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:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

By the use of recombinant technology, several stable Chinese hamster ovary (CHO) cell lines expressing human FVIII were established. Thrombin treatment and SDS-PAGE analysis of the purified recombinant FVIII (rFVIII) revealed a striking difference from plasma-derived FVIII (pFVIII). A 43-kDa fragment of the FVIII heavy chain appears as a double band from rFVIII, while a single band from pFVIII is observed. All other fragments from the two samples appeared similar by SDS-PAGE. The heterogeneity is caused by incomplete tyrosine sulfation of one or more of the three potential tyrosine sulfation sites (Tyr718, Tyr719, Tyr723). To investigate if there is a general limitation and heterogeneity in the tyrosine sulfation of rFVIII, two other potential tyrosine sulfation sites on the FVIII light chain (Tyr1664, Tyr1680) were analyzed. The results show that both sites on the pFVIII light chain and on the rFVIII light chain are completely sulfated. The limitation of CHO cells to tyrosine sulfate rFVIII is therefore only restricted to a few sites. The two sulfated forms of rFVIII can easily be separated by ion-exchange chromatography, indicating the importance of the sulfate groups on the charge and/or conformation of FVIII. Both forms of rFVIII possess identical in vitro coagulation activity, von Willebrand factor binding, and thrombin activation profile. However, the difference in tyrosine sulfation may change other biological properties of FVIII.
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PMID:Heterogeneity in the tyrosine sulfation of Chinese hamster ovary cell produced recombinant FVIII. 189 19

Factor VIII delta II is a genetically engineered deletion variant of factor VIII expressed by recombinant Chinese hamster ovary cells, in which a major portion of the central (B) domain and a part of the light chain (Pro771-Asp1666) are missing. After immunoaffinity purification, the kinetics of thrombin cleavage of the novel molecule was analysed by SDS/PAGE, Western blotting and N-terminal amino acid sequencing. Thrombin first cleaves factor VIII delta II at Arg740-Ser741 to generate the 90-kDa heavy chain and an 80-kDa fusion polypeptide consisting of the remaining portion of the B domain and the 73-kDa light chain. The 90-kDa fragment is further cleaved, giving rise to 50-kDa and 40-kDa fragments while the 80-kDa fragment generates a 71/73-kDa doublet. The 71/73-kDa doublet, 50-kDa and 40-kDa fragments were further analysed by N-terminal amino acid sequencing and found to correspond to the predicted amino acid sequences. Our study shows that, in spite of the 900 amino acid deletion present in factor VIII delta II, the essential structural elements required for thrombin activation are conserved.
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PMID:Thrombin cleavage analysis of a novel antihaemophilic factor variant, factor VIII delta II. 190 Feb 36

Heterodimeric human factor VIII was proteolytically activated by catalytic levels of thrombin to yield the (labile) active cofactor factor VIIIa possessing an initial specific activity of approximately 80 units/microgram. Activation paralleled the generation of fragments A1 and A2 derived from the heavy chain and A3-C1-C2 derived from the light chain. Chromatography of factor VIIIa, on Mono-S buffered at pH 6.0 resulted in separation of the bulk of the A2 fragment from a fraction composed predominantly of A1/A3-C1-C2 dimer plus low levels of A2 fragment. Only the latter fraction contained clotting activity (approximately 20 units/microgram) which was stable and represented a less than 10% yield when compared with the peak activity of unfractionated factor VIIIa. Further depletion of A2 fragment from Mono-S-purified factor VIIIA, achieved using an immobilized monoclonal antibody to the A2 domain, yielded a relatively inactive A1/A3-C1-C2 dimer (less than 0.4 unit/microgram). Factor VIIIa (greater than 40 units/microgram) was reconstituted from the A1/A3-C1-C2 dimer plus the A2 fragment in a reaction that was Me(2+)-independent and inhibited by moderate ionic strength. Reassociation of A2 required the A1 subunit in that the A2 subunit associated weakly if at all to A3-C1-C2 in the absence of A1. These results indicated that human factor VIIIa is a trimer represented by the subunits A1/A2/A3-C1-C2 and that the A2 subunit is required for expression of factor VIIIa activity.
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PMID:Human factor VIIIa subunit structure. Reconstruction of factor VIIIa from the isolated A1/A3-C1-C2 dimer and A2 subunit. 190 33

