Lysine-Binding Site-Dependent Interaction with Plasmin and Factor Va Responsible for Plasmin-Catalyzed Factor Va Inactivation.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2016-2016
Author(s):  
Katsumi Nishiya ◽  
Keiji Nogami ◽  
Kiyotaka Okada ◽  
Osamu Matsuo ◽  
Kenichi Ogiwara ◽  
...  
Keyword(s):  
Binding Site ◽  
Heavy Chain ◽  
Light Chain ◽  
Active Form ◽  
Limited Proteolysis ◽  
Coagulation Factor ◽  
Dependent Manner ◽  
Competitive Binding Assay ◽  
Factor Va ◽  
Sds Page

Abstract Plasmin (Plm), an active form of plasminogen (Plg), functions as a key enzyme in the fibrinolytic system. Furthermore, this enzyme directly inactivates various coagulation factors such as factor V (FV) and factor VIII (FVIII) by limited proteolysis, suggesting another role of Plm in the regulation of the coagulation system. We recently reported that Plm/Plg interacts with FVIII and its active form (FVIIIa), both dependently and independently of lysine-binding site (LBS) (Blood2007; 110, 522a). In this study, we attempted to localize a factor Va (FVa)-interactive region on Plm (and Plg) using Plm/Plg kringle fragments. Surface plasmon resonance-based assays showed that FVa directly bound to active-site modified Plm (anhydro-Plm) with an ~2-fold higher affinity, compared to Plg (Kd; 97 and 198 nM, respectively). In particular, FVa bound to the immobilized-Plg fragment consisting of kringle 1-2-3 domains (K1-3) (Kd: 706 nM), whilst FVa failed to bind both the kringle 4 domain (K4) and Plg fragment consisting of kringle 5 and catalytic domains (K5-CD). A similar experiment using immobilized FVa also revealed that the K1-3 solely bound to FVa. These results were quite different from those obtained by FVIII and Plm/Plg binding experiment that the K5-CD bound to FVIII(a) more preferably. Competitive binding assay using 6-aminohexanoic acid (6-AHA), a competitor of LBS of Plm/Plg, showed that 6-AHA markedly inhibited (by >90%) the K1-3 binding to FVa (IC50; ~25 μM), suggesting that interaction of FVa with Plm is mostly dependent upon LBS. According to the one stage-clotting assay, 6-AHA inhibited (>90%) Plm-catalyzed inactivation of FVa in a dose-dependent manner (IC50; ~10 μM). Furthermore, Plm-catalyzed inactivation of FVa was blocked by an anti-K1-3 monoclonal antibody (mAb), not by either anti-K4 or anti-K5-CD mAb, although Plm-catalyzed inactivation of FVIII was blocked by anti-K5-CD mAb. In order to confirm that the inhibitory effect of 6-AHA on the Plm-catalyzed inactivation, we performed SDS-PAGE experiment. Plm cleaves FVa at Lys309 and Arg348 in the heavy chain, and at Arg1752 in the light chain. SDS-PAGE analysis revealed that 6-AHA blocked Plm-catalyzed cleavages of the light chain more prominently than that of the heavy chain (IC50; ~10 and ~>100 μM, respectively). These findings suggest that the K1-3 of Plm (and Plg) interacts with the FVa through the LBS-dependent mechanisms, and these interactions likely contribute to the FVa-catalyzed inactivation by proteolytic cleavages at Arg1752 in the light chain. Present study indicated that plasmin-catalyzed protelytic inactivation of coagulation factor is complicatedly regulated by the LBS dependency in the protein and protein interaction.

