The Prevalence and Molecular Landscape of Lynch Syndrome in the Affected and General Population.

BACKGROUND: Lynch syndrome (LS) is the most frequent genetically pre-disposed colorectal cancer (CRC) syndrome, accounting for 2-3% of all CRC cases. In Estonia, ~1000 new cases are diagnosed each year. This retroactive and prospective study aimed to estimate the prevalence of LS and describe disease-causing variants in mismatch repair (MMR) genes in a diagnostic setting and in the Estonian general population. METHODS: LS data for the diagnostic cohort were gathered from 2012 to 2022 and data for the general population were acquired from the Estonian Biobank (EstBB). Furthermore, we conducted a pilot study to estimate the improvement of LS diagnostic yield by raising the age limit to >50 years for immunohistochemistry analysis of MMR genes. RESULTS: We estimated LS live birth prevalence between 1930 and 2003 in Estonia at 1:8638 (95% CI: 1: 9859-7588). During the study period, we gathered 181 LS individuals. We saw almost a six-fold increase in case prevalence, probably deriving from better health awareness, improved diagnostic possibilities and the implementation of MMR IHC testing in a broader age group. CONCLUSION: The most common genes affected in the diagnostic and EstBB cohorts were MLH1 and PMS2 genes, respectively. The LS diagnosis mean age was 44.8 years for index cases and 36.8 years (p = 0.003) for family members. In the MMR IHC pilot study, 29% had LS.

Policy implementation and priorities to create healthy food environments using the Healthy Food Environment Policy Index (Food-EPI): A pooled level analysis across eleven European countries.

Background: Food environments have been recognised as highly influential on population diets. Government policies have great potential to create healthy food environments to promote healthy diets. This study aimed to evaluate food environment policy implementation in European countries and identify priority actions for governments to create healthy food environments. Methods: The Healthy Food Environment Policy Index (Food-EPI) was used to evaluate the level of food environment policy and infrastructure support implementation in Estonia, Finland, Germany, Ireland, Italy, the Netherlands, Norway, Poland, Portugal, Slovenia, and Spain in 2019-2021. Evidence of implementation of food environment policies was compiled in each country and validated by government officials. National experts evaluated the implementation of policies and identified priority recommendations. Findings: Finland had the highest proportion (32%, n = 7/22) of policies shaping food environments with a "high" level of implementation. Slovenia and Poland had the highest proportion of policies rated at very low implementation (42%, n = 10/24 and 36%, n = 9/25 respectively). Policies regarding food provision, promotion, retail, funding, monitoring, and health in all policies were identified as the most important gaps across the European countries. Experts recommended immediate action on setting standards for nutrients of concern in processed foods, improvement of school food environments, fruit and vegetable subsidies, unhealthy food and beverage taxation, and restrictions on unhealthy food marketing to children. Interpretation: Immediate implementation of policies and infrastructure support that prioritize action towards healthy food environments is urgently required to tackle the burden of obesity and diet-related non-communicable diseases in Europe. Funding: This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 774548 and from the Joint Programming Initiative "A Healthy Diet for a Healthy Life".

The Unique Identification of an Unknown Soldier from the Estonian War of Independence.

The identification of human remains is challenging mostly due to the bad condition of the remains and the available background information that is sometimes limited. The current case report is related to the identification of an unknown soldier from the Estonian War of Independence (1918-1920). The case includes an anthropological study of the remains, examinations of documents found with the exhumed remains, and kinship estimations based on archival documents, and DNA analyses. As the preliminary data pointed to remains of male origin, Y-chromosomal STR (short tandem repeat) analyses of 22 Y-STR loci were used to analyze the exhumed teeth. Reference samples from individuals from two paternal lineages were collected based on archival documents. Y-chromosomal STR results for the tooth samples were consistent with a patrilineal relationship to only one reference sample out of two proposed paternal lineages. Based on the provided pedigrees in the consistent case, the Y-STR results are approximately four million times more likely if the tooth sample originated from an individual related along the paternal line to the matching reference sample, than if the tooth sample originated from another person in the general population. Special considerations have to be met when limited evidence is available.

The composition of faecal microbiota is related to the amount and variety of dietary fibres.

