Identification of molecular sites on factor VII which mediate its assembly and function in the extrinsic pathway activation complex

Macromolecular substrate affinity for free factor VIIa is independent of a buried protease domain N-terminus

The initial recognition and binding of macromolecular substrates by factor VIIa (FVIIa) in complex with tissue factor has been shown to be mediated by areas distinct from the active site (so-called exosites). The present aim was to shed light on whether the N-terminal tail of the protease domain of FVIIa influences factor X (FX) binding, and whether the zymogen-like conformation of free FVIIa has a decreased affinity for FX compared to the active conformation. Two derivatives of FVIIa, one (FFR-FVIIa) with a stably buried N-terminus representing the active conformation of FVIIa and one (V154G-FVIIa) with a fully exposed N-terminus representing the zymogen-like conformation, were used as inhibitors of FVIIa-catalyzed FX activation. Their inhibitory capacities were very similar, with K(i) values not significantly different from the K(m) for FX. This indicates that the conformational state of the N-terminus does not affect FX binding or, alternatively, that the activation domain including the N-terminal insertion site is easily shifted to the stable conformation ensuing FX docking to the zymogen-like conformation. The net outcome is that FX binding to the zymogen-like form of FVIIa does not appear to be impaired.

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.

The first epidermal growth factor domain of human coagulation factor VII is essential for binding with tissue factor

The intrinsic pathway of coagulation is initiated when zymogen factor VII binds to its cell surface receptor tissue factor to form a catalytic binary complex. Both the activation of factor VIIa and the expression of serine protease activity of factor VIIa are dependent on factor VII binding to tissue factor lipoprotein. To better understand the molecular basis of these rate-limiting events, the interaction of zymogen factor VII and tissue factor was investigated using as probes both a murine monoclonal antibody and a monospecific rabbit antiserum to human factor VII. To measure factor VIIa functional activity, a two-stage chromogenic assay was used; an assay which measures the factor Xa generated by the activation of factor VII to factor VIIa. Purified immunoglobulin from murine monoclonal antibody 231-7, which was shown to be reactive with amino acid residues 51-88 of the first epidermal growth factor-like (EGF) domain of human factor VII, inhibited the activation of factor VII to factor VIIa in a dose-dependent manner. The mechanism of this inhibition was demonstrated using a novel solid-phase ELISA which quantitatively measured the binding of purified factor VII zymogen to tissue factor adsorbed onto microtiter wells. Thus, the binding of factor VII zymogen to immobilized tissue factor was inhibited by antibody 231-7, again in a dose-dependent manner. Similar results were obtained using a monospecific rabbit antiserum to human factor VII which also reacted with the beta-galactosidase fusion proteins containing amino acid residues 51-88 (exon 4) of human factor VII. We conclude therefore that the exon 4-encoded amino acids of the first EGF domain of human factor VII constitute an essential domain participating in the binding of factor VII to tissue factor.

Synthesis, biological activity, and solution structures of a cyclic dodecapeptide from the EGF-2 domain of blood coagulation factor VII

The cyclic dodecapeptide, disulfide-cyclo-[H-Cys-Val-Asn-Glu-Asn-Gly-Gly-Cys(Acm)-Glu-Gln-Tyr-Cys-OH], which corresponds to the 91-102 sequence of the second epidermal growth factor domain of human blood coagulation factor VII, was synthesized using solid-phase procedures. It was shown to be an inhibitor at the key step in the induction of coagulation by the extrinsic pathway, i.e. the factor VII/tissue factor-catalyzed activation of coagulation factor X. The solution structure of this peptide was investigated by NMR spectroscopy and was computer-modeled via molecular mechanics. Structures were calculated based on 112 distance and nine dihedral angle constraints. The resulting backbone structures were classified into two structural subsets: one which exhibited a twisted '8'-shaped folding and another describing an open, circular 'O' outline. The local backbone structures of segments Asn3-Glu4-Asn5, Gly7-Cys8 and Gln10-Tyr11 were well preserved among the two subsets. Apart from the unrestrained N- and C-termini, Gly6 and Glu9 sites exhibited marked local disorder between the two subsets, suggesting localized flexible hinges likely to govern tertiary structure interconversion between the two subsets. Two transient hydrogen bonds were identified from pH chemical shift titrations by matching the pKa values of NH and carboxylate groups, which supported the occurrence of the '8' structure, and agreed with temperature coefficients of peptidyl NH resonances. Structure-function relationships of the peptide were discussed in terms of the likely physiological function of the disulfide-bonded loop in factor VII which the peptide represents.

