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)

Factor X is a plasma protein involved in both the intrinsic and extrinsic pathways of blood coagulation. Post-translational modifications of the protein involve gamma-carboxylation of specific glutamic acid residues, beta-hydroxylation of one aspartic acid residue, and N- and O-linked glycosylation. Even though it is known that gamma-carboxylation is instrumental in regulating biological activity, the role of glycosylation in the function and properties of factor X has not been previously investigated. We utilized lectin binding and glycosidase treatment to investigate the functional role of carbohydrates on the activation peptide of factor X. Sambucus nigra agglutinin, a lectin that binds to sialic acid terminally linked alpha(2-6) to galactose or N-acetyl-galactosamine inhibits activation of human factor X in a dose-dependent manner. Inhibition of activation was observed for both intrinsic (factor IXa/VIIIa) and extrinsic (factor VIIa/tissue factor) pathway complexes. In accordance with this, selective removal of sialic acid residues on the activation peptide of factor X by neuraminidase also results in a drastic reduction of activation of the zymogen by these complexes. Corresponding reduction of activity in classical clotting assays (activated partial thromboplastin time and prothrombin time) also agrees with this observation. These results suggest a possible role of N-linked carbohydrates in the activation of factor X.
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PMID:Carbohydrate residues modulate the activation of coagulation factor X. 842 82

We investigated the functional role of gamma-carboxyglutamic acid (Gla) residue 21 of human factor IX, using site-directed mutagenesis to change the glutamic acid residue to aspartic acid (FIX21D). FIX21D had reduced activity in an activated partial thromboplastin time (aPTT) assay and was activated by factor XIa more slowly than wild-type factor IX (FIXwt). FIX21D underwent normal, two-stage calcium-dependent intrinsic fluorescence quenching, indicating that a folding event similar to that seen in FIXwt occurred upon the addition of calcium ions. Antibody A-7, which recognizes factor IX-specific residues at positions 33-40, bound FIX21D as well as FIXwt; however, the calcium-specific monoclonal antibody, JK-IX-2, whose epitope includes residues 1 and 22, did not recognize FIX21D. FIX21D bound phosphatidylserine/phosphatidylcholine (PS/PC) vesicles with Kd approximately 10-fold greater than FIXwt, as measured by a fluorescence light scattering assay. Finally, although FIXwt binds endothelial cells with a Kd of 2.8 nM, FIX21D did not bind endothelial cells. Molecular modeling simulations of FIXwt and FIX21D indicate that mutating Gla 21 to Asp causes structural changes in residues 3-5 and 8-10, as well as in two exposed calcium ions, consistent with the reduced function of FIX21D. Immunological and intrinsic fluorescence quenching assays and the molecular dynamics simulations suggest normal folding in the C-terminal region of the Gla domain. Thus we hypothesize the FIX21D has reduced JK-IX-2 and phospholipid and endothelial cell binding due to localized structural changes in residues 3-10 and the exposed calcium ions. Our study suggests that the Gla 21 to Asp mutation disrupts function in the N-terminal region of the Gla domain without affecting structure in the C-terminal Gla domain region.
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PMID:Characterization of gamma-carboxyglutamic acid residue 21 of human factor IX. 875 87

