibitory activity against Factor XIa (FXIa) was tested. WPK5 showed inhibitory activity against FXIa with an IC₅₀ value of 978.20 nM. To improve its potency, the loop replacement strategy was used. The loop 1 (TGPCRSNLER) and loop 2 (QYGGC) in WPK5 were replaced by loop 1 (TGPCRAMISR) and loop 2 (FYGGC) in PN2KPI, respectively, and the resulting peptide named WPK5-Mut showed an IC₅₀ value of 8.34 nM to FXIa, which is about 100-fold the potency of FXIa compared to that of WPK5. WPK5-Mut was further evaluated for its extensive bioactivity in vitro and in vivo. It dose-dependently prolonged APTT on both murine plasma and human plasma, and potently inhibited FeCl₃-induced carotid artery thrombosis in mice at a dose of 1.5 mg/kg. Additionally, WPK5-Mut did not show significant bleeding risk at a dose of 6 mg/kg. Together, these results showed that WPK5-Mut is a promising candidate for the development of an antithrombotic drug.

Pharmacological Activities and Mechanisms of Hirudin and Its Derivatives - A Review

Hirudin, an acidic polypeptide secreted by the salivary glands of Hirudo medicinalis (also known as "Shuizhi" in traditional Chinese medicine), is the strongest natural specific inhibitor of thrombin found so far. Hirudin has been demonstrated to possess potent anti-thrombotic effect in previous studies. Recently, increasing researches have focused on the anti-thrombotic activity of the derivatives of hirudin, mainly because these derivatives have stronger antithrombotic activity and lower bleeding risk. Additionally, various bioactivities of hirudin have been reported as well, including wound repair effect, anti-fibrosis effect, effect on diabetic complications, anti-tumor effect, anti-hyperuricemia effect, effect on cerebral hemorrhage, and others. Therefore, by collecting and summarizing publications from the recent two decades, the pharmacological activities, pharmacokinetics, novel preparations and derivatives, as well as toxicity of hirudin were systematically reviewed in this paper. In addition, the clinical application, the underlying mechanisms of pharmacological effects, the dose-effect relationship, and the development potential in new drug research of hirudin were discussed on the purpose of providing new ideas for application of hirudin in treating related diseases.

European Medicinal Leeches-New Roles in Modern Medicine

Before the advent of modern medicine, natural resources were widely used by indigenous populations for the prevention and treatment of diseases. The associated knowledge, collectively described as folk medicine or traditional medicine, was largely based on trial-and-error testing of plant extracts (herbal remedies) and the use of invertebrates, particularly medicinal maggots of the blowfly Lucilia sericata and blood-sucking leeches. The widespread use of traditional medicine in the West declined as scientific advances allowed reproducible testing under controlled conditions and gave rise to the modern fields of biomedical research and pharmacology. However, many drugs are still derived from natural resources, and interest in traditional medicine has been renewed by the ability of researchers to investigate the medical potential of diverse species by high-throughput screening. Likewise, researchers are starting to look again at the benefits of maggot and leech therapy, based on the hypothesis that the use of such animals in traditional medicine is likely to reflect the presence of specific bioactive molecules that can be developed as drug leads. In this review, we consider the modern medical benefits of European medicinal leeches based on the systematic screening of their salivary proteins.

The Research Progress of Direct Thrombin Inhibitors

Blood coagulation is the process of changing the blood from the flowing state to the gel state. It is an important part of the hemostatic function. Coagulation is a process by which a series of coagulation factors are sequentially activated, and finally thrombin is formed to form fibrin clot. Direct thrombin inhibitors are important anticoagulant drug. These drugs can selectively bind to the active site of thrombin, inhibit thrombin activity, have strong action and high specificity, and have important significance in the clinical treatment of thrombus diseases. Some of them come from natural products of animals or plants, and many of them have been applied in the clinic. The other part is derived from the design, synthesis and activity studies of small molecule inhibitors. This review discusses the progress of direct thrombin inhibitors in recent years.

