Evidence that a region in the catalytic domain of factor VII is important for the association with tissue factor

Testing strategies used in the diagnosis of rare inherited bleeding disorders

INTRODUCTION

Rare Bleeding Disorders have a low population prevalence and may not be recognized by most clinicians. In addition, knowledge gaps of the indicated laboratory tests and their availability add to the potential for delayed diagnosis or misdiagnosis. The lack of widely available commercial, regulatory body approved esoteric tests limit them to reference laboratories, thus limiting easy access for patients.

AREAS COVERED

A literature search of Pubmed, Medline, Embase and review of international society guidelines was performed. Additional references from published articles were reviewed. A patient-centered approach to recognition and evaluation of RBD is discussed.

EXPERT OPINION

Recognition of RBD relies on obtaining a detailed patient personal and family hemostatic history. Inquiry into a history of involvement of other organ systems is important and if present should lead to suspicion of an inherited platelet disorder or a variant of Ehlers Danlos Syndrome. Multiple factors contribute to the complexity of development of efficient algorithms for diagnostic testing. Limitations in diagnostic sensitivity and specificity of screening tests, diagnostic tests, and esoteric tests further compound the complexity of establishing a diagnosis. Educational efforts focusing on clinician awareness of RBDs and available testing options are vital for optimal management of such patients.

Factor VII Padua in Iran: clinical and laboratory findings of three unrelated patients

The congenital factor VII (FVII) deficiency with an estimated incidence of one per 300 000 is the most common rare congenital bleeding disorder. The heterogeneous clinical pictures, including asymptomatic to life-threatening manifestations, are seen in patients with FVII deficiency. A variety of gene variants throughout the FVII ( F7 ) gene have been reported so far. In this setting, very rare FVII Padua polymorphism provokes an interesting condition in which results of prothrombin time and FVII activity are different based on the thromboplastin sources used in these tests. The current study aimed to report the phenotype and genotyping of patients with Padua variant. During the workup of the laboratory for FVII deficiency for diagnosis of FVII Padua, all patients with FVII deficiency who had prolonged prothrombin time, normal activated partial thromboplastin time, and variable FVII activity results using different sources of thromboplastin were included. Demographic data and clinical findings were recorded. For the molecular study, the F7 gene sequencing was performed using the Sanger sequencing technique. Five patients with FVII Padua and a history of mild-to-moderate bleeding, including easy bruising, epistaxis, gingivorrhagia, and bleeding after surgical challenges (including dental extraction and tonsillectomy), were detected during the study. DNA sequencing revealed a heterozygote CGG to CAG (Arg364Gln) variant in exon 9 at nucleotide position 1091, consistent with the genetic variant of FVII Padua. Timely diagnosis of FVII Padua is vital to avoid unnecessary exposure of patients to replacement therapy.

Thromboelastometry as an Ancillary Tool for Evaluation of Coagulation Status after rFVIIa Therapy in a Pregnant Woman with Severe Hypoproconvertinemia-A Case Series and Review of the Literature

Introduction: Factor VII (FVII) deficiency is a rare hemorrhagic diathesis. In females, heavy menstrual and postpartum bleeding can appear as a consequence of its deficiency. Supplementation of the recombinant FVIIa is widely accepted. The supplementation effect in FVII-deficient subjects is difficult to predict, and severe hemorrhage has been described even when FVII levels after supplementation were within normal ranges. The aim of this report is to present the application of thromboelastometry to control the coagulation status in a patient with severe FVII deficiency during pregnancy and delivery, supplemented by rFVIIa per protocol complicated with life-threatening venous thromboembolism. Methods: Rotational thromboelastometry (ROTEM) was performed in 16 pregnant women: in one 28 year old primigravida at 35 weeks of pregnancy with congenital FVII deficiency after rFVIIa administration and 15 healthy women at 38 gestational weeks. The results were compared. Results: The thromboelastometry results showed significant shortening of the clotting time in the extrinsic and the intrinsic pathway in the hypoproconvertinemia patient after rFVIIa administration in relation to healthy pregnant women. A significant reduction in maximum lysis of the clot after FVII supplementation was observed. Conclusions: The thromboelastometry results showed a significant hypercoagulable state with hypoproconvertinemia. Thrombotic complications after delivery might be prevented by the reduction in rFVIIa guided by thromboelastometry. Thromboelastometry performed on a pregnant woman with factor VII deficiency during the supplementation of rFVIIa in peripartum time might be helpful in order to determine an individual, effective dosage regimen of rFVIIa to ensure full correction of clotting disorders without the tendency to develop thrombosis, but further studies are needed.

A novel compound heterozygous variant linked to hematuria in a family with hereditary factor VII deficiency

BACKGROUND

Hereditary Factor VII Deficiency (FVIID) is a rare congenital autosomal recessive bleeding disorder. In clinical manifestations, its onset is caused by variant of the F7 gene (NM_019616) with strong heterogeneity. We identified a family with hematuria caused by a novel F7 compound heterozygous variant and studied the FVIID-dependent mechanism impacted by these variants.

METHODS

Coagulation factors in the proband were functionally verified. We located pathogenic variants in relevant genes using next-generation sequencing after target enrichment and verified them by Sanger sequencing. We examined the coagulation activity and secretion pattern of recombinant FVII variants expressed in cells and observed their location and stability by immunofluorescence.

RESULTS

We found a missense variant c.1207G>A (p.Gly403Ser) and a frameshift variant c.154_155del (p.Arg53fs) in the F7 gene of the proband. FVII activity tests showed that the variants significantly decreased its presence in the cell culture supernatant. Moreover, the R53fs mutant lacked the FVII functional domain and had no detectable activity. Immunofluorescence indicated that the p.Gly403Ser variant was distributed to the cell membrane and cytoplasm, while the FVII R53fs variant was not detected. Deficient FVII protein function and severe coagulation disorder are the likely causes of hematuria and other bleeding symptoms in the proband.