A series of site-specific mutants of the phosphatidylcholine-preferring phospholipase C from Bacillus cereus (PLCBc) was prepared in which the glutamic acid residue at position 146 was replaced with glutamine, aspartic acid, histidine, and leucine to elucidate what role Glu146 might play in catalysis. An expression system for the native enzyme in Escherichia coli was first developed to provide PLCBc that was fused via an intervening factor Xa protease recognition sequence at its N-terminus to maltose binding protein (MBP). This MBP-PLCBc fusion protein was isolated at levels of 50-70 mg/L of culture; selective trypsin digestion of the MBP-PLCBc fusion protein followed by chromatographic purification yielded recombinant PLCBc at levels of ca. 10 mg/L. Polymerase chain reaction (PCR) mutagenesis on the PLCBc gene (plc) was then used to replace the Glu146 codon with those for glutamine (E146Q), aspartic acid (E146D), histidine (E146H), and leucine (E146L). The catalytic efficiency of the E146Q mutant was 1.6% that of native PLCBc, while the other mutants each possessed activities of 0.2-0.3% of the wild type. The kcat/Km vs pH profiles for both E146Q and native PLCBc have ascending acidic limbs, suggesting that Glu146 does not serve as the general base in the hydrolysis reaction. As measured by circular dichroism, all of the mutant proteins contained less helical structure and underwent denaturation at lower temperatures than the wild type in the order: wild type > E146Q > E146D approximately E146H approximately E146L. Atomic absorption analyses indicated that the mutant proteins also exhibited lower Zn2+ content than the wild type. Thus, the Glu146 residue in PLCBc stabilizes the secondary and tertiary structure of the enzyme and serves as a critical ligand for Zn2, but it does not appear to have any specific catalytic role.
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PMID:Expression and site-directed mutagenesis of the phosphatidylcholine-preferring phospholipase C of Bacillus cereus: probing the role of the active site Glu146. 884 Nov 44

Mouse factor X was highly purified from plasma using barium ion precipitation and chromatography on anion-exchange and heparin-agarose affinity chromatography columns. Intact and reduced patterns of mouse factor X in SDS-PAGE were similar to those of human factor X. The specific absorption E 1%/1 cm at 280 nm of mouse factor X was found to be 11.2. Content of carbohydrate moieties of mouse factor X, determined to be 10% by weight, differs both quantitatively and quantitatively from that of human factor X, while the gamma-carboxyglutamic acid (Gla) and beta-hydroxy-aspartic acid (beta-OH-Asp) content were essentially the same as for human factor X. The amino-terminal amino acid sequences of the light and heavy chains of mouse factor X separated by SDS-PAGE were ANSFF--FKK and SVALXTSDSE, respectively. Underlined residues are non-identical with those of human factor X. Clotting time-based assays using human factor X-deficient plasma as substrate exhibited the following apparent extents of activation of factor X in mouse plasma, using human plasma as the standard: 195% (intrinsic); 200% (extrinsic); and 190% (RVV-X). Using the purified proteins in the same assay systems, the following apparent activation of mouse factor X was demonstrated, compared with human factorX: 195% (intrinsic); 27% (extrinsic); and 41% (RVV-X). These activity profiles suggest that the human extrinsic coagulation pathway functions less efficiently than the corresponding mouse pathway in the activation of mouse factor X. Furthermore, mouse brain thromboplastin satisfactorily replaced rabbit brain thromboplastin in extrinsic activation of factor X in mouse plasma, but not of human plasma or purified mouse or human factor X, in line with studies by others suggesting that human factor VIIa poorly activates factor X in the presence of mouse tissue factor. While fully RVV-X-activated mouse factor X activated human prothrombin at a rate equal to about 117% of that for human factor X, it hydrolyzed the synthetic substrate, S-2222, at a rate of only about 18% of that for human factor X. These results are expected to be useful in making the mouse suitable for study of the mammalian blood coagulation pathways.
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PMID:Isolation and characterization of mouse coagulation factor X -- biophysical and enzymological properties. 930 52

A 64-year-old white male was referred for evaluation of prolonged prothrombin time (PT) and activated partial thromboplastin time (aPTT) obtained before elective surgery with initial PT and PTT results of 14.9 and 38.4 seconds, respectively, which corrected to normal in 1:1 mixes with normal plasma. Functional prothrombin assay indicated a level of 51% with thromboplastin as an activator. The prothrombin antigen was 102%. This discordance in the functional and immunologic prothrombin levels was evidence for dysprothrombinemia. Western blotting showed that thrombin was formed at a normal rate in diluted plasma consistent with a mutation within the thrombin portion of prothrombin. DNA was isolated from leukocytes and the thrombin exons were amplified by polymerase chain reaction, cloned, and sequenced. For exon 13, eight clones were sequenced with four clones showing a point mutation in the codon for Arg517, which would result in substitution by Gln. Arg517 is part of the Arg-Gly-Asp(RGD) sequence in thrombin and contributes to an ion cluster with aspartic acid residues 552 and 554. Mutation at this residue most probably distorts the structure of the Na+ binding site in thrombin. This is the first report indicating the critical role of Arg517 in the normal physiological interaction of thrombin with fibrinogen. This dysprothrombin is designated Prothrombin Greenville.
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PMID:Prothrombin Greenville, Arg517-->Gln, identified in an individual heterozygous for dysprothrombinemia. 949 Jun 87