Identification and characterization of hirudin-HN, a new thrombin inhibitor, from the salivary glands of Hirudo nipponia

Transcriptome sequencing data (6.5 Gb) of the salivary glands of the haematophagous leech Hirudo nipponia was obtained by using the BGIseq-500 platform. After identification and analysis, one transcript (Unigene5370) was annotated to hirudin HV3 from Hirudo medicinalis with an e-value of 1e-29 and was named hirudin-HN. This transcript was a new thrombin inhibitor gene belonging to the proteinase inhibitor I14 (hirudin) family. Hirudin-HN, with a 270-bp cDNA, encodes an 89-aa protein containing a 20-aa signal peptide. The mature hirudin-HN protein contains the typical structural characteristics of hirudin, e.g., three conserved disulfide bonds and the PKP and DFxxIP motifs. Proteins (Hir and M-Hir) were obtained via prokaryotic expression, and the mature hirudin-HN protein was shown to have anticoagulant activity and thrombin affinity by using the chromogenic substrate S2238 and surface plasmon resonance (SPR) interaction analysis, respectively. The N-terminal structure of the mature hirudin-HN protein was shown to be important for anticoagulant activity by comparing the activity and thrombin affinity of Hir and M-Hir. The abundances of Hirudin-HN mRNA and protein were higher in the salivary glands of starving animals than in those of feeding or fed leeches. These results provided a foundation for further study on the structure-function relationship of hirudin-HN with thrombin.

Thrombin inhibitor from the salivary gland of the camel tick Hyalomma dromedarii

Blood-sucking arthropods have different types of anticoagulants to allow the ingestion of a blood meal from their hosts. In this study, five anticoagulants prolonging the activated partial thromboplastin time were resolved from the salivary gland crude extract of the camel tick Hyalomma dromedarii by chromatography on diethylaminoethyl (DEAE)-cellulose column. They were designated P1, P2, P3, P4 and P5 according to their elution order. P5 was found to be a potent thrombin inhibitor and purified by ultrafiltration through two centrifugal concentrators of 50 and 30 kDa molecular weight cut-off (MWCO), respectively. The camel tick salivary gland thrombin inhibitor was purified 60.6 folds with a specific activity of 564 units/mg protein. It turned out to be homogenous on native-PAGE with molecular weight of 36 kDa as detected on 12% SDS-PAGE. It inhibits bovine thrombin competitively with K _i value of 0.55 μM. A task for the future will be the elucidation of this thrombin inhibitor structure to allow its application in thrombosis treatment.

Protective effect of Shouwu Yizhi decoction against vascular dementia by promoting angiogenesis

Shouwu is a traditional Chinese medicine (TCM) with neuroprotective effect. Shouwu Yizhi decoction (SYD) was designed based on TCM theory. However, little is known about the roles of SYD in Vascular dementia (VaD). The present study aimed to evaluate the potential effects of SYD on the vascular cognitive impairment and explore the underlying mechanism by establishing focal cerebral ischemia/reperfusion (I/R) rat model to induce VaD. SYD administration (54 mg·kg^-1) for 40 days obviously improved the vascular cognitive impairment in the middle cerebral artery occlusion (MCAO) rats as evidenced by the declined neurological deficit score and shortened escape latency via neurological deficit assessment and Morris water maze test. Moreover, SYD decreased neuron damage-induced cell death and ameliorated the ultrastructure of endothelial cells in the MCAO rats, thereby alleviating VaD. Mechanistically, SYD caused increases in the expression of vascular endothelial growth factor (VEGF), CD34 and CD31, compared with the MCAO rats in coronal hippocampus. Simultaneously, the expression level of miR-210 was elevated significantly after SYD administration, compared with the vehicle rats (P < 0.01). The expression of Notch 4 at both mRNA and protein levels was upregulated remarkably along with the notably downregulated DLL4 expression under SYD administration compared with the vehicle rats (P < 0.05). Overall, the above results indicated that SYD promoted angiogenesis by upregulating VEGF-induced miR210 expression to activate Notch pathway, and further alleviated neuron damage and ameliorated the ultrastructure of endothelial cells in the MCAO rats, ultimately enhancing the cognition and memory of MCAO rats. Therefore, our findings preliminarily identified the effect and the mechanism of action for SYD on VaD in rats. SYD could be a potential candidate in treatment of VaD.

Hirudins and hirudin-like factors in Hirudinidae: implications for function and phylogenetic relationships

Haematophagous leeches express a broad variety of bioactive factors that are released from the salivary gland cells into the wound of a host during feeding. Among these, hirudin is probably the best studied factor and, moreover, the only one that has successfully made the transition from nature to clinical use. Many components of the leech saliva still remain either poorly characterized or yet completely unknown. Only recently, a new class of leech-derived factors has been discovered in Hirudo medicinalis, the hirudin-like factors (HLFs). HLFs comprise typical structural features of hirudin but lack others. We were able to verify the expression of HLFs not only in two additional species of the genus Hirudo, but also in Hirudinaria manillensis. Various phylogenetic analyses based on gene and protein sequences support a sister group relationship between hirudins and HLFs. Although potential molecular targets of HLFs remain unknown, the presence of multiple isoforms in individual leeches of different genera points to key functions in the regulation of several processes associated with the blood-sucking life style of leeches.

