Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.6 (thromboplastin)
13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Coagulation factor V is a high molecular weight plasma glycoprotein that participates as a cofactor in the conversion of prothrombin to thrombin by factor Xa. A phage lambda gt11 Hep G2 cell cDNA expression library was screened by using an affinity-purified antibody to human factor V, and 11 positive clones were isolated and plaque-purified. The clone containing the largest cDNA insert contained 2970 nucleotides and coded for 938 amino acids, a stop codon, and 155 nucleotides of 3' noncoding sequence including a poly(A) tail. The coding region includes 651 amino acids from the carboxyl terminus that constitute the light chain of human factor Va and 287 amino acids that are part of the connecting region of the protein. The predicted amino acid sequence agreed completely with 147 amino acid residues that were identified by Edman degradation of cyanogen bromide peptides isolated from the light chain. During the activation of factor V, several peptide bonds are cleaved by thrombin, giving rise to a heavy chain, a connecting fragment(s), and a light chain. The light chain is generated by the cleavage of an Arg-Ser peptide bond. The amino acid sequence of the light chain is homologous (40%) with the carboxyl-terminal fragment (Mr, 73,000) of human factor VIII. Both fragments have a similar domain structure that includes a single ceruloplasmin-related domain followed by two C domains. The carboxyl terminus of the connecting region, however, shows no significant amino acid sequence homology with factor VIII. It is very acidic and contains a number of potential N-linked glycosylation sites. It also contains about 20 tandem repeats of nine amino acids.
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PMID:Cloning of a cDNA coding for human factor V, a blood coagulation factor homologous to factor VIII and ceruloplasmin. 309 20

Coagulation factor V, an integral component of the prothrombinase complex, possesses two C-type domains at the carboxyl-terminal end of the molecule. Homologous C-type domains are present in factor VIII as well as several non-coagulation proteins. Deletion of the second C-type domain of factor V results in the loss of procoagulant activity and the ability to bind phosphatidylserine. We now report the effect of substitution of all or a portion of the C2 domain of factor V with the corresponding regions of factor VIII or the human breast carcinoma protein BA46. Substitution of the entire domain with a heterologous C2 domain does not restore significant procoagulant activity, although smaller, exon-size substitutions do result in chimeras with partial activity (approximately 10% of factor Va). Using chimeras with partial substitutions, we determined that the amino-terminal region of the domain is involved in binding to phosphatidylserine. In contrast, the central region of the domain is not involved in phosphatidylserine binding, but an antibody binding at or near this site inhibits procoagulant activity, suggesting that this region is involved in a separate function. Lastly, the molecular basis for the light chain doublet, which is important in the expression of full procoagulant activity, is located within the carboxyl-terminal region of the C2 domain.
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PMID:Localization of functionally important epitopes within the second C-type domain of coagulation factor V using recombinant chimeras. 751 64

Coagulation factor V is a critical cofactor for the activation of prothrombin to thrombin, the penultimate step in the generation of a fibrin blood clot. Genetic deficiency of factor V results in a congenital bleeding disorder (parahaemophilia), whereas inheritance of a mutation rendering factor V resistant to inactivation is an important risk factor for thrombosis. We report here that approximately half of homozygous embryos deficient in factor V (Fv-/-), which have been generated by gene targeting, die at embryonic day (E) 9-10, possibly as a result of an abnormality in the yolk-sac vasculature. The remaining Fv-/- mice progress normally to term, but die from massive haemorrhage within 2 hours of birth. Considered together with the milder phenotypes generally associated with deficiencies of other clotting factors, our findings demonstrate the primary role of the common coagulation pathway and the absolute requirement for functional factor V for prothrombinase activity. They also provide direct evidence for the existence of other critical haemostatic functions for thrombin in addition to fibrin clot formation, and identify a previously unrecognized role for the coagulation system in early mammalian development.
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PMID:Fatal haemorrhage and incomplete block to embryogenesis in mice lacking coagulation factor V. 890 Feb 78