For normal gut and body function, the diet should contain variety of dietary fibres. To elucidate the links between food intake, especially the variety of dietary fibres, faecal microbiota, body mass index and content of blood lipids, 59 healthy subjects on common Estonian diet were enrolled. The dietary records were analysed at nutrient level while seven categories of fibres were characterised to differentiate variety of fibre profiles consumed. The data of the high fibre (HF) intake (>15.1 g/1000 kcal) and the low fibre (LF) intake (<9.4 g/1000 kcal) groups were comparatively evaluated. LF diets associated with Collinsella, Coprococcus and Dorea, and higher consumption of meat and white flour products while HF diet with Roseburia, Bacteroides xylanisolvens and Oxalobacter formigenes, and arabinoxylan and pectin rich cereals and vegetables. Based on the results, modulation of the colon microbiota can be suggested by careful variation and enrichment of dietary fibre sources.

Biochemistry and pharmacology of proteins and peptides purified from the venoms of the snakes Macrovipera lebetina subspecies.

The isolation and characterization of individual snake venom components is important for a deeper understanding of the pathophysiology of envenomations, for improving the therapeutic procedures of patients, and it also opens possibilities for the discovery of novel toxins that might be useful as tools for understanding cellular and molecular processes. This review provides a summary of the different toxins that have been isolated and characterized from the venoms of Vipera lebetina (Macrovipera lebetina) subspecies Macrovipera lebetina cernovi, Macrovipera lebetina lebetina, Macrovipera lebetina obtusa, Macrovipera lebetina transmediterranea, Macrovipera lebetina turanica, the snake species causing the majority of human envenomings in Central Asia (Middle East) and North Africa. The venoms of these snakes contain proteins belonging to different families: Zn2+- metalloproteinases, serine proteinases, L-amino acid oxidase, 5'-nucleotidase, phosphodiesterase, phosphomonoesterase, nucleases, hyaluronidase, phospholipase A2, C-type lectin-like protein, disintegrin, DC-fragment, cystein-rich secretory protein, proteinase inhibitors, nerve growth factor (NGF), vascular endothelial growth factor (VEGF), low molecular weight peptides. Their main biochemical properties, toxic and pharmacological actions have been described. In this review we will provide an overview of the proteins and peptides from the venoms of M. lebetina subspecies, their biochemical, pharmacological and structural features and their role in snake venom toxinology. A lot of contributions have been made for better understandings of these venomous snakes, their venom, and their pharmacological effects. Many of these components are also fascinating models for drug design.

Vipera lebetina venom nucleases.

Nucleases, in particular ribo- and deoxyribonucleases, are among the least-studied snake venom enzymes. In the present study we have partially purified different nucleases from Vipera lebetina venom. The DNase activity has been proved by DNA degradation both in solution as well as in-gel (zymogram-method). In DNA-containing SDS-PAGE V. lebetina venom exhibits DNA-degrading activity in bands with molecular masses of ∼120, 30-35 and 22-25 kDa. The 120 kDa band corresponds to phosphodiesterase, a 3', 5'-exonuclease. The endonucleolytic activity of the lower-molecular-mass protein has been confirmed by plasmid degradation and the visualization of the results in agarose gel (with ethidium bromide) electrophoresis. A partial DNA sequence of putative RNase H1 has been determined from the V. lebetina venom gland cDNA library. The translated sequence is similar to the assumed RNase H1 from Crotalus adamanteus (AFJ51163). The RNA/DNA hybrid is hydrolysed by V. lebetina venom and venom fractions. The masses of tryptic peptides from the SDS-PAGE 30-35 kDa band are in concordance with the theoretical peptide masses from the respective translated sequence. For the first time RNase H1-like enzyme activity has been ascertained in snake venom, and sequencing a relevant partial transcript confirmed the identification of this enzyme.

Diversity and Stability of Lactic Acid Bacteria in Rye Sourdoughs of Four Bakeries with Different Propagation Parameters.

We identified the lactic acid bacteria within rye sourdoughs and starters from four bakeries with different propagation parameters and tracked their dynamics for between 5-28 months after renewal. Evaluation of bacterial communities was performed using plating, denaturing gradient gel electrophoresis, and pyrosequencing of 16S rRNA gene amplicons. Lactobacillus amylovorus and Lactobacillus frumenti or Lactobacillus helveticus, Lactobacillus pontis and Lactobacillus panis prevailed in sourdoughs propagated at higher temperature, while ambient temperature combined with a short fermentation cycle selected for Lactobacillus sanfranciscensis, Lactobacillus pontis, and Lactobacillus zymae or Lactobacillus helveticus, Lactobacillus pontis and Lactobacillus zymae. The ratio of species in bakeries employing room-temperature propagation displayed a seasonal dependence. Introduction of different and controlled propagation parameters at one bakery (higher fermentation temperature, reduced inoculum size, and extended fermentation time) resulted in stabilization of the microbial community with an increased proportion of L. helveticus and L. pontis. Despite these new propagation parameters no new species were detected.

