Design and construction of a phage-displayed Camelid nanobody library using a simple bioinformatics method

BACKGROUND

Rational design of synthetic phage-displayed libraries requires the identification of the most appropriate positions for randomization using defined amino acid sets to recapitulate the natural occurrence. The present study uses position-specific scoring matrixes (PSSMs) for identifying and randomizing Camelidae nanobody (VHH) CDR3. The functionality of a synthetic VHH repertoire designed by this method was tested for discovering new VHH binders to recombinant coagulation factor VII (rfVII).

METHODS

Based on PSSM analysis, the CDR3 of cAbBCII10 VHH framework was identified, and a set of amino acids for the substitution of each PSSM-CDR3 position was defined. Using the Rosetta design SwiftLib tool, the final repertoire was back-translated to a degenerate nucleotide sequence. A synthetic phage-displayed library was constructed based on this repertoire and screened for anti-rfVII binders.

RESULTS

A synthetic phage-displayed VHH library with 1 × 108 variants was constructed. Three VHH binders to rfVII were isolated from this library with estimated dissociation constants (KD) of 1 × 10-8 M, 5.8 × 10-8 M and 2.6 × 10-7 M.

CONCLUSION

PSSM analysis is a simple and efficient way to design synthetic phage-displayed libraries.

Extracellular vesicles from amniotic fluid, milk, saliva, and urine expose complexes of tissue factor and activated factor VII

BACKGROUND

Tissue factor (TF) is expressed in the adventitia of the vessel wall and on extracellular vesicles (EVs) in body fluids. TF and activated coagulation factor (F) VII(a) together form the so-called extrinsic tenase complex, which initiates coagulation.

AIM

We investigated whether EVs in amniotic fluid, milk, saliva, and urine expose functional extrinsic tenase complexes that can trigger coagulation.

METHODS

Milk, saliva, and urine were collected from healthy breastfeeding women (n = 6), and amniotic fluid was collected from healthy women undergoing routine amniocentesis (n = 7). EVs were isolated from body fluids by size exclusion chromatography (SEC) and clotting experiments were performed in the presence and absence of antibodies against TF and FVIIa in normal plasma and in FVII-deficient plasma. The ability of body fluids to generate FXa also was determined.

RESULTS

Amniotic fluid, milk, saliva, and urine triggered clotting of normal plasma and of FVII-deficient plasma, which was almost completely inhibited by an anti-FVII antibody and to a lesser extent by an anti-TF antibody. Fractionation of body fluids by SEC showed that only the fractions containing EVs triggered clotting in normal plasma and FVII-deficient plasma and generated FXa, which again was almost completely inhibited by an anti-FVII antibody and partially by an anti-TF antibody.

CONCLUSION

Here we show that EVs from amniotic fluid, milk, saliva, and urine expose complexes of TF and FVIIa (i.e., extrinsic tenase complexes) that directly activate FX. Based on our present findings we propose that these EVs from normal body fluids provide hemostatic protection.

Molecular View into Preferential Binding of the Factor VII Gla Domain to Phosphatidic Acid

Factor VII (FVII) is a serine protease with a key role in initiating the coagulation cascade. It is part of a family of vitamin K-dependent clotting proteins, which require vitamin K for formation of their specialized membrane-binding domains (Gla domains). Membrane binding of the FVII Gla domain is critical to the activity of FVII, mediating the formation of its complex with other clotting factors. While Gla domains among coagulation factors are highly conserved in terms of amino acid sequence and structure, they demonstrate differential binding specificity toward anionic lipids. Although most Gla domain-containing clotting proteins display a strong preference for phosphatidylserine (PS), it has been demonstrated that FVII and protein C instead bind preferentially to phosphatidic acid (PA). We have developed the first model of the FVII Gla domain bound to PA lipids in membranes containing PA, the highly mobile membrane mimetic model, which accelerates slow diffusion of lipids in molecular dynamics simulations and therefore facilitates the membrane binding process and enhances sampling of lipid interactions. Simulations were performed using atomic level molecular dynamics, requiring a fixed charge to all atoms. The overall charge assigned to each PA lipid for this study was -1. We also developed an additional model of the FVII Gla domain bound to a 1:1 PS/PC membrane and compared the modes of binding of PS and PA lipids to FVII, allowing us to identify potential PA-specific binding sites.

Identification of two novel mutations in three children with congenital factor VII deficiency

Congenital factor VII deficiency (FVIID) is a rare F7 gene mutation causing bleeding disorder inherited in an autosomal recessive manner. In this study, we aimed to identify genetic defects and analyze their relationships with phenotype in three Chinese FVIID patients. The diagnosis of FVIID was made based on FVII coagulant activity (FVII:C) levels assessed through prothrombin time assay. Direct sequencing and protein modeling were performed to detect genetic mutations and the resulting protein expression. Patient 1, a 2-year-old girl, presented with mild bleeding and was found to have a FVII:C of 0.2% and a compound heterozygous F7 Cys389Gly/Cys115Arg mutation. Patient 2, a 7-year-old boy, consulted for moderate bleeding and was found to have a FVII:C of 0.8% and a compound heterozygous F7 Thr241Asn/Pro324Leu mutation. Patient 3, a 5-year-old boy who developed a mild bleeding after trauma was found to have a FVII:C of 1.8% and a compound heterozygous F7 Thr241Asn/ IVS5-2A>G mutation. We hereby report three congenital FVIID patients with FVII:C less than 2% and their respective F7 mutations, two of which (F7 Cys115Arg, Pro324Leu) are novel. The molecular model analysis of the two novel mutations F7 Cys115Arg and Pro324Leu respectively indicated impairment of the proper folding of epidermal growth factor 1 domain situated on F7 gene and impairment of the procoagulant function of FVII both leading to the congenital deficiency of FVII.

Conformational Plasticity-Rigidity Axis of the Coagulation Factor VII Zymogen Elucidated by Atomistic Simulations of the N-Terminally Truncated Factor VIIa Protease Domain

The vast majority of coagulation factor VII (FVII), a trypsin-like protease, circulates as the inactive zymogen. Activated FVII (FVIIa) is formed upon proteolytic activation of FVII, where it remains in a zymogen-like state and it is fully activated only when bound to tissue factor (TF). The catalytic domains of trypsin-like proteases adopt strikingly similar structures in their fully active forms. However, the dynamics and structures of the available corresponding zymogens reveal remarkable conformational plasticity of the protease domain prior to activation in many cases. Exactly how ligands and cofactors modulate the conformational dynamics and function of these proteases is not entirely understood. Here, we employ atomistic simulations of FVIIa (and variants hereof, including a TF-independent variant and N-terminally truncated variants) to provide fundamental insights with atomistic resolution into the plasticity-rigidity interplay of the protease domain conformations that appears to govern the functional response to proteolytic and allosteric activation. We argue that these findings are relevant to the FVII zymogen, whose structure has remained elusive despite substantial efforts. Our results shed light on the nature of FVII and demonstrate how conformational dynamics has played a crucial role in the evolutionary adaptation of regulatory mechanisms that were not present in the ancestral trypsin. Exploiting this knowledge could lead to engineering of protease variants for use as next-generation hemostatic therapeutics.

A novel gene mutation in the 60s loop of human coagulation factor VII – inhibition of interdomain crosstalk

A novel mutation in the factor VII gene resulting in procoagulant activity of 7.5% and antigen levels of 23% is presented. Single-stranded conformational polymorphism and DNA sequencing analysis revealed heterozygous shifts, and mutations were detected in exons 5, 7 and 8. The mutant L204P in exon 7 was novel, while the common polymorphisms, H115H and R353Q, were located in exons 5 and 8, respectively.The molecular effect of the L204P mutation was characterized using recombinant mammalian expression in Chinese hamster ovary cells. Low levels (4 ng/ml) of secreted mutant protein were found in transiently transfected cells compared to wild-type factor VII (83 ng/ml). Metabolic labeling demonstrated that the rate of mutant protein synthesis was similar to that of wild-type FVII, and the mutant protein accumulated intracellularly with no signs of increased degradation during a four-hour chase. No interaction between secreted P204 protein and immobilized soluble tissue factor was detected using surface plasmon resonance. The activation rate of recombinant mutant FVII protein was strongly reduced compared to wild-type FVII. A 9-fold reduction in the rate of FX activation was detected whereas Km was nearly the same for wild-type and the mutant. This slow rate was caused by a correspondingly lowered rate of P204 activation. A synthetic peptide sequence comprising amino acids 177−206 blocked binding of FVIIa to the TF-chip, and the subsequent factor X activation with an IC50 value of 0.5 μM in a chromogenic factor Xa assay. Additionally, evaluation of the peptide by surface plasmon resonance analysis resulted in inhibition of complex formation with an apparent Ki of 7 μM.