Coagulation factor V circulates in plasma as a single chain protein which expresses little procoagulant activity. After its activation by limited proteolysis by thrombin or factor Xa, factor Va functions as cofactor to factor Xa in the activation of prothrombin. Thrombin cleaves human factor V at Arg709, Arg1018 and Arg1545 and factor Va is formed by the heavy and light chains, which correspond to the N-terminal and C-terminal fragments, respectively. Factor Xa has been shown to cleave factor V at Arg1018 and at a second undefined position close to Arg709. The factor-Xa-mediated cleavage at Arg1018 has been proposed to be sufficient for expression of full factor Va activity. To study the activation of factor V by factor Xa, site-directed mutagenesis was used to convert Arg709 to Gln, Arg1018 to Ile, and Arg1545 to Gln. Constructs containing all possible combinations of native and mutated residues in these positions were expressed transiently in COS 1 cells. The various factor-V mutants were incubated with factor Xa or thrombin. The proteolytic cleavage pattern was analyzed by Western blotting, and the specific factor-Va activities determined in a prothrombinase assay. Control experiments using thrombin gave results which were in agreement with those on record, i.e. cleavages at both Arg709 and Arg1545 were required for expression of full factor-Va activity, whereas the cleavage at Arg1018 enhanced the rate of cleavage at Arg1545. Factor Xa was found to cleave factor V at all three thrombin cleavage sites, i.e. at Arg709, Arg1018 and Arg1545. An additional factor-Xa-cleavage site was found in the light chain region at Arg1765. Cleavage at Arg1018 by factor Xa was not sufficient for expression of full factor-Va activity. Full factor-Va activity was only obtained after cleavage at both Arg709 and Arg1545. The factor-Xa-mediated cleavage at Arg709 was kinetically favourable over that at Arg1545. Factor V which was mutated at all three sites (at positions 709, 1018 and 1545) was resistant to activation by thrombin. However, treatment with factor Xa yielded an increased factor-Va activity which was associated with the cleavage at Arg1765. Our study extends previously results on thrombin activation of factor V and elucidates the relative importance of the different cleavage sites for activation of factor V by factor Xa.
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PMID:Cleavage requirements for activation of factor V by factor Xa. 924 3

Coagulation factor V is composed of domains A1-A2-B-A3-C1-C2 and is activated by thrombin through proteolytic cleavage at Arg 709, Arg 1018 and Arg 1545. Upon thrombin activation, the B-domain is released and the active factor Va is formed by the heavy (A1-A2) and light chains (A3-C1-C2). Factor Va functions as an essential cofactor to factor Xa in the conversion of prothrombin to thrombin during coagulation. Recently it was shown that coagulation factor V, apart from being a precursor form to the procoagulant factor Va, also has anticoagulant properties, as it functions as a cofactor to activated protein C (APC). APC is a member of the anticoagulant pathway and downregulates the coagulation process through proteolytic inactivation of factors VIII/VIIIa and factors V/Va. In a factor VIIIa degradation assay, the APC-mediated inactivation of factor VIIIa is potentiated by the synergistic cofactors protein S and factor V. Protein S alone has little cofactor activity, whereas in the presence of factor V it is dramatically enhanced. This study provides insights into the molecular mechanisms that regulate the anticoagulant activity of factor V. Thrombin cleavage of factor V occurs in a sequential order. The thrombin cleavage site Arg 1545 is kinetically less favored than the other two sites, and cleavage at this site is the last to occur during thrombin activation of factor V As a consequence of this, different activation intermediates exist that express different levels of procoagulant activity. The anticoagulant activities of these intermediates have now been studied. It was found that factor V could be cleaved by thrombin at both Arg 709 and Arg 1018 and still work fully as a cofactor to APC, whereas cleavage at Arg 1545 completely abolished the anticoagulant activity of factor V. This suggests that the APC cofactor function of factor V depends on the B-domain remaining attached to the A3 domain. This study further shows that APC converts coagulation factor V into a member of the anticoagulant pathway by cleaving factor V in the A2 domain at Arg 506. By cleavage of factor V, APC not only produces an anticoagulant cofactor, but at the same time eliminates the pool of procoagulant factor V, since APC cleaved factor V will have no future as a cofactor in the coagulation. The unique way by which APC and thrombin, through proteolytic cleavage, can convert factor V into either an anticoagulant or a procoagulant adds to the intriguing mechanisms that balance the procoagulant and anticoagulant forces.
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PMID:Mechanisms that regulate the anticoagulant function of coagulation factor V. 1009 86

Coagulation factor V has been at the centre of investigation for several years. In addition to factor V Leiden, various other polymorphisms are becoming the object of interest. Different results have been published about the association of the HR2 haplotype with decreased factor V levels and with reduced response to activated protein C (APC). Due to the central position of factor V in the clotting process, its activity can be determined in both thromboplastin-based and activated partial thromboplastin time (aPTT)-based assays. A multitude of assays are known for the determination of APC response. The aim of our study was to investigate whether different methods disclose genotype-dependent differences in factor V activity as well as APC response. Three wild-type carriers, three carriers homozygous for the R2 allele (4070G), and three carriers homozygous for the G allele (2391G, 2663G, 2684G, 2863G) were investigated. For each individual plasma sample, the factor V activity was determined using 12 different reagent combinations of three different thromboplastins, three different aPTT reagents, and two different factor V deficient plasma sources. The determination of factor V activity in the thromboplastin system revealed differences between the genotypes. These differences were independent of the thromboplastin reagent and the factor V-deficient plasma. The aPTT system exhibited a dependency on the aPTT reagent and the factor V-deficient plasma. Analysis of APC response disclosed genomic differences in specific test systems only. One type of assay could be more appropriate than other types in dependence of the position of genomic variations. Therefore, the applied assay is an important influential factor in investigations of functional consequences of genomic variations.
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PMID:Investigation of genotype-dependent differences in factor V activity as well as response to activated protein C by application of different methods. 1173 69

