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

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

Phage displaying APPI Kunitz domain libraries have been used to design potent and selective active site inhibitors of human plasma kallikrein, a serine protease that plays an important role in both inflammation and coagulation. Selected clones from two Kunitz domain libraries randomized at or near the binding loop (positions 11-13, 15-19, and 34) were sequenced following five rounds of selection on immobilized plasma kallikrein. Invariant preferences for Arg at position 15 and His at position 18 were found, whereas His, Ala, Ala, and Pro were highly preferred residues at positions 13, 16, 17, and 19, respectively. At position 11 Pro, Asp, and Glu were favored, while hydrophobic residues were preferred at position 34. Selected variants, purified by trypsin affinity chromatography and reverse phase high performance liquid chromatography, potently inhibited plasma kallikrein, with apparent equilibrium dissociation constants (Ki*) ranging from approximately 75 to 300 pM. From sequence and activity data, consensus mutants were constructed by site directed mutagenesis. One such mutant, KALI-DY, which differed from APPI at 6 key residues (T11D, P13H, M17A, I18H, S19P, and F34Y), inhibited plasma kallikrein with a Ki* = 15 +/- 14 pM, representing an increase in binding affinity of more than 10,000-fold compared to APPI. Similar to APPI, the variants also inhibited Factor XIa with high affinity, with Ki* values ranging from approximately 0.3 to 15 nM; KALI-DY inhibited Factor XIa with a Ki* = 8.2 +/- 3.5 nM. KALI-DY did not inhibit plasmin, thrombin, Factor Xa, Factor XIIa, activated protein C, or tissue factor. Factor VIIa. Consistent with the protease specificity profile, KALI-DY did not prolong the clotting time in a prothrombin time assay, but did prolong the clotting time in an activated partial thromboplastin time assay > 3.5-fold at 1 microM.
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PMID:Potent and selective Kunitz domain inhibitors of plasma kallikrein designed by phage display. 759 8

The extrinsic coagulation pathway is initiated by the binding of plasma factor VII(a) (VIIa) to the cell surface receptor tissue factor (TF), which serves as the cofactor for the ligand protease VIIa in the activation of macromolecular substrate factors X and IX. The catalytic function of the TF.VIIa complex is regulated by a specific Kunitz-type inhibitor, tissue factor pathway inhibitor (TFPI), which forms a stoichiometric complex with the serine protease factor Xa (Xa), resulting in greatly accelerated inhibition of the extrinsic initiation complex as compared to free inhibitor. In the present study we identify specific residues in the TF-VIIa complex that are involved in the factor Xa-mediated acceleration of TFPI inhibitory function. VIIa residue Arg290, which contributes to extended recognition of macromolecular substrate factor X, is not involved in the interaction with the TFPI.Xa complex. In contrast, TF residues Lys165 and Lys166, which are important for the activation of factor X, are required for the accelerated inhibition of the TF.VIIa complex by TFPI mediated by factor Xa. These data indicate that similar interactions contribute to the assembly of substrate factor X as well as of product Xa after complex formation with TFPI, suggesting a central role for the carboxyl-terminal structural module of TF in regulating the proteolytic activity of TF.VIIa.
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PMID:Tissue factor residues Lys165 and Lys166 are essential for rapid formation of the quaternary complex of tissue factor.VIIa with Xa.tissue factor pathway inhibitor. 766 67

Ecotin, an Escherichia coli periplasmic protein of 142 amino acids, has been shown to be a potent inhibitor of a group of homologous serine proteases with widely differing substrate recognition. It is highly effective against a number of enzymes, including both pancreatic and neutrophil-derived elastases, chymotrypsin, trypsin, factor Xa, and kallikrein. Recent structural and functional studies on ecotin and its interactions with different serine proteases have clarified these initial observations and revealed the remarkable features of this protein in inhibiting a strikingly large subset of the chymotrypsin family of serine proteases. The structures of the ecotin:serine protease complexes provide the first examples of protein-protein recognition where the concept of specificity of interactions needs to be reexamined. The binding sites show a fluidity of protein contacts derived from ecotin's innate flexibility in fitting itself to proteases while strongly interfering with their function.
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PMID:Ecotin: lessons on survival in a protease-filled world. 775 4