A novel protein C-factor VII chimera provides new insights into the structural requirements for cytoprotective protease-activated receptor 1 signaling

Essentials The basis of cytoprotective protease-activated receptor 1 (PAR1) signaling is not fully understood. Activated protein C chimera (APCFVII-82 ) was used to identify requirements for PAR1 signaling. APCFVII-82 did not initiate PAR1 signaling, but conferred monocyte anti-inflammatory activity. APC-specific light chain residues are required for cytoprotective PAR1 signaling.

SUMMARY

Background Activated protein C (APC) cell signaling is largely reliant upon its ability to mediate protease-activated receptor (PAR) 1 proteolysis when bound to the endothelial cell (EC) protein C (PC) receptor (EPCR). Furthermore, EPCR-bound PC modulates PAR1 signaling by thrombin to induce APC-like EC cytoprotection. Objective The molecular determinants of EPCR-dependent cytoprotective PAR1 signaling remain poorly defined. To address this, a PC-factor VII chimera (PCFVII-82 ) possessing FVII N-terminal domains and conserved EPCR binding was characterized. Methods Activated PC-FVII chimera (APCFVII-82 ) anticoagulant activity was measured with calibrated automated thrombography and activated FV degradation assays. APCFVII-82 signaling activity was characterized by the use of reporter assays of PAR1 proteolysis and EC barrier integrity. APCFVII-82 anti-inflammatory activity was assessed according to its inhibition of nuclear factor-κB (NF-κB) activation and cytokine secretion from monocytes. Results PCFVII-82 was activated normally by thrombin on ECs, but was unable to inhibit plasma thrombin generation. Surprisingly, APCFVII-82 did not mediate EPCR-dependent PAR1 proteolysis, confer PAR1-dependent protection of thrombin-induced EC barrier disruption, or limit PAR1-dependent attenuation of interleukin-6 release from lipopolysaccharide (LPS)-stimulated macrophages. Interestingly, EPCR occupation by active site-blocked APCFVII-82 was, like FVII, unable to mimic EC barrier stabilization induced by PC upon PAR1 proteolysis by thrombin. APCFVII-82 did, however, diminish LPS-induced NF-κB activation and tumor necrosis factor-α release from monocytes in an apolipoprotein E receptor 2-dependent manner, with similar efficacy as wild-type APC. Conclusions These findings identify a novel role for APC light chain amino acid residues outside the EPCR-binding site in enabling cytoprotective PAR1 signaling.

One amino acid in mouse activated factor VII defines its endothelial protein C receptor (EPCR) binding and modulates its EPCR-dependent hemostatic activity in vivo

Essentials The lack of factor (F) VIIa-endothelial protein C receptor (EPCR) binding in mice is unresolved. A single substitution of Leu4 to Phe in mouse FVIIa (mFVIIa) enables its interaction with EPCR. mFVIIa with a Phe4 shows EPCR binding-dependent enhanced hemostatic function in vivo vs. mFVIIa. Defining the FVIIa-EPCR interaction in mice allows for further investigating its biology in vivo.

SUMMARY

Background Human activated factor VII (hFVIIa), which is used in hemophilia treatment, binds to the endothelial protein C (PC) receptor (EPCR) with unclear hemostatic consequences. Interestingly, mice lack the activated FVII (FVIIa)-EPCR interaction. Therefore, to investigate the hemostatic consequences of this interaction in hemophilia, we previously engineered a mouse FVIIa (mFVIIa) molecule that bound mouse EPCR (mEPCR) by using three substitutions from mouse PC (mPC), i.e. Leu4→Phe, Leu8→Met, and Trp9→Arg. The resulting molecule, mFVIIa-FMR, modeled the EPCR-binding properties of hFVIIa and showed enhanced hemostatic capacity in hemophilic mice versus mFVIIa. These data implied a role of EPCR in the action of hFVIIa in hemophilia treatment. However, the substitutions in mFVIIa-FMR only broadly defined the sequence determinants for its mEPCR interaction and enhanced function in vivo. Objectives To determine the individual contributions of mPC Phe4, Met8 and Arg9 to the in vitro/in vivo properties of mFVIIa-FMR. Methods The mEPCR-binding properties of single amino acid variants of mFVIIa or mPC at position 4, 8 or 9 were investigated. Results and conclusions Phe4 in mFVIIa or mPC was solely critical for interaction with mEPCR. In hemophilic mice, administration of mFVIIa harboring a Phe4 resulted in a 1.9-2.5-fold increased hemostatic capacity versus mFVIIa that was EPCR binding-dependent. This recapitulated previous observations made with triple-mutant mFVIIa-FMR. As Leu8 is crucial for hFVIIa-EPCR binding, we describe the sequence divergence of this interaction in mice, now allowing its further characterization in vivo. We also illustrate that modulation of the EPCR-FVIIa interaction may lead to improved FVIIa therapeutics.

Monitoring of treatment with vitamin K antagonists: recombinant thromboplastins are more sensitive to factor VII than tissue-extract thromboplastins

Essentials Differences in sensitivity to factor VII (FVII) have been suggested between thromboplastins. FVII-induced International Normalized Ratio (INR) changes differ between commercial reagents. Recombinant human thromboplastins are more sensitive to FVII than tissue-extract thromboplastins. Thromboplastin choice may affect FVII-mediated INR stability.

SUMMARY

Background Differences regarding sensitivity to factor VII have been suggested for recombinant human and tissue-extract thromboplastins used for International Normalized Ratio (INR) measurement, but the evidence is scarce. Differences in FVII sensitivity are clinically relevant, as they can affect INR stability during treatment with vitamin K antagonists (VKAs). Objectives To determine whether commercial thromboplastins react differently to changes in FVII. Methods We studied the effect of addition of FVII on the INR in plasma by using three tissue-extract (Neoplastin C1+, Hepato Quick, and Thromborel S) and three recombinant human (Recombiplastin 2G, Innovin, and CoaguChek XS) thromboplastins. Three different concentrations of purified human FVII (0.006, 0.012 and 0.062 μg mL-1 plasma), or buffer, were added to five certified pooled plasmas of patients using VKAs (INR of 1.5-3.5). Changes in FVII activity were measured with two bioassays (Neoplastin and Recombiplastin), and relative INR changes were compared between reagents. Results After addition of 0.062 μg mL-1 FVII, FVII activity in the pooled plasmas increased by approximately 20% (Neoplastin) or 32% (Recombiplastin) relative to the activity in pooled normal plasma. All thromboplastins showed dose-dependent INR decreases. The relative INR change in the pooled plasmas significantly differed between the six thromboplastins. No differences were observed among recombinant or tissue-extract thromboplastins. Pooled results indicated that the FVII-induced INR change was greater for recombinant than for tissue-extract thromboplastins. Conclusions Differences regarding FVII sensitivity exist between various thromboplastins used for VKA monitoring. Recombinant human thromboplastins are more sensitive to FVII than tissue-extract thromboplastins. Therefore, thromboplastin choice may affect FVII-mediated INR stability.