Whole mitochondrial genome genetic diversity in an Estonian population sample.

Mitochondrial DNA is a useful marker for population studies, human identification, and forensic analysis. Commonly used hypervariable regions I and II (HVI/HVII) were reported to contain as little as 25% of mitochondrial DNA variants and therefore the majority of power of discrimination of mitochondrial DNA resides in the coding region. Massively parallel sequencing technology enables entire mitochondrial genome sequencing. In this study, buccal swabs were collected from 114 unrelated Estonians and whole mitochondrial genome sequences were generated using the Illumina MiSeq system. The results are concordant with previous mtDNA control region reports of high haplogroup HV and U frequencies (47.4 and 23.7% in this study, respectively) in the Estonian population. One sample with the Northern Asian haplogroup D was detected. The genetic diversity of the Estonian population sample was estimated to be 99.67 and 95.85%, for mtGenome and HVI/HVII data, respectively. The random match probability for mtGenome data was 1.20 versus 4.99% for HVI/HVII. The nucleotide mean pairwise difference was 27 ± 11 for mtGenome and 7 ± 3 for HVI/HVII data. These data describe the genetic diversity of the Estonian population sample and emphasize the power of discrimination of the entire mitochondrial genome over the hypervariable regions.

5'-Nucleotidase from Vipera lebetina venom.

5'-Nucleotidase (5'-NT) is widely represented in animal tissues (CD73) as well as in almost all snake venoms. In the present study, a 5'-NT isoform has been isolated from Vipera lebetina venom. The homodimeric isoform consists of monomers with molecular masses of 60 kDa. The enzyme is thermolabile and has pH optimum at 7.5. The 5'-NT activity is inhibited by metal ions Fe(3+), Cu(2+) and Zn(2+), enhanced by Mn(2+) while Mg(2+) and Ca(2+) have no remarkable effect. In addition to 120-kDa protein there are higher molecular forms of 5'-NT present in the V. lebetina venom. The cloning and sequencing of the 5'-NT coding cDNA resulted in 5'-truncated construct. MALDI-TOF and Orbitrap mass-spectrometry of the tryptic peptides confirmed the translated N-terminally truncated protein sequence concordance to the 5'-NT isolated from the venom. The isolated protein strongly inhibited ADP- or collagen-induced platelet aggregation.

Phosphodiesterase from Vipera lebetina venom - structure and characterization.

Nucleases and phosphatases are ubiquitous but mostly marginal components of snake venoms. These proteins have been studied quite extensively but up to now no data regarding their amino acid sequences confirmed at protein level have been published. The present study deals with purification, characterization, and structural properties of a phosphodiesterase from Vipera lebetina venom (VLPDE). The VLPDE with molecular mass of about 120 kDa hydrolyses ADP but not ATP and 5'-AMP. The aggregation of platelets induced by ADP or collagen is dose-dependently inhibited by VLPDE. The cloning and sequencing of the VLPDE-encoding cDNA resulted in 2772-nt sequence with ORF of 2556 nt. The translated sequence comprises 851 amino acids including the 23-amino acid signal peptide. VLPDE is synthesized as a 828-amino acid single-chain protein but subsequently cleaved to form a two-chain protein held together with disulfide bonds. In reducing conditions the enzyme behaves like a heterodimeric protein but, differently from the real heterodimers, it is synthesized as a single-chain protein. VLPDE is the first snake venom phosphodiesterase with established and confirmed primary structure.

A validated biorepository of retina and choroid tissues for gene expression studies.

Research studies on pathologies affecting the posterior segment of the eye are usually carried out either in animal models or cell lines of human origin that mimic the molecular patterns occurring in the human retina-pigment epithelium-choroid (RPC) complex in vivo. As this is not always the case, we were prompted to validate a biorepository of RPC tissues for research purposes. A PubMed literature search on "retina," "choroid," "bio-bank," or "biorepository" as keywords did not lead to any publication describing the collection and banking of samples from the RPC complex for research purposes. The possibility to obtain access to a validated collection of high quality human RPC tissues as starting material is likely to lead to more appropriate findings and treatments, which eventually may improve human ocular health. Here we show that when tissues are harvested (T <25 hours from donor death) and stored appropriately, RNAs are not degraded (RNA Integrity Number Values >8.0) and express specific genes and molecular/biochemical pathways occurring in the RPC complex. These quality controlled tissues/RNAs comprising the biorepository could therefore be used for gene expression studies by research scientists and clinicians interested in testing their hypotheses in a more appropriate setting, thus replacing studies performed on less relevant animal models and cells in vitro, and directly extrapolating the findings to human pathophysiology.

