Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The erythrocyte membrane inhibitor of the human terminal complement proteins, surface antigen CD59, has previously been shown to enter into a detergent-resistant complex with either the membrane-bound complex of C5b-8 or C5b-9 (Meri, S., Morgan, B. P., Davies, A., Daniels, R. H., Olavesen, M. G., Waldmann, H. and Lachmann, P. J. (1990) Immunology 71, 1-9; Rollins, S. A., Zhao, J., Ninomiya, H., and Sims, P. J. (1991) J. Immunol, 146, 2345-2351). In order to further define the interactions that underlie the complement-inhibitory function of CD59, we have examined the binding interactions between 125I-CD59 and the isolated components of human complement membrane attack complex, C5b6, C7, C8, and C9. By density gradient analysis, we were unable to detect interaction of 125I-CD59 with any of these isolated complement components in solution. Specific binding of 125I-CD59 to C8 and C9 was detected when these human complement proteins were adsorbed to either plastic or to nitrocellulose, suggesting that a conformational change that accompanies surface adsorption exposes a CD59-binding site that is normally buried in these serum proteins. The binding of 125I-CD59 to plastic-adsorbed C8 and C9 was saturable and competed by excess unlabeled CD59, with half-maximal binding observed at 125I-CD59 concentrations of 80 and 36 nM, respectively. No specific binding of 125I-CD59 was detected for surface-adsorbed human C5b6 or C7 nor was such binding observed for C8 or C9 isolated from rabbit serum. Binding of CD59 to human C8 and C9 was not mediated by the phospholipid moiety of CD59, implying association by protein-protein interaction. In order to further define the binding sites for CD59, ligand blotting with 125I-CD59 was performed after separation of C8 into its noncovalently associated subunits (C8 alpha-gamma and C8 beta) and after alpha-thrombin digestion of C9. These experiments revealed specific and saturable binding of 125I-CD59 to C8 alpha-gamma subunit (half-maximal binding at 75 nM), but not to C8 beta, and specific and saturable binding to the 37-kDa fragment (C9b) of thrombin-cleaved C9 (half-maximal binding at 35 nM), but not to the 25-kDa C9a fragment. Partial reduction of C8 alpha-gamma revealed that only C8 alpha polypeptide exhibited affinity for CD59, and no specific binding to the C8 gamma chain was detected.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:The human complement regulatory protein CD59 binds to the alpha-chain of C8 and to the "b"domain of C9. 137 90

Three distinct gene products, the alpha and beta chains of glycoprotein (GP) Ib and GP IX, constitute the platelet membrane GP Ib-IX complex, a receptor for von Willebrand factor and thrombin involved in platelet adhesion and aggregation. Defective function of the GP Ib-IX complex is the hallmark of a rare congenital bleeding disorder of still undefined pathogenesis, the Bernard-Soulier syndrome. We have analyzed the molecular basis of this disease in one patient in whom immunoblotting of solubilized platelets demonstrated absence of normal GP Ib alpha but presence of a smaller immunoreactive species. The truncated polypeptide was also present, along with normal protein, in platelets from the patient's mother and two of his four children. Genetic characterization identified a nucleotide transition changing the Trp-343 codon (TGG) to a nonsense codon (TGA). Such a mutation explains the origin of the smaller GP Ib alpha, which by lacking half of the sequence on the carboxyl-terminal side, including the trans-membrane domain, cannot be properly inserted in the platelet membrane. Both normal and mutant codons were found in the patient, suggesting that he is a compound heterozygote with a still unidentified defect in the other GP Ib alpha allele. Nonsense mutation and truncated GP Ib alpha polypeptide were found to cosegregate in four individuals through three generations and were associated with either Bernard-Soulier syndrome or carrier state phenotype. The molecular abnormality demonstrated in this family provides evidence that defective synthesis of GP Ib alpha alters the membrane expression of the GP Ib-IX complex and may be responsible for Bernard-Soulier syndrome.
 ...
PMID:Nonsense mutation in the glycoprotein Ib alpha coding sequence associated with Bernard-Soulier syndrome. 230 62