State-of-the-Art Review : Antithrombotic Agents from Hematophagous Animals

Bloodsucking animals produce anticoagu lantly effective substances that are a challenge to coagu lation studies. In the past 40 years efforts have been fo cused on the isolation and chemical characterization of such agents as well as on the clarification of their modes of action. Following the success in the development of the anticoagulant agent hirudin from medicinal leeches, these naturally occurring anticoagulants were recently in vestigated as a source of antithrombotics for pharmaceu tical use. These polypeptides or miniproteins were shown to be specific inhibitors of certain coagulation factors that block either the formation or the effect of thrombin or are supported by substances that inhibit the aggregation and adhesion of blood platelets and by proteolytic enzymes with fibrinolytic activity. By advances in biotechnology of protein-like substances, especially gene technology, these antithrombotics have been obtained in amounts suf ficient for preclinical and clinical studies. Thus, the in vestigation of the anticoagulant agents from hematopha gous animals offers a new line of research in antithrom botic drugs. Key Words: Bloodsucking animals— Naturally occurring anticoagulants—Fibrinolytics and platelet inhibitors.

Transcripts involved in hemostasis: Exploring salivary complexes from Haementeria vizottoi leeches through transcriptomics, phylogenetic studies and structural features

Throughout evolution, parasites have adapted in order to successfully intervene in the host defense, producing specific peptides and proteins. Interestingly, these peptides and proteins have been exploited as potential drug candidates against several diseases. Furthermore, biotechnology studies and cDNA libraries have remarkably contributed to identify potentially bioactive molecules. In this regard, herein, a cDNA library of salivary complexes from Haementeria vizottoi leeches was constructed, the transcriptome was characterized and a phylogenetic analysis was performed considering antistasin-like and antiplatelet-like proteins. Hundred twenty three transcripts were identified coding for putative proteins involved in animal feeding (representing about 10% of the expression level). These sequences showed similarities with myohemerythrins, carbonic anhydrases, anticoagulants, antimicrobials, proteases and protease inhibitors. The phylogenetic analysis, regarding antistasin-like and antiplatetlet-like proteins, revealed two main clades in the Rhynchobdellida leeches. As expected, the sequences from H. vizottoi have presented high similarities with those types of proteins. Thus, our findings could be helpful not only to identify new coagulation inhibitors, but also to better understand the biological composition of the salivary complexes.

More than just one: multiplicity of Hirudins and Hirudin-like Factors in the Medicinal Leech, Hirudo medicinalis

Blood-sucking leeches like the medicinal leech, Hirudo medicinalis, have been used for medical purposes since ancient times. During feeding, medicinal leeches transfer a broad range of bioactive substances into the host's wound to prevent premature hemostasis and blood coagulation. Hirudin is probably the best known of these substances. Despite its long history of investigation, recombinant production and clinical use, there still exist conflicting data regarding the primary structure of hirudin. Entirely unclear is the potential biological significance of three different subtypes and many isoforms of hirudins that have been characterized so far. Furthermore, there is only incomplete information on their cDNA sequences and no information at all on gene structures and DNA sequences are available in the databases. Our efforts to fill these gaps revealed the presence of multiple hirudin-encoding genes in the genome of Hirudo medicinalis. We have strong evidence for the expression of all three subtypes of hirudin within individual leeches and for the expression of additional hirudins or hirudin-like factors that may have different biological functions and may be promising candidates for new drugs.

Anticoagulation activity of salivary gland extract of oriental blackfly Simulium indicum

OBJECTIVE

To study the morphology of the salivary gland of the female blackfly of the species Simulium indicum (S. indicum) along with protein profile and anticoagulant activity of the salivary gland extract.

METHODS

Sodium dodecyl sulphate polyacrylamide gel electrophoresis was used to analyze the protein profile of the salivary gland extract (SGE) and anticoagulant activities against thrombin, and the extrinsic and intrinsic coagulation pathways were found in S. indicum SGE in the TT, PT and APTT assays, respectively.

RESULTS

Results revealed that each gland consisted of a cylindrical U-shaped secretory lobe and a more or less spherical reservoir. The protein contents of whole salivary glands were also quantified and the amount of salivary gland proteins in the adult female S. indicum was found out to be approximately 1.12±0.13 µg/female. At least 16 major and several minor protein bands were detected in the female salivary glands. The molecular masses of these major protein bands were estimated at 69, 65, 61, 58, 44, 42, 39, 33, 30, 28, 27, 26, 23, 21, 18 and 16 kDa, consecutively. Anticoagulant activities were found in S. indicum SGE in all the assays. It was found that SGE prolonged human plasma clotting time in a dose-dependent manner. Factor Xa inhibition was shown by the SGE of S. indicum. Percent inhibition value was 93.8. A positive correlation (r=0.89) was observed between total protein and percent inhibition of factor Xa.