Calcium-activated neutral proteinase (calpain) has been shown to cleave proteins involved in the maintenance of cell structure. In human platelets, substrates of calpain include glycoprotein Ib (GPIb), actin-binding protein (ABP), and talin. GPIb-ABP complexes can be isolated in detergent extracts and are thought to represent membrane-cytoskeleton attachment sites. It has been hypothesized that the hydrolysis of GPIb-ABP by calpain is regulated by the extent of binding of this proteinase to the plasma membrane-cytoskeleton interface with platelet activation. Recently, another calpain substrate (talin) has been shown to redistribute from the cytoplasm to the plasma membrane-cytoskeleton interface as the result of thrombin stimulation. To investigate the intracellular distribution of calpain I, we employed the monoclonal antibody B27D8, specific for the heavy chain (catalytic subunit) of calpain I. Indirect immunofluorescent staining of resting human platelets revealed undetectable surface antigen. Permeabilization with Triton X-100, however, revealed a diffuse intracellular antigen consistent with a cytosolic distribution. To determine whether this antigen distribution reflected the proenzyme or the activated form of calpain I and to assess the degree of hydrolysis of ABP, GPIb, and talin, we employed B27D8 and murine monoclonal antibodies against ABP (1B3 and 3D1), GPIb (LJIb10), and rabbit polyclonal antibodies against talin (A2 and B11) in a quantitative immunotransblot assay. Examination of resting platelets revealed that calpain I existed as the 85-kd proenzyme form and that ABP, GPIb, and talin existed in their native intact forms. When platelets were aggregated with thrombin, autoproteolysis of calpain I occurred within the 30 seconds required to completely solubilize platelet aggregates in sodium dodecyl sulfate-containing buffer and not as a direct result of thrombin-induced activation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Activation of calpain I and hydrolysis of calpain substrates (actin-binding protein, glycoprotein Ib, and talin) are not a function of thrombin-induced platelet aggregation. 190 52

The kininogens, high molecular weight kininogen (HK) and low molecular weight kininogen (LK), are multifunctional, single-gene products that contain bradykinin and identical amino-terminal heavy chains. Studies were performed to determine if LK would bind directly to platelets. 125I-LK specifically bound to gel-filtered platelets in the presence of 50 microM Zn2+. HK effectively competed with 125I-LK for the same binding site (Ki = 27 +/- 9 nM, n = 5). Similarly, the Ki for LK inhibition of 125I-LK binding was 12 +/- 1 nM (n = 3). Albumin, fibrinogen, factor XIII, and kallikrein did not inhibit 125I-LK binding to unstimulated platelets. 125I-LK (66 kDa) was not cleaved upon binding to platelets. The binding of 125I-LK to unstimulated platelets was found to be fully reversible by the addition of a 50 molar excess of unlabeled LK at both 10 and 20 min. LK binding to platelets was saturable with an apparent Kd of 27 +/- 2 nM (mean +/- S.E., n = 9) and 647 +/- 147 binding sites/platelet. Both LK and HK at plasma concentrations inhibited thrombin-induced platelet aggregation. LK and HK at about 5% of plasma concentration also inhibited thrombin-induced secretion of both stirred and unstirred platelets. Both kininogens were found to be noncompetitive inhibitors of proteolytically active thrombin binding to platelets. The kininogens did not inhibit D-phenylalanyl-prolyl-arginine chloromethyl ketone-treated thrombin from binding to platelets. These studies indicated that both kininogens have a region on their heavy chain which allows them to bind to platelets. Further, kininogen binding by its heavy chain modulates thrombin activation of platelets since it prevents proteolytically active thrombin from binding to its receptor.
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PMID:Low molecular weight kininogen binds to platelets to modulate thrombin-induced platelet activation. 201 93

