tPA Molecule Research Articles

Visualizing the degradation of fibrin fibers.

Polymeric fibrin provides the structural and mechanical stability of a blood clot. Fibrin fibers are rod-like and create a network mesh that holds blood cells. When a clot has performed its physiological function in wound healing and preventing excessive blood loss, it must be resolved by the enzymatic degradation of fibrin, otherwise known as fibrinolysis. If a blood clot forms when or where it is not needed, as occurs in ischemic strokes and myocardial infarctions, the blood clot (thrombus) can obstruct blood flow to downstream organs. Obstructive thrombi must be degraded or removed to prevent further complications. If a clot is not degraded on its own, lytic agents (i.e., tissue plasminogen activator, tPA) are given exogenously to induce fibrinolysis. Here, we fluorescently labeled both fibrin and tPA to visualize degradation at the edge of the clot. The fibers with bound tPA were looped or coiled while the fibers farther into the clot remain straight and stable displaying the diffusion of tPA and depth of lysis. This image provides (1) a new method to monitor fibrinolysis with a commercially available chamber with convenient inlets and (2) the visualization of tPA-bound fibrin and the behavior of fibers during degradation. Future work could utilize this technique to study tPA molecule and fibrin interactions, lysis front degradation, and fibrin fiber linearity to understand the mechanisms of intermolecular dynamics dependent on network structure. An enhanced insight into this process can aid in the development of optimized therapeutics to target stubborn clots.

The phase stability of terephthalic acid under high pressure

Terephthalic acid has been investigated by Raman spectroscopy up to 15 GPa. According to ab initio calculations, it can be speculated that both of π-π stacking interactions between molecules and the symmetry of hydrogen bonds are enhanced with gradually increasing pressure. Furthermore, we use the Hirshfeld surface to map the π-π stacking interaction in the TPA molecule at high pressure. The Raman spectra and ab initio calculation results indicate that the phase stability of TPA is related to the one-dimensional hydrogen bond network and inter-chain aromatic π-π stacking interaction.

High photoluminescent TPA and the ratiometric sensor for free chlorine

A facile and high yield method is introduced to synthesize 3,5-dihydro-5-oxo-2H-thiazolo[3,2-a]pyridine-3,7-dicarboxylic acid (TPA) through the “one-step” condensation reaction of citric acid and l-cysteine. For the first time, the produced TPA molecules are purified by the simple crystallization, and the photoluminescence (PL) properties of the TPA are investigated. The obtained purified TPA shows bright blue PL, with a PL quantum yield as high as 90.5%. The sulfur atom of TPA molecule can be selectively oxidized by free chlorine into sulfoxide, which is a strong electron withdrawing group. As a result, the conjugation is decreased, leading to a great PL quenching. On the basis, a sensitive and selective PL sensor is developed for the detection of free chlorine. Furthermore, tris(2,2-bipyridine)ruthenium(II) chloride hexahydrate, whose red PL signal is inert to the free chlorine, can be used to provide a background PL signal. Thus, a visual PL ratiometric sensor is developed, which is convenient for the on-site and on-line detection of free chlorine.

Modelling fibrinolysis: a 3D stochastic multiscale model

Fibrinolysis, the proteolytic degradation of the fibrin fibres that stabilize blood clots, is initiated when tissue-type plasminogen activator (tPA) activates plasminogen to plasmin, the main fibrinolytic enzyme. Many experiments have shown that coarse clots made of thick fibres lyse more quickly than fine clots made of thin fibres, despite the fact that individual thick fibres lyse more slowly than individual thin fibres. The generally accepted explanation for this is that a coarse clot with fewer fibres to transect will be degraded faster than a fine clot with a higher fibre density. Other experiments show the opposite result. The standard mathematical tool for investigating fibrinolysis has been deterministic reaction-diffusion models, but due to low tPA concentrations, stochastic models may be more appropriate. We develop a 3D stochastic multiscale model of fibrinolysis. A microscale model representing a fibre cross section and containing detailed biochemical reactions provides information about single fibre lysis times, the number of plasmin molecules that can be activated by a single tPA molecule and the length of time tPA stays bound to a given fibre cross section. Data from the microscale model are used in a macroscale model of the full fibrin clot, from which we obtain lysis front velocities and tPA distributions. We find that the fibre number impacts lysis speed, but so does the number of tPA molecules relative to the surface area of the clot exposed to those molecules. Depending on the values of these two quantities (tPA number and surface area), for given kinetic parameters, the model predicts coarse clots lyse faster or slower than fine clots, thus providing a possible explanation for the divergent experimental observations.