A widely accepted model for the association of extrinsically bound proteins with acidic lipid-containing membranes has been that approach of the protein to the membrane induces a domain of acidic lipids that serves as the protein binding site. This model has been applied to a variety of membrane proteins including those that participate in the proteolytic complex that converts prothrombin to thrombin during the final stages of the blood coagulation cascade. The 'prothrombinase complex' consists of a serine protease (factor Xa), its protein co-factor (factor Va) and the substrate itself (prothrombin), all bound to phosphatidylserine (PS)-containing membranes derived from stimulated platelets. We have used three approaches to test the domain model as it applies to the proteins of this complex. First, phase diagrams describing the mixing of acidic and neutral lipids have failed to provide evidence for extensive acidic lipid domains (on the order of 50 or more lipid molecules) induced by protein biding. Second, pyrene-containing neutral and acidic phospholipids have been used to test for the occurrence of domains of as few as 20-30 lipids associated with binding of the membrane-binding fragment 1 region of prothrombin. Again, no evidence for domains was obtained. Finally, we have shown that binding of these proteins can be described in terms of a generalized model that presumes an acidic-lipid-independent surface adsorption combined with specific binding of acidic lipids to 'm' sites on a protein. Our results suggest that the concept of a protein-induced domain should not be applied indistriminately to explain binding of extrinsic membrane proteins such as the protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Are acidic lipid domains induced by extrinsic protein binding to membranes? 776 85

Planar-supported phospholipid bilayers formed by the adsorption of vesicles are increasingly used in the investigation of lipid-dependent reactions. We have studied the way in which these bilayers are formed with phospholipid vesicles containing the transmembrane protein Tissue Factor (TF). TF complexed with the serine protease, factor VIIa, is the primary initiator of blood coagulation by way of activation of the zymogen factor X. TF has been shown to orient randomly on the inner and outer leaflets of vesicles. We used proteolytic digestion to produce vesicles in which the extracellular domain of TF is located on the inner leaflet. These vesicles show no cofactor activity for factor VIIa as a result of the inability of the extracellular domain of TF to bind VIIa. After freeze/thawing, 50% of the cofactor activity was regained, indicating reorientation of the sequestered, inner leaflet TF. Adsorption of these vesicles to the inner surface of glass microcapillaries results in a continuous phospholipid bilayer. The microcapillaries were perfused with a solution of factors VIIa and X, and the effluent was monitored for factor Xa production, a sensitive measure of the activity of the TF-VIIa complex. For coatings produced with the digested vesicles, minimal TF-VIIa activity was observed, showing that the supported bilayer preserves the orientation of the leaflets in the vesicles, i.e., the outer leaflet of the vesicles forms the outer leaflet of the supported bilayer.
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PMID:Use of an oriented transmembrane protein to probe the assembly of a supported phospholipid bilayer. 781 22