Determination of a factor VIII-interactive region within plasmin responsible for plasmin-catalysed activation and inactivation of factor VIII(a)

2010 ◽  
Vol 104 (07) ◽  
pp. 105-117 ◽  
Author(s):  
Katsumi Nishiya ◽  
Kiyotaka Okada ◽  
Osamu Matsuo ◽  
Masahiro Takeyama ◽  
Kenichi Ogiwara ◽  
...  
Keyword(s):  
Factor Viii ◽  
Binding Site ◽  
Light Chain ◽  
Catalytic Domain ◽  
Active Form ◽  
Limited Proteolysis ◽  
Sds Page ◽  
A2 Domain ◽  
Domain Independent

SummaryPlasmin, an active form of plasminogen, activates and inactivates factor VIII (FVIII) by limited proteolysis. We have previously identifiedly sine-binding site-independent plasmin-interactive sites on the FVIII A2 domain responsible for cleavages at Arg336 and Arg372, together with lysine-binding site-dependent plasmin sites on the light chain responsible for cleavage at Lys36. We have now characterised FVIII-interactive regions on plasmin. SDS-PAGE analysis demonstrated that a monoclon al antibody (mAb) against kringle (K)5-catalytic domain (K5-CD) of plasmin significantly blocked plasmin-catalysed cleavages at Arg336 and Arg372. K5-CD fragment and this mAb blocked plasmincatalysed activation and inactivation of FVIII(a). Anti-K1–2–3 and anti-K4 mAbs blocked plasmin-catalysed cleavages at Lys36, and K1–2–3 and K4 fragments inhibited plasmin-catalysed inactivation of A11–336 FVIIIa. The K5-CD preferentially bound to the A2 domain (Kd app ; 52 nM), whilst the K1–2–3 and K4 bound to the light chain (Kd app; 75 and 106 nM, respectively) in ELISA. Binding was attributed to the A2 484–509 region and A3 1690–1705/1804–1818 region, respectively. 6-aminohexanoic acid, a lysine analogue, significantly inhibited the light chain/K1–2–3 (and K4) binding by ∼90%, whilst A2/K5-CD binding was moderated by only ∼35%. Furthermore, an anti-CD antibody blocked plasmin-catalysed cleavage by inhibiting the A2/K5-CD interaction. These data demon strate that the K5-CD of plasmin (and plasminogen) interacts with the A2 domain independent of lysine-binding site, whilst interactions of K1–2–3 and K4 with the light chain are lysine-binding site-dependent. Interactions between the K5-CD and A2 likely constitute the major regulatory mechanism for activation and inactivation of FVIII(a) mediated by cleavage at Arg372 and Arg336.

scholarly journals Platelet coagulation factor Va: the major secretory platelet phosphoprotein

Blood ◽  
1994 ◽  
Vol 83 (8) ◽  
pp. 2180-2190
Author(s):  
MD Rand ◽  
M Kalafatis ◽  
KG Mann
Keyword(s):  
Heavy Chain ◽  
Light Chain ◽  
Activated Protein C ◽  
Coagulation Factor ◽  
Casein Kinase Ii ◽  
Casein Kinase ◽  
Factor V ◽  
Platelet Factor ◽  
Factor Va ◽  
Plasma Factor

Platelet-derived coagulation factor Va is the primary secreted substrate for a thrombin-stimulation-dependent platelet kinase. Human platelet factor Va, consisting of a molecular weight (M(r)) 105,000 heavy chain and an M(r) 74,000 light chain, incorporates phosphate in at least two sites on the light chain. Phosphorylated factor Va represents 50% of the secreted protein-associated phosphate. This modification occurs exclusively at serine residues and is inhibited by H-7 and staurosporine, which suggests a protein kinase C (PKC)-mediated event. Purified plasma factor V and Va are phosphorylated in the light chain region by rat brain PKC. The activity of platelet factor Va in prothrombinase on platelets is not altered when phosphorylation is inhibited by staurosporine. Plasma-derived factor Va in the presence of thrombin stimulated platelets is phosphorylated on both the heavy chain and the light chain. Plasma factor V and factor Va heavy chain phosphorylation occurs without light chain phosphorylation in the presence of added 32P gamma-ATP and non-stimulated or collagen- stimulated platelets or casein kinase II. This differential phosphorylation of factor Va heavy and light chain shows two independent platelet kinase activities that act on factor Va. The heavy chain factor V/Va kinase activity is similar to casein kinase II, which we have demonstrated previously to act on factor Va and accelerate activated protein C inactivation of the cofactor. Our data show platelet-dependent phosphorylation of platelet and plasma factor V and Va resulting in significant covalent modifications of the cofactor. These modifications may play a role in directing the extracellular distribution of factor V and factor Va.