CONCLUSIONS

The present study demonstrated that the mode of action of the anticoagulant(s) is mainly on the inhibition of thrombin and factor Xa along with other target factors of the coagulation cascade.

Direct thrombin inhibitors: patents 2002-2012 (Review)

Acute vascular diseases and other thromboses of the blood system constitute major health risks in developing countries. Thrombin plays a central role in blood coagulation, which is a crucial process involved in thrombosis. Direct thrombin inhibitors (DTIs) such as argatroban, dabigatran, dabigatran etexilate, lepirudin, desirudin and bivalirudin, which bind to thrombin and block its enzymatic activity, are widely and effectively used in the treatment of thromboembolic diseases. DTIs appear to overcome the disadvantages of indirect thrombin inhibitors such as unfractionated heparins (UFH). Although these DTIs show specific advantages over indirect inhibitors, they still present limitations, such as a narrow therapeutic window, and bleeding and anaphylaxis as side-effects. Novel anticoagulant drugs need thus to be developed to overcome these limitations. In the search for additional candidate agents with improved efficacy, safety and high bioavailability in oral administration, a high number of compounds has been identified, such as those derived from the tripeptide template D-Phe-Pro-Arg, aptamers and peptides isolated from blood-sucking animals. These candidates may prove the new agents of choice for the treatment of cardiovascular diseases.

Thrombin inhibitors from different animals

Venous and arterial thromboembolic diseases are still the most frequent causes of death and disability in high-income countries. Clinical anticoagulants are inhibitors of enzymes involved in the coagulation pathway, such as thrombin and factor X(a). Thrombin is a key enzyme of blood coagulation system, activating the platelets, converting the fibrinogen to the fibrin net, and amplifying its self-generation by the activation of factors V, VIII, and XI. Thrombin has long been a target for the development of oral anticoagulants. Furthermore, selective inhibitors of thrombin represent a new class of antithrombotic agents. For these reasons, a number of specific thrombin inhibitors are under evaluation for possible use as antithrombotic drugs. This paper summarizes old and new interests of specific thrombin inhibitors described in different animals.

Variegin, a novel fast and tight binding thrombin inhibitor from the tropical bont tick

Tick saliva contains potent antihemostatic molecules that help ticks obtain their enormous blood meal during prolonged feeding. We isolated thrombin inhibitors present in the salivary gland extract from partially fed female Amblyomma variegatum, the tropical bont tick, and characterized the most potent, variegin, one of the smallest (32 residues) thrombin inhibitors found in nature. Full-length variegin and two truncated variants were chemically synthesized. Despite its small size and flexible structure, variegin binds thrombin with strong affinity (K(i) approximately 10.4 pM) and high specificity. Results using the truncated variants indicated that the seven residues at the N terminus affected the binding kinetics; when removed, the binding characteristics changed from fast to slow. Further, the thrombin active site binding moiety of variegin is in the region of residues 8-14, and the exosite-I binding moiety is within residues 15-32. Our results show that variegin is structurally and functionally similar to the rationally designed thrombin inhibitor, hirulog. However, compared with hirulog, variegin is a more potent inhibitor, and its inhibitory activity is largely retained after cleavage by thrombin.

Protein mapping of the salivary complex from a hematophagous leech

The salivary complex of leeches contains many components able to modulate physiological mechanisms, such as coagulation and fibrinolysis, and it is composed by the salivary glands and proboscis, encompassing two different proteomes. The bidimensional electrophoretic pattern of the salivary complex from the Haementeria depressa leech revealed a total of 352 spots, 103 in common with the muscular tissue and 249 exclusive from the salivary complex as detected by silver staining; these spots showed isoelectric points from 3.5 to 9.5 and covered an apparent molecular weight range from 10 to 105 kDa. The following isoforms of proteins were identified by mass spectrometry analysis: antiplatelet protein, myohemerythrin and carbonic anhydrase. Since the leeches were not fed for about 2-3 months to stimulate the secretion of proteins that facilitates the blood metabolism, these most abundant proteins in the salivary complex excised from leeches, are expected to play a role during feeding and might have some anti-hemostatic properties. Furthermore, by zymography, a gelatinolytic and a fibrinolytic protein were identified.