CONCLUSION

The newly discovered F7 gene variants enrich the spectrum of hereditary FVII deficiency and provide a new foundation for the diagnosis and treatment of this type of coagulation disorder.

Novel mutation in coagulation factor VII (Carmel mutation): Identification and characterization

BACKGROUND

Measurement of factor VII (FVII) activity does not enable prediction of bleeding tendency in individuals with inherited FVII deficiency.

OBJECTIVE

To characterize the molecular and functional features of FVII in a family with FVII deficiency and correlate them with the bleeding tendency.

PATIENTS/METHODS

We studied 7 family members with very low FVII activity using prothrombin time (PT), activated factor VII (FVIIa), FVII activity level, and thrombin generation. The factor 7 gene was sequenced and the mutation was analyzed by prediction software.

RESULTS

The proband has very low FVII activity (0%-4%), with PT ranging between 5% to 18% depending on the tissue factor (TF) origin. Direct sequencing demonstrated a single homozygous nucleotide substitution G > A in exon 6, predicting a novel missense mutation Cys164Tyr. Three members of the family were found to be heterozygous carriers of this mutation. One of them was a compound heterozygote, carrying both the Cys164Tyr and Ala244Val mutation (linked to Arg353Gln polymorphism). Her FVII activity and antigen levels were 3%-7% and 8%, respectively. The other heterozygous carriers demonstrated FVII activity of 41%-54%, FVII antigen of 46%-66%, and FVIIa activity of 30%. FVIIa was undetectable in the homozygous and compound heterozygous subjects. Thrombin generation was normal in the presence of calcium, but no response to TF addition was observed in the homozygous proband, and a reduced response was observed in the compound heterozygous subject.

CONCLUSION

The patient homozygous for the "Carmel" mutation has mild clinical manifestations despite very low FVII activity, which correlates with thrombin generation results.

The EAHAD blood coagulation factor VII variant database

Hereditary blood coagulation factor VII (FVII) deficiency is a rare autosomal recessive bleeding disorder resulting from variants in the gene encoding FVII (F7). Integration of genetic variation with functional consequences on protein function is essential for the interpretation of the pathogenicity of novel variants. Here, we describe the integration of previous locus-specific databases for F7 into a single curated database with enhanced features. The database provides access to in silico analyses that may be useful in the prediction of variant pathogenicity as well as cross-species sequence alignments, structural information, and functional and clinical severity described for each variant, where appropriate. The variant data is shared with the F7 Leiden Open Variation Database. The updated database now includes 221 unique variants, representing gene variants identified in 728 individuals. Single nucleotide variants are the most common type (88%) with missense representing 74% of these variants. A number of variants are found with relatively high minor allele frequencies that are not pathogenic but contribute significantly to the likely pathogenicity of coinherited variants due to their effect on FVII plasma levels. This comprehensive collection of curated information significantly aids the assessment of pathogenicity.

Thrombotic Events in Homozygotes with a Proven or Highly Probable Arg304Gln Factor VII Mutation (FVII Padua)1): Only Limited Replacement Therapy is Needed in Case of Surgery

OBJECTIVE

To investigate the prevalence of thrombotic events among patients with proven or highly probable homozygosis for the Arg304Gln (Factor VII Padua) defect or compound heterozygosis containing the Arg304Gln mutation.

METHODS

Homozygotes and compound heterozygotes proven by molecular studies to have the Arg304Gln mutation were gathered from personal files and from two PubMed searches. In addition, patients with probable homozygosis on the basis of clotting tests (discrepancies among Factor VII activity levels according to the tissue thromboplastin used) were also gathered.

RESULTS

30 proven homozygotes and 17 probable ones were gathered together with 8 compound heterozygotes. In the latter use, the associated mutation was Cys135Arg (twice), Gly180Arg, Arg304Trp, Arg315Trp, His348Gln, Gly365Cys. The prevalence of venous thrombotic events was 16.6, 11.8 and 11.1 percent, respectively for the three groups of patients. Heterozygotes showed no thrombotic event. The difference for proven homozygotes was statistically significant, while for the other groups only a trend was present.

CONCLUSION

proven homozygous or compound heterozygous patients with the Arg304Gln mutation showed a higher than expected incidence of thrombotic events. The same is true for probable cases gathered only on the basis of clotting tests. These patients, because of their frequent lack of bleeding and for their relatively high prevalence of thrombosis should probably receive only limited replacement therapy in case of surgical procedures.

Identification of genetic defects underlying FVII deficiency in 10 patients belonging to eight unrelated families of the North provinces from Tunisia

Inherited factor VII (FVII) deficiency is a rare disorder characterized by a bleeding phenotype varying from mild to severe. To date, more than 200 mutations have been described along the F7 gene encoding for FVII. The aim of this study was the identification of genetic defects underlying FVII deficiency in 10 patients belonging to eight unrelated families of the North provinces from Tunisia. Mutation detection was performed by sequencing the whole F7 gene coding region, exon-intron boundaries and about 400 bp of the promoter region. We identified 5 mutations in five unrelated families; the novel p.F328Y mutation and the reported mutations: p.R304Q, p.M298I, IVS1aG > A and p.G-39G. For the remaining 5 patients we didn’t identified any mutations using PCR/Sequencing protocol. In conclusion, this study represents the first comprehensive molecular series of FVII deficiency affected patients in Tunisia from the North. We will try in the future to continue the molecular study for Tunisian patients from Center and South provinces in order to have a complete idea about the FVII deficiency mutational profile in our country.

Considerations on a tentative classification of FVII deficiency suited for practical clinical purposes

Adequate classifications of disorders are of paramount importance in the management of congenital bleeding disorders. Classification of congenital FVII deficiency should be simple, based on few tests using thromboplastins of different origin. The first thromboplastin to be used is a rabbit brain preparation since it has been proven that this is the one that, overall, yields the lowest activity level. This is particularly so since molecular biology techniques have supplied important information with regard to the structure-function relation but have failed to supply a satisfactory classification of the defect. Mutations in the same domain have yielded different forms of FVII deficiency. Furthermore, molecular biology techniques are time consuming and are not feasible in every laboratory. A classification of FVII deficiency based on clinical, clotting, and immunological assays is proposed. This classification is suited for practical clinical purposes and may represent a useful preparatory basis for molecular biology studies.