scholarly journals Platelet coagulation factor Va: the major secretory platelet phosphoprotein

Blood ◽  
1994 ◽  
Vol 83 (8) ◽  
pp. 2180-2190 ◽  
Author(s):  
MD Rand ◽  
M Kalafatis ◽  
KG Mann
Keyword(s):  
Heavy Chain ◽  
Light Chain ◽  
Activated Protein C ◽  
Coagulation Factor ◽  
Casein Kinase Ii ◽  
Casein Kinase ◽  
Factor V ◽  
Platelet Factor ◽  
Factor Va ◽  
Plasma Factor

Abstract Platelet-derived coagulation factor Va is the primary secreted substrate for a thrombin-stimulation-dependent platelet kinase. Human platelet factor Va, consisting of a molecular weight (M(r)) 105,000 heavy chain and an M(r) 74,000 light chain, incorporates phosphate in at least two sites on the light chain. Phosphorylated factor Va represents 50% of the secreted protein-associated phosphate. This modification occurs exclusively at serine residues and is inhibited by H-7 and staurosporine, which suggests a protein kinase C (PKC)-mediated event. Purified plasma factor V and Va are phosphorylated in the light chain region by rat brain PKC. The activity of platelet factor Va in prothrombinase on platelets is not altered when phosphorylation is inhibited by staurosporine. Plasma-derived factor Va in the presence of thrombin stimulated platelets is phosphorylated on both the heavy chain and the light chain. Plasma factor V and factor Va heavy chain phosphorylation occurs without light chain phosphorylation in the presence of added 32P gamma-ATP and non-stimulated or collagen- stimulated platelets or casein kinase II. This differential phosphorylation of factor Va heavy and light chain shows two independent platelet kinase activities that act on factor Va. The heavy chain factor V/Va kinase activity is similar to casein kinase II, which we have demonstrated previously to act on factor Va and accelerate activated protein C inactivation of the cofactor. Our data show platelet-dependent phosphorylation of platelet and plasma factor V and Va resulting in significant covalent modifications of the cofactor. These modifications may play a role in directing the extracellular distribution of factor V and factor Va.

LIPOPOLYSACCHARIDE-SENSITIVE SERINE-PROTEASE ZYMOGEN (FACTOR C) OF LIMULUS HEMOCYTES: IDENTIFICATION AND ALIGNMENT OF PROTEOLYTIC FRAGMENTS PRODUCED DURING THE ACTIVATION SHOW THAT IT IS A NOVEL TYPE OF SERINE-PROTEASE

1987 ◽  
Author(s):  
F Tokunaga ◽  
T Miyata ◽  
T Nakamura ◽  
T Morita ◽  
S Iwanaga
Keyword(s):  
Serine Protease ◽  
Heavy Chain ◽  
Light Chain ◽  
Interleukin 2 ◽  
Coagulation Factor ◽  
Clotting Factor ◽  
Single Chain ◽  
Terminal Sequence ◽  
A Chain ◽  
Factor C