Factor VII Deficiency Caused by a Structural Variant N57D of the First Epidermal Growth Factor Domain

We have previously described a kindred with factor VII (FVII) deficiency whose members exhibited reduced procoagulant activity relative to FVII antigen concentration. In this report, the molecular genetic basis of the FVII defect has been determined to be a heterozygous substitution of Asp for Asn at position 57 in the first epidermal growth factor (EGF) domain. Recombinant FVII (N57D) cDNA was created by site-directed mutagenesis and transiently expressed in human 293 cells. The transfected cells synthesized an immunoprecipitable protein with an apparent molecular weight of 50 kD. Quantitation of expression by FVII enzyme-linked immunosorbent assay indicated that mutant protein yields were consistently low, typically 10% to 30% of wild-type FVII. FVII (N57D) protein did not accumulate intracellularly, and Northern blot analysis indicated equivalent FVII mRNA levels in 293 cells expressing either wild-type FVII or FVII (N57D). Secreted FVII (N57D) protein did not bind tissue factor, exhibited no procoagulant activity, and failed to bind a conformation-dependent monoclonal antibody specific for the first EGF domain of FVII. Molecular modeling of the first EGF domain of FVII predicted that the N57D amino acid substitution would disrupt tertiary bonding structure. We conclude that the N57D mutation affects folding of the first EGF domain of FVII resulting in decreased cellular secretion of a mutant FVII molecule, which is unable to bind tissue factor and is therefore biologically inactive.

Factor VII Deficiency Caused by a Structural Variant N57D of the First Epidermal Growth Factor Domain

We have previously described a kindred with factor VII (FVII) deficiency whose members exhibited reduced procoagulant activity relative to FVII antigen concentration. In this report, the molecular genetic basis of the FVII defect has been determined to be a heterozygous substitution of Asp for Asn at position 57 in the first epidermal growth factor (EGF) domain. Recombinant FVII (N57D) cDNA was created by site-directed mutagenesis and transiently expressed in human 293 cells. The transfected cells synthesized an immunoprecipitable protein with an apparent molecular weight of 50 kD. Quantitation of expression by FVII enzyme-linked immunosorbent assay indicated that mutant protein yields were consistently low, typically 10% to 30% of wild-type FVII. FVII (N57D) protein did not accumulate intracellularly, and Northern blot analysis indicated equivalent FVII mRNA levels in 293 cells expressing either wild-type FVII or FVII (N57D). Secreted FVII (N57D) protein did not bind tissue factor, exhibited no procoagulant activity, and failed to bind a conformation-dependent monoclonal antibody specific for the first EGF domain of FVII. Molecular modeling of the first EGF domain of FVII predicted that the N57D amino acid substitution would disrupt tertiary bonding structure. We conclude that the N57D mutation affects folding of the first EGF domain of FVII resulting in decreased cellular secretion of a mutant FVII molecule, which is unable to bind tissue factor and is therefore biologically inactive.