Human blood coagulation factor XI was activated by either autoactivation or thrombin. These reactions occurred only in the presence of negatively charged materials, such as dextran sulfate (approximately Mr 500,000), sulfatide, and heparin. During the activation, factor XI was cleaved at a single Arg-Ile bond by thrombin or factor XIa to produce an amino-terminal 50-kDa heavy chain and a carboxyl-terminal 35-kDa light chain. This activation pattern is identical to that produced by factor XIIa. The addition of a small amount of thrombin and sulfatide to factor XII-deficient plasma produced shorter clotting times than when these agents were added to factor XI/factor XII combined-deficient plasma. These results suggest that the activation of factor XI by thrombin and possibly the autoactivation of factor XI proceed in plasma to lead fibrin clot formation. These reactions may have a role on an appropriate negatively charged surface in normal hemostasis.
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PMID:Activation of human blood coagulation factor XI independent of factor XII. Factor XI is activated by thrombin and factor XIa in the presence of negatively charged surfaces. 201 70

Human protein C (HPC) is an antithrombotic serine protease that circulates in the plasma as several glycoforms. To examine the role of glycosylation in the function of this protein, we singly eliminated each of the four potential N-linked glycosylation sites by site-directed mutagenesis of Asn to Gln at amino acid positions 97, 248, and 313 (HPC derivatives Q097, Q248, and Q313) or at the unusual consensus sequence Asn-X-Cys at 329 (HPC derivative Q329). The cDNAs for wild type and each derivative were inserted into expression vectors and expressed both transiently and stably in human 293 and hamster AV12-664 cells. We demonstrate that N-linked glycosylation at position 97 in the light chain of HPC is critical for efficient secretion and affects the degree of core glycosylation at Asn-329. Glycosylation at position 248 affects the intracellular processing of the internal Lys-Arg (KR) KR cleavage site, and partial glycosylation at the sequence Asn-329-X-Cys is responsible for the natural alpha-glycoform. Altering the glycosylation pattern of the protein had no significant effect on the level of fully gamma-carboxylated HPC secreted from the 293 cell line. However, elimination of glycosylation sites in the heavy chain resulted in a 2- to 3-fold increase in anticoagulant activity. Utilizing synthetic substrate, both the Km and kcat were affected, depending on the specific glycosylation site eliminated. However, there were no significant differences in the inhibition kinetics by alpha-1-antitrypsin (association rate constants of 10-11 M-1s-1 and t1/2 of 27-29 min at 40 microM alpha-1-antitrypsin) or t1/2 in human plasma (17-18 min). A comparison of the rate of activation of each derivative by thrombin alone or in complex with thrombomodulin revealed that Q313 was activated approximately 2.5-fold faster than wt HPC, independent of calcium concentration. This increase in rate was due to an enhanced affinity of thrombin-thrombomodulin for Q313, as indicated by a 3-fold reduction in Km. Overall, our studies demonstrate that glycosylation at different sites in HPC affects distinct properties of this complex protein. Furthermore, we demonstrate the ability to improve the catalytic efficiency of this enzyme through carbohydrate modifications.
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PMID:Glycosylation of human protein C affects its secretion, processing, functional activities, and activation by thrombin. 203 65

Factor VIII heavy chain (FVIII HC) polypeptides have been studied in both normal plasma and FVIII concentrates on exposure to three coagulation proteases. FVIII samples were incubated with labelled affinity-purified anti-FVIII Fab' fragments, immunocomplexes formed were visualized by autoradiography after sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), and apparent relative molecular masses (Mr) of each band assigned. FVIII HC polypeptides were detected in all types of samples, including plasma, without further purification. Normal plasma contained a range of polypeptides with the largest dominant band at a net apparent Mr of 250-300 kD, and the smallest at 80-90 kD: the bands visualized correspond to the 90-210 kD HC species seen on conventional analysis of purified FVIII. No bands were produced from samples of haemophilic plasma. Treatment of plasma or FVIII concentrate with low concentrations (1 IU/ml) of thrombin removed the 250-300 kD and other intermediate bands, intensified then removed the 80-90 kD polypeptide and produced a band at 40-50 kD. Thrombin-associated rise and fall in FVIII clotting activity by one-stage assay correlated with intensity of the 80-90 kD polypeptide. A polypeptide of Mr 40-50 kD was also produced after incubation with activated factor X: activated factor VII plus thromboplastin had no effect on HC structure. FVIII polypeptides were visualized in prothrombin complex concentrates, with a more degraded profile seen in a deliberately 'activated' product.
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PMID:Proteolysis of factor VIII heavy chain polypeptides in plasma and concentrates. 206 61