Limulus clotting factor, factor C, is a lipopolysaccharide (LPS)-sensitive serine-protease zymogen present in the hemocytes. It is a two-chain glycoprotein (M.W. = 123,000) composed of a heavy chain (M.W. = 80,000) and a light chain (M.W. = 43,000) T. Nakamura et al. (1986) Eur. J. Biochem. 154, 511-521 .On further studies of this zymogen, a single-chain factor C (M.W. = 123,000) was identified by Western blotting technique. The heavy chain had an NH2-terminal sequence of Ser-Gly-Val-Asp-, which was consistent with the NH2-terminal sequence of the single-chain factor C, indicating that the heavy chain is located in the NH2-terminal part of the zymogen. The light chain had an NH22-terminal sequence of Ser-Ser-Gln-Pro-. Incubation of the two-chain zymogen with LPS resulted in the cleavage of a Phe-Ile bond between residues 72 and 73 of the light chain. Concomitant with this cleavage, the A (72.amino acids) and B chains derived from the light chain was formed. The complete amino acid sequence of the A chain was determined by automated Edman degradation. The A chain contained a typical segment which is similar structuraly to those a family of repeats in human β2 -glycoprotein I, complement factors B, Clr, Cls, H, C4b-binding protein, 02, coagulation factor XIII b subunit, haptoglobin a chain, and interleukin 2 receptor. The NH2-terminal sequence of the B chain was Ile-Trp-Asn-Gly-. This chain contained the serine-active site sequence of -ASP-Ala-Cys-Ser-Gly-Asp-SER-Gly-Gly-Pro-.These results indicate that limulus factor C exists in the hemocytes in a single-chain zymogen form and is converted to an active serine-protease by hydrolysis of a specific Phe-Ile peptide bond. The correlation of limulus factor C and mammalian complement proteins was also suggested.

THE PHOSPHOLIPID-BINDING SITE OF FACTOR VIII IS LOCATED ON THE 80 kD LIGHT CHAIN

1987 ◽  
Author(s):  
G Kemball-Cook ◽  
S J A Edwards ◽  
K Sewerin ◽  
L-O Andersson ◽  
T W Barrowcliffe
Keyword(s):  
Binding Site ◽  
Light Chain ◽  
Binding Sites ◽  
Immunoaffinity Chromatography ◽  
The Other ◽  
Immunological Methods ◽  
Electrophoretic Separation ◽  
Antigenic Sites ◽  
Reducing Conditions ◽  
Sds Page

The binding of Factoi. VIII (F.VIII) peptides to phospholipid (PL) vesicles has been studied by two different methods involving the use of fractionated anti-F.VIII:C I-Fab123’pre viously reported, i-Fab123’ was fractionated by immunoadsorptionwith F.VIII-PL complexes into two pools:one binding only to PL-binding sites on F.VIIIsAg (PL-site antibody), the other directed against other antigenic sites (non-PL-site antibody).The first technique used was a modification of the method of Weinstein et al. (Proc.Natl.Acad.Sci.USA, 78, 5137-5141, 1981), and involved incubation of the two anti-F.VIII pool swith F.VIII-containing samples, followed by electrophoretic separation of the complexes on the basis of size in non-denaturing SDS gels: this technique allows qualitative analysis of antibody reactive peptides in highly impure samples. Non-PL-site pool reacted with a range of peptides with MrMapparent Mr 90 kD up to 280 kD, a similar pattern to that of ’heavy chain’(HC) peptides of F.VIII seen on SDS-PAGE under reducing conditions; the PL-site antibody, however, reacted only with peptides at apparent Mrs of 80 kD and sometimes150 kD, but not with bands of higher Mr a pattern more consistent with binding to light chain (LC) peptides. Thesame patterns with the two labels were seen in both plasma and F.VIII concentrateThe second approach employed the two labels described above in direct immunoradiometric assays (IFMA’s) on purified human F.VIII peptides prepared by immunoaffinity chromatography and ion exchange on Mono Q gel. Both PL-site and non-PL-site labels measured similar amounts of F.VIII m a sample containing both HC and LC peptides; however, on assaying a sample containing purified HC peptides alone, PL-site antibody measured only 2% of F.VIII:Ag found by non-PL-site label, indicating that PL-binding sites present in samples containing both HC and LC are absent in HC alone.Results from both these immunological methods indicate that the 80 kD LC peptide of F.VIII carries the PL-binding site.