Peptides corresponding to the second epidermal growth factor-like domain of human blood coagulation factor VII: synthesis, folding and biological activity

Factor VIIa (FVIIa) is the enzymatically active constituent of the FVIIa/tissue factor (TF) complex, the initiator of the extrinsic pathway of blood coagulation. The zymogen FVII and FVIIa are composed of discrete domains, two of which are homologous to the epidermal growth factor (EGF). This investigation examined the significance of the FVII EGF-2 domain in the processes leading to activation of factor X (FX). Peptides 47 residues in length and corresponding to the amino acid sequence of the EGF-2 domain of human FVII were prepared by solid-phase synthesis methods. Peptide variants with all six Cys residues replaced by L-2-aminobutyryl residues (1), or containing one (2a-c), two (3a,b) or three (4) disulfide bonds, were obtained by application of various S-protecting groups and oxidation methods. Peptide 4, containing the cystine bridge arrangement corresponding to that found in the native protein, was prepared by a two-step regioselective disulfide bond formation method. An evaluation of the anti-coagulant properties of peptides 1-4 revealed that all peptides, with the exception of the two-cystine isomer containing non-native disulfide pairings (3b), were potent inhibitors of TF/FVIIa-mediated activation of FX. The fully constrained peptide 4 was found to be twice as active as its completely non-constrained counterpart 1, the two peptides showing IC50 values of 1.6 +/- 0.5 microM (1) and 0.8 +/- 0.2 microM (4) with respect to TF/FVIIa-dependent FX activation. The results of this study demonstrate the functional importance of the EGF-2 domain of FVII in the induction of coagulation by the extrinsic pathway.

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.

A peptide sequence from the EGF-2 like domain of FVII inhibits TF-dependent FX activation

We have found that synthetic peptides derived from the two epidermal growth factor-like domains of factor VII are inhibitors of tissue factor dependent factor X activation. Inhibition was most pronounced for a constrained sequence of amino acids corresponding to positions 91-102 of factor VII, Cys-Val-Asn-Glu-Asn-Gly-Gly-Cys-Glu-Gin-Tyr-Cys. The biological activity appeared to be localized to the tripeptide 'motif', Glu-Gln-Tyr, within the larger sequence. The cyclic peptide was also an inhibitor of tissue factor induced coagulation of plasma, using lipidated tissue factor or tissue factor expressed on the surface of living cells. However, it did not interfere with intrinsic coagulation. Inhibition of factor X activation was dose-dependent with an IC50 value of 350 microM. Kinetic analyses revealed non-competitive inhibition with respect to factor X and suggested that the peptide sequence interferes with the factor VII/tissue factor/factor X complex formation and function. A pentapeptide analog of the putative pharmacophore was also a dose-dependent inhibitor of factor X activation with an IC50 value of 560 microM, but the tripeptide, Glu-Gin-Tyr, alone was without effect. Our results suggest a direct role for the second epidermal growth factor-like domain of factor VII, and in particular its loop I, in the formation and function of the factor VII/tissue factor/factor X complex.

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.

Synthetic peptide analogs of tissue factor and factor VII which inhibit factor Xa formation by the tissue factor/factor VIIa complex

Factor VII (FVII) and tissue factor (TF) form a binary complex which initiates the extrinsic pathway of the blood coagulation cascade. The infrequent tripeptide motif Trp-Lys-Ser (WKS) is found three times in TF. It has been suggested that the motif is involved in binding of TF to FVII(a). Also. Lys165 and Lys166 of TF have been reported to be important for factor X activation. To elucidate the molecular interactions between TF and FVIIa, and the interactions between the binary complex and FX, we examined the inhibitory effect of synthetic TF and FVII peptide analogs. One- and two-stage chromogenic assays were employed, as well as one-stage coagulation assay. The peptide analogs of TF possessed the WKS motif, the double lysine residues or other regions of TF. Synthetic peptides of FVII encompassing sequences of the FVII285-305 region were included for comparative purposes. TF154-167 and FVII300-305 significantly inhibited both FX activation and plasma coagulation. FVII285-294 acted synergistically, increasing that effect observed by FVII300-305 on FX activation. However, TF163-175 possessing the double lysine residues did not inhibit FX activation, indicating that inhibition of FXa formation and coagulation by TF154-167 is due to the region 154-162 of TF. None of the peptides, including the WKS tripeptide, interfered with the FVIIa activity of the TF/FVIIa complex. Thus, the results do not suggest that the WKS motifs are necessary for binding of TF to FVIIa but that the third WKS motif may be of importance for the activation of FX.