Exploration of conformational transition in the aryl-binding site of human FXa using molecular dynamics simulations

Human coagulation Factor X (FX), a member of the vitamin K-dependent serine protease family, is a crucial component of the human coagulation cascade. Activated FX (FXa) participates in forming the prothrombinase complex on activated platelets to convert prothrombin to thrombin in coagulation reactions. In the current study, 30-ns MD simulations were performed on both the open and closed states of human FXa. Root mean squares (RMS) fluctuations showed that structural fluctuations concentrated on the loop regions of FXa, and the presence of a ligand in the closed system resulted in larger fluctuations of the gating residues. The open system had a gating distance from 9.23 to 11.33 Å, i.e., significantly larger than that of the closed system (4.69-6.35 Å), which allows diversified substrates of variable size to enter. Although the solvent accessible surface areas (SASA) of FXa remained the same in both systems, the open system generally had a larger total SASA or hydrophobic SASA (or both) for residues surrounding the S4 pocket. Additionally, more hydrogen bonds were formed in the closed state than in the open state of FXa, which is believed to play a significant role in maintaining the closed confirmation of the aryl-binding site. Based on the results of MD simulations, we propose that an induced-fit mechanism governs the functioning of human coagulation FX, which helps provide a better understanding of the interactions between FXa and its substrate, and the mechanism of the conformational changes involved in human coagulation.

EGFP-EGF1 protein-conjugated PEG-PLA nanoparticles for tissue factor targeted drug delivery

In a strategy for anti-thrombotic therapy, we have expressed EGFP-EGF1 fusion protein, in which EGF1 can bind with tissue factor (TF). EGFP has previously been widely used as a fluorescent protein marker. EGFP-EGF1 protein was thiolated and conjugated to the malemide covering on the pegylated nanoparticles (NP) to form the EGFP-EGF1-NP. The EGFP-EGF1-NP was characterized in terms of morphology, size and zeta potential. In vitro cell viability experiment confirmed that the biodegradable EGFP-EGF1-NP was safe. To evaluate the delivering ability of EGFP-EGF1-NP, a fluorochrome dye, Dir, was incorporated into the nanoparticle, and the loading capacity and release property of the particle were examined. In vitro results showed that the binding ability of EGFP-EGF1-NP with TF-expressing cells was significantly stronger than that of non-conjugated NP. In vivo multispectral fluorescent imaging demonstrated that EGFP-EGF1-NP had high specificity and sensitivity in targeting thrombi. Our study demonstrated that EGFP-EGF1-NP is a promising TF-targeting drug delivery system for thrombolytic treatment.

Calibration of human coagulation factor VII concentrate Ph. Eur. BRP batch 2

The potency assay of human coagulation factor VII concentrate preparations as described in the European Pharmacopoeia (Ph. Eur.) requires a reference preparation calibrated in International Units (IU). The current Ph. Eur. Biological Reference Preparation (BRP) batch 1 was established in 2005 during an international collaborative study. It has an assigned potency of 8.2 IU/vial for the chromogenic assay method. Stocks of this BRP are dwindling and a replacement batch needs to be established. A candidate material was produced by a manufacturer from a plasma-derived concentrate preparation, with the same formulation and approximately the same potency, in the interest of continuity. The candidate material fulfilled the requirements of a BRP with regard to precision and homogeneity of fill, residual water content and stability. The potency of the candidate BRP (cBRP) was determined using chromogenic assays as required by the Ph. Eur. and in-house clotting assays in an attempt to assign a potency for both methods, as is the case for the current batch. The statistical model used for most laboratories was the maximum likelihood of the parallel line model using a logarithmic transformation of the responses. In the chromogenic assay, a potency of 9.9 IU/vial (+/- 1.8 %) was obtained for the cBRP with a very good consistency between laboratories. The results from the clotting assay, however, were less homogenous and yielded consistently higher results (13 IU/vial +/- 12 %), probably due to a higher activated factor VII (FVIIa) content than in the current BRP (3 % as compared to 0.3 %). Due to the large difference between the values obtained with the 2 different methods, it was not possible to reconcile the outcomes with each other. On the other hand, the uncertainty observed with the clotting assay method was quite large and seemed questionable for a reference preparation. Therefore the use of BRP batch 2 as a reference for the clotting assay method is not recommended. Nevertheless, the results of the study showed that the candidate BRP (cBRP) is suitable as a reference standard for the chromogenic assay according to the Ph. Eur. general chapter 2.7.10 Assay of human coagulation factor VII. It was adopted by the Ph. Eur. Commission in December 2009 as an official Ph. Eur. BRP for human coagulation factor VII concentrate with an assigned potency of 9.9 IU/vial.

Molecular mechanism of dysfunctional factor VII associated with the homozygous missense mutation 331Gly to Ser

We have identified a Japanese homozygous FVII deficiency associated with the mutation G331S (c184 [in chymotrypsin numbering]), and have determined the mechanisms responsible for the dysfunctional FVII variant by expressing the mutant recombinant FVII protein. In addition, the recombinant proteins FVIIG331D, G331W and G331F were expressed. The purified recombinant FVII proteins ran as a single chain form on SDS-PAGE having a molecular mass of approximately 50 Kda. The recombinant FVIIG331S expressed the level of the recombinant wild type FVII at 2.0%, and this mutant form was also similar to FVII in the patient's plasma. However, the amidolytic activity of FVIIa using peptidyl substrate S-2288 differed little between the wild type and the four mutant FVII molecules. We suggest that the functional defect found in these mutants is not directly associated with peptidyl substrate recognition or catalysis. The Km values of FX and FIX for the mutant proteins were approximately 7.6- to 15-fold and 13- to 19-fold higher than those for the wild-type protein, respectively. Molecular modelling indicated that the side chain of the S331 mutant is oriented close to the side chain of D338 (c189) at the bottom of the specificity pocket of FVIIa. We show that the replacement of G331 with a serine likely results in a steric hindrance of macromolecular substrate binding, leading to a loss of FVIIa enzymatic activity.

Procoagulant activities of plasma factor VIIc and factor Xc are positively and independently associated with concentrations of the high-density lipoprotein apolipoprotein, apo A-II

The pro- and antiatherogenic roles of apolipoproteins B and A-I, respectively, are well-established although the importance of apolipoprotein A-II remains unclear. There is extensive evidence for the involvement of plasma lipoproteins in haemostatic function. However, in-vivo studies of relationships between haemostatic variables and apolipoprotein concentrations are very limited. Plasma fibrinogen, factors VIIc and Xc (FVIIc and FXc, respectively), apolipoproteins (apo) A-I, A-II and B, triglycerides, total, low-density and high-density lipoprotein (HDL) cholesterol, and cholesterol in HDL subfractions 2 and 3 were measured in 186 apparently healthy Caucasian men (aged 26-78 years; body mass index 19.9-37.8 kg/m(2)). Associations between haemostatic, apolipoprotein, lipid and lipoprotein variables were explored in uni- and multivariable analyses. Fibrinogen did not correlate with any of the lipid-related variables. FVIIc and FXc were significant positive univariate correlates of total cholesterol (correlation coefficients 0.26, p<0.001 and 0.19, p<0.05, respectively) triglycerides (0.37, p<0.001 and 0.36, p<0.001), and apoB (0.21, p<0.01 and 0.17, p<0.05) and apoA-II (0.19, p<0.05 and 0.29, p<0.001). HDL(2) subfraction cholesterol correlated negatively with FVIIc and FXc (-0.20, p<0.01 and -0.22, p<0.01, respectively). In multivariable analysis, only the associations of FVIIc and FXc with total cholesterol, triglycerides and apoA-II remained statistically significant. In conclusion, total cholesterol and triglycerides were the major independent lipid correlates of FVIIc and FXc. The independent and positive associations of apoA-II with FVIIc and FXc suggest a prothrombotic involvement for this apolipoprotein.

Fetal corticotrophin-releasing hormone mRNA, but not phosphatidylserine-exposing microparticles, in maternal plasma are associated with factor VII activity in pre-eclampsia

BACKGROUND

Pre-eclampsia is associated with increased placental debris circulating in maternal plasma.

OBJECTIVES

This study related placental debris to maternal markers of coagulation and endothelial activation in pre-eclampsia.