Localization of Factor VIII Interactive Site within Plasmin/Plasminogen Which Is Responsible for Plasmin-Catalyzed Activation/Inactivation of Factor VIII.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1759-1759 ◽  
Author(s):  
Katsumi Nishiya ◽  
Keiji Nogami ◽  
Kiyotaka Okada ◽  
Osamu Matsuo ◽  
Masahiro Takeyama ◽  
...  
Keyword(s):  
Factor Viii ◽  
Light Chain ◽  
Catalytic Domain ◽  
Active Form ◽  
Coagulation Factors ◽  
Competitive Binding Assay ◽  
Key Enzyme ◽  
Proteolytic Cleavages ◽  
20 Nm ◽  
A2 Domain

Abstract Plasmin (Plm), an active form of plasminogen (Plg), not only functions as a key enzyme in the fibrinolytic system, but also directly inactivates several coagulation factors. Especially, factor VIII is inactivated by Plm immediately after the activation by limited proteolytic cleavage at Lys36, Arg336, Arg372, and Arg740 in the heavy chain, and at Arg1689 and Arg1721 in the light chain (Nogami et al. J. Biol. Chem. 2007, 282, 5287). We recently have identified the plasmin-interactive sites on the A2 domain responsible for cleavages at Arg336 and Arg372, and on the light chain responsible for cleavage at Lys36 (Abst #1991/1709, BLOOD 102/108, 2005/2006). In the present study, we attempted to localize a factor VIII-interactive site on Plm (and Plg). Competitive binding assay using 6-aminohexanoic acid (6-AHA), a competitor of lysine-binding site (LBS) of Plm/Plg, showed that 6-AHA markedly inhibited (by >90%) the light chain binding to active-site modified Plm (anhydro-Plm), whilst inhibited weakly the A2 binding (by ∼30%). These results suggested that the light chain interaction with Plm was mainly dependent upon LBS, but the A2 interaction was independent. The addition of monoclonal antibody (mAb) against Plg kringle 5-catalytic domain (K5-CD) significantly inhibited Plm-catalyzed activation/inactivation of factor VIII or VIIIa with an ∼4-fold lower rate constant. On the other hand, anti-K1-3 and anti-K4 mAbs any little affected. SDS-PAGE analysis revealed that only anti-K5-CD mAb blocked Plm-catalyzed cleavages at Arg336 and Arg372 by ∼90% in dose-dependent manners (IC50: ∼20 nM). Surface plasmon resonance-based assays showed that the isolated K5-CD bound to factor VIII with an ∼50-fold higher affinity (Kd: 3 nM) compared to the K1-3 and K4, similar to the affinity obtained with anhydro-Plm (Kd: 4 nM). In particular, the K5-CD bound to the A2 domain with an ∼5-fold higher affinity (Kd: 42 nM) than those obtained with the K1-3 and K4. In contrast, both the K1-3 and K4 bound to the light chain predominantly (Kd: 43 and 87 nM, respectively), whilst the K5-CD failed to bind. Furthermore, the addition of a goat antibody against the CD (C-14; Santa Cruz Biotechnology) completely blocked the A2 and K5-CD interaction (by ∼95%). These findings suggest that the CD of Plm (and Plg) interacts with the factor VIII A2 domain through the LBS-independent mechanisms, whilst the K1-3 (and/or K4) interacts with the light chain through the LBS-dependent mechanisms. Furthermore, the CD and A2 interaction would regulate the activation/inactivation of factor VIII by proteolytic cleavages of Arg336 and Arg372.

