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)

A glutathione S-transferase fusion to the COOH-terminal acidic transactivation domain of Vmw65 from herpes simplex virus type 1 was overexpressed in Escherichia coli and isolated by affinity chromatography on glutathione-Sepharose. Following cleavage of the fusion protein with thrombin, the transactivation domain was purified to homogeneity by ion exchange chromatography yielding approximately 0.6 mg of protein/liter of bacterial culture. Equilibrium sedimentation analysis showed the purified polypeptide to be monomeric; however, it displayed aberrant electrophoretic and chromatographic properties. Contrary to secondary structure predictions, circular dichroism spectroscopy demonstrated that this transactivation domain was devoid of significant alpha-helical structure at physiological conditions. The polypeptide, however, became notably more structured under hydrophobic conditions or at low pH, suggesting that it was sensitive to its environment. Near-UV circular dichroism suggested that phenylalanyl and tyrosyl residues were under influence from tertiary structure.
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PMID:Purification and characterization of the carboxyl-terminal transactivation domain of Vmw65 from herpes simplex virus type 1. 130 82

Thrombin is thought to stimulate responsive cells by cleaving cell-surface receptors coupled to intracellular second-messenger-generating enzymes via G-proteins. In order to understand this process better, we have examined the regulation of adenylate cyclase by thrombin in the megakaryoblastic HEL cell line and compared it with platelets. A notable difference was found. In HEL-cell membrane preparations, thrombin inhibited cyclic AMP (cAMP) formation by a pertussis-toxin-sensitive mechanism comparable with that observed in platelets. In contrast, when added to intact HEL cells, thrombin activated adenylate cyclase and caused an increase in cAMP formation synergistic with that produced by forskolin and prostaglandin I2. This increase, which was not seen with platelets, was accompanied by an increase in cAMP metabolism by phosphodiesterase. Like other responses to thrombin, the increase in cAMP formation required proteolytically active thrombin and was subject to homologous desensitization. An equivalent response could be evoked by the addition of a polypeptide, derived from the N-terminus of the thrombin receptor, that has been shown to activate the receptor. The effects of thrombin could not, however, be reproduced by the addition of phorbol ester and the Ca2+ ionophore, A23187, nor be prevented with inhibitors of arachidonate metabolism. Preincubation of the cells with adrenaline, which inhibited Gs-mediated activation of adenylate cyclase, or pertussis toxin, which inhibited phospholipase C activation, had no effect on thrombin-induced cAMP formation. These results suggest that thrombin can regulate cAMP formation by two different mechanisms. First, thrombin can inhibit adenylate cyclase in a Gi-dependent manner. This effect predominates in HEL-cell membrane preparations, as it does in platelets, but is not detectable when thrombin is added to intact HEL cells. Instead, in intact HEL cells thrombin activates adenylate cyclase. Although clearly receptor-mediated, this response does not appear to involve Gi, Gs, protein kinase C, eicosanoid formation or changes in the cytosolic Ca2+ concentration.
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PMID:Dual regulation of cyclic AMP formation by thrombin in HEL cells, a leukaemic cell line with megakaryocytic properties. 131 10

Thrombomodulin is an endothelial cell thrombin receptor that serves as a cofactor for thrombin-catalyzed activation of protein C. Structural requirements for thrombin binding and cofactor activity were studied by mutagenesis of recombinant human thrombomodulin expressed on COS-7 and CV-1 cells. Deletion of the fourth epidermal growth factor (EGF)-like domain abolished cofactor activity but did not affect thrombin binding. Deletion of either the fifth or the sixth EGF-like domain markedly reduced both thrombin binding affinity and cofactor activity. Thrombin binding sequences were also localized by assaying the ability of synthetic peptides derived from thrombomodulin to compete with diisopropyl fluorophosphate-inactivated 125I-thrombin binding to thrombomodulin. The two most active peptides corresponded to (a) the entire third loop of the fifth EGF-like domain (Kp = 85 +/- 6 microM) and (b) parts of the second and third loops of the sixth EGF-like domain (Kp = 117 +/- 9 microM). These data suggest that thrombin interacts with two discrete elements in thrombomodulin. Deletion of the Ser/Thr-rich domain dramatically decreased both thrombin binding affinity and cofactor activity and also prevented the formation of a high molecular weight thrombomodulin species containing chondroitin sulfate. Substitutions of this domain with polypeptide segments of decreasing length and devoid of glycosylation sites progressively decreased both cofactor activity and thrombin binding affinity. This correlation suggests that increased proximity of the membrane surface to the thrombin binding site may hinder efficient thrombin binding and the subsequent activation of protein C. Membrane-bound thrombomodulin therefore requires the Ser/Thr-rich domain as an important spacer, in addition to EGF-like domains 4-6, for efficient protein C activation.
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PMID:Functional domains of membrane-bound human thrombomodulin. EGF-like domains four to six and the serine/threonine-rich domain are required for cofactor activity. 131 30