Historical perspective and future direction of coagulation research

Over the past 100 years, remarkable advances have been made in our understanding of the mechanisms of blood coagulation. Starting with the early clinical observations of rare patients with hereditary clotting disorders, our knowledge has increased in keeping pace with the introduction of new technologies: from simple laboratory tests to protein chemistry, to DNA technology, and to gene targeting technology. Advances in basic research have been successfully translated into improved methods for the diagnosis of bleeding disorders as well as thrombosis, and the development of recombinant clotting factors for replacement therapy in patients with haemophilia. New promising anticoagulants have also been developed for the treatment of thrombotic disorders. Based on the unique nature of blood coagulation research the close interactions and collaborations between basic scientists and clinicians have played a major role in these developments. It is anticipated that blood coagulation research will continue to play a leading role in promoting better care of the patients with bleeding disorders or thromboembolism.

Impaired secretion of carboxyl-terminal truncated factor VII due to an F7 nonsense mutation associated with FVII deficiency

INTRODUCTION

Factor VII (FVII) is a vitamin K-dependent glycoprotein secreted into the blood circulation from hepatic cells. We investigated the molecular basis of the congenital FVII deficiency found in a Japanese patient.

MATERIALS AND METHODS

We analyzed the F7 gene of the patient, who was diagnosed with a FVII deficiency at pregnancy. We expressed a carboxyl-terminal truncated FVII (Arg462X FVII) corresponding to the identified mutation in CHO-K1 cells. To study roles of the carboxyl-terminus in the secretion of FVII, we also expressed a series of recombinant FVIIs deleted of limited numbers of carboxyl-terminal amino acids (462Arg-466Pro).

RESULTS

We identified a nonsense mutation (c.1384C>T: p.Arg462X) in F7, leading to a lack of five amino acids in the carboxyl-terminus. In expression experiments, Arg462X FVII was undetectable not only by Western blotting, but also by ELISA. A Western blot analysis of the truncated FVIIs revealed that all mutants were expressed in the cells the same as the wild type, but were secreted into the culture medium in lesser amounts than the wild type depending on the length of the deletion, which was confirmed by ELISA. Arg462X FVII did not colocalize with the Golgi on immunofluorescence staining, suggesting that it might be retained in the ER and degraded in the cell.

CONCLUSION

The carboxyl-terminal amino acids of FVII play an important role in its secretion, and the p.Arg462X mutation was likely to have caused the FVII deficiency in this patient.

The influence of different glycosylation patterns on factor VII biological activity

In this study the bioactivity of three differently glycosylated blood coagulation factor VII (FVII) variants (human plasma FVII, recombinant human FVII produced in CHO and BHK cell cultures) were analyzed and compared. Surface plasmon resonance studies of FVII interaction with soluble and full length TF together with FVII autoactivation assays revealed that BHK-derived FVII has the highest bioactivity, while human plasma and CHO-derived FVII showed very similar bioactivity. The affinity of FVII variants to TF correlates with FVII autoactivation rates--the higher the affinity, the faster the autoactivation rate.

Mathematical modeling of blood coagulation cascade: kinetics of intrinsic and extrinsic pathways in normal and deficient conditions

A mathematical model has been developed to simulate the generation of thrombin through intrinsic and extrinsic pathways. The time course of clotting factor activation during coagulation was calculated, and the sensitivity of the kinetics due to a decrease or deficiency in the concentrations of coagulation proteins or their activities was studied. The model gives reasonable predictions without the adjustment of any parameter values. The calculated clotting time was approximately 44 s for the intrinsic pathway and approximately 8.6 s for the extrinsic pathway using normal protein concentrations in plasma. Various prolonged clotting times were observed in different factor-deficient disorders using this model.

Hemostasis as an optimal system

Zymogen and procofactor concentrations in physiological biochemical systems (PBS) have not yet been explained. The problem in question is to determine optimal plasma clotting factor (factors II, VII, IX, and X and cofactors V and VIII) concentrations for coagulation system (CS) as a whole. Constrained optimization technique is used to solve this problem. The constraint is determined by the ability of the CS to perform its physiological function--thrombin generation (and hence clot formation)--under vessel injury conditions. The constraint statement is based on the CS dynamics equations. In solving the problem the Lagrange multiplier is used. A hypothesis is advanced that this problem can be solved based on principle of minimum protein consumption subject to an above constraint. The results obtained indicate that the optimal clotting factor concentrations are in good agreement with those measured by biochemical techniques. A comparison between the theoretical results and experimental data lends support for our hypothesis that zymogen and procofactor concentrations in the CS (and, probably, for other biochemical systems) are determined by the principle of minimum protein consumption.

Allosteric regulation of the cofactor-dependent serine protease coagulation factor VIIa

The integration of structure and function analysis of the tissue factor-factor VIIa complex has provided a detailed view of the functional surface of the extrinsic activation complex. An incomplete zymogen to enzyme transition is responsible for the strict cofactor dependence of catalytic function of factor VIIa. The mutational analysis demonstrates that factor VIIa is allosterically regulated by specific conformational linkages that involve the cofactor binding site, the catalytic cleft, and the macromolecular substrate exosite. Regions of the flexible activation domain appear to play an important role in the allosteric regulation of this cofactor-dependent coagulation serine protease.