PATIENTS/METHODS

Circulating fetal corticotrophin-releasing hormone (CRH) mRNA and phosphatidylserine (PS)-exposing microparticles were assayed in third trimester plasma from women with pre-eclampsia (n = 32) and controls (n = 32) matched for age, body mass index, parity, and gestational age at sampling. Markers of maternal hemostasis and endothelial function were assessed.

RESULTS

Fetal CRH mRNA levels were higher in pre-eclampsia [mean 0.75 (SD 2.77) CRH/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA ratio] than in control pregnancies [0.20 (0.74), P = 0.014]. PS-exposing microparticle levels were not different between the groups. Women with pre-eclampsia had higher levels of tissue factor pathway inhibitor (TFPI), prothrombin F(1+2) fragment (F(1+2)), factor XIIa, soluble vascular cell adhesion molecule 1, von Willebrand factor and plasminogen activator inhibitor 1 than controls. Fetal CRH mRNA correlated with TFPI in pre-eclampsia and control groups (r = 0.38, P = 0.031, and r = 0.37, P = 0.039, respectively). Fetal CRH mRNA correlated with FVII activity (r = 0.43, P = 0.017) and PS-exposing microparticles correlated inversely with F(1+2) (r = -0.64, P < 0.001) in pre-eclampsia.

CONCLUSIONS

Placental debris, assessed by fetal CRH mRNA levels in maternal blood, is related to coagulation potential, i.e. FVII activity, but not to markers of coagulation or endothelial activation in pre-eclampsia.

Comparison of coagulant activity of factor VII and activated factor VII activity assays when used for determination of recombinant activated factor VII levels in plasma

Two assays [coagulant activity of factor VII (FVII:C) and activated factor VII (FVIIa) activity] are currently available for the assessment of factor VII and FVIIa pharmacokinetics. This article presents the results of a comparison of the two assays when applied both in vitro as well as during clinical pharmacokinetic trials of recombinant FVIIa (rFVIIa) administered to healthy individuals and haemophilia patients. The in-vitro data showed that, for the FVII:C assay, plasma samples do not dilute in parallel. For the FVIIa activity assay, dilutions of samples are both parallel and linear with different dilutions of the calibrator. Moreover, intra-assay variation was found to be smaller for the FVIIa activity assay than for the FVII:C assay. When adding different amounts of rFVIIa (0-6 microg/ml) to normal plasma, a mean specific activity of rFVIIa of 48.6 U/mug was observed on applying the FVII:C assay; however, the specific activity decreased with increasing levels of rFVIIa. For the FVIIa activity assay, the mean specific activity was 45.4 IU/mug. Direct comparison of the two activity assays showed that no simple conversion between FVII:C and FVIIa activity measurements are possible. When applying the two assays for pharmacokinetic assessments in two clinical trials, statistically significant different estimates for the area under the curve, half-life, clearance and volume of distribution were obtained. In conclusion, for evaluation of rFVIIa pharmacokinetic properties, activity should be measured with the FVIIa activity assay - which is a more specific and reliable assay of the two available factor VII activity assays, especially when assessing low activity levels.

Factor VII coagulant activity, factor VII -670A/C and -402G/A polymorphisms, and risk of venous thromboembolism

BACKGROUND

Most epidemiological studies have found no association between levels of factor (F) VII:C and venous thromboembolism (VTE). Our Longitudinal Investigation of Thromboembolism Etiology (LITE) had, in contrast, reported an independent, increased risk of VTE after 7.8 years of follow-up for those with high baseline levels of FVII:C.

OBJECTIVE

To confirm whether FVII:C is associated with VTE after 12.6 years of follow-up and to examine whether two FVII gene polymorphisms (-670A/C and -402G/A) are related to VTE occurrence.

METHODS

In 19 091 LITE participants with no prior history of VTE or cancer, we measured FVII:C at baseline and identified 404 new VTEs. We also performed a nested case-control study to relate the polymorphisms to VTE (n = 490 without exclusion for cancer or prior VTE).

RESULTS

FVII:C was not independently associated with VTE occurrence after extended follow-up. Multivariable-adjusted rate ratios for VTE were 1.00, 1.00, 0.94, 1.00, and 1.38 (P-trend = 0.48) for the <25th, 25th-49th, 50th-74th, 75th-94th, and >or=95th percentiles of FVII:C, respectively. The -670C and -402A alleles were in high linkage disequilibrium, and both were associated with greater FVII:C levels. However, neither polymorphism was associated with VTE occurrence.

CONCLUSION

After extended follow-up, LITE offers little evidence that a greater FVII level is a risk factor for VTE.

Tissue factor around dermal vessels has bound factor VII in the absence of injury

BACKGROUND

'Idling' or ongoing low-level activity of the tissue factor (TF) pathway is a postulated mechanism by which the coagulation process can become active without a lag period at sites of injury.

OBJECTIVE

To determine whether TF around cutaneous vessels has bound factor VIIa in the absence of injury, and thus could participate in the idling process.

METHODS

Immunostaining of mouse skin with antibodies against a 15-residue peptide from the sequence of mouse TF, and against the whole extracellular portion of TF.

RESULTS

The whole TF antibody recognized TF in squamous epithelium and around vessels in the dermis. By contrast, the monospecific antibody only recognized TF in the squamous epithelium, but not around vessels. We also found that biotinylated, active site-inhibited FVIIa (FVIIai) bound to tissue sections in the same areas in which TF was recognized by the monospecific antibody (squamous epithelium), but did not bind around vessels. Molecular modeling revealed that FVIIa and FX binding to TF masked a significant part of the surface of the target peptide.

CONCLUSIONS

In the aggregate, these data are most consistent with the interpretation that TF in perivascular sites has bound FVIIa, even in the absence of any injury. The presence of endogenously bound FVIIa prevents the subsequent binding of the monospecific antibody or exogenous FVIIai to perivascular TF.

Activity and regulation of factor VIIa analogs with increased potency at the endothelial cell surface

BACKGROUND

Variants of recombinant factor VIIa (rFVIIa) with increased intrinsic activity have been developed to improve efficacy in the treatment of bleeding disorders in the future. The increased potency of FVIIa variants was demonstrated in limited in vitro and in vivo studies. However, further characterization of FVIIa variants is needed to evaluate their potential clinical use.

METHODS

In the present study, we investigated the interactions of two FVIIa variants, FVIIa(Q) and FVIIa(DVQ), with plasma inhibitors, tissue factor pathway inhibitor (TFPI) and antithrombin (AT), and vascular endothelium. TF-FVIIa activity or its inhibition was measured directly in an amidolytic activity assay or for its ability to activate factor X.

RESULTS

Both TFPI and AT/heparin inhibited the FVIIa variants more rapidly than the wild-type (WT) FVIIa in the absence of tissue factor (TF). In the presence of TF, TFPI, TFPI-Xa, and AT/heparin inhibited FVIIa and FVIIa variants at similar rates. Although the WT FVIIa failed to generate significant amounts of FXa on unperturbed endothelial cells, FVIIa variants, particularly FVIIa(DVQ), generated a substantial amount of FXa on unperturbed endothelium. Annexin V fully attenuated the FVIIa-mediated activation of FX on unperturbed endothelial cells. On stimulated human umbilical vein endothelial cells, FVIIa and FVIIa variants activated FX at similar rates, and annexin V blocked the activation only partly. AT/heparin and TFPI-Xa inhibited the activity of FVIIa and FVIIa variants bound to endothelial cell TF in a similar fashion. Interestingly, despite significant differences observed in FXa generation on unperturbed endothelium exposed to FVIIa and FVIIa analogs, no differences were found in thrombin generation when cells were exposed to FVIIa or FVIIa analogs under plasma mimicking conditions.

CONCLUSION

Overall, the present data suggest that although FVIIa variants generate substantial amounts of FXa, they do not generate excessive thrombin on the surface of endothelium.