The anticoagulant fraction from the leaves ofDiospyros kaki L. has an antithrombotic activity

The leaves of Persimmon (Diospyros kaki L.) has long been used for tea in Korea since it was thought to be effective against hypertension. An anticoagulant fraction was purified through gel filtration G-100, hydrophobic, gel filtration G-150, and FPLC, Phenyl superpose column chromatographies. The purified fraction was homogenous and its Mr was estimated 10,000 Da by gel filtration and SDS-PAGE. The purified fraction was sensitive to treatment of subtilisin B, but not to heat and its activity was not changed after periodate oxidation, indicating that the activity was not due to carbohydrates. It delayed thrombin time (TT), activated partial thromboplastin time (APTT), and prothrombin time (PT) using human plasma. TT was more sensitive than APTT and PT, suggesting that the anticoagulant activity may be caused by a degradation or a defect of fibrin or thrombin. It did not cause the hydrolysis of fibrin after incubation. However, it inhibited thrombin-catalyzed fibrin formation with a competitive inhibition pattern. These results indicate that it may be an antithrombotic agent and that it is bound to fibrinogen binding sites of thrombin.

Inhibition mechanisms of hematophagous invertebrate compounds acting on the host blood coagulation and platelet aggregation pathways

To facilitate blood feeding, hematophagous invertebrates have evolved a sophisticated array of physiological compounds that counteract homeostatic systems and inflammatory reactions of the vertebrate host. For this reason, hematophagous invertebrates possess a variety of anticoagulation components that are inhibitors of coagulant factors or antagonists of the platelet receptor. The examination of kinetic data and the crystal structure analysis have exposed the inhibition mechanisms for many of these anticoagulant reagents. Here, we attempt to classify the antihemostatic molecules and to focus on the kinetic approaches that have been instrumental in defining these mechanisms.

A novel class of small functional peptides that bind and inhibit human alpha-thrombin isolated by mRNA display

Here we report the in vitro selection of novel small peptide motifs that bind to human alpha-thrombin. We have applied mRNA display to select for thrombin binding peptides from an unbiased library of 1.2 x 10(11) different 35-mer peptides, each containing a random sequence of 15 amino acids. Two clones showed binding affinities ranging from 166 to 520 nM. A conserved motif of four amino acids, DPGR, was identified. Clot formation of human plasma is inhibited by the selected clones, and they downregulate the thrombin-mediated activation of protein C. The identified peptide motifs do not share primary sequence similarities to any of the known natural thrombin binding motifs. As new inhibitors for human thrombin open interesting possibilities in thrombosis research, our newly identified peptides may provide further insights into this field of investigation and may be possible candidates for the development of new anti-thrombotic agents.

Factor Xa inhibition in the prevention of venous thromboembolism and treatment of patients with venous thromboembolism

Venous thromboembolism (VTE) is a life-threatening complication following orthopedic surgery. Selective factor Xa inhibition is a new antithrombotic approach designed to avoid difficulties associated with heparins and other current anticoagulants. Several antifactor Xa compounds are in early investigation, but fondaparinux (Arixtra; NV Organon, Oss, The Netherlands; Sanofi-Synthelabo, Paris, France) is the first and most advanced compound in the development of a new class of synthetic antithrombotic agents--the selective factor Xa inhibitors. Fondaparinux has a highly favorable pharmacokinetic profile; four large phase 3 trials comparing subcutaneous fondaparinux 2.5 mg once daily with the low molecular weight heparin (LMWH) enoxaparin in doses approved by regulatory bodies showed that fondaparinux reduced the overall risk of VTE in major orthopedic surgery by > 50% without increasing clinically relevant bleeding. Fondaparinux also appears to be a very promising candidate for the treatment of patients with existing VTE.

Anticoagulant from Taraxacum platycarpum

An anticoagulant was purified from a Chinese herb, Taraxacum platycarpum. Its activity was heat-labile, and was decreased by incubation with subtilisin Carlburg or proteinase K, indicating that the active component was a protein. The protein had a molecular mass of 31 kDa by gel filtration and 33 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, so it probably was a monomer. When present at the concentration of 70, 255, and 873 nM, respectively, the protein doubled the thrombin time, prothrombin time, and activated partial thromboplastin time. It inhibited thrombin and kallikrein, but did not hydrolyze fibrinogen. The protein bound the anion-binding exosite of thrombin, competing with the fibrinogen binding site. In addition, the protein caused the murine macrophage cell line Raw 264.7 to produce cyclooxygenase-2, nitric oxide synthase, nitric oxide, and tumor necrosis factor-alpha.