Plasma Procofactor Activation by Factor Xla

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1024-1024
Author(s):  
Matthew F Whelihan ◽  
Kenneth G. Mann
Keyword(s):  
Sequence Analysis ◽  
Heavy Chain ◽  
Light Chain ◽  
Thrombin Generation ◽  
Coagulation Cascade ◽  
Sequencing Analysis ◽  
Reducing Conditions ◽  
Sds Page ◽  
Initial Cleavage ◽  
Contact Pathway

Abstract The procofactors FV and FVIII are activated by thrombin, FXa and plasmin. During contact pathway-initiated thrombin generation, FXIa activates FIX thus feeding into the coagulation cascade; however, the procofactors FVIII and FV must be activated to achieve a robust level of thrombin generation. We tested the hypothesis that FXIa can activate FV and FVIII. FV (1uM) was subjected to FXIa (100nM) proteolysis. During the reaction the relative activity and integrity were measured at selected time points using a one stage PT clotting assay and SDS-PAGE. Over the 60 minute time course, FV showed a transient 50% activation followed by a reduction in activity to 20%. SDS-PAGE analyses showed that proteolysis of FV by FXIa initially generated fragments with mobilities similar to those produced by α-thrombin. This activation and inactivation pattern suggested that FXIa makes the required activation cleavages at R709, R1018 and R1545 coincidently with inactivating proteolyses. FV was activated with α-thrombin and the reaction quenched by the addition of hirudin prior to FXIa proteolysis. FVa’s cofactor activity was reduced by 50% after 30 min and 80% after 60 min. Analysis of the FXIa cleavage process by SDS-PAGE under reducing conditions showed no intact heavy chain and significant proteolysis of the light chain after 30 minutes. In addition to the Mr = 105000 (HC) and Mr = 75000 (LC), six new products were identified by SDS-PAGE under reducing conditions: Mr = 54000, 50000, 48000, 30000, 22000 and 20000. NH2-terminal sequence analysis indicated a single cleavage in the light chain at R1765 yielding the products Mr = 50000, 48000: (1766à2196) and the Mr = 30000 (1546à1764), also seen with plasmin and FXa. A cleavage in the heavy chain represented by the Mr = 22000, 20000 (R511à709) fragments is also observed. Sequence analysis determined that the Mr = 54000 fragment represented the NH2-terminus of the heavy chain. Western analysis using a heavy chain antibody showed a transient band Mr = 75000 lying under the light chain that is consistent with an initial cleavage R510. A subsequent cleavage, which is coincident with a decrease in the cofactor’s activity, results in a Mr = 30000 product which is consistent with a cleavage somewhere COOH-terminal to R306(R316?). Activity analyses suggest that the initial cleavage in the heavy chain at R510 leads to a FVaXla 1 molecule with similar activity (50%) to that seen in FVa cleaved by APC in the absence of phospholipid. The FVaXla 1 was treated with APC resulting in complete inactivation of the cofactor. We have also observed an analogous FXIa cleavage pattern in FVIII; however sequencing analysis has not yet been attempted. These data suggest that factor XIa may play a role in procofactor activation and inactivation of FV and FVIII in the context of contact pathway-initiated blood coagulation. Figure Figure

Specific Leucine, Isoleucine and Threonine Residues In The TFPIα C-Terminal Region Are Necessary For Inhibition Of Prothrombinase

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 3562-3562
Author(s):  
Jeremy P Wood ◽  
Alan E. Mast
Keyword(s):  
Inhibitory Activity ◽  
Thrombin Generation ◽  
Factor Viia ◽  
Specific Binding ◽  
Mammalian Species ◽  
Limited Proteolysis ◽  
Dependent Manner ◽  
Factor Va ◽  
C Terminus ◽  
Acidic Region