A polymer lab-on-a-chip for genetic analysis using the arrayed primer extension on microarray chips.

In this work a polymer lab-on-a-chip (LOC), fabricated through MEMS technology, was employed to execute a genetic protocol for the Single Nucleotide Polymorphisms (SNPs) detection. The LOC was made in Poly (methyl methacrylate) (PMMA) and has two levels: the lower one for the insertion and mixing of the reagents, the upper one for the interfacing with the DNA microarray chip. The hereditary hearing loss was chosen as case of study, since the demand for testing such a particular disorder is high and genetics behind the condition is quite clear. The Arrayed Primer EXtension (APEX) genetic protocol was implemented on the LOC to analyze the SNPs. A low density (for detection of up to 10 mutations) and a high density microarray chips (for detection of 245 mutations in 12 genes), containing the primers for the extension, were employed to carry out the APEX reaction on the LOC. Both the microarray chips provide a signal to noise ratio and efficiency comparable with a detection obtained in a conventional protocol in standard conditions. Moreover, significant reduction of the employed PCR volume (from 30 µL to 10 µL) was obtained using the low density chip.

Characterization of the vaginal micro- and mycobiome in asymptomatic reproductive-age Estonian women.

The application of high-throughput sequencing methods has raised doubt in the concept of the uniform healthy vaginal microbiota consisting predominantly of lactobacilli by revealing the existence of more variable bacterial community composition. As this needs to be analyzed more extensively and there is little straightforward data regarding the vaginal mycobiome of asymptomatic women we aimed to define bacterial and fungal communities in vaginal samples from 494 asymptomatic, reproductive-age Estonian women. The composition of the vaginal microbiota was determined by amplifying bacterial 16S rRNA and fungal internal transcribed spacer-1 (ITS-1) regions and subsequently sequencing them using 454 Life Sciences pyrosequencing. We delineated five major bacterial community groups with distinctive diversity and species composition. Lactobacilli were among the most abundant bacteria in all groups, but also members of genus Gardnerella had high relative abundance in some of the groups. Microbial diversity increased with higher vaginal pH values, and was also higher when a malodorous discharge was present, indicating that some of the women who consider themselves healthy may potentially have asymptomatic bacterial vaginosis (BV). Our study is the first of its kind to analyze the mycobiome that colonizes the healthy vaginal environment using barcoded pyrosequencing technology. We observed 196 fungal operational taxonomic units (OTUs), including 16 OTUs of Candida spp., which is more diverse than previously recognized. However, assessing true fungal diversity was complicated because of the problems regarding the possible air-borne contamination and bioinformatics used for identification of fungal taxons as significant proportion of fungal sequences were assigned to unspecified OTUs.

Molecular epidemiology of Usher syndrome in Italy.

PURPOSE: Usher syndrome is an autosomal recessive disorder characterized by hearing and vision loss. Usher syndrome is divided into three clinical subclasses (type 1, type 2, and type 3), which differ in terms of the severity and progression of hearing loss and the presence or absence of vestibular symptoms. Usher syndrome is defined by significant genetic heterogeneity, with at least 12 distinct loci described and 9 genes identified. This study aims to provide a molecular epidemiology report of Usher syndrome in Italy. METHODS: Molecular data have been obtained on 75 unrelated Italian patients using the most up-to date technology available for the screening of Usher syndrome gene mutations, i.e., the genotyping microarray developed by Asper Biotech (Tartu, Estonia), which simultaneously investigates 612 different marker positions using the well established arrayed primer extension methodology (APEX). RESULTS: Using this method, we found that 12% of cases (9 out of 75) harbored homozygous or compound heterozygous mutations in the gene positions analyzed, whereas 20% (15 out of 75) of the patients were characterized by the presence of only one mutated allele based on the positions analyzed. One patient was found to be compound heterozygous for mutations in two different genes and this represents an example of possible digenic inheritance in Usher syndrome. A total of 66.6% of cases (50 out of 75) were found to be completely negative for the presence of Usher syndrome gene mutations in the detected positions. Mutations detected by the array were confirmed by direct sequencing. CONCLUSIONS: These findings highlight the efficacy of the APEX-based genotyping approach in the molecular assessment of Usher patients, suggesting the presence of alleles not yet identified and/or the involvement of additional putative genes that may account for the pathogenesis of Usher syndrome.