Previous studies have shown that hepsin is a putative membrane-associated serine protease that is required for cell growth (Torres-Rosado, A., O'Shea, K. S., Tsuji, A., Chou, S.-H., and Kurachi, K. (1993) Proc. Natl. Acad. Sci. U.S. A. 90, 7181 7185). In the present study, we have transfected baby hamster kidney (BHK) cells with a plasmid containing the cDNA for human hepsin and examined these cells for their ability to activate several blood coagulation factors including factors X, IX, VII, prothrombin, and protein C. Little, if any, proteolytic activation of factors X, IX, prothrombin, or protein C was observed when these clotting factors were incubated with hepsin-transfected cells. On the other hand, hepsin-transfected cells proteolytically activated significant concentrations of human factor VII in a time- and calcium-dependent manner, whereas essentially no activation of factor VII was observed in BHK cells transfected with plasmid lacking the cDNA for hepsin. The factor VII activating activity in the hepsin-transfected BHK cell line was confined exclusively to the total membrane fraction and was inhibited > 95% by antibody raised against a fusion protein consisting of maltose-binding protein and the extracellular domain of human hepsin. An active site factor VII mutant, S344A factor VII, was cleaved as readily as plasma-derived factor VII by hepsin-transfected cells, indicating that factor VII was not converted to factor VIIa autocatalytically on the cell surface. In contrast, an activation cleavage site factor VII mutant, R152E factor VII, was not cleaved by hepsin-transfected cells, suggesting that factor VII and S344A factor VII were activated on these cells by cleavage of the Arg152-Ile153 peptide bond. In the copresence of factor VII and factor X, hepsin-transfected BHK cells supported the formation of factor Xa. In addition, in the copresence of factor VII, factor X, and prothrombin, hepsin-transfected BHK cells supported the formation of thrombin. These results strongly suggest that membrane-associated hepsin converts zymogen factor VII to factor VIIa, which in turn, is capable of initiating a coagulation pathway on the cell surface that ultimately leads to thrombin formation.
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PMID:Hepsin, a putative membrane-associated serine protease, activates human factor VII and initiates a pathway of blood coagulation on the cell surface leading to thrombin formation. 781 21

Protein C (PC) is the zymogen of an anticoagulant serine protease and is converted to its active form (activated protein C: APC) by thrombin in the presence of thrombomodulin. APC plays an important role in regulating thrombosis and fibrinolysis by inhibiting not only blood coagulation factors Va and VIIIa but also type-1 plasminogen activator inhibitor (PAI-1). In the present study we examined the effects of human APC on tissue thromboplastin-induced disseminated intravascular coagulation (DIC) in rabbits and compared them with those of heparin. Both APC (300-3000 U/kg) and heparin (100-300 IU/kg) inhibited the decreases in platelet count and fibrinogen level equally. APC improved the prolonged bleeding time, but heparin aggravated bleeding with potent prolongation of activated partial thromboplastin time (APTT). Furthermore, in APC-treated animals, fibrin deposition in glomeruli was less than in heparin-treated animals. This result that APC accelerated local fibrinolysis by neutralizing PAI-1. From our findings, we concluded that APC can improve both coagulation and fibrinolysis in a DIC model and should be useful for the clinical remedy of DIC without having an adverse side effect like a bleeding tendency.
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PMID:Characteristic effects of activated human protein C on tissue thromboplastin-induced disseminated intravascular coagulation in rabbits. 787 94

Squash family inhibitors are the smallest protein serine protease inhibitors, being composed of approximately 30 amino acid residues. We isolated 8 squash family inhibitors from the seeds of bitter gourd, squash, gourd and luffa and examined their effect on serine proteases of the blood coagulation system. Five of them prolonged the activated partial thromboplastin time of human plasma to various extents, but three did not. Only Momordica charantia (bitter gourd) trypsin inhibitor-II prolonged the prothrombin time of human plasma. All inhibitors inhibited the amidolytic activities of factor XIIa, plasma kallikrein, factor Xa, but did not inhibit significantly those of factor XIa, factor IXa, factor VIIa, and thrombin. Ki values for factor XIIa, plasma kallikrein, and factor Xa were in the order of 10(-6)-10(-9), 10(-4)-10(-5), and 10(-4)-10(-6)M, respectively. The prolongation of the activated partial thromboplastin time by inhibitors appeared to correspond to their inhibitory potencies for factor XIIa. Momordica charantia trypsin inhibitor-II, which has the strongest inhibitory potency toward the amidolytic activity of factor Xa, with a Ki value 10-100 times smaller than those of other inhibitors, inhibited the activation of factor X by factor VIIa-tissue factor complex or factor IXa, while others did not.
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PMID:Inhibition of serine proteases of the blood coagulation system by squash family protease inhibitors. 789 27