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.

High affinity Ca(2+)-binding site in the serine protease domain of human factor VIIa and its role in tissue factor binding and development of catalytic activity

Factor VIIa, in the presence of Ca2+ and tissue factor (TF), initiates the extrinsic pathway of blood coagulation. The light chain (amino acids 1-152) of factor VIIa consists of an N-terminal gamma-carboxyglutamic acid (Gla) domain followed by two epidermal growth factor-like domains, whereas the heavy chain (amino acids 153-406) contains the serine protease domain. In this study, both recombinant factor VIIa (rVIIa) and factor VIIa lacking the Gla domain were found to contain two high-affinity (Kd approximately 150 microM) Ca2+ binding sites. The rVIIa also contained approximately 6-7 low-affinity (Kd approximately 1 mM) Ca(2+)-binding sites. By analogy to other serine proteases, one of the two high affinity Ca(2+)-binding sites in factor VIIa may be formed involving Glu-210 and Glu-220 of the protease domain. In support of this, a synthetic peptide composed of residues 206-242 of factor VIIa bound one Ca2+ with Kd approximately 230 microM; however, Ca2+ binding was observed only in Tris buffer (pH 7.5) containing 1 M NaCl and not in buffer containing 0.1 M NaCl. In both low or high salt +/- Ca2+, the peptide existed as a monomer as determined by sedimentation equilibrium measurements and had no detectable secondary structure as determined by CD measurements. This indicates that subtle changes undetectable by CD may occur in the conformation of the peptide that favor calcium binding in high salt. In the presence of recombinant TF and 5 mM Ca2+, the peptide inhibited the amidolytic activity of rVIIa toward the synthetic substrate, S-2288. The concentration of the peptide required for half-maximal inhibition was approximately 5-fold higher in the low salt buffer than that in the high salt buffer. From direct binding and competitive inhibition assays of active site-blocked 125I-rVIIa binding to TF, the Kd for peptide-TF interaction was calculated to be approximately 15 microM in the high salt and approximately 55 microM in the low salt buffer containing 5 mM Ca2+. Moreover, as inferred from S-2288 hydrolysis, the Kd for VIIa.TF interaction was approximately 1.5 microM in the absence of Ca2+, and, as inferred from factor X activation studies, it was approximately 10 pM in the presence of Ca2+. Thus, Ca2+ decreases the functional Kd of VIIa.TF interaction approximately 150,000-fold.(ABSTRACT TRUNCATED AT 400 WORDS)

Involvement of the hydrophobic stack residues 39-44 of factor VIIa in tissue factor interactions

Des(1-38) factor VIIa and des(1-44) factor VIIa were obtained by limited proteolysis. The binding of tissue factor to these factor VIIa-derivatives was assessed from its stimulation of the proteolytic activity on chromogenic oligopeptide substrates. Compared to native factor VIIa (KTF = 0.6 +/- 0.1 nM), Tissue factor binds to des(1-38) factor VIIa with a lower, but still significant affinity (KTF = 4.8 +/- 0.3 nM). The activity of des(1-44) factor VIIa was only slightly stimulated by TF (KTF approximately 200 nM). Binding of TF depends critically on the presence of Ca2+ ions. Ca2+ ions stimulated the activity of factor VIIa/TF with an apparent KCa = 0.16 +/- 0.02 mM. Factor VIIa in the absence of tissue factor was stimulated by Ca2+ with an apparent KCa = 0.05 +/- 0.01 mM, and similar KCa values were obtained for the truncated derivatives of factor VIIa. Measurements of Ca(2+)-induced changes in intrinsic protein fluorescence suggest a conformational change. The Ca2+ ion concentration at which this change occurred was higher for des(1-44) factor VIIa (apparent KCa = 0.14 mM) than for des(1-38)- and native factor VIIa (apparent KCa = 0.04 mM). The Tb3+ ion luminescence technique was used to further investigate the Ca2+ binding sites. Tb3+ ions bound with a lower affinity to des(1-44) factor VIIa than to des(1-38)-and native factor VIIa. The observed drastic decrease in affinity for tissue factor as a result of truncation of the 'hydrophobic stack' residues 39-44, suggest that this region of factor VIIa provides a structural determinant that together with other regions participates in tissue factor binding.