Rat 1a fibroblasts transformed by the Gi2 oncogene, gip2, exhibit a constitutively elevated mitogen-activated protein (MAP) kinase activity that correlates with enhanced tyrosine phosphorylation of the p42 MAP kinase polypeptide. The MAP kinase activity in gip2 transformed cells is 50-60% of the pertussis toxin-sensitive, thrombin-stimulated activity observed in wild-type Rat 1a cells. A similar activation of MAP kinase is observed in src but not ras or raf transformed Rat 1a cells, indicating that the persistent MAP kinase activity results from the action of the specific oncoprotein and is not the consequence of cellular transformation. The enhanced transactivation function of c-Jun characteristic of the transformed phenotype, measured using a collagenase promoter-CAT reporter gene, is observed in gip2, src, ras, and raf transformed Rat 1a cells. The regulatory networks controlled by the four transforming oncogenes therefore alter the activity of specific transcription factors, but only gip2 and src constitutively activate MAP kinase. The findings demonstrate that the catalytic activity of growth factor-regulated cytoplasmic kinases are selectively and stably activated as a consequence of specific oncogene expression.
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PMID:MAP kinase is constitutively activated in gip2 and src transformed rat 1a fibroblasts. 131 14

Based upon its recently cloned nucleotide sequence, the human platelet thrombin receptor is thought to be formed by a single polypeptide chain with seven transmembrane domains and an extracellular N terminus that can be cleaved by thrombin. As yet, however, little is known from studies of the receptor protein itself. To obtain such information, we have prepared monoclonal antibodies against a peptide corresponding to receptor residues Ser42 through Phe55, the domain immediately distal to the site of cleavage by thrombin. By flow cytometry, all of the antibodies reacted with the thrombin-responsive megakaryoblastic CHRF-288 and HEL cell lines, but not with the T-lymphoid Sup-T1 cell line. Functionally, the antibodies inhibited platelet responses to alpha-thrombin, gamma-thrombin, and trypsin, but had no effect on platelet activation by ADP, epinephrine, or the thromboxane analog U46619. Radioiodinated antibody bound to approximately 1,800 sites/platelet, a value similar to the reported number of moderate affinity thrombin binding sites per platelet. On Western blots, the antibodies recognized a 66-kDa protein in platelet, HEL, and CHRF-288 membranes. The discrepancy between this apparent size and the predicted mass of the receptor suggests that, as with other G protein-coupled receptors, one or more of the potential sites for N-linked glycosylation have been utilized. Therefore, these results suggest that: 1) the cloned thrombin receptor is involved in a broad range of platelet responses to thrombin, as well as gamma-thrombin and trypsin; 2) as predicted, the N terminus of the receptor is accessible on the platelet surface; 3) the moderate affinity thrombin binding site noted in earlier studies may be the receptor; 4) potentially as much as one third of the mass of the receptor is carbohydrate.
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PMID:Structure and function of the human platelet thrombin receptor. Studies using monoclonal antibodies directed against a defined domain within the receptor N terminus. 132 Nov 25

