Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.6 (thromboplastin)
 13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Salivary gland extracts from the yellow fever mosquito Aedes aegypti contain a factor Xa-specific anticoagulant detectable in vitro by clotting assays. The anticoagulant is found only in female salivary glands, which is consistent with its role in bloodfeeding. Extracts of adult female glands significantly delay both the prothrombin time and the activated partial thromboplastin time, but have no effect on the thrombin clotting time. The anticoagulant has been shown to result from the specific inhibition of coagulation factor Xa based on a FXa clotting assay and the inhibition of FXa-directed cleavage of the synthetic chromogenic substrate, chromozym X. The inhibition of FXa by female salivary gland extracts exhibits noncovalent, noncompetitive inhibition kinetics and is reversible. The anticoagulant is destroyed by boiling for 10 min or heating at 56 degrees C for 30 min, has a 4 mM calcium optimum with no magnesium requirement, and has a pH optimum of 8.0. The anticoagulant activity has an apparent molecular weight of 35.5 kDa, as determined by molecular sieve. We propose that the A. aegypti anticoagulant is a novel, proteinaceous serine protease inhibitor specific for FXa.
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PMID:A factor Xa-directed anticoagulant from the salivary glands of the yellow fever mosquito Aedes aegypti. 749 29

Mosquito salivary glands secrete a number of proteins that inhibit mammalian hemostasis and facilitate blood feeding. We have isolated the protein product and corresponding cDNA of a gene designated Anticoagulant-factor Xa (AFXa), that encodes the factor Xa (FXa)-directed anticoagulant of the yellow fever mosquito, Aedes aegypti. The protein was purified partially by cation exchange chromatography and shown by enzyme activity profiles and SDS-polyacrylamide gel electrophoresis analysis to have an Mr = 54, 000. The protein was purified further by preparative SDS-polyacrylamide gel electrophoresis and subjected to internal protein sequencing, and the sequence of five peptides was determined. Degenerate oligonucleotides were designed based on three of the peptide sequences, and these were used to screen an adult female salivary gland cDNA library from A. aegypti. A 1.8-kilobase pair cDNA was isolated and shown to encode a 415-amino acid conceptual translation product with a predicted molecular mass of 47.8 kDa that contains the five sequenced peptides. Hydrophobicity analysis predicts a 19-amino acid signal peptide typical for secreted proteins. Northern analysis demonstrated that AFXa is expressed only in female salivary glands. Baculovirus-expressed AFXa protein has the appropriate size and expected FXa-directed anticoagulant activity. Analysis of the primary amino acid sequence shows that the AFXa gene product has similarities to the serpin superfamily of serine protease inhibitors and may represent a novel, highly diverged member of this family.
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PMID:Isolation and characterization of the gene encoding a novel factor Xa-directed anticoagulant from the yellow fever mosquito, Aedes aegypti. 969 25

The molecular mechanism of factor Xa (FXa) inhibition by Alboserpin, the major salivary gland anticoagulant from the mosquito and yellow fever vector Aedes albopictus, has been characterized. cDNA of Alboserpin predicts a 45-kDa protein that belongs to the serpin family of protease inhibitors. Recombinant Alboserpin displays stoichiometric, competitive, reversible and tight binding to FXa (picomolar range). Binding is highly specific and is not detectable for FX, catalytic site-blocked FXa, thrombin, and 12 other enzymes. Alboserpin displays high affinity binding to heparin (K(D) ~ 20 nM), but no change in FXa inhibition was observed in the presence of the cofactor, implying that bridging mechanisms did not take place. Notably, Alboserpin was also found to interact with phosphatidylcholine and phosphatidylethanolamine but not with phosphatidylserine. Further, annexin V (in the absence of Ca(2+)) or heparin outcompetes Alboserpin for binding to phospholipid vesicles, suggesting a common binding site. Consistent with its activity, Alboserpin blocks prothrombinase activity and increases both prothrombin time and activated partial thromboplastin time in vitro or ex vivo. Furthermore, Alboserpin prevents thrombus formation provoked by ferric chloride injury of the carotid artery and increases bleeding in a dose-dependent manner. Alboserpin emerges as an atypical serpin that targets FXa and displays unique phospholipid specificity. It conceivably uses heparin and phosphatidylcholine/phosphatidylethanolamine as anchors to increase protein localization and effective concentration at sites of injury, cell activation, or inflammation.
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PMID:Alboserpin, a factor Xa inhibitor from the mosquito vector of yellow fever, binds heparin and membrane phospholipids and exhibits antithrombotic activity. 2167 7