Molecular defects in CRM+ factor VII deficiencies: modelling of missense mutations in the catalytic domain of FVII

The molecular defects causing CRM+ factor VII deficiency were investigated in seven unrelated subjects and several members of their families. Four missense mutations located in the catalytic domain of factor VII were found. The previously reported 304Arg-->Gln substitution was present in the homozygous and heterozygous forms, with different polymorphic haplotypes, thus demonstrating that it is recurrent and frequent in the Italian population. The 310Cys-->Phe substitution was found in the homozygous form and in the compound heterozygous condition with the nonsense mutation 356Trp-->stop. Two missense mutations, 298Met-->Ile and 342Gly-->Arg, were found in the homozygous and in the heterozygous condition respectively. Molecular heterogeneity was further increased by finding of the 353Arg-->Gln polymorphism in the doubly heterozygous condition with the 304 and 342 mutations. Plausible explanations for loss of FVII function were found by inspecting a model of the serine protease domain of factor VIIa. Inefficient activation of the catalytic site is predicted for 298Met-->Ile. 342Gly-->Arg would directly distort the geometry of the 'oxyanion hole' preventing formation of a substrate enzyme intermediate. 310Cys-->Phe is predicted to have an adverse effect on tissue factor interaction. These mutations point to important regions of the factor VII molecule.

Synthesis and characterization of wild-type and variant gamma-carboxyglutamic acid-containing domains of factor VII

Synthetic peptides corresponding to portions of the wild-type and variant sequences of the human factor VII gamma-carboxyglutamic acid (Gla)-containing domain have been prepared by direct peptide synthesis using the Fmoc-based protection strategy. Peptides were purified by ion-exchange and reversed-phase chromatography and characterized as the correct products. A peptide comprising residues 1-49 (GP 1-49) inhibited the activation of factor X (FX) by soluble tissue factor (sTF) and recombinant activated factor VII (rFVIIa). In the absence of phospholipid, no inhibition by this peptide was observed. GP 1-49 did not inhibit the hydrolysis of a peptidyl substrate by rFVIIa in the presence of either sTF or relipidated TF apoprotein in the presence or absence of phospholipid. A similar peptide (residues 1-38, GP 1-38) that did not contain the aromatic stack region was also inhibitory. Two variant peptides, one identical to GP 1-49 but lacking the N-terminal alanine residue (GP 2-49) and one identical to GP 1-38 but with an arginine to alanine substitution at position 9 (GP 1-38 R9A), showed substantially reduced inhibitory activity. Kinetic analysis of the inhibition of Xa generation by GP 1-49 revealed a noncompetitive mode of inhibition, probably via a substrate-depletion mechanism. GP 1-49 does not inhibit by preventing FX binding to phospholipid surfaces. This indicates that the N-terminal residues of the FVII Gla domain are important for the structural integrity of the peptide, and implicates the Gla domain per se in a direct interaction with phospholipid-bound FX.

Specific molecular interaction sites on factor VII involved in factor X activation