Molecular characterization of two novel mutations causing factor X deficiency in a Chinese pedigree

Factor X (FX) deficiency is a rare bleeding disorder inherited as an autosomal recessive trait. In this study, we investigated the molecular basis of FX deficiency in a Chinese pedigree. The proposita showed a markedly prolonged activated partial thromboplastin time and a mild prolongation of prothrombin time. The levels of FX antigen and FX activity were 58.6% and 2.5%, respectively. Molecular analysis revealed that the proposita was compound heterozygous for two novel mutations: IVS1 + 1G > A and G1185A (Arg347His). The aberrant transcripts from the IVS1 + 1G > A mutant allele were not detected by analyzing the splicing pattern of ectopic transcripts in leukocytes of the patient with nested polymerase chain reaction after reverse transcription. We thus hypothesize that the mRNA molecules originating from the IVS1 + 1G > A mutation were rapidly destroyed in vivo. Site-directed mutagenesis of FX cDNA was used to introduce FXG1185A mutation, and wild-type as well as mutant FX proteins were expressed by transient transfection in HEK 293 cells. Normal FX antigen levels both in the conditioned media of cells expressing the mutant and in cell lysates were detected by an enzyme-linked immunoadsorbent assay. Evaluation of wild-type and mutant coagulant activity demonstrated that the FX molecules carrying the Arg347His mutation have dramatically decreased activity.

The P303T mutation in the human factor VII (FVII) gene alters the conformational state of the enzyme and causes a severe functional deficiency

We report the results of in vitro expression and biochemical characterization of the naturally occurring type II mutation Pro303Thr (P303T) in the factor VII (FVII) gene. Recombinant activated mutated FVII (FVIIa303T), compared with the activated wild-type FVII (FVIIaWT), showed reduced amidase activity toward synthetic substrates, especially when the observed reduced binding affinity for human soluble tissue factor (TF) (K(d) from 4.4 nmol/l for FVIIaWT to 17.3 nmol/l for FVIIa303T) was overcome by a fully saturating TF concentration. Likewise, factor X (FX) hydrolysis by FVIIa303T showed a reduced activity in the absence (and more severely in the presence) of TF (k(cat)/K(m) from 2.3 x 10(7)/mol/l s for FVIIaWT to 8.7 x 10(5)/mol/l s for FVIIa303T). These results showed that the mutant FVIIa is more shifted toward a zymogen-like form compared to FVIIaWT, suggesting that P303 facilitates the conformational transitions that stabilize the active form of FVIIa. The alteration of these allosteric equilibria is especially evident in the presence of TF, which was unable to shift the equilibrium toward a fully active FVIIa form. Additional experiments showed that both TF-catalysed FVII303T autoactivation and FVII303T activation by activated FX in the presence of TF were severely impaired, mainly because of an increase of the K(m) value. Altogether, these defects may explain the severe bleeding symptoms in a patient carrying the FVIIP303T mutation.

Characterization of mutations causing factor VII deficiency in 61 unrelated Israeli patients

Inherited factor (F)VII deficiency is rare in most populations but relatively common in Israel. The aim of this study was to characterize the molecular and functional defect in unrelated Israeli patients with FVII deficiency. Mutations were identified by direct sequencing of PCR-amplified genomic DNA fragments. Selected mutations were expressed in baby hamster kidney (BHK) cells and tested for binding to tissue factor (TF), activation by FXa and activation of FX. In 61 patients with FVII deficiency, the causative mutation in the FVII gene was discerned. The predominant mutation found in this and a previously reported cohort of 27 unrelated patients in Israel was Ala244Val substitution; of 121 independent mutant alleles defined in all 88 patients ascertained in Israel, 102 (84%) bore this alteration. Eleven additional mutations were identified of which one, Cys22Arg, is novel. Expression of the mutations in BHK cells revealed that four (Ala244Val, 11128delC, Leu300Pro and Cys22Arg) were cross-reacting material (CRM)- negative, and three (Ala294Val, Cys310Phe and Phe24del) were CRM-positive. As predicted by modeling, we observed no binding to TF of FVII Phe24del, diminished binding of FVII Cys310Phe and normal binding of FVII Ala294Val. The main defect of FVII Ala294Val was its inability to activate FX in the presence of TF. Coexpression of Ala294Val and Arg353Gln, a polymorphism known to affect FVII secretion, did not reveal an additive effect on FVII secretion, while coexpression of Ala244Val and Arg353Gln did yield an additive effect.

The dynamics of thrombin formation

The central event of the hemostatic process is the generation of thrombin through the tissue factor pathway. This is a highly regulated, dynamic process in which thrombin itself plays many roles, positively and negatively its production and destruction. The hemostatic process is essential to normal physiology and is also the Achilles heel of our aging population. The inappropriate generation of thrombin may lead to vascular occlusion with the consequence of myocardial infarction, stroke, pulmonary embolism, or venous thrombosis. In this review, we summarize our present views regarding the tissue factor pathway by which thrombin is generated and the roles played by extrinsic and intrinsic factor Xa generating complexes in hemostasis and the roles of the stoichiometric and dynamic inhibitors that regulate thrombin generation.

Residues Y179 and H101 of a hydrophobic patch of factor VII are involved in activation by factor Xa

We studied factor Xa activation of human factor VII in hopes of identifying factor VII residues, not adjacent to the cleavage site, involved in this interaction. We made eight factor VIIs with single mutations (N100A, H101A, D102Q, L144A, R147A, Y179A, D186A, and F256A) and two factor VIIs with multiple mutations [MM3 (L144A/R147A/D186A) and MM4 (N100A/H101A/Y179A/F256A)]. Residues in MM3 have previously been identified as affecting factor X activation, and the residues of MM4 are located at a hydrophobic patch of factor VII on the opposite side of the catalytic domain from those in MM3. Only H101A, Y179A, and MM4 were activated significantly more slowly than the wild type. Results of our kinetic analyses showed that the catalytic efficiency of factor Xa for activation of factor VII was 176- and 234-fold higher than that for H101A andY179A, respectively. All the mutants with measurable activity had affinities for tissue factor similar to those of the wild type. The activated hydrophobic patch residues, except N100A, which is adjacent to one of the catalytic residues, had normal activities toward both a small peptide substrate and factor X. The rest of the activated mutants (except D102Q with no activity) had reduced activities toward the small substrate (except R147A) and factor X. We conclude that factor VII activation by factor Xa and factor VIIa's catalytic interaction with factor X involve different regions in the catalytic domain, and residues H101 and Y179, part of an aromatic hydrophobic patch, are specifically involved in factor Xa activation of factor VII.