The Bead blot: A method for identifying ligand–protein and protein–protein interactions using combinatorial libraries of peptide ligands

Small molecules that bind proteins can be used as ligands for protein purification and for investigating protein-protein and protein-drug interactions. Unfortunately, many methods used to identify new ligands to desired proteins suffer from common shortcomings, including the requirement that the target protein be purified and/or the requirement that the ligands be selected under conditions different from those under which it will be used. We have developed a new method called the Bead blot that can (i) select ligands to unpurified proteins, including trace proteins, present in complex materials (e.g., unfractionated plasma); (ii) select ligands to multiple proteins under a variety of conditions in a single experiment; and (iii) be used with libraries of different types of ligands. In the Bead blot, a library of ligands, synthesized on chromatography resin beads, is incubated with a starting material containing a target protein for which a ligand is sought. The proteins in the material bind to their complementary ligands according to specific affinity interactions. Then the protein-loaded beads are immobilized in a porous matrix, and the proteins are directionally eluted from the beads and captured on a membrane superimposed on the beads. The location of the target protein on the membrane is determined, and because the position of the protein(s) on the membrane reflects the position of the bead(s) in the matrix, the bead that originally bound the protein is identified, with subsequent elucidation of the ligand sequence. Ligands to several targets can be identified in one experiment. Here we demonstrate the broad utility of this method by the selection of ligands that purify plasma protein complexes or that remove pathogens from whole blood with very high affinity constants. We also select ligands to a protein based on competitive elution.

Intracellular evaluation of ER targeting elucidates a mild form of inherited coagulation deficiency

Missense mutations reduce protein levels through several molecular mechanisms. Among them, altered targeting to endoplasmic reticulum (ER) and its relationship with clinical phenotypes in patients have been poorly investigated. To address this point, we studied the prepeptide mutations (L-48P, L-42P) associated with mild deficiency of factor VII (FVII), the serine-protease triggering blood coagulation. Mutations were introduced into the native FVII to evaluate secreted and intracellular protein levels, and into a chimeric FVII-GFP to study ER targeting in living cells. In conditioned medium from stably or transiently transfected cells, expression levels of the -48PFVII (9% and 55%, respectively) and particularly those of the -42PFVII (2% and 12%) were decreased compared with those of WtFVII, indicating the causative nature of mutations. Markedly reduced protein levels were observed in cell organelles for -48PFVII (10.5 +/- 4.9 ng/mL; Wt-FVII, 130 +/- 43.4 ng/mL) and -42PFVII (approximately 5 ng/mL), thus suggesting impaired ER targeting. Fluorescence of the -48PFVII-GFP and -42PFVII-GFP was diffuse, covered the nucleus, and declined upon plasma membrane permeabilization with digitonin, which demonstrated mislocalization of variants in the cytosol. Noticeably, the residual fluorescence of -48PFVII-GFP (10%) and -42PFVII-GFP (20%) in organelles was fairly compatible with FVII levels in patients' plasma. The studies with the native and chimeric proteins indicated that both prepeptide mutations were associated with residual expression of normal FVII, which explained the mild form of FVII deficiency in patients. This approach, extendable to other coagulation serine proteases, clearly contributed to elucidate the relationship of genotype with plasma and clinical phenotype.

Establishment of the human coagulation factor VII concentrate European Pharmacopoeia biological reference preparation batch 1

For the potency assay of human coagulation factor VII concentrate preparations according to the European Pharmacopoeia (Ph. Eur.) a reference preparation calibrated in International Units (IU) is needed. Currently, the 1st International Standard (97/592, potency: 6.3 IU/ampoule) but no Ph. Eur. reference preparation is available. A collaborative study was run to calibrate a candidate Ph. Eur. Biological Reference Preparation (BRP) for human coagulation factor VII concentrate against the 1st International Standard; the BRP is intended to be used as working standard. A candidate BRP batch 1 was produced from a plasma-derived human factor VII concentrate preparation available on the European market. It fulfilled the requirements of a BRP with regard to precision and homogeneity of fill, residual water content and stability. In addition, the content of activated factor VII was low. Sixteen laboratories from 9 countries participated in the collaborative study. The potency of the candidate BRP was determined using the participants' chromogenic assay based on the Ph. Eur. and their in-house clotting assay, if available. The statistical model used for analysis of the results from most laboratories was the maximum likelihood of the parallel line model following a logarithmic transformation of the responses. In the chromogenic assay, a potency estimate of 8.2 IU/vial (+/-3.7%) was obtained for the candidate BRP. Results from the clotting assay were lower and less homogenous (6.7 IU/vial+/-11.6%). The results from the collaborative study showed that the candidate BRP is suitable as a reference standard for the chromogenic assay according to the Ph. Eur. It was adopted by the Ph. Eur. Commission in March 2006 as official Ph. Eur. BRP for this purpose.

Recombinant factor VIIa, its clinical properties, and the tissue factor pathway of coagulation

Recombinant factor VIIa (rFVIIa) is a synthetic coagulation protease that is structurally similar to human-derived plasma FVIIa. Pharmacologic doses of rFVIIa have been shown to enhance thrombin generation and assist in forming stable fibrin plugs at the site of injury. Recombinant factor VIIa appears to emerge as a valuable treatment alter-native for the treatment of bleeding episodes and for achieving hemostasis post surgery in those with bleeding disorders.

Tissue factor initiated blood coagulation

Tissue factor (TF) is the cellular receptor and cofactor for blood coagulation factor (F) VII. Exposure of flowing blood to cells that express TF leads to the initiation of blood coagulation. Blood coagulation is tightly regulated to generate a local fibrin clot at the site of vascular injury without compromising blood flow in the vasculature. This chapter describes the initiation and propagation of the response and how it is ultimately down-regulated to prevent widespread inappropriate blood coagulation.

[Novel double heterozygous mutations on Met306Val and Thr181Asn related to a hereditary coagulation factor VII deficiency]

OBJECTIVE

To identify the genetic defect of coagulation factor VII in a Chinese family with hereditary FVII deficiency.

METHODS

Peripheral blood samples were collected from the proband of hereditary FVII deficiency, female, aged 15, 4 members of her family, and 100 healthy persons. Genomic DNA was isolated. All the exons and exon-intron boundaries of FVII gene were amplified by PCR, then the PCR products were sequenced by direct sequencing. Restrictive endonuclease analysis was performed in all of the family members and the 100 healthy donors to exclude gene polymorphism. Biostructural analysis of the mutated FVII was completed by molecular modeling.

RESULTS

Double heterozygous mutations in the proband were identified: A-->G mutation at position 10833 and C-->A mutation at position 9643, resulting in Met306Val and Thr181Asn substitution respectively. Heterozygosity for Met306Val was confirmed in the proband's mother and her elder sister; heterozygosity for Thr181Asn was confirmed in the proband's father. It was found by computer simulated molecular model that the Met306Val replacement, which was located on the surface of the FVII molecule, might cause steric hindrance and change the configuration and function of FVII protein.

CONCLUSION

Double heterozygous mutations for Met306Val and Thr181Asn in FVII gene have been found in a proband with hereditary FVII deficiency. The Met306Val substitution in FVII gene is a novel mutation in hereditary FVII deficiency. The heterozygous mutation of FVII gene may change the configuration of FVII protein and result in FVII dysfunction.

Of four mutations in the factor VII gene in Tunisian patients, one novel mutation (Ser339Phe) in three unrelated families abrogates factor X activation

Hereditary factor VII (FVII) deficiency is a rare bleeding disorder. Dysfunctional FVII variants characterized by normal or reduced levels of FVII antigen and discordantly low FVII activity have been described. In this study, seven unrelated Tunisian patients with FVII deficiency were examined. Molecular analysis revealed that three probands harbored a novel Ser339Phe mutation, one proband was inferred to have a novel splice site mutation in intron 2, c.226-2 A>G and three probands had two previously described mutations, Arg304Gln and Cys310Phe. Expression of Ser339Phe in baby hamster kidney cells yielded secretion of FVII antigen at a concentration of 225+/-50 ng/ml, compared with 181+/-47 ng/ml in cells transfected with wild-type FVII but with no demonstrable FVII activity. FVII Ser339Phe bound to tissue factor similarly to the binding of commercial recombinant activated FVII or recombinant wild-type FVII and was normally activated by activated factor X. The major defect of FVII Ser339Phe was its inability to activate factor X in the presence of tissue factor. Modeling predicted that the substitution of Ser339 by Phe abrogated substrate docking.