We have used a guinea pig gastric longitudinal (LM) smooth muscle bioassay system to evaluate the contractile activities of a previously described thrombin receptor-derived polypeptide, S42FLLRNPNDKYEPF55 (one-letter amino acid code) (TRP42-55) and of a series of peptides derived from this sequence. The contractile activities of the polypeptides were compared with the actions of thrombin. Shortened peptides of the sequences S42FLLRNPND50, S42FLLRN47, and S42FLLR46 (TRP42-46) all exhibited contractile activities that were equivalent to or greater than those of the parent polypeptide, TRP42-55. Both TRP42-55 and TRP42-46 mimicked the action of thrombin, in terms of two different signal transduction pathways that were activated either in the LM preparation or in the related but distinct gastric circular muscle assay. In the LM preparation, the peptide FSLLR also exhibited appreciable, but much reduced, activity. Minimal activity was exhibited in the LM by the sequence SFLLA, but the lysine-containing analogue S42FLLK46 was about one fifth as potent as TRP42-46. In contrast, the receptor-derived sequences S42FLL45, S42FL44-NH2, F43LLR46, and S42ALLR46, as well as arginine-containing polypeptides beginning with the SF motif, SFRG and SFRGHITR, were inactive in the LM bioassay system, at concentrations of greater than or equal to 200 microM, as either agonists or antagonists against TRP42-55. In addition to its actions in the LM and circular muscle preparations, the active pentapeptide, TRP42-46, also exhibited thrombin-mimetic intrinsic activity in a rat aortic arterial ring relaxation bioassay, whereas the pentapeptide S42FLLA46 and the tetrapeptide S42FLL45 were inactive. We conclude that the intrinsic biological activity of the thrombin receptor-derived peptide resides in the pentapeptide TRP42-46 and that the phenylalanine and arginine residues at positions 43 and 46 play key roles in the activity of this pentapeptide in smooth muscle systems.
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PMID:Action of thrombin receptor polypeptide in gastric smooth muscle: identification of a core pentapeptide retaining full thrombin-mimetic intrinsic activity. 132 29

Hirudin, a 65 amino acid polypeptide from the medicinal leech, is the most potent thrombin inhibitor known to date. Recently, recombinant forms have been reported, which are as effective as the isolated forms. The studies presented here demonstrate sensitive spectroscopic methods for distinguishing binding of two recombinant hirudins, HV1 and HV2-Lys 47, with active site-labeled human alpha-, epsilon- and zeta-thrombins. Specifically, fluorosulfonylphenyl nitroxide spin labels, dansyl fluoride and p-nitrophenylanthranilate, were employed as active site-directed covalent reporter groups. In general, the nitroxide immobilization was greater for spin-labeled thrombin complexes with HV2-Lys 47 vs. HV1. The two fluorophore moieties, dansyl and anthraniloyl, were also sensitive to differences in HV1 and HV2-Lys 47 binding, including interactions with loop 145-150 of the thrombin structure where the epsilon- and zeta-thrombin cleavages exist. Speculation over sequence differences between the two isoinhibitors centers on residues 24 and 47, both of which involve either a loss or gain of charge on the side chain.
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PMID:Structural differences in active site-labeled thrombin complexes with hirudin isoinhibitors. 133 13

We have examined the action of the thrombin receptor-derived polypeptide, S42FLLRNPNDKYEPF55 (TRP 42-55), in rat and guinea pig aortic rings and helical arterial strips, and we have compared the actions of the peptide with those of thrombin. In rat preparations, both TRP 42-55 and thrombin caused a concentration-dependent endothelium-dependent relaxation that was blocked by N omega-nitro-L-arginine methyl ester; the relaxation response of the intact rat aortic strip preparation to concentrations of the peptide in the range 30-60 micrograms/mL (17-34 microM) was equivalent to the response to 0.03-0.1 U/mL of thrombin (about 0.3-0.9 nM), yielding a potency ratio (TRP 42-55:thrombin) of about 38,000:1. In contrast with the complete desensitization of thrombin-treated rat aortic preparations to a second administration of the enzyme, the rat aortic tissue was not desensitized by repeated exposures to TRP 42-55 and remained responsive to the peptide even after treatment of the tissue by thrombin. In contrast with the rat aortic tissue, in either intact or endothelium-free guinea pig aortic preparations both TRP 42-55 and thrombin caused a concentration-dependent endothelium-independent contraction. The contractile action of 60 micrograms/mL of receptor peptide (34 microM) in guinea pig aortic strip preparations was equivalent to the contractile action of 0.1-0.3 U/mL thrombin (0.9-3 nM), yielding a potency ratio of about 17,000:1. In guinea pig aortic preparations with an intact endothelium that were precontracted with noradrenaline, neither thrombin nor TRP42-55 caused relaxation, whereas substance P did so.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Vascular actions of thrombin receptor peptide. 133 53