Factor VIIa modified in the 170 loop shows enhanced catalytic activity but does not change the zymogen-like property

Factor VIIa (VIIa) is an unusual trypsin-type serine proteinase that appears to exist in an equilibrium between minor active and dominant zymogen-like inactive conformational states. The binding of tissue factor to VIIa is assumed to shift the equilibrium into the active state. The proteinase domain of VIIa contains a unique structure: a loop formed by a disulfide bond between Cys310 and Cys329, which is five residues longer than those of other trypsin types. To examine the functional role of the loop region, we prepared two mutants of VIIa. One of the mutants, named VII-11, had five extra corresponding residues 316-320 of VII deleted. The other mutant, VII-31, had all of the residues in its loop replaced with those of trypsin. Functional analysis of the two mutants showed that VIIa-11 (Kd = 41 nm) and VIIa-31 (Kd = 160 nm) had lower affinities for soluble tissue factor as compared with the wild-type VIIa (Kd = 11 nm). The magnitude of tissue factor-mediated acceleration of amidolytic activities of VIIa-11 (7-fold) and that of VIIa-31 (2-fold) were also smaller than that of wild-type VIIa (30-fold). In the absence of tissue factor, VIIa-31 but not VIIa-11 showed enhanced activity; the catalytic efficiencies of VIIa-31 toward various chromogenic substrates were 2-18-fold greater than those of the wild-type VIIa. Susceptibility of the alpha-amino group of Ile-153 of VIIa-31 to carbamylation was almost the same as that of wild-type VIIa, suggesting that VIIa-31 as well as wild-type VIIa exist predominantly in the zymogen-like state. Therefore, the tested modifications in the loop region had adverse effects on affinity for tissue factor, disturbed the tissue factor-induced conformational transition, and changed the catalytic efficiency of VIIa, but they did not affect the equilibrium between active and zymogen-like conformational states.

Factor VII deficiency and the FVII mutation database

Factor VII (FVII) is a zymogen for a vitamin K-dependent serine protease essential for the initiation of blood coagulation. It is synthesized primarily in the liver and circulates in plasma at a concentration of approximately 0.5 microg/ml (10 nmol/L). The FVII gene (F7) is located on chromosome 13 (13q34), consists of 9 exons, and spans approximately 12kb. It encodes a mature protein of 406 amino acids, which has an N-terminal domain (Gla) post-translationally modified by gamma-carboxylation of glutamic acid residues, two domains with homology to epidermal growth factor (EGF1 and 2), and a C-terminal serine protease domain. The single chain zymogen is activated by proteolytic cleavage at Arg152-Ile153. There are 238 individuals described in the world literature with mutations in their F7 genes (FVII mutation database; europium.csc. mrc.ac.uk). Complete absence of FVII activity in plasma is usually incompatible with life, and individuals die shortly after birth due to severe hemorrhage. The majority of individuals with mutations in their F7 gene(s), however, are either asymptomatic or the clinical phenotype is unknown. In general, a severe bleeding phenotype is only observed in individuals homozygous for a mutation in their F7 genes with FVII activities (FVII:C) below 2% of normal, however, a considerable proportion of individuals with a mild-moderate bleeding phenotype have similar FVII:C by in vitro assay. The failure of in vitro tests to differentiate between these groups may be due to lack of sensitivity in the assays to the very low amounts of FVII:C, which are sufficient to initiate coagulation in vivo. A number of polymorphisms have been identified in the F7 gene and some have been shown to influence plasma FVII antigen levels.

Role of residue Phe225 in the cofactor-mediated, allosteric regulation of the serine protease coagulation factor VIIa

Functional regulation by cofactors is fundamentally important for the highly ordered, consecutive activation of the coagulation cascade. The initiating protease of the coagulation system, factor VIIa (VIIa), retains zymogen-like features after proteolytic cleavage of the activating Arg(15)-Ile(16) peptide bond and requires the binding of the cofactor tissue factor (TF) to stabilize the protease domain in an active enzyme conformation. Structural comparison of TF-bound and free VIIa failed to provide a conclusive mechanism for this catalytic activation. This study provides novel insight into the cofactor-dependent regulation of VIIa by demonstrating that the side chain of Phe(225), an aromatic residue that is common to allosterically regulated serine proteases, is necessary for optimal TF-mediated activation of VIIa's catalytic function. However, mutation of Phe(225) did not abolish the cofactor-induced stabilization of the Ile(16)-Asp(194) salt bridge, previously considered the primary switch mechanism for activating VIIa. Moreover, mutation of other residue side chains in the VIIa protease domain resulted in a reduced level of or no stabilization of the amino-terminal insertion site upon TF binding, with little or no effect on the TF-mediated enhancement of catalysis. This study thus establishes a crucial role for the aromatic Phe(225) residue position in the allosteric network that transmits the activating switch from the cofactor interface to the catalytic cleft, providing insight into the highly specific conformational linkages that regulate serine protease function.