Abstract Background In addition to regulating the initiation of coagulation through inhibition of the tissue factor/factor VIIa complex, we have recently demonstrated a previously unrecognized anticoagulant function of TFPIα: inhibition of the prothrombinase complex (factor Xa (FXa), factor Va (FVa), Ca++, and phospholipids). No endogenous protein has previously been identified to inhibit prothrombinase under physiologically relevant conditions. The inhibition of prothrombinase is mediated by two specific binding events: (1) binding of TFPI’s second Kunitz domain to the FXa active site; and (2) an essential high–affinity exosite interaction between the TFPIα C-terminus and an acidic region within the factor V B-domain, retained in forms of FVa present in platelet alpha granules or generated through limited proteolysis with FXa. The TFPIα C-terminus contains a basic region (LIKTKRKRK) nearly identical to one found in the FV B-domain (LIKTRKKKK). Both of these sequences are highly conserved across mammalian species, suggesting they have an important physiological function. The basic residues of these sequences are necessary for the charge-based interaction with the FVa B-domain acidic region. We sought to determine the function of the absolutely conserved L, I, and T residues of this sequence. Methods Seven peptides containing different changes in the LIKT portion of the sequence, as shown below, were synthesized and tested in thrombin generation assays using forms of Factor Va containing (FVaAR) or lacking (FVaIIa) the acidic region of the B-domain. Results The wild type peptide (LIKTKRKRKK) inhibited FVaAR prothrombinase (IC50 = 1.03 µM) but did not inhibit FVaIIa prothrombinase at concentrations up to 225 µM, confirming that inhibition requires the presence of the B-domain acidic region. Substitution of LIKT with AAAA (AAAAKRKRKK) essentially abolished inhibitory activity with only ∼20% inhibition observed at 350 µM peptide, as did substitution of the L, I, and T (AAKAKRKRKK), demonstrating that the positively charged K and R residues alone do not mediate the inhibitory activity. Individual Ala substitutions of the L, I, and T residues resulted in decreased, but measurable, inhibitory function (IC50= 70.2 µM, 16.7 µM, and 107 µM, respectively). Finally, the peptide LIETKRKRKK was made to assess the effect of a K254E mutation, which has been identified in the NHLBI Exome Sequencing Project. This also essentially abolished inhibitory activity with only 20% inhibition observed in the presence of 340 µM peptide. Conclusions TFPIα inhibits thrombin generation by prothrombinase assembled with forms of FVa that retain the acidic region of the B-domain, which serves as a key exosite, binding the TFPIα basic C-terminus in a charge-dependent manner. The peptide studies presented here demonstrate that the hydrophobic residues L, I, and T are also absolutely essential for exosite binding and inhibition of thrombin generation. In addition, a natural mutation in the LIKT sequence (LIET) results in complete loss of prothrombinase inhibition, and therefore may represent a previously unrecognized prothrombotic risk factor. Thus, the regulation of coagulation occurring through TFPIα-mediated inhibition of prothrombinase appears to be relevant during normal hemostasis, as well as under pathologic conditions. Disclosures: Mast: Novo Nordisk: Honoraria, Research Funding.

scholarly journals Pathways in the activation of human coagulation factor X

1980 ◽  
Vol 185 (3) ◽  
pp. 647-658 ◽  
Author(s):  
K Mertens ◽  
R M Bertina
Keyword(s):  
Heavy Chain ◽  
Active Form ◽  
Factor Xa ◽  
Coagulation Factor ◽  
Terminal Region ◽  
Factor Vii ◽  
Factor X ◽  
Catalytically Active ◽  
A Site ◽  
Polypeptide Chains

Purified human Factor X (apparent mol.wt. 72000), which consists of two polypeptide chains (mol.wt. 55000 and 19000), was activated by both Russell's-viper venom and the purified physiological activators (Factor VII/tissue factor and Factor IXa/Factor VIII). They all convert Factor X to catalytically active Factor Xa (mol.wt. 54000) by cleaving the heavy chain at a site on the N-terminal region. In the presence of Ca2+ and phospholipid, the Factor Xa formed catalyses (a) the cleavage of a small peptide (mol.wt. 4000) from the C-terminal region of the heavy chain of Factor Xa, resulting in a second active form (mol.wt. 50000), and (b) the cleavage of a peptide containing the active-site serine residue (mol.wt. 13000) from the C-terminal region of the heavy chain of Factor X, resulting in an inactivatable component (mol.wt. 59000). A nomenclature for the various products is proposed.

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