A new tyrosine-specific chymotrypsin-like and angiotensin-degrading serine proteinase from Vipera lebetina snake venom.

Vipera lebetina venom contains different metallo- and serine proteinases that affect coagulation and fibrin(ogen)olysis. A novel serine proteinase from V. Lebetina venom having ChymoTrypsin Like Proteolytic activity (VLCTLP) was purified to homogeneity from the venom using Sephadex G-100sf, DEAE-cellulose, heparin-agarose and FPLC on Superdex 75 chromatographies. VLCTLP is a glycosylated serine proteinase with a molecular mass of 41926 Da. It reacts with N-acetyl-L-tyrosine ethyl ester (ATEE) but not with Suc-Ala-Ala-Pro-Phe-pNA or Suc-Ala-Ala-Pro-Leu-pNA. The complete amino acid sequence of the VLCTLP is deduced from the nucleotide sequence of the cDNA encoding this protein. The full-length cDNA sequence of the VLCTLP encodes open reading frame of 257 amino acid residues that includes a putative signal peptide of 18 amino acids, a proposed activation peptide of six amino acid residues and serine proteinase of 233 amino acid residues. VLCTLP belongs to the S1 (chymotrypsin) subfamily of proteases. The multiple alignment of its deduced amino acid sequence showed structural similarity with other serine proteases from snake venoms. The protease weakly hydrolyses azocasein, Aα-chain and more slowly Bß-chain of fibrinogen. VLCTLP does not cleave fibrin and has no gelatinolytic activity. Specificity studies against peptide substrates (angiotensin I and II, oxidized insulin B-chain, glucagon, fibrinogen fragments etc.) showed that VLCTLP catalysed the cleavage of peptide bonds after tyrosine residues. VLCTLP is the only purified and characterized serine proteinase from snake venoms that catalyses ATEE hydrolysis. We detected ATEE-hydrolysing activities also in 9 different Viperidae and Crotalidae venoms.

Purification, characterization, and cDNA cloning of acidic platelet aggregation inhibiting phospholipases A(2) from the snake venom of Vipera lebetina (Levantine viper).

Two novel acidic phospholipase A(2)s (PLA(2)) were isolated by size exclusion chromatography and reversed-phase chromatography from the crude Vipera lebetina venom. The molecular masses of VLPLA(2)-1 (13,704 Da) and VLPLA(2)-2 (13,683 Da) and their internal tryptic peptides were determined by MALDI-TOF mass-spectrometry. When tested in human platelet-rich plasma, both enzymes showed a potent inhibitory effect on aggregation induced by ADP and collagen. Chemical modification with p-bromophenacylbromide abolished the enzymatic activity of PLA(2); its anti-platelet activity was fully inhibited in case of collagen as inducer and partially inhibited in case of ADP as inducer. The complete cDNAs encoding PLA(2) were cloned from a single venom gland cDNA library. Complete amino acid sequences of the VLPLA(2) were deduced from the cDNA sequences. The full-length cDNA sequences of the VLPLA(2) possess 615bp and encode an open reading frame of 138 amino acids that include signal peptide (16 amino acids) and mature enzyme (122 amino acids). The VLPLA(2)s have significant sequence similarity to many other phospholipase A(2)s from snake venoms. The phylogenetic analysis on the basis of the amino acid sequence homology demonstrates that VLPLA(2)s grouped with other Asp49 PLA(2)s and they appear to share a close evolutionary relationship with the European vipers.

VGD and MLD-motifs containing heterodimeric disintegrin viplebedin-2 from Vipera lebetina snake venom. Purification and cDNA cloning.