Components of the CDw18 leukocyte surface glycoprotein complex (Mo1/LFA-1/GP 150,95 or MAC-1, LFA-1 family) are required for some adhesion-related functions of human neutrophils (PMNs). We evaluated the ability of monoclonal antibodies (MoAb) directed against specific determinants on the CDw18 glycoproteins to inhibit neutrophil adherence to cultured human endothelial cells (EC) stimulated by a variety of agonists, including thrombin and leukotriene C4, which induce the EC-dependent adhesion of PMNs. MoAb 60.3, an antibody that binds to an epitope common to the 3 heterodimer subunits of the neutrophil CDw18 complex, potently inhibited (90-100%) the rapid (5-30 minute) adherence response stimulated by N-formyl-methyionyl-leucyl-phenylalanine, leukotriene B4, platelet-activating factor, phorbol myristate acetate, Ionophore A23187, and tumor necrosis factor. MoAbs directed against epitopes on the alpha polypeptide of the CD11b (Mol, MAC-1) heterodimer also inhibited PMN adherence to EC and to cell-free surfaces induced by these agonists. In contrast, the anti-CDw18 MoAbs had a trivial effect on maximal EC-dependent neutrophil adherence stimulated by thrombin and leukotriene C4, and incompletely inhibited PMN adherence induced by these agonists under submaximal conditions. These findings indicate that there is an alternative mechanism for neutrophil adherence, presumably resulting from molecular alterations of the EC surface, that does not require the PMN CDw18 glycoproteins. They also suggest that the inability to adhere to endothelium may not completely account for the defect in chemotaxis that is observed in vivo in neutrophils that are deficient in the CDw18 complex.
 ...
PMID:Neutrophil adherence to human endothelium in vitro occurs by CDw18 (Mo1, MAC-1/LFA-1/GP 150,95) glycoprotein-dependent and -independent mechanisms. 282 29

A cathepsin L proteinase secreted by the parasitic helminth Fasciola hepatica can cleave fibrinogen and produce a fibrin clot with a specific activity of 4.7 National Institutes of Health thrombin-equivalent U/mg. This is the first report of a fibrinogen-clotting activity aside that of thrombin and the snake venom proteinases, which are all serine proteinases. Clot formation by cathepsin L is not inhibited by the thrombin inhibitor hirudin or by the anti-polymerant H-Gly-Pro-Arg-Pro-OH. The enzyme exerts its activity on fibrinogen in a unique manner. Although the cleavage of fibrinogen may involve the initial removal of fibrinopeptides, additional proteolysis of the alpha, beta and gamma fibrinogen polypeptides takes place. SDS/PAGE analysis of the cathepsin-L-produced clots revealed that cleavage of the alpha polypeptide (66 kDa) precedes that of the beta (52 kDa) and gamma (46.5 kDa) polypeptides. Concurrent with the cleavage of these polypeptides is the appearance of components of 120, 100 and 25 kDa. The appearance of higher molecular-sized components in the cathepsin L clots suggests that polymerisation involves the formation of molecular interactions that are resistant to boiling in mercaptoethanol and SDS.
 ...
PMID:Fasciola hepatica cathepsin L proteinase cleaves fibrinogen and produces a novel type of fibrin clot. 755 57

A method to produce highly purified thrombin from salmon blood is described, and a series of biochemical, cell biologic, and biophysical assays demonstrate the functional similarities and some differences between salmon and human thrombins. Salmon thrombin with specific activity greater than 1000 units/mg total protein can be prepared by modifications of the methods used for purification of human thrombin. Using a synthetic substrate based on the human fibrinogen A-alpha polypeptide sequence as an indicator of enzymatic activity, salmon and human thrombin preparations contain similar specific activities per mass of purified protein. Salmon thrombin activates human fibrinogen and initiates the formation of fibrin clots whose structure and rheologic properties are indistinguishable from those of human fibrin clotted by human thrombin. Salmon thrombin also activates human platelets. Approximately 10 times higher activities are needed for the same rate of platelet aggregation compared to human thrombin, and some aspects of platelet activation, most notably phosphatidylserine exposure, are diminished relative to the effects of human thrombin. This latter finding suggests that salmon thrombin may not activate all of the receptors that are targets of human thrombin, although it does appear to activate signals that are sufficient to produce normal rates of activation and aggregation as measured by conventional aggregometry. Together with the recent purification of salmon fibrinogen and its application in mammalian wound healing, the availability of salmon thrombin allows the formulation of biological sealants devoid of any exogenous mammalian proteins and so may aid the design of materials with increased safety from infectious disease transmission.
 ...
PMID:Purification of salmon thrombin and its potential as an alternative to mammalian thrombins in fibrin sealants. 1247 86