Infestin, a thrombin inhibitor presents in Triatoma infestans midgut, a Chagas' disease vector: gene cloning, expression and characterization of the inhibitor

This work describes the purification, gene cloning and expression of infestin, a thrombin inhibitor from midguts of Triatoma infestans. Infestin is located in the midgut and its purification was performed by anion-exchange and affinity chromatographies. The N-terminal sequence and the sequence of tryptic peptides were determined. Using RT-PCR, total RNA and infestin cDNA information, a DNA fragment was cloned which encodes a multi non-classical Kazal-type serine protease inhibitor. Isolated native infestin has two non-classical Kazal-type domains and shows an apparent molecular mass of 13 kDa, while its gene codes for a protein with four non-classical Kazal-type domains corresponding to an apparent molecular mass of 22 kDa. Two recombinant infestins, r-infestin 1-2 and r-infestin 1-4, were constructed using the vector pVT102U/alpha and expressed in S. cerevisiae. Native and r-infestin 1-2 showed very similar inhibitory activities towards thrombin and trypsin with dissociation constants of 43.5 and 25 pM for thrombin and 2.0 and 3.1 nM for trypsin, respectively. No other serine protease of the blood coagulation cascade was inhibited by the r-infestin 1-2. Surprisingly, r-infestin 1-4 inhibited not only thrombin and trypsin (K(i) of 0.8 and 5.2 nM, respectively), but also factor XIIa, factor Xa and plasmin (K(i) of 78 pM, 59.2 and 1.1 nM, respectively).

Characterization of the residues involved in the human alpha-thrombin-haemadin complex: an exosite II-binding inhibitor

Haemadin is a 57-amino acid thrombin inhibitor from the land-living leech Haemadipsa sylvestris, whose structure has recently been determined in complex with human alpha-thrombin. Here we communicate the effect of ionic strength on the kinetics of the inhibition of human alpha-thrombin by haemadin, by using thrombin mutants modified in exosite II. Data analysis has allowed both the ionic and nonionic binding contributions to be ascertained, with the nonionic component being virtually the same for all of the thrombins that have been examined, while the ionic binding energy contributions varied from molecule to molecule. In the case of the native human alpha-thrombin-haemadin complex, ionic interactions contribute -17 kJ/mol to the Gibbs free energy of binding, this being the equivalent of up to six salt bridges. These salt bridges make up 20% of the total binding energy at zero ionic strength, and this has been attributed to the C-terminal tail alone. In addition, the contributions of the N-terminal and C-terminal regions of haemadin to its tight binding have been ascertained by using derivatives of both haemadin and thrombin. Limited proteolysis using formic acid produced haemadin cleaved between residues 40 and 41, removing the majority of the C-terminal tail. This truncated haemadin displayed a 20000-fold reduced affinity for thrombin, and was no longer a tight binding inhibitor. A form of thrombin in which the active site serine has been blocked by diisopropyl fluorophosphate binds to haemadin, but with a 72000-fold reduced affinity, indicating that the N-terminus is more important than the C-terminus for strong binding.

Fibrinolytic and antithrombotic protease from Spirodela polyrhiza

A fibrinolytic protease was purified from a Chinese herb (Spirodela polyrhiza). The protease has a molecular mass of 145 kDa and 70 kDa in gel filtration and SDS-polyacrlamide gel electrophoresis (PAGE), respectively, implying it is a dimer. Its optimum pH was 4.5-5.0. The enzyme was stable below 42 degrees C and after lyophilization. The enzyme activity was inhibited significantly by leupeptin and aprotinin. The protease hydrolyzed not only fibrin but also fibrinogen, cleaving Aalpha and Bbeta without affecting the gamma chain of fibrinogen. It preferentially cleaved the peptide bond of Arg or Lys of synthetic substrates (P1 position). The enzyme had an anticoagulating activity measured with activated partial thromboplastin time (APTT), thrombin time (TT), and prothrombin time (PT) tests. It delayed APTT, TT, and PT two times at the concentration of 36, 39, and 128 nM, respectively and this was drastically reduced after heat treatment.

Anticoagulants and inhibitors of platelet aggregation derived from leeches

Increased life expectancy is associated with aging populations in the developed countries, and we can expect an increased incidence of cardiovascular and inflammatory diseases and cancers. A priority for medical research is to reduce such morbidity. Leeches have been demonstrated to be a useful source of drugs to treat cardiovascular diseases, as they have evolved highly specific mechanisms to feed on their hosts by blocking blood coagulation. Powerful molecules acting at different points in the coagulation cascade or in the inhibition of platelet aggregation have been purified from these animals. Moreover, clinical trials confirm their potential to treat cardiovascular diseases.