Functional consequences of mutations in Ser-52 and Ser-60 in human blood coagulation factor VII

Human blood coagulation factor VII has unique carbohydrate moieties O-glycosidically linked to serine 52 and serine 60 residues in its first epidermal growth factor-like domain. To study the functional role of these glycosyl moieties in factor VII, we constructed, expressed, and purified site-specific recombinant mutants of human factor VII in which serine 52 and serine 60 were conservatively replaced with alanine residues. S52A factor VIIa (Ser-52-->Ala), S60A factor VIIa (Ser-60-->Ala), and S52,60A factor VIIa (Ser-52, Ser-60-->Ala) exhibited 56, 73, and 44%, respectively, of the clotting activity of wild-type factor VIIa using human brain thromboplastin as a source of tissue factor/phospholipids and 32, 43, and 14% of wild-type factor VIIa using a mixture of recombinant soluble tissue factor and mixed brain phospholipids. The tissue factor-dependent and -independent amidolytic activities of these mutants were essentially indistinguishable from that of wild-type factor VIIa. In addition, equilibrium dialysis experiments indicated that the profiles of 45Ca2+ binding to these mutants were identical with that of wild-type factor VII. In the presence of either Ca2+ or EGTA, the Kd values for the interaction of the three factor VIIa mutants to full-length tissue factor were 2- to 5-fold higher than that of wild-type factor VIIa, while the Kd values for the interaction of these mutants to soluble tissue factor were 4- to 15-fold higher than that of wild-type factor VIIa. Measurement of the association and dissociation rate constants for factor VIIa binding to relipidated tissue factor apoprotein revealed that the association rate constants of the three factor VII mutants were decreased in comparison with that of wild-type factor VIIa, while the dissociation rate constants of these three mutants were virtually identical to that of wild-type factor VIIa. These findings strongly suggest that glycosyl moieties attached to Ser-52 and Ser-60 in factor VII/VIIa provide unique structural elements that are important for the rapid association of factor VII/VIIa with its cellular receptor and cofactor.

Coagulation factor VII Gln100 --> Arg. Amino acid substitution at the epidermal growth factor 2-protease domain interface results in severely reduced tissue factor binding and procoagulant function

We have used recombinant mammalian expression and purification of the factor VII (FVII) variant Gln100 --> Arg (Q100RFVII) to study FVII deficiency in subjects with this mutation. Q100RFVII was secreted poorly in comparison with wild-type FVII (WTFVII) in a stable mammalian expression system, and purified variant protein was found to have undetectable clotting activity. Following activation by immobilized factor Xa, Q100RFVIIa had amidolytic activity similar to WTFVIIa in the absence of soluble tissue factor (sTF); however, unlike WTFVIIa no typical increase in activity was seen after addition of sTF. In a factor X activation assay using relipidated transmembrane truncated tissue factor (residues 1-243), Q100RFVIIa showed less than 5% of the ability of WTFVIIa to activate factor X. We performed direct binding analysis of WT and Q100RFVII/FVIIa to immobilized sTF using surface plasmon resonance, and severely reduced binding of both non-activated and activated Q100RFVII to sTF was seen, indicating a pronounced defect in tissue factor (TF) interaction with this variant. In the sTF-FVIIa crystal structure the candidate residue Gln100 is not in contact with TF but is at the epidermal growth factor 2-protease domain interface. We suggest that the mutation results in a global fold change severely reducing tissue factor interaction; mutation of FVII residues not directly involved in the interaction with TF may still result in variant FVII unable to take part in the initiation of coagulation.

Mathematical model for the blood coagulation prothrombin time test

A mathematical model for the prothrombin time test is proposed. The time course of clotting factor activation during coagulation was calculated, and the sensitivity of the test to a decrease in the concentrations of coagulation proteins or their activities was studied. The model predicts that only severe coagulation disorders connected with a more than five-fold decrease in the concentrations or activities of the blood coagulation factors can be revealed by the test.

Characterization of transcriptional regulatory elements in the promoter region of the murine blood coagulation factor VII gene

To identify the 5' sequences of the murine coagulation factor VII (fVII) gene that resulted in its efficient transcription, a variety of 5'-flanking sequences up to 7 kilobase pairs upstream of the translation ATG initiation codon were fused to the reporter gene, bacterial chloramphenicol acetyltransferase, and relative expression levels of this gene in mouse Hepa 1-6 cells were determined. It was found that the 5' region extending approximately 85 base pairs (bp) upstream of the transcriptional initiation site served as the minimal DNA region that provided full relative promoter activity for chloramphenicol acetyltransferase expression. This region of the gene also contains consensus sequences for liver-enriched transcription factors, C/EBP beta and HNF4, as well as for the ubiquitous protein factors, AP1, H4TF1, NF1, and Sp1. In vitro DNase I footprinting of the 200-bp proximal region of the promoter with a murine Hepa 1-6 cell nuclear extract revealed a clear footprint of a region corresponding to -80 to -28 bp of the murine fVII gene, suggesting that liver factors interact with this region of the DNA. Competitive gel shift and supershift assays with different synthetic oligonucleotide probes demonstrate that proteins contained in the nuclear extract, identified as C/EBP beta, H4TF1, and HNF4, bind to a region of the murine fVII DNA from 85 to 32 bp upstream of the transcription start site. Purified Sp1 also interacts with this region of the DNA at a site that substantially overlaps, but is not identical to, the H4TF1 binding locus. Binding of Sp1 to the mouse DNA was not observed with the nuclear extract as the source of the transcription factors, suggesting that Sp1 is likely displaced from its binding site by H4TF1 in the crude extract. In vivo dimethyl sulfate footprint analysis confirmed the existence of these sites and additionally revealed two other binding regions slightly upstream of the CCAAT/enhancer-binding protein (C/EBP) binding locus that are homologous to NF1 binding sequences. The data demonstrate that appropriate transcription factor binding sites exist in the proximal promoter region of the murine fVII gene that are consistent with its strong liver-based expression in a highly regulated manner.