Large Enhancement of Functional Activity of Active Site-Inhibited Factor VIIa Due to Protein Dimerization: Insights into Mechanism of Assembly/Disassembly from Tissue Factor

Active site-inhibited blood clotting factor VIIa (fVIIai) binds to tissue factor (TF), a cell surface receptor that is exposed upon injury and initiates the blood clotting cascade. FVIIai blocks binding of the corresponding enzyme (fVIIa) or zymogen (fVII) forms of factor VII and inhibits coagulation. Although several studies have suggested that fVIIai may have superior anticoagulation effects in vivo, a challenge for use of fVIIai is cost of production. This study reports the properties of dimeric forms of fVIIai that are cross-linked through their active sites. Dimeric wild-type fVIIai was at least 75-fold more effective than monomeric fVIIai in blocking fVIIa association with TF. The dimer of a mutant fVIIai with higher membrane affinity was 1600-fold more effective. Anticoagulation by any form of fVIIai differed substantially from agents such as heparin and showed a delayed mode of action. Coagulation proceeded normally for the first minutes, and inhibition increased as equilibrium binding was established. It is suggested that association of fVIIa(i) with TF in a collision-dependent reaction gives equal access of inhibitor and enzyme to TF. Assembly was not influenced by the higher affinity and slower dissociation of the dimer. As a result, anticoagulation was delayed until the reaction reached equilibrium. Properties of different dissociation experiments suggested that dissociation of fVIIai from TF occurred by a two-step mechanism. The first step was separation of TF-fVIIa(i) while both proteins remained bound to the membrane, and the second step was dissociation of the fVIIa(i) from the membrane. These results suggest novel actions of fVIIai that distinguish it from most of the anticoagulants that block later steps of the coagulation cascade.

Small FVIII gene rearrangements in 18 hemophilia A patients: five novel mutations

Hemophilia A (HA) is a disorder caused by mutations of the FVIII gene, which is located on the tip of the long arm of the X chromosome. In a cohort of 18 unrelated Italian patients affected with HA of varying severity, we performed mutational screening of the gene by denaturing high-performance liquid chromatography (DHPLC) and direct sequencing of abnormal peaks. We identified five novel mutations and 9 previously reported DNA alterations. Two of the 9 previously reported alterations were each common to 3 unrelated patients. Six different mutations were characterized as missense alterations, while 8 were non-missense mutations. Among the new gene alterations, one created a stop codon, one consisted of an out-of frame deletion, and one was a splice-site mutation. The last two were missense alterations. In an attempt to better understand the causative effect of the mutations and the clinical variability of the patients, we investigated the consequences of each missense mutation and visualized the effect of the amino acid change on structural FVIII models.

Inherited factor VII deficiency: identification of two novel mutations (A191V and T239P) in the catalytic domain

We describe here five F7 mutations found in four patients without bleeding history, despite constitutional coagulation Factor VII (FVII) deficiency. All five mutations are missense and affect the catalytic domain of FVII (A191T, A191V, T239P, R224Q and M298I). The A191V and T239P mutations are novel and were found in homozygous patients with no clinical bleeding tendency. The patient diagnosed with the A191V mutation had a phenotype corresponding to a moderate type 1 FVII deficiency (FVII:C 4%, FVII:Ag 5%). The T239P mutation was found in a patient with mild type 2 FVII deficiency (FVII:C 25%, FVII:Ag 95%). Novel mutations are both in close vicinity to the charge-stabilizing system of FVII. Modeling studies allow understanding in part the molecular basis for the loss of function.

The first epidermal growth factor-like domains of factor Xa and factor IXa are important for the activation of the factor VII--tissue factor complex

During tissue factor (TF)-induced coagulation, the factor (F)VIIa-TF complex activates factor (F)X and factor (F)IX. Through positive feedback, the generated FXa and FIXa activate FVII-TF. The first epidermal growth factor-like (EGF1) domains of FX and FIX serve as important TF-recognition motifs when FVIIa-TF activates FX or FIX. Here, we investigated the role of EGF1 domains of FXa and FIXa during the activation of FVII-TF and inhibition by tissue factor pathway inhibitor (TFPI). FXaPCEGF1 (EGF1 domain of FXa replaced with that of protein C), and FXaQ49P (EGF1 domain mutant with impaired calcium-binding), and the corresponding FIXa mutants were generated, and their abilities to activate FVII-TF were compared with the wild-type (WT) enzymes. In the absence of TF, the rates of FVII activation were similar between WT enzymes and mutant FXa and FIXa proteases. In the presence of either soluble TF (sTF) or relipidated TF, each mutant of FXa or FIXa activated FVII-TF at a slower rate than the corresponding WT enzyme. Kinetics of inhibition of the amidolytic activity of WT and the mutant FXa proteases by either two-domain or full-length TFPI were similar. However, compared with the complex of TFPI-FXaWT, the abilities of the complexes of TFPI-FXa mutants to inhibit FVIIa-TF were impaired. We conclude that the EGF1 domains of FXa and FIXa are important for the activation of FVII-TF and for the formation of FVIIa-TF-FXa-TFPI complex.

Posttranslational N-glycosylation takes place during the normal processing of human coagulation factor VII

N-glycosylation is normally a cotranslational process that occurs during translocation of the nascent protein to the endoplasmic reticulum. In the present study, however, we demonstrate posttranslational N-glycosylation of recombinant human coagulation factor VII (FVII) in CHO-K1 and 293A cells. Human FVII has two N-glycosylation sites (N145 and N322). Pulse-chase labeled intracellular FVII migrated as two bands corresponding to FVII with one and two N-glycans, respectively. N-glycosidase treatment converted both of these band into a single band, which comigrated with mutated FVII without N-glycans. Immediately after pulse, most labeled intracellular FVII had one N-glycan, but during a 1-h chase, the vast majority was processed into FVII with two N-glycans, demonstrating posttranslational N-glycosylation of FVII. Pulse-chase analysis of N-glycosylation site knockout mutants demonstrated cotranslational glycosylation of N145 but primarily or exclusively posttranslational glycosylation of N322. The posttranslational N-glycosylation appeared to take place in the same time frame as the folding of nascent FVII into a secretion-competent conformation, indicating a link between the two processes. We propose that the cotranslational conformation(s) of FVII are unfavorable for glycosylation at N332, whereas a more favorable conformation is obtained during the posttranslational folding. This is the first documentation of posttranslational N-glycosylation of a non-modified protein in mammalian cells with an intact N-glycosylation machinery. Thus, the present study demonstrates that posttranslational N-glycosylation can be a part of the normal processing of glycoproteins.

Factor VII deficiency

As yet, there have been neither systematic reviews nor reports of randomized, controlled trials involving factor VII (FVII) deficiency. Hence, a picture of this disorder can only be drawn by reviewing and summarizing the data that is available. This article provides an overview of the understanding of this rare, inherited disorder of coagulation. In particular, the status of current knowledge of the disorder's prevalence, clinical presentation, diagnostic characteristics and molecular genetics is reviewed, followed by a summary of currently available options for its treatment and management.

In vivo neutralization of a C2 domain–specific human anti–Factor VIII inhibitor by an anti-idiotypic antibody

Factor VIII (FVIII) administration elicits specific inhibitory antibodies (Abs) in about 25% of patients with hemophilia A. The majority of such Abs reacts with FVIII C2 domain. mAbBO2C11 is a high-affinity human monoclonal antibody (mAb) directed toward the C2 domain, which is representative of a major class of human FVIII inhibitors. Anti-idiotypic Abs were raised to mAbBO2C11 to establish their neutralizing potential toward inhibitors. One mouse anti-idiotypic mAb, mAb14C12, specifically prevented mAbBO2C11 binding to FVIII C2 domain and fully neutralized mAbBO2C11 functional inhibitory properties. Modeling of the 3-D conformation of mAb14C12 VH and alignment with the 3-D structure of the C2 domain showed putative 31 surface-exposed amino acid residues either identical or homologous to the C2 domain. These included one C2 phospholipid-binding site, Leu2251-Leu2252, but not Met2199-Phe2200. Forty putative contact residues with mAbBO2C11 were identified. mAb14C12 dose-dependently neutralized mAbBO2C11 inhibitory activity in mice with hemophilia A reconstituted with human recombinant FVIII (rFVIII), allowing full expression of FVIII activity. It also neutralized in an immunoprecipitation assay approximately 50% of polyclonal anti-C2 Abs obtained from 3 of 6 unrelated patients. mAb14C12 is the first example of an anti-idiotypic Ab that fully restores FVIII activity in vivo in the presence of an anti-C2 inhibitor. The present results establish the in vitro and in vivo proof of concept for idiotype-mediated neutralization of a major class of FVIII inhibitors.