Factor VII, a serine-protease zymogen, and tissue factor, the cellular receptor/coenzyme, are the protein components of the macromolecular complex which initiates the extrinsic pathway of the coagulation cascade. Previous studies were directed to the identification of functional sites on factor VII which mediate factor X activation, employing a series of potentially inhibitory synthetic peptides representing the primary structure of factor VII and antibodies to selected peptides. The involvement of at least four high-affinity interactive regions [factor VII (44-50), (196-229), (285-305) and (376-396) peptides] on the surface of factor VII was clearly demonstrated. The minimal sequences for the expression of inhibitory activity of these four molecular recognition domains on factor VII were identified using short and overlapping peptides. The short factor VII-(206-218)-peptide (most inhibitory peptide in the sequence 196-229 on factor VII) inhibited the binding of factor VII to the tissue-factor-expressing J82 cell line. Furthermore, radiolabeled [Tyr201] factor VII-(199-221)-peptide, with a tyrosine substituted for the normal tryptophan residue, was specifically bound to J82 cells, and also the binding of the radiolabeled peptide to this cell line was specifically inhibited by a monoclonal antibody to tissue factor, confirming that the interaction site for tissue factor on factor VII is present within the peptide sequence 196-229. Kinetic analyses suggested that the regions represented by factor VII-(285-305)- and factor VII-(376-396)-peptides are involved in factor X recognition and the chemical cross-linking of the radiolabeled peptides resulted in specific binding to factor X, confirming that these two regions on factor VII represent the substrate-recognition site. Furthermore, these radiolabeled peptides specifically interact with the heavy chain of factor X, suggesting that the complementary binding region for the substrate-recognition site on factor VII are present on the heavy chain of factor X.

Interactions and inhibition of blood coagulation factor Va involving residues 311-325 of activated protein C

Activated protein C (APC) exerts its physiologic anticoagulant role by proteolytic inactivation of the blood coagulation cofactors Va and VIIIa. The synthetic peptide-(311-325) (KRNRTFVLNFIKIPV), derived from the heavy chain sequence of APC, potently inhibited APC anticoagulant activity in activated partial thromboplastin time (APTT) and Xa-1-stage coagulation assays in normal and in protein S-depleted plasma with 50% inhibition at 13 microM peptide. In a system using purified clotting factors, peptide-(311-325) inhibited APC-catalyzed inactivation of factor Va in the presence or absence of phospholipids with 50% inhibition at 6 microM peptide. However, peptide-(311-325) had no effect on APC amidolytic activity or on the reaction of APC with the serpin, recombinant [Arg358]alpha 1-antitrypsin. Peptide-(311-325) surprisingly inhibited factor Xa clotting activity in normal plasma, and in a purified system it inhibited prothrombinase activity in the presence but not in the absence of factor Va with 50% inhibition at 8 microM peptide. The peptide had no significant effect on factor Xa or thrombin amidolytic activity and no effect on the clotting of purified fibrinogen by thrombin, suggesting it does not directly inhibit these enzymes. Factor Va bound in a dose-dependent manner to immobilized peptide-(311-325). Peptide-(311-315) inhibited the binding of factor Va to immobilized APC or factor Xa.(ABSTRACT TRUNCATED AT 250 WORDS)

The dysfunction of coagulation factor VIIPadua results from substitution of arginine-304 by glutamine

This study addresses whether a mutation in the factor VIIPadua gene could explain the reduced activity of the inherited variant protein. All nine exons of the normal and Padua factor VII gene were amplified using the polymerase chain reaction, cloned into pUC19 and sequenced. A point mutation (G to A at nucleotide position 10828) was found which results in the substitution of a glutamine (CAG) for arginine (CGG) at amino acid position 304. This substitution creates a PvuII restriction site useful in screening for the defect and in demonstrating homozygosity. This substitution involves an arginine residue in the catalytic domain within a Leu*****Pro******Cys motif which occurs in conserved region 5 in up to 16 coagulation and other serine proteinases. On the basis of conformational homology among serine proteinases, it is suggested that the observed amino acid substitution in factor VIIPadua could cause structural changes affecting its activation and/or catalytic activity.

Complete nucleotide sequence of the cDNA encoding rabbit coagulation factor VII

Rabbit coagulation factor VII cDNA has been cloned and sequenced. Two rabbit liver cDNA libraries in lambda gt11 were screened using both random-primed, 32p-labelled, factor VII cDNAs and polymerase chain reaction technology. Three overlapping cDNA clones were isolated comprising a sequence of 1572 base pairs of DNA encoding an open-reading-frame of 443 amino acids. Mature circulating rabbit factor VII is predicted to contain 404 amino acids, two less than its human counterpart and three less than bovine factor VII.