Conformation of factor VIIa stabilized by a labile disulfide bond (Cys-310-Cys-329) in the protease domain is essential for interaction with tissue factor

Unlike other trypsin-type serine proteases, zymogento-enzyme transition of conformation of factor VII apparently requires not only conversion of the zymogen to active form factor VIIa (VIIa) but also interaction of VIIa with tissue factor (TF). To determine the region of interaction that correlates with maturation of the VIIa active site, we modified intramolecular disulfide bonds in VIIa and examined the interaction of the modified VIIa with soluble TF (sTF). We found that partial reduction and S-carboxamidomethylation of disulfide bonds in VIIa led to losses of amidolytic activity and the binding ability to sTF. To determine the sites of modification that associate with the loss of functions, partially S-carboxamidomethylated VIIa was separated on a column of immobilized sTF. Each of the sTF-bound and sTF-unbound fractions and native VIIa was then digested by trypsin, and the digest was analyzed by reversed-phase high performance liquid chromatography. We found that reduction and S-carboxamidomethylation of a disulfide bond between Cys-310 and Cys-329 in the protease domain of VIIa led to loss of the binding ability with sTF, and the modification of a disulfide bond between Cys-340 and Cys-368 of VIIa led to loss of the amidolytic activity. In the three-dimensional structures of trypsinogen and trypsin, the disulfide bonds corresponding to Cys-340-Cys-368 and Cys-310-Cys-329 of VIIa are, respectively, in and adjacent to the activation domain, which has flexible conformation in trypsinogen but not in trypsin. Furthermore, the crystal structure of human VIIa.TF complex indicates that the region next to Cys-310-Cys-329 is in contact with sTF. We speculate that a regional flexibility, reflected by the labile nature of disulfide bonds of Cys-310-Cys-329 and Cys-340-Cys-368 in the protease domain, contributes to the inability of VIIa to attain the active conformation. Interaction of TF with this flexible region may stabilize the structure in a conformation similar to that of the active state of VIIa.

Identification of surface residues mediating tissue factor binding and catalytic function of the serine protease factor VIIa

Factor VIIa (VIIa), the serine protease that initiates the coagulation pathways, is catalytically activated upon binding to its cell surface receptor and cofactor tissue factor (TF). This study provides a comprehensive analysis of the functional surface of VIIa by alanine scanning mutagenesis of 112 residues. Residue side chains were defined which contribute to TF binding and factor X hydrolysis. Energetically important binding contacts at the interface with TF were identified in the first epidermal growth factor domain of VIIa (Gln-64, Ile-69, Phe-71, Arg-79) and in the protease domain (Arg-277, Met-306, Asp-309). The observed energetic defects are in good agreement with the corresponding residues in TF, suggesting that the VIIa light chain plays a prominent role in high affinity binding of cofactor. Mutation of protease domain interface residues indicated that TF allosterically influences the active site of VIIa. Stabilization of a labile zymogen to enzyme transition could explain the activating effect of TF on VIIa catalytic function. Residues important for factor X hydrolysis were found in three regions of the protease domain: (i) specificity determinants in the catalytic cleft and adjacent loops, (ii) an exosite near the TF binding site, and (iii) a large electronegative exosite which is in a position analogous to the basic exosite I of thrombin. TF regions involved in factor X activation are positioned on the same face of the TF-VIIa complex as the two exosites identified on the protease domain surface, providing evidence for an extended interaction of TF-VIIa with macromolecular substrate.

Factor VII central. A novel mutation in the catalytic domain that reduces tissue factor binding, impairs activation by factor Xa, and abolishes amidolytic and coagulant activity

Factor VII is a vitamin K-dependent zymogen of a serine protease that participates in the initial phase of blood coagulation. A factor VII molecular variant (factor VII Central) was identified in a 24-year-old male with severe factor VII deficiency and whose plasma factor VII antigen was 38% of normal, but expressed <1% factor VII procoagulant activity. DNA sequence analysis of the patient's factor VII gene revealed a thymidine to cytidine transition at nucleotide 10907 in exon VIII that results in a novel amino acid substitution of Phe328 to Ser. The patient was homozygous for this mutation, whereas each parent of the patient was heterozygous for this mutation. To investigate the molecular properties of this variant, a recombinant F328S factor VII mutant was prepared and analyzed in relation to wild-type factor VII. F328S factor VII exhibited <1% factor VII procoagulant activity and a 2-fold decreased affinity for tissue factor and failed to activate factor X or IX in the presence of tissue factor following activation by factor Xa. In addition, F328S factor VIIa exhibited no detectable amidolytic activity in the presence of tissue factor. The rate of F328S factor VII activation by factor Xa was markedly decreased relative to the rate of wild-type factor VII activation as revealed by densitometry scanning of SDS gels. Temporal analysis of this reaction by SDS-polyacrylamide gel electrophoresis also revealed the formation of two novel F328S factor VII degradation products (40 and 9 kDa) resulting from factor Xa proteolysis of the Arg315-Lys316 peptide bond in intact F328S factor VII. Computer modeling and molecular dynamics simulations of the serine protease domain of factor VIIa suggested that the inability of F328S factor VIIa to cleave substrates may result from the apparent formation of a hydrogen bond between Tyr377 and Asp338, a residue at the bottom of the substrate-binding pocket important for the interaction of substrate arginine side chains with the enzyme. These findings suggest that Phe328, which is conserved in prothrombin, factor IX, factor X, factor VII, and trypsin, is important for factor VIIa catalysis.

Molecular mechanism of tissue factor-mediated acceleration of factor VIIa activity