Similar Molecular Interactions of Factor VII and Factor VIIa with the Tissue Factor Region that Allosterically Regulates Enzyme Activity

Tissue factor (TF) binds the zymogen (VII) and activated (VIIa) forms of coagulation factor VII with high affinity. The structure determined for the sTF-VIIa complex [Banner, D. W., et al. (1996) Nature 380, 41-46] shows that all four domains of VIIa (Gla, EGF-1, EGF-2, and protease) are in contact with TF. Although a structure is not available for the TF-VII complex, the structure determined for free VII [Eigenbrot, C., et al. (2001) Structure 9, 675-682] suggests a significant conformational change for the zymogen to enzyme transition. In particular, the region of the protease domain that must contact TF has a conformation that is altered from that of VIIa, suggesting that the VII protease domain interacts with TF in a manner different from that of VIIa. To test this hypothesis, a panel of 12 single-site sTF mutants, having substitutions of residues observed to contact the proteolytic domain of VIIa, have been evaluated for binding to both zymogen VII and VIIa. Affinities were determined by surface plasmon resonance measurements using a noninterfering anti-TF monoclonal antibody to capture TF on the sensor chip surface. Dissociation constants (K(D)) measured for binding to wild-type sTF are 7.5 +/- 2.4 nM for VII and 5.1 +/- 2.3 nM for VIIa. All of the sTF mutants except S39A and E95A exhibited a significant decrease (>2-fold) in affinity for VIIa. The changes in affinity measured for VII or VIIa binding with substitution in sTF were comparable in magnitude. We conclude that the proteolytic domain of both VII and VIIa interacts with this region of sTF in a nearly identical fashion. Therefore, zymogen VII can readily adopt a VIIa-like conformation required for binding to TF.

Performance of 3D-Database Molecular Docking Studies into Homology Models

The performance of docking studies into protein active sites constructed by homology model building was investigated using CDK2 and factor VIIa screening data sets. When the sequence identity between model and template near the binding site area is greater than approximately 50%, roughly 5 times more active compounds are identified than would be found randomly. This performance is comparable to docking to crystal structures.

Glycosaminoglycans Bind Factor Xa in a Ca2+-Dependent Fashion and Modulate Its Catalytic Activity

Recent studies have demonstrated the existence of a Ca(2+)-dependent heparin-binding site on factor Xa. To characterize this heparin-binding site, the extrinsic fluorescence of fluorescein-labeled, active site-blocked factor Xa was monitored as it was titrated with glycosaminoglycans of various sulfate content and chain length. The binding of glycosaminoglycans to factor Xa appears to be charge-dependent because affinity is correlated with degree of glycosaminoglycan sulfation. All glycosaminoglycans bind factor Xa with higher affinity in the presence of Ca(2+) than in its absence. In contrast, when Gla-domainless factor Xa was substituted for factor Xa, glycosaminoglycans bound with similar affinities in the absence and presence of Ca(2+). These results support the hypothesis that the anionic Gla domain impairs glycosaminoglycan binding in the absence of Ca(2+). The changes in fluorescence intensity of factor Xa when titrated with glycosaminoglycans suggest that glycosaminoglycans induce conformational changes in the active site environment of factor Xa. To explore the consequences of these conformational changes, the effect of glycosaminoglycans on the catalytic activity of factor Xa was examined. Glycosaminoglycans influenced the ability of factor Xa to cleave chromogenic substrates and attenuated the capacity of factor Xa to activate factor VII. The potency of glycosaminoglycans in these assays reflected their affinity for factor Xa. These studies suggest that glycosaminoglycan binding perturbs exosites on the surface of factor Xa, potentially modifying interactions with cofactors or substrates.

450 million years of hemostasis

In mammalian blood coagulation, five proteases (factor VII [FVII]; factor IX [FIX]; factor X [FX]; protein C [PC] and prothrombin [PT]) act with five cofactors (tissue factor [TF]; factor V [FV]; factor VIII [FVIII]; thrombomodulin and protein S) to control the generation of fibrin. Biochemical evidence, molecular cloning data and comparative sequence analysis support the existence of all components of this network in all jawed vertebrates, and strongly suggest that it evolved before the divergence of teleosts over 430 million years ago. Phylogenetic analysis of the amino acid sequences of the Gla-EGF1-EGF2-SP domain serine proteases (FVII, FIX, FX, PC) and the A domain-containing cofactors (FV and FVIII) strongly supports the evolution of the blood coagulation network through two rounds of gene duplication, and supports the hypothesis that vertebrate evolution benefited from two global genome duplications. The jawless vertebrates (hagfish and lamprey) that diverged over 450 million years ago have a blood coagulation network involving TF, PT and fibrinogen. Preliminary evidence indicates that they may have a smaller complement of Gla-EGF1-EGF2-SP domain proteins, suggesting the existence of a 'primitive' coagulation system in jawless vertebrates.

Do oxidized fatty acids activate coagulation factor VII during post-prandial lipemia in women?

Factor VII is activated to VIIa within hours after dietary fat, irrespective of its fatty acid composition. Edible oils contain oxidized material (hydroxy fatty acids, HOFA). Twenty-five fasting women, aged 38 (10) years, consumed 30 g walnut oil containing 26 (6) mg HOFA. Blood was collected 2-hourly to measure plasma triglycerides and plasma lipid HOFA by gas chromatography/mass spectrometry. VII and sTF-dependent VIIa were quantified at 0, 6 and 24 h. Increased plasma triglycerides and HOFA (areas under the curve 0-8 h, AUC) were related r = 0.83, p < 0.001. VIIa increased from 2.6 (1.4) to 4.2 (1.9) ng/mL at 6 h (p < 0.001). Plasma VII remained constant. VIIa (6 h) was related to plasma triglycerides- and HOFA-AUC: r = 0.38 and 0.53, respectively (both p < 0.05). Plasma VIIa was also related to body weight, fasting triglycerides, HOFA and VII. Only HOFA-AUC and body weight related to VIIa (6 h) in stepwise regression analysis (p = 0.007 and 0.038, respectively). Oxidized, not normal, fat activates VII and could increase coronary risk in humans.

Factor VII mutant V154G models a zymogen-like form of factor VIIa

Proteolytic cleavage of the peptide bond between Arg(152) and Ile(153) converts the procoagulant protein Factor VII (FVII) to an activated two-chain form (FVIIa). The formation of a salt bridge between Ile(153) and Asp(343) drives the conversion of FVIIa from being zymogen-like to the active form. In the present paper, we describe the novel FVII mutant V154G (Val(154)-->Gly mutation; residue 17 in the chymotrypsin numbering system), found in three FVII-deficient patients, which models a zymogen-like form of FVIIa. Recombinant V154G FVIIa, although normally cleaved, shows markedly reduced activity towards peptidyl substrate and undetectable activity towards macromolecular substrates. Susceptibility of Ile(153) to chemical modification, in either the presence or the absence of tissue factor (TF), suggests that the reduced V154G FVIIa activity is caused by impaired salt-bridge formation, thus resulting in a zymogen-like FVIIa form. The TF-mediated protection from chemical modification of V154A indicated that Gly(154) is responsible for this peculiar feature, and suggests that this region, proximal to the heavy chain N-terminus, is directly involved in the conversion of FVII into FVIIa. V154G FVII was exploited to study the FVII-TF interaction, together with three additional FVII variants that were expressed to serve as models for different FVII forms. The comparison of binding affinities of full-length TF after relipidation in L-alpha-phosphatidylcholine for the zymogen FVII (Arg(152)-->Gln, K (d)=1.04+/-0.27 nM), inactive FVIIa (Ser(344)-->Ala, K (d)=0.27+/-0.06 nM) and a zymogen-like FVIIa (V154G, K (d)=1.15+/-0.16 nM) supports the hypothesis that preferential binding of TF to active FVIIa is insufficient to drive the 10(5)-fold enhancement of FVIIa activity. In addition, the inability of V154G FVIIa to accommodate an inhibitor in the active site, indicating an improperly shaped specificity pocket, would explain the low activity of the zymogen-like form of FVIIa, which is predominant in the absence of TF.