The three-dimensional structure of the N-terminal 51-residue domain of recombinant hirudin in aqueous solution was determined by 1H nuclear magnetic resonance (NMR) spectroscopy, and the resulting high-quality solution structure was compared with corresponding structures obtained from studies with the intact, 65-residue polypeptide chain of hirudin. On the basis of 580 distance constraints derived from nuclear Overhauser effects and 109 dihedral angle constraints, a group of 20 conformers representing the solution structure of hirudin(1-51) was computed with the program DIANA and energy-minimized with a modified version of the program AMBER. Residues 3 to 30 and 37 to 48 form a well-defined molecular core with two antiparallel beta-sheets composed of residues 14 to 16 and 20 to 22, and 27 to 31 and 36 to 40, and three reverse turns at residues 8 to 11 (type II), 17 to 20 (type II') and 23 to 26 (type II). The average root-mean-square deviation of the individual NMR conformers relative to their mean co-ordinates is 0.38 A for the backbone atoms and 0.77 A for all heavy atoms of these residues. Increased structural disorder was found for the N-terminal dipeptide segment, the loop at residues 31 to 36, and the C-terminal tripeptide segment. The solution structure of hirudin(1-51) has the same molecular architecture as the corresponding polypeptide segment in natural hirudin and recombinant desulfatohirudin. It is also closely similar to the crystal structure of the N-terminal 51-residue segment of hirudin in a hirudin-thrombin complex, with root-mean-square deviations of the crystal structure relative to the mean solution structure of 0.61 A for the backbone atoms and 0.91 A for all heavy atoms of residues 3 to 30 and 37 to 48. Further coincidence is found for the loop formed by residues 31 to 36, which shows increased structural disorder in all available solution structures of hirudin, and of which residues 32 to 35 are not observable in the electron density map of the thrombin complex. Significant local structural differences between hirudin(1-51) in solution and hirudin in the crystalline thrombin complex were identified mainly for the N-terminal tripeptide segment and residues 17 to 21. These are further analyzed in an accompanying paper.
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PMID:Nuclear magnetic resonance solution structure of hirudin(1-51) and comparison with corresponding three-dimensional structures determined using the complete 65-residue hirudin polypeptide chain. 133 15

1. The activation of the native enzyme was achieved by a proteolytic procedure involving thrombin. 2. The pH profile was independent of the nature of the substrates assayed (casein or dimethylcasein plus putrescine). The optimum pH was between 7.6 and 7.9 and the pK values were 6.5/7 and 8.7/9. A cysteinyl residue appeared to be involved in the pH-dependence activity. 3. In the presence of calcium, the thermostability of enzyme was increased: the temperature at which enzyme lost half of its activity increased up to 7 degrees C. 4. The kinetics of the thermal deactivation of F XIIIa depended on the presence or absence of calcium. 5. In its presence the reaction obeyed second order kinetics, while in its absence, the kinetics were of first order. In the first case, the irreversible thermal deactivation could be described by a two-step mechanism (N----X----D) while in the second case, the deactivation followed the simple model (N----D). 6. Neither divalent cations like Sr2+, Ba2+, Mg2+, nor bovine serum-albumin and polyhydric alcohols were able to increase the thermostability of F XIIIa. 7. Thermal deactivation of F XIIIa did not appear linked to the redox state of enzyme, nor to the modification of SH groups. 8. We observed a good correlation between the loss of activity and the unfolding of the polypeptide chain of F XIIIa during heating. 9. The optimum temperature of F XIIIa activity was 40 degrees C at pH 8 and 45 degrees C at pH 7.
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PMID:Effect of temperature and pH on factor XIIIa from human placenta. 135 52


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