We have previously demonstrated that the fibrinolytic enzyme lebetase is synthesized with disintegrin-like domain that is cleaved posttranslationally (Siigur et al., 1996). Now we isolated a heterodimeric disintegrin viplebedin-2 containing this disintegrin-like part from Vipera lebetina venom using size-exclusion chromatography on Sephadex G-100 sf and HPLC on C18 column. The molecular masses of viplebedin-2 and tryptic peptides from both chains of viplebedin-2 were determined by MALDI-TOF mass spectrometry. Using cDNA library of the venom gland of a single V. lebetina turanica snake the viplebedin-2 coding cDNAs were cloned and sequenced. Viplebedin-2 chains are synthesized from two different genes. One chain, containing VGD sequence in disintegrin loop, is synthesized as a disintegrin-like part of the PII-type metalloprotease, lebetase. The other chain, containing MLD sequence in disintegrin loop, is synthesized from the gene without metalloproteinase domain. Two polyadenylation signal sequences have been found in MLD sequence coding chain precursor cDNAs. Viplebedin-2 dose-dependently inhibited adhesion of platelets to immobilized collagen and inhibited collagen-induced platelet aggregation.

cDNA cloning of a novel P-I lebetase isoform Le-4.

In order to better understand the function of fibrinolytic enzyme lebetase isoforms and the synthesis of disintegrins we have isolated a cDNA encoding the most basic isoform (Le-4) from the cDNA library prepared from the poly(A)(+) RNA of the venomous gland of an individual Vipera lebetina snake. The truncated 5'-sequence of 1112 basepairs encodes the mature protein with 203 amino acid residues with calculated isoelectric point and size of 5.6 and 22,930 Da, respectively. Multiple comparison of the deduced amino acid sequence of the metalloprotease part of Le-4 is related to short reprolysins, identities were within the range of 60--87%. The two lebetase isoforms are synthesized in different way: Le-4 is synthesized with metalloprotease domain only; Le-3 is synthesized with metalloprotease and disintegrin-like domain and processed posttranslationally. The sequence of the disintegrin-like part of Le-3 is identical to A-chain of the heterodimeric disintegrin VLO5 from Vipera lebetina obtusa venom (Calvete et al., 2003).

A novel metalloprotease from Vipera lebetina venom induces human endothelial cell apoptosis.

A novel endothelial cell apoptosis inducing metalloprotease (VLAIP) was found in the snake venom of Vipera lebetina. This metalloprotease is a heterodimeric glycoprotein with molecular mass of about 106 kDa. The protease hydrolyzes azocasein, fibrinogen and oxidized insulin B-chain. The enzyme readily hydrolyzes the Aalpha-chain and more slowly Bbeta-chain of fibrinogen. VLAIP does not cleave fibrin. The complete amino acid sequences of the two different monomers of VLAIP are deduced from the nucleotide sequences of cDNAs encoding these proteins. The full-length cDNA sequences of the VLAIP-A and VLAIP-B encode open reading frames of 616 and 614 amino acids that include signal peptide, propeptide and mature metalloproteinase with disintegrin-like and cysteine-rich domains. VLAIP belongs to the metalloprotease/disintegrin family of reprolysins and has high identity with the proteins that induce apoptosis of endothelial cells. Treatment of HUVEC cells with VLAIP induces changes in the attachment of cells to the substrate and causes cell death. We demonstrated that VLAIP inhibits endothelial cell adhesion to extracellular matrix proteins: fibrinogen, fibronectin, vitronectin, collagen I, and collagen IV. The induction of apoptosis by VLAIP was shown by means of a typical DNA fragmentation pattern of apoptotic cells as well as by monitoring phosphatidylserine externalization using annexin V-FITC staining and flow cytometric analysis.

Factor X activator from Vipera lebetina venom is synthesized from different genes.

Vipera lebetina venom contains specific coagulant Factor X activator (VLFXA) that cleaves the Arg52-Ile53 bond in the heavy chain of human factor X. VLFXA is a glycoprotein that is composed of a heavy chain (HC) and two light chains (LC) linked by disulfide bonds. The complete amino acid sequences of the three chains of the factor X activator from V. lebetina snake venom are deduced from the nucleotide sequences of cDNAs encoding these chains. The full-length cDNA (2347 bp) sequence of the HC encodes an open reading frame (ORF) of 612 amino acids that includes signal peptide, propeptide and mature metalloproteinase with disintegrin-like and cysteine-rich domains. The light chain LC1 contains 123 and LC2 135 amino acid residues. Both light chains belong to the class of C-type lectin-like proteins. The N-termini of VLFXA chains and inner sequences of peptide fragments detected by liquid chromatography-electrospray ionization tandem mass spectrometry (LC MS/MS) from protein sequence are 100% identical to the sequences deduced from the cDNA. The molecular masses of tryptic fragments of VLFXA chains analyzed by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) also confirm the protein sequences deduced from the cDNAs. These are the first cloned factor X activator heavy and light chains. We demonstrate that the heavy and light chains are synthesized from different genes.