Two naturally occurring mutations on FVII gene (S363I-W364C) altering intrinsic catalytic activity

Factor VII (FVII) requires the cleavage of an internal peptide bond and the association with tissue factor (TF) to attain its fully active FVIIa conformation. This event alone leaves FVIIa in a zymogen-like state of relatively low specific activity. The TF-induced allosteric enhancement of FVIIa's activity contributes to the procoagulant activity of the complex. We have characterized two naturally occurring mutations (S363I - W364C) on FVII gene. Both homozygous patients for each mutation have a normal FVII: Ag level associated to an undetectable FVII coagulant activity. The patient carrying the allele 364C had a more severe hemorrhagic diathesis than the S363I mutant. To understand the mechanism of these deficiency, in vitro expression analysis with further biochemical characterization of recombinant proteins of both mutants FVII-363I, FVII-364C and wild type (WTFVII) FVII constructs were done. The results recapitulated the patients' plasma data with normal Ag level and no detectable coagulant activity. The D-F-Pip-R-pNA and CH(3)SO(2)-D-CHA-A-But-R chromogenic substrates were used to evaluate the amidolytic activity of WT and mutant FVII in presence and absence of recombinant tissue factor (rTF). Binding of FVII to rTF by a solid phase binding assay was done using recombinant human rTF. The results of amidolytic assays showed that rTF enhances 28 fold the value of the specificity of constant (kcat/K(m)) in WT but no activity was detectable in either mutant constructs under any condition. The equilibrium dissociation constant of rTF-FVIIa interaction showed Kd equal to 4.4 +/- 0.2nM, 4.9 +/- 0.5nM and 6 +/- 0.9 of WT, 363I and 364C FVII forms, respectively. The K(d) values of the non activated forms were equal to 24.7 +/- 3.3, 24.4 +/- 3.1 and 20.6 +/- 4nM, respectively. These data demonstrate that, compared to the WT form, FVII-363I and FVII-364C have no significant affinity change for TF and that the detrimental effect of these two mutations is attributable to the loss of an efficient catalytic machinery in the FVII molecule causing a severe deficiency of coagulant activities.

Detection and quantification of insertion/deletion variations by allele-specific real-time PCR: application for genotyping and chimerism analysis

The DNA-based quantitative analysis of genetic chimerism is becoming increasingly more important for molecular biology in general and molecular medicine in particular. Useful genomic targets for these analyses are polymorphic sequences, but here the problem of a reliable quantification with high dynamic range is not yet satisfactorily solved. To this end we have combined the allele-specific amplification with a real-time PCR-based quantification for rapid allelotyping and chimerism analysis. The sequence variations are discriminated by the 3'-end of the allele-specific primer. Amplification is monitored by SYBR-Green I fluorescence. We demonstrate the efficiency of this method for two clinically relevant targets: (i) the 10 bp insertion/deletion polymorphism in the promoter of the factor VIIc (F-VIIc) gene and (ii) the 4G/5G single nucleotide polymorphism in the promoter of the plasminogen activator inhibitor-1 (PAI-1) gene. Both polymorphisms are associated with clinical risk factors. Allelotyping results were in complete agreement with those obtained by reference methods. Mixed chimeric DNA samples could be quantified reliably with a dynamic range of 1:3000 for an easy target (F-VIIc) and of 1:64 for a difficult target (PAI-1). Our protocol is particularly useful for rapid, reliable and inexpensive genotyping and quantitative chimerism analysis without requiring expensive fluorophor dye labelled probes.

A novel approach to the synthesis of EGF-like domains: a method for the one-pot regioselective formation of the three disulfide bonds of a human blood coagulation factor VII EGF-1 analogue

The study of EGF-like domains is of great general interest in protein science because of their participation in a multitude of protein-protein interactions. A common structural feature of EGF-like modules is the presence of three disulfide bonds, the regioselective formation of which still remains a challenge to peptide chemists. We report here on a method for the one-pot regioselective synthesis of an analogue of the EGF-1 domain of human coagulation Factor VII (residues 45-83) comprising an Asn57beta-Asp substitution. The cysteine protecting groups trityl, t-butyl and acetamidomethyl were chosen for the three disulfide bond pairings. All three disulfide bridges were prepared directly from the crude starting product, obviating the need for the timely and costly purification of the intermediate folded products. The fully folded product was purified by preparative high-pressure liquid chromatography prior to evaluation of its biological activity in an assay to detect inhibition of FVII/TF complex formation. In addition circular dichroism spectroscopy was employed to elucidate the main structural similarities between this peptide analogue and the native human Factor VII EGF-1 domain.

Human factor VII deficiency caused by S339C mutation located adjacent to the specificity pocket of the catalytic domain

This report documents our identification of a novel factor VII (FVII) gene mutation in a Japanese boy with FVII deficiency. The proband's FVII activity was 34% and his FVII antigen level was 40% of normal controls. DNA sequence analysis of the proband's FVII gene identified a C to G point mutation at nucleotide position 10 933 in exon 8, which results in the substitution of Cys (TGC) for Ser339 (TCC). Hinf I digestion results indicate the proband and his mother were heterozygous for the mutation. Both wild-type and mutant FVIIs were transiently expressed in COS-1 cells. FVII levels measured in the culture medium of FVII Ser339Cys mutants were markedly reduced as compared to those of cells with FVII wild-type. The amount of intracellular FVII in FVII Ser339Cys mutants was 80% of that in wild-type. In the wild-type FVII, Ser339 is juxtaposed to Asp338, which is positioned at the bottom of the substrate-binding pocket in the protease domain and located adjacent to FVII Cys340, that forms a disulphide bond with Cys368. We suspect that the creation of a novel unpaired cysteine through this mutation leads to abnormal disulphide bonding during protein folding, thereby reducing the secretion of FVII.

Role of zymogenicity-determining residues of coagulation factor VII/VIIa in cofactor interaction and macromolecular substrate recognition

Factor VIIa (VIIa) remains in a zymogen-like state following proteolytic activation and depends on interactions with the cofactor tissue factor (TF) for function. Val(21), Glu(154), and Met(156) are residues that are spatially close in available zymogen and enzyme structures, despite major conformational differences in the corresponding loop segments. This residue triad displays unusual side chain properties in comparison to the properties of other coagulation serine proteases. By mutagenesis, we demonstrate that these residues cooperate to stabilize the enzyme conformation and to enhance the affinity for TF. In zymogen VII, however, substitution of the triad did not change the cofactor affinity, further emphasizing the crucial role of the activation pocket in specifically stabilizing the active enzyme conformation. In comparison to VIIa(Q156), the triple mutant VIIa(N21I154Q156) had a stabilized amino-terminal Ile(16)-Asp(194) salt bridge and enhanced catalytic function. However, proteolytic and amidolytic activities of free VIIa variants were not concordantly increased. Rather, a negatively charged Asp at position 21 was the critical factor that determined whether an amidolytically more active VIIa variant also more efficiently activated the macromolecular substrate. These data thus demonstrate an unexpected complexity by which the zymogenicity-determining triad in the activation pocket of VIIa controls the active enzyme conformation and contributes to exosite interactions with the macromolecular substrate.