Coagulation factor V (FV) is the protein cofactor required in vivo for the rapid generation of thrombin catalyzed by the prothrombinase complex. It also represents a central regulator in the early phases of blood clot formation, as it contributes to the anticoagulant pathway by participating in the downregulation of factor VIII activity. Conversion of precursor FV to either a procoagulant or anticoagulant cofactor depends on the local concentration of procoagulant and anticoagulant enzymes, so that FV may be regarded as a daring tight-rope walker gently balancing opposite forces. Given this dual role, genetic defects in the FV gene may result in opposite phenotypes (hemorrhagic or thrombotic). Besides a concise description on the structural, procoagulant and anticoagulant properties of FV, this review will focus on bleeding disorders associated with altered levels of this molecule. Particular attention will be paid to the mutational spectrum of type I FV deficiency, which is characterized by a remarkable genetic heterogeneity and by an uneven distribution of mutations throughout the FV gene.
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PMID:Inherited defects of coagulation factor V: the hemorrhagic side. 1705 27

Coagulation factor V (FV) is an essential component of the prothrombinase complex, which activates the zymogen prothrombin to thrombin. Acquired FV inhibitor is rare and clinical symptoms are quite variable. The aim of this study was to summarize the spectrum of the bleeding presentation of acquired FV deficiency and characterize the underlying causes of the clinical symptoms. This study was designed as a descriptive retrospective and 30 case reports were included for further analysis. At least 33 cases of acquired FV inhibitor were investigated. Most patients have a presentation of bleeding and most of those are from hematuria and bleeding at surgical sites. Seven cases of asymptomatic acquired FV inhibitor were also detected. A total of 39.4% (19 of 33) of those cases with acquired FV inhibitor have an unknown cause. For those with known etiologies, chemical and drug-induced causes are the most common (30.8%).
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PMID:Spectrum of bleeding in acquired factor V inhibitor: a summary of 33 cases. 1700 Aug 94

Coagulation factor V (FV) deficiency is a rare bleeding disorder characterized by low coagulant and antigen levels of FV with bleeding symptoms ranging from mild to severe. Only a limited number of mutations have been reported because of the large size of the factor V gene (F5) as well as the low prevalence. In this study, we have identified four novel mutations in F5 in five unrelated patients with congenital FV deficiency. All the patients, including two with undetectable FV activity, were asymptomatic and were found to have prolonged prothrombin time and activated partial thromboplastin time during preoperative screening or routine examinations. All four mutations found in this study are either missense or in-frame deletion. This is in contrast with previous reports of a high frequency of mutations introducing premature termination codons in inherited FV deficiency. Missense mutations of F5 might produce a mild phenotype and are not frequently diagnosed. Although FV deficiency is a very rare disorder with a predicted incidence of one in 1 million, this study suggests that the numbers of F5 mutations, especially missense mutations, are higher than estimated.
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PMID:Identification of four novel mutations in F5 associated with congenital factor V deficiency. 1905 95

Coagulation factor V (FV) plays an important role in the blood coagulation cascade as part of the prothrombinase complex. FV deficiency is a rare autosomal recessive bleeding disorder with variable phenotypic expression. Thus, our study reports 39 patients with FV deficiency. In 36 cases, we were able to identify a causative mutation. Of these, 20 patients were heterozygous for the identified mutation, nine were homozygous, six were compound heterozygous and one proband was pseudohomozygous. In the remaining patients, no mutation was found. A total of 42 genetic alterations (of which 33 were uniquely different mutations), comprising 19 missense mutations, eight nonsense mutations, four small deletions and two splice site mutations, were identified by this study. Twenty-three of these were novel sequence variations not previously described in the literature. Interestingly, all changes found in exon 13 resulted in null alleles as either nonsense mutations or small deletions. The overall profile of these new mutations corresponds well with the data published in the F5 database. In those cases, where data were available, information on FV activity levels and/or bleeding history is given. Interestingly, some patients with mild FV deficiency (FV:C about 50% of normal) also exhibited bleeding episodes. Our data substantially contribute to the broadening and better understanding of the FV deficiency mutational spectrum. Identifying the molecular basis of mutations underlying this rare coagulation disorder will allow more insight into the mechanisms involved in the variable clinical phenotypes of patients with FV deficiency.
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PMID:Factor 5 mutation profile in German patients with homozygous and heterozygous factor V deficiency. 1948 70


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