The mechanism of the acceleration of the catalytic activity of factor VIIa (VIIa) in the presence of tissue factor (TF) was investigated. To explore the VIIa's site(s) that correlates with TF-mediated acceleration, zymogen VII, VIIa, and active site-modified VIIa were prepared, and dissociation constants (Kd) for their bindings to TF or soluble TF in solution were determined. We found that conversion of zymogen VII to VIIa led to an increase in affinity (DeltaDeltaG = 4.3-4.4 kJ/mol) for TFs. Dansyl-Glu-Gly-Arg chloromethyl ketone (DNS-EGRck) treatment of VIIa led to a further increase in the affinity (DeltaDeltaG = 7.3-12 kJ/mol). Neither removal of the Gla domain from VIIa nor truncation of the COOH-terminal membrane and cytoplasmic regions of TF affected the affinity enhanced after DNS-EGRck treatment of VIIa. Treatment of VIIa with (p-amidinophenyl)methanesulfonyl fluoride also enhanced its affinity for soluble TF, whereas treatment with 4-(2-aminoethyl)benzenesulfonyl fluoride, phenylmethylsulfonyl fluoride, or diisopropyl fluorophosphate had a slight effect on the affinity. On the other hand, DNS-EGRck and (p-amidinophenyl)methanesulfonyl fluoride treatments, but not diisopropyl fluorophosphate treatment, of VIIa led to protection of its alpha-amino group of Ile-153 from carbamylation. Protection of the alpha-amino group was consistent with formation of a critical salt bridge between Ile-153 and Asp-343 in the protease domain of VIIa. Therefore, TF may preferentially bind to the active conformational state of VIIa. When one assumes that free VIIa exists in equilibrium between minor active and dominant zymogen-like inactive conformational states, preferential binding of TF to the active state leads to a shift in equilibrium. We speculate that TF traps the active conformational state of VIIa and converts its zymogen-like state into an active state, thereby accelerating the VIIa activity.

Activation of a recombinant human factor VII structural analogue alters its affinity of binding to tissue factor

A competitive enzyme-linked immunoadsorbent assay (ELISA) technique has been developed to facilitate quantitative analysis of the earliest step in the initiation of the extrinsic pathway of coagulation, i.e., complex formation of factor VII/VIIa with tissue factor. The ELISA measures the binding of biotinylated human plasma factor VII to relipidated recombinant human tissue factor. Quantitation of the relative affinity (expressed as IC50) of any factor VII molecular population or structural analogue for tissue factor can be determined by competitive binding. Subnanomolar concentrations of both wild-type recombinant human factor VII (rFVII) and rFVII(R152Q), a mutation at the FVII activation site, competed effectively with biotinylated plasma-derived factor VII in binding to tissue factor. In contrast, the affinity of rFVII(R79Q), a mutation in the first epidermal growth factor-like domain, was 12-fold lower. Following activation of rFVII(R79Q), its affinity for tissue factor and enzymatic activity increased 4-fold and 6-fold, respectively. For wild-type rFVII, enzymatic activity rose significantly following activation. However, its affinity for tissue factor was unchanged. We conclude that both the activation state of factor VII and the mutation of amino-acid residues within the first epidermal growth factor-like domain may alter the affinity of factor VII for tissue factor.

Kinetics of human factor VII activation

In this study the activation of human factor VII by a variety of potential activators in the presence and absence of mixed phospholipid vesicles [25% phosphatidylserine (PS), 75% phosphatidylcholine (PC)] is evaluated. At the plasma concentration of factor VII, 10 nM, the activation rate of the zymogen by 0.05 nM factor Xa is anionic phospholipid (PCPS) dependent and achieves a maximum value of 18 pM/s at 5-20 microM PCPS; further increases in the levels of PCPS decrease the activation rate of factor VII. The maximum activation rate of factor VII (10 nM) by the factor VIIa-tissue factor complex (0.1 nM), 0.76 pM/s, is achieved at 200 microM PCPS. No detectable activation of 10 nM factor VII is observed under similar conditions when either thrombin (0.1 nM) or factor IXa (0.1 nM) is used as an activator. Factor VIIa (10 nM) and factor XIa (1 nM) are not observed to activate factor VII at detectable rates. The observed Michaelis-Menten constants (KM) for factor VII activation in the presence of PCPS at optimal concentrations vary from 1.2 microM for factor Xa to 3.2 microM for the factor VIIa-tissue factor complex. The highest catalytic constant (kcat) value (15.2 s-1) is observed for factor Xa-PCPS. The factor VIIa-tissue factor complex, factor IXa, and thrombin kcat values are 1.4, 0.32, and 0.061 s-1, respectively. Tissue factor does not increase the factor VII activation rate by factor Xa, factor IXa, or thrombin. Factor VIIIa in the presence of PCPS has no effect on factor VII activation by factor IXa. In contrast, factor Va decreases the factor VII activation rate by factor Xa, reaching saturation at concentrations consistent with complete prothrombinase complex formation. The formed prothrombinase complex activates factor VII at approximately 30% the rate of factor Xa bound to phospholipids. These data allow us to conclude that the predominant physiological factor VII activator is, most likely, membrane-bound factor Xa.

The roles of factor VII's structural domains in tissue factor binding

Factor VIIa binds to tissue factor in one of the initial steps of blood clotting. In order to determine the role of the various domains of the factor VII molecule in this interaction, we made several chimeric factor VII proteins using recombinant DNA techniques. The molecules have factor IX domains substituted into factor VII and vice versa. The domains exchanged were the 4-carboxyglutamic acid plus aromatic stack domain (gla), the first epidermal growth factor-like domain (Egf-1), the second epidermal growth factor-like domain (Egf-2), and the catalytic domain. Using tissue factor-coated microtiter wells, competition binding studies with 125I-labeled factor VIIa indicated factor VIIa's Kd is 4.2 nM. Employing the same microtiter plate assay, koff and kon were determined and yielded a Kd of 1.5 nM. The results of competitive binding experiments and activation assays using chimeric proteins indicated the interaction between factor VIIa and tissue factor involves direct contact between tissue factor and factor VIIa's Egf-1 domain and catalytic domain. On the other hand, the gla and Egf-2 domains, while necessary for optimal binding, may merely impart structure to the rest of the molecule. However, either one or both of the latter domains might contribute a relatively small amount of energy to direct binding.

Localization of an epitope of a calcium-dependent monoclonal antibody to the N-terminal region of the Gla domain of human factor VII

The epitope of a calcium-dependent murine monoclonal antibody specific for human factor VII (Thim et.al., Biochemistry (1988) 27, 7785-7793) has been determined. Site-directed mutagenesis of residues 3 through 10 of factor VII eliminates the binding of this antibody but does not disturb the binding of a second antibody which binds nearby.