Factor IX is a vitamin K-dependent procoagulant zymogen of a serine protease. In the presence of Ca2+ the active form of factor IX (factor IXa beta) forms a complex with factor VIIIa on suitable phospholipid surfaces such as aggregated platelets. This macromolecular complex rapidly activates factor X. We have previously provided data that suggest an interaction between the NH2-terminal epidermal growth factor (EGF)-like module of factor IXa beta and the substrate factor X. In an alternative approach to study this protein-protein interaction, we have expressed three recombinant baculovirus constructs encoding the EGF-like modules of human factor IX and a truncated form of fibronectin in a system based on the infection of insect cells (Spodoptera frugiperda 21). This strategy allows a simple one-step purification of the recombinant proteins on a gelatin-Sepharose column, followed by removal of the gelatin-binding part derived from fibronectin by proteolytic cleavage. The fusion proteins were isolated at yields of 20-50 micrograms/ml culture medium. The recombinant EGF-like modules contained 0.2-0.4 mol of erythro-beta-hydroxyaspartic acid/mol of protein, i.e. similar to the amount found in factor IX from human plasma, and appeared to be glycosylated at Ser-53. The NH2-terminal EGF-like module, which contained a transamidation acceptor site derived from fibronectin, was cross-linked by factor XIIIa in solution to intact and Gla-domainless factor X. There was no evidence of cross-linking to activated factor X or to factor X fragments containing only the gamma-carboxyglutamic acid module and the two EGF-like modules. The cross-linking results suggest a specific interaction between the NH2-terminal EGF-like module of factor IXa beta and the heavy chain of unactivated factor X. This interaction, albeit weak as judged by competition experiments, may be important for the targeting of factor X to the factor IXa beta-factor VIIIa complex on biological membranes and for the subsequent dissociation of factor Xa from the complex after activation.
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PMID:Baculovirus-mediated expression of the epidermal growth factor-like modules of human factor IX fused to the factor XIIIa transamidation site in fibronectin. Evidence for a direct interaction between the NH2-terminal epidermal growth factor-like module of factor IXa beta and factor X. 790 69

The seminal vesicle protein No. 4 (SV-IV) secreted from the rat seminal vesicle epithelium, possesses immunosuppressive and anti-inflammatory properties and it is a potent inhibitor of platelet aggregation both in vivo and in vitro. This research aimed to investigate the possible effect of SV-IV on the process of human blood coagulation. Preliminary experiments showed that the recalcification time (RT) of platelet-poor plasma (PPP) samples, obtained from both normal subjects and patients affected by some hemorrhagic disorders, was found to be markedly reduced in the presence of micromolar amounts of SV-IV. It was demonstrated that the concentration of free antithrombin III (AT III) occurring in blood sera obtained from PPP samples recalcified in the presence of SV-IV was significantly decreased in comparison with sera obtained from PPP recalcified in the absence of SV-IV. It was also shown that PPP treatment with SV-IV significantly reduced the concentration of free AT III without affecting the levels of other plasma serine protease inhibitors, such as alpha 2-macroglobulin, alpha 1-antitrypsin and C1-inhibitor. In addition, the RT of PPP treated with a specific rabbit anti-AT III polyclonal antiserum (anti-AT III treated PPP) was not modified by SV-IV. These findings were confirmed by the observation that the addition of SV-IV into an in vitro coagulation system, containing pure fibrinogen, alpha-thrombin and AT-III, resulted in complex suppression of thrombin inhibition by AT III. No other steps of the blood clotting process (prothrombinase complex, factor XIII, fibrinogen concentration) were affected by SV-IV.
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PMID:Rat protein SV-IV (seminal vesicle protein No. 4) accelerates human blood coagulation in vitro by selective inhibition of antithrombin III. 805 30


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