We have purified factor VIII from a patient with moderately severe hemophilia A (FVIII, 4 U/dL; FVIII:Ag, 110 U/dL) and subjected the protein to Western blot analysis after time course activation with thrombin. The cross reacting material-positive (CRM+) FVIII has the normal distribution of heavy and light chains before thrombin activation, and, after incubation with the enzyme, appropriate cleavages are made at positions 740 and 1689. However, the normal thrombin cleavage at position 372 in the heavy chain of this molecule does not occur. This result is consistent with the demonstration in the patient's leukocyte DNA of a C to T transition in codon 372, leading to the substitution of a cysteine for an arginine residue at the heavy chain internal cleavage site. The severely impaired functional activity of this molecule confirms that the heavy chain of FVIII must be proteolysed in order to effect full cofactor activation in vivo. However, a threefold activation was detected when this protein was incubated with thrombin. No evidence of thrombin-mediated cleavage at position 336 in the heavy chain was detected, in contrast to the variant recombinant B domainless-molecule, FVIII 372-Ile, described by Pittman and Kaufman (Proc Natl Acad Sci USA 85:2429, 1988). Using gel permeation studies of the FVIII/von Willebrand factor (vWF) complex before and after thrombin activation, we have demonstrated that the 40 Kd A2 domain of wild type FVIII dissociates from vWF after cleavage by the enzyme. In contrast, incomplete dissociation was detected in the case of FVIII 372-Cys. We conclude that the functional defect in FVIII 372-Cys is a consequence of the resistance to proteolysis of the internal scissile bond in the heavy chain.
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PMID:Purification and characterization of factor VIII 372-Cys: a hypofunctional cofactor from a patient with moderately severe hemophilia A. 210 44

Porcine plasma factor VIII (fVIII) molecules are heterodimers composed of a 76,000-mol wt light chain (-A3-C1-C2) and a heavy chain ranging in molecular weight from 82,000 (A1-A2) to 166,000 (A1-A2-B). Proteolytic activation of fVIII by thrombin results in fVIIIa heterotrimers lacking B domains (A1, A2, A3-C1-C2). In this study, immunoaffinity purified fVIII was further fractionated by mono S or mono Q chromatography to prepare heterodimers containing a light chain and an A1-A2-B heavy chain (fVIII 166/76) or an A1-A2 heavy chain (fVIII 82/76). Mass analysis of scanning transmission electron microscopic (STEM) images of fVIII 166/76 indicated that heterodimers (mass 237 +/- 20 kD) had irregularly globular core structures 10-12 nm across, and frequently displayed a diffuse, occasionally globular to ovoid satellite structure extending 5-14 nm from the core, and attached to it by a thin stalk. Factor VIII 82/76 molecules (mass 176 +/- 20 kD) had the same core structures as fVIII 166/76 molecules, but lacked the satellite structure. These findings indicate that A1-A2 domains of heavy chains and the light chains of the fVIII procofactor molecule are closely associated and constitute the globular core structure, whereas the B domainal portion of heavy chains comprises the peripheral satellite appendage. Factor VIII core structures commonly displayed a finger-like projection near the origin of the B domainal stalk that was also a consistent feature of the free heavy chains (mass 128-162 kD) found in fVIII 166/76 preparations. Factor VIII light chain monomers (mass, 76 +/- 16 kD) were globular to c-shaped particles 6-8 nm across. These chains commonly possessed a v-shaped projection originating from its middle region, that could also be observed at the periphery of fVIII core molecules. Factor VIIIa preparations contained heterotrimers (mass 162 +/- 13 kD) that had the same dimensions as fVIII core structures, lacked the B domainal appendage, and sometimes possessed the same core features as fVIII molecules. Molecular species corresponding to heterodimers (mass, 128 +/- 13 kD) and unassociated subunit chains (40-100 kD) were also observed in fVIIIa preparations, suggesting that heterotrimers have an appreciable tendency to dissociate, a phenomenon that could explain the decay of fVIIIa activity after thrombin activation of fVIII.
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PMID:Structural model of porcine factor VIII and factor VIIIa molecules based on scanning transmission electron microscope (STEM) images and STEM mass analysis. 211 58


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