Asparaginase (ASNase) is a widely used and successful agent against childhood acute lymphoblastic leukemia (ALL). Asparaginase cleaves asparagine (Asn) to give aspartic acid and ammonia, thereby depleting free Asn in the blood. However, treatment with ASNase has been implicated in significant reduction of plasma levels of the coagulation serine protease inhibitor (serpin) antithrombin III (AT3), predisposing patients to thromboembolic complications. Our investigation was designed to delineate the biochemical mechanism of AT3 depletion that can occur in the plasma of ALL patients undergoing ASNase therapy. SDS-PAGE showed no cleavage of purified AT3 following treatment with ASNase. Furthermore, purified AT3 treated with ASNase demonstrated no decrease in inhibitory activity. Human plasma and whole blood treated with approximate therapeutic concentrations of ASNase showed no loss of AT3 activity as detected by a plasma-based factor Xa inhibition assay. Treatment of a confluent monolayer of HepG2 (hepatocarcinoma) cells with ASNase showed no gross loss in AT3 message levels detected by rtPCR. However, a decrease of cell viability was observed in cultures treated with ASNase. Interestingly, medium from HepG2 cells treated with ASNase showed a marked decrease in secretion of AT3 and another serpin, heparin cofactor II. Collectively, these data show that ASNase has no direct effect on AT3 in blood or plasma, but that ASNase may affect plasma levels of AT3 by interfering with translation and/or secretion of the protein in liver cells.
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PMID:Insight into the mechanism of asparaginase-induced depletion of antithrombin III in treatment of childhood acute lymphoblastic leukemia. 1086 29

Based on homology, amino acids 326-336 (143-154 in chymotrypsin numbering) of factor X (fX) comprise a flexible surface loop, which is susceptible to self-proteolysis and influences substrate catalysis. To investigate the role of this autolysis loop in fX function, a recombinant variant with a new site for asparagine-linked glycosylation has been produced by changing glutamine 333 to asparagine. Q333N fX is activated normally by factor VIIa and tissue factor, factors IXa and VIIIa, and Russell's viper venom. Proteolysis of the loop is prevented by the mutation. Reactivity of the free enzyme toward substrates and inhibitors is attenuated 4-20-fold; relative to wild type fXa, Spectrozyme Xa(TM) hydrolysis is 25%, inhibition by antithrombin III and the tissue factor pathway inhibitor is approximately 20%, and prothrombin activation in the absence of the cofactor Va is only 5%. Surprisingly, activities of the variant and wild type enzymes are equivalent when part of the prothrombinase complex. N-Glycanase cleaves the new oligosaccharide from Q333N fXa leaving aspartic acid. Q333D fXa is approximately 1.6-fold more reactive with Spectrozyme Xa(TM), antithrombin III and tissue factor pathway inhibitor, and prothrombin than its glycosylated counterpart, Q333N fXa, but still quite abnormal relative to wild type fXa. Like Q333N fXa, Q333D fXa is fully functional as part of the prothrombinase complex. We conclude that Gln-333 is geographically close to a site of proteolytic degradation but not to activator, cofactor, or membrane binding sites. Mutation of Gln-333 impairs catalytic function, but given normal prothrombin activation by the complexed enzyme, the importance of Gln-333 for catalysis is not manifest in the prothrombinase assembly, suggesting a conformational change in complexed fXa.
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PMID:Directed glycosylation of human coagulation factor X at residue 333. Insight into factor Va-dependent prothrombin catalysis. 1099 46