Biochemical evidence of specific trypsin-chymotrypsin inhibitors in the rhynchobdellid leech, Theromyzon tessulatum

The presence of two specific trypsin-chymotrypsin inhibitors from head parts of the rhynchobdellid leech Theromyzon tessulatum is reported. Two proteins, anti-trypsin chymotrypsin A (ATCA; 14636.6 +/- 131 Da) and anti-trypsin-chymotrypsin B (ATCB; 14368 +/- 95 Da) were purified by size exclusion and anion-exchange chromatography followed by reversed-phase HPLC. Based on amino-acid composition, N-terminal sequence determination (MELCELGQSCSRD-NPQPSNM), matrix assisted laser desorption-time of flight measurement (MALDI-TOF), trypsin mapping comparison, inhibition constant determination (Ki), and influence on amidolytic activity of different serine proteases, it is demonstrated that ATCA and ATCB are novel and highly potent serine-protease inhibitors of trypsin and chymotrypsin (ATCA: 350fM towards trypsin and chymotrypsin; ATCB: 400 and 75 fM towards trypsin and chymotrypsin, respectively). It is further surmised that ATCA and ATCB are linked, in that ATCB would lead to the formation of ATCA after loss of few amino acid residues.

Theromin, a novel leech thrombin inhibitor

We purified the most potent thrombin inhibitor described to date from the rhynchobdellid leech Theromyzon tessulatum. Designated theromin, it was purified to apparent homogeneity by gel permeation and anion exchange chromatography followed by two reverse-phase steps of high performance liquid chromatography. The primary sequence of theromin (a homodimer of 67 amino acid residues including 16 cysteine residues) was determined by a combination of reduction and s-beta-pyridylethylation, Edman degradation, trypsin enzymatic digestion, and matrix-assisted laser desorption mass spectrometry measurement. Theromin exhibits no sequence homology with any other thrombin inhibitors. Furthermore, theromin significantly diminishes, in a dose-dependent manner, the level of human granulocyte and monocyte activation induced by lipopolysaccharides. In summary, this potent thrombin inhibitor promises to have high biomedical significance.

From natural to synthetic multisite thrombin inhibitors

A large number of potent and selective therapeutic agents, useful for the treatment of several diseases, have been isolated from natural sources. For example, the most active thrombin inhibitors are those secreted by the salivary glands of leeches. One peculiar feature of these agents is the lack of any significant inhibitory cross-reaction with other serine proteinases. Hence, the knowledge of the exact mechanism of action of these molecules provides the basis for the development of new and efficient synthetic drugs. For this reason, many studies have been undertaken on the structure-activity relationships of natural thrombin inhibitors, and a large amount of detailed information has been obtained by the crystal structures of these inhibitors when complexed with thrombin. In this paper, we review natural and synthetic multisite thrombin inhibitors, whose structural aspects have been determined in detail. We also report here the approach used by us to develop a new class of synthetic, multisite directed thrombin inhibitors, named hirunorms, designed to mimic the distinctive binding mode of hirudin.

Dipetalogastin, a potent thrombin inhibitor from the blood-sucking insect. Dipetalogaster maximus cDNA cloning, expression and characterization

A cDNA coding for the thrombin inhibitor dipetalogastin has been isolated from a stomach library of Dipetalogaster maximus, a blood-sucking insect. The open reading frame of the cloned inhibitor cDNA codes for a protein of 344 amino-acid residues. Sequence analysis reveals the existence of three repeated homologous main regions, indicating that the inhibitor consists of three domains. Each domain shows a double-headed structure with an internal sequence homology like rhodniin, the thrombin inhibitor from the blood-sucking insect Rhodnius prolixus. Peptide sequence comparisons of the deduced amino-acid sequence exhibit a high homology of the domains I and II to the natural inhibitor dipetalogastin from the stomach content of D. maximus and to rhodniin, respectively. Significant sequence similarities to Kazal-type inhibitors, like the conserved sequence CGXDXXTYXNXC and several cysteine residues, indicate that the thrombin inhibitor from D. maximus is a further blood-sucking insect which belongs to the Kazal-type family (besides rhodniin). A biologically active recombinant protein corresponding to domain II of the dipetalogastin cDNA was expressed in Escherichia coli. The isolated recombinant dipetalogastin with a molecular mass of 12.91 kDa has proved to be a specific thrombin inhibitor similar to its natural counterpart as well as rhodniin and hirudin. The Ki value of the recombinant dipetalogastin was determined to be 49.3 +/- 22.28 fM.