Ceramide plays a crucial role as a basic building block of sphingolipids, but also as a signalling molecule mediating cell-fate decisions. Three genes, LAG1, LAC1 and LIP1, have been shown to be required for ceramide synthase activity in Saccharomyces cerevisiae [Guillas, Kirchman, Chuard, Pfefferli, Jiang, Jazwinski and Conzelman (2001) EMBO J. 20, 2655-2665; Schorling, Vallee, Barz, Reizman and Oesterhelt (2001) Mol. Biol. Cell 12, 3417-3427; Vallee and Riezman (2005) EMBO J. 24, 730-741]. In the present study, the topology of the Lag1p and Lac1p subunits was investigated. The N- and C-termini of the proteins are in the cytoplasm and eight putative membrane-spanning domains were identified in Lag1p and Lac1p by insertion of glycosylation and factor Xa cleavage sites at various positions. The conserved Lag motif, potentially containing the active site, is most likely embedded in the membrane. We also present evidence that histidine and aspartic acid residues in the Lag motif are essential for the function of Lag1p in vivo.
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PMID:Transmembrane topology of ceramide synthase in yeast. 1675 12

Peptidomimetics have found wide application as bioavailable, biostable, and potent mimetics of naturally occurring biologically active peptides. L-Arginine is a guanidino group-containing basic amino acid, which is positively charged at neutral pH and is involved in many important physiological and pathophysiological processes. Many enzymes display a preference for the arginine residue that is found in many natural substrates and in synthetic inhibitors of many trypsin-like serine proteases, e.g. thrombin, factor Xa, factor VIIa, trypsin, and in integrin receptor antagonists, used to treat many blood-coagulation disorders. Nitric oxide (NO), which is produced by oxidation of L-arginine in an NADPH- and O(2)-dependent process catalyzed by isoforms of nitric oxide synthase (NOS), exhibits diverse roles in both normal and pathological physiologies and has been postulated to be a contributor to the etiology of various diseases. Development of NOS inhibitors as well as analogs and mimetics of the natural substrate L-arginine, is desirable for potential therapeutic use and for a better understanding of their conformation when bound in the arginine binding site. The guanidino residue of arginine in many substrates, inhibitors, and antagonists forms strong ionic interactions with the carboxylate of an aspartic acid moiety, which provides specificity for the basic amino acid residue in the active side. However, a highly basic guanidino moiety incorporated in enzyme inhibitors or receptor antagonists is often associated with low selectivity and poor bioavailability after peroral application. Thus, significant effort is focused on the design and preparation of arginine mimetics that can confer selective inhibition for specific trypsin-like serine proteases and NOS inhibitors as well as integrin receptor antagonists and possess reduced basicity for enhanced oral bioavailability. This review will describe the survey of arginine mimetics designed to mimic the function of the arginine moiety in numerous peptidomimetic compounds (thrombin inhibitors, factor Xa inhibitors, factor VIIa inhibitors, integrin receptor antagonists, nitric oxide synthase inhibitors), with the aim of obtaining better activity, selectivity and oral bioavailability.
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PMID:Arginine mimetic structures in biologically active antagonists and inhibitors. 1716 27

Factor XI (FXI) deficiency is a rare autosomal recessive coagulation disorder most commonly found in Ashkenazi and Iraqi Jews, but it is also found in other ethnic groups. It is a trauma or surgery-related bleeding disorder, but spontaneous bleeding is rarely seen. The clinical manifestation of bleeding in FXI deficiency cases is variable and seems to poorly correlate with plasma FXI levels. The molecular pathology of FXI deficiency is mutation in the F11 gene on the chromosome band 4q35. We report a novel mutation of the F11 gene in an 18-year-old asymptomatic Korean woman with mild FXI deficiency. Pre-operative laboratory screen tests for lipoma on her back revealed slightly prolonged activated partial thromboplastin time (45.2 sec; reference range, 23.2-39.4 sec). Her FXI activity (35%) was slightly lower than the normal FXI activity (reference range, 50-150%). Direct sequence analysis of the F11 gene revealed a heterozygous A to G substitution in nucleotide 1517 (c.1517A>G) of exon 13, resulting in the substitution of aspartic acid with glycine in codon 506 (p.Asp506Gly). To the best of our knowledge, the Asp506Gly is a novel missense mutation, and this is the first genetically confirmed case of mild FXI deficiency in Korea.
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PMID:A novel missense mutation Asp506Gly in Exon 13 of the F11 gene in an asymptomatic Korean woman with mild factor XI deficiency. 2201 85


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