Functional phage display of leech-derived tryptase inhibitor (LDTI): construction of a library and selection of thrombin inhibitors

The recombinant phage antibody system pCANTAB 5E has been used to display functionally active leech-derived tryptase inhibitor (LDTI) on the tip of the filamentous M13 phage. A limited combinatorial library of 5.2 x 10(4) mutants was created with a synthetic LDTI gene, using a degenerated oligonucleotide and the pCANTAB 5E phagemid. The mutations were restricted to the P1-P4' positions of the reactive site. Fusion phages and appropriate host strains containing the phagemids were selected after binding to thrombin and DNA sequencing. The variants LDTI-2T (K8R, I9V, S10, K11W, P12A), LDTI-5T (K8R, I9V, S10, K11S, P12L) and LDTI-10T (K8R, I9L, S10, K11D, P12I) were produced with a Saccharomyces cerevisiae expression system. The new inhibitors, LDTI-2T and -5T, prolong the blood clotting time, inhibit thrombin (Ki 302 nM and 28 nM) and trypsin (Ki 6.4 nM and 2.1 nM) but not factor Xa, plasma kallikrein or neutrophil elastase. The variant LDTI-10T binds to thrombin but does not inhibit it. The relevant reactive site sequences of the thrombin inhibiting variants showed a strong preference for arginine in position P1 (K8R) and for valine in P1' (I9V). The data indicate further that LDTI-5T might be a model candidate for generation of active-site directed thrombin inhibitors and that LDTI in general may be useful to generate specific inhibitors suitable for a better understanding of enzyme-inhibitor interactions.

The crystal structure of alpha-thrombin-hirunorm IV complex reveals a novel specificity site recognition mode

The X-ray crystal structure of the human alpha-thrombin-hirunorm IV complex has been determined at 2.5 A resolution, and refined to an R-factor of 0.173. The structure reveals an inhibitor binding mode distinctive of a true hirudin mimetic, which justifies the high inhibitory potency and the selectivity of hirunorm IV. This novel inhibitor, composed of 26 amino acids, interacts through the N-terminal end with the alpha-thrombin active site in a nonsubstrate mode, and binds specifically to the fibrinogen recognition exosite through the C-terminal end. The backbone of the N-terminal tripeptide Chg1"-Arg2"-2Na13" (Chg, cyclohexyl-glycine; 2Na1, beta-(2-naphthyl)-alanine) forms a parallel beta-strand to the thrombin main-chain segment Ser214-Gly216. The Chg1" side chain occupies the S2 site, Arg2" penetrates into the S1 specificity site, while the 2Na13" side chain occupies the aryl binding site. The Arg2" side chain enters the S1 specificity pocket from a position quite apart from the canonical P1 site. This notwithstanding, the Arg2" side chain establishes the typical ion pair with the carboxylate group of Asp189.

The role of the leech in medical therapeutics

Leeching is considered by many to be a discredited medical relic of the past. This view is not justified, since leeches still play an important part in modern medicine, as in microsurgery and in the treatment of patients with post-phlebitic syndrome. Hirudin, the potent thrombin inhibitor of leech saliva, has been cloned and is used in the treatment of cardiological and hematological disorders. In our search for other antihemostatic factors in Hirudo medicinalis saliva, we found inhibitors of platelet aggregation induced by thrombin, collagen, adenosine 5'-diphosphate, epinephrine, platelet-activating factor and arachidonic acid. We purified apyrase (adenosine 5'-triphosphate diphosphohydrolase), which is a non-specific inhibitor of platelet aggregation by virtue of its action on adenosine 5'-diphosphate. We isolated and characterized the platelet-activating factor antagonist and also identified and recovered an inhibitor of coagulation factor Xa from leech saliva. This report summarizes our findings and those of other investigators, as well as the experience of one of us (A.E.) in leech therapy.

Isolation and characterization of an anticoagulant from the salivary glands of the tick, Ornithodoros savignyi (Acari: Argasidae)

An inhibitor of activated coagulation factor X (fXa) was isolated from salivary gland extracts prepared from Ornithodoros savignyi using a two-step procedure, involving reversed-phase high-performance liquid chromatography (RP-HPLC) and diethylaminoethyl (DEAE) ion-exchange chromatography. From its behaviour during DEAE chromatography it could be deduced that it possesses an acidic pI (approximately 4.6). Capillary zone electrophoresis (CZE) of the purified inhibitor showed it to be homogeneous. The molecular mass was determined as 12 kDa using capillary gel electrophoresis (CGE) and as 7183.4 using laser desorption mass spectrometry (LDMS). The N-terminal amino acid sequence (residues 1-12) was determined and found to share a 66% identity with tick anticoagulant peptide (TAP). The O. savignyi peptide is a slow, tight-binding inhibitor of fXa (Ki = 0.83 +/- 0.10 nM). The interaction of the fXa--inhibitor was found to be competitive and dependent on ionic strength. Preliminary investigations show that the inhibitor may be specific for fXa.