Molecular orientation of terephthalic acid assembly on epitaxial graphene: NEXAFS and XPS study

The adsorption of terephthalic acid molecules [C(6)H(4)(COOH)(2)), TPA] on a single layer of graphene grown epitaxially on Ni(111) has been investigated by means of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) at room temperature. The assignment of the NEXAFS resonances was aided by ab initio calculations for the free TPA molecule. For coverages up to a monolayer the molecular plane of TPA adopts a parallel orientation with regard to the epitaxial graphene (EG) layer. Deprotonation of TPA molecules at one monolayer coverage can be excluded. For TPA multilayers, the molecular plane is tilted on average by approximately 45° with respect to the sample surface.

Preferential Siting of Iron Atoms in an MFI‐type Ferrisilicate Zeolite Framework: An Attempt to Explain Experimental Data with TPA‐Silicate Solution Chemistry

AbstractIn this paper an attempt is made to explain the experimentally observed iron siting in ferrisilicate MFI‐type zeolites based on TPA‐silicate solution chemistry. A critical molecular step in the formation of Silicalite‐1 zeolite is the formation of the precursor, counting 36 T‐atoms, by condensation of three pentacyclic dodecamers around a TPA molecule. Incorporation of a tetracyclic undecamer instead of a pentacyclic dodecamer results in a precursor with a missing Si atom at a position that becomes a T9 or T10 site of the orthorhombic unit cell of the MFI‐type zeolite. The incorporation of iron at these empty positions of the precursor explains the experimentally observed preferred iron positions. Close examination of the precursor formation mechanism reveals that the iron is incorporated at the same T‐atom positions, viz. T9 and T10, when the precursor is formed from an iron‐containing pentacyclic dodecamer. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Tenecteplase: a review

Background: Certain shortcomings of the available thrombolytic agents have prompted the search for a more fibrin specific fibrinolytic agent with a longer half-life. Such properties would allow bolus administration, possibly leading to faster reperfusion of occluded arteries. Objective: This article focuses on the new thrombolytic agent tenecteplase, reviewing its mechanism of action, pharmacokinetic characteristics, clinical efficacy, tolerability, and potential for drug interactions in the management of acute myocardial infarction. Methods: English-language articles for inclusion in this review were identified through searches of MEDLINE ®, EMBASE ®, and International Pharmaceutical Abstracts from 1966 to April 2001. The search terms used included tenecteplase, myocardial infarction, TNK, and TNK-tPA. Abstracts from recent conferences and symposia were also consulted. Results: Tenecteplase is a variant of the native tissue-type plasminogen activator (tPA) molecule that has 14-fold greater fibrin specificity than alteplase, a longer half-life, slower plasma clearance, and 80-fold greater resistance to inhibition by plasminogen activator inhibitor type 1. Its half-life of ∼18 minutes allows single-bolus administration. In comparative clinical trials, tenecteplase was found to have equivalent efficacy to recombinant tPA (alteplase). The rate of intracranial hemorrhage with tenecteplase was similar to that with alteplase, and tenecteplase was associated with fewer noncerebral complications and less need for blood transfusions. Conclusions: Tenecteplase appears to be as effective and well tolerated as alteplase in the management of acute myocardial infarction and offers the convenience of single-bolus administration.

Computer simulation of Fe-ZSM5 — comparison to EXAFS studies

Computer simulations have been used to determine the siting and local environment of the framework iron and related Brønsted acid site in (calcined) Fe-ZSM5. Simulated FT of the Fe K-edge EXAFS from the calculated distances are in agreement with experimental data. The detailed geometry information allows us to improve on the experimental models proposed. Further calculations on the as-prepared material, containing tetrapropylammonium, are also in excellent agreement with the experimental EXAFS. The calculations show only a slight deviation of the TPA molecule from its site in silicalite. The higher shell features in the EXAFS data can be assigned to the calculated template atoms, which is contrary to a speculative model proposed from previous analysis of the experimental data.

Kringle glycosylation in a modified human tissue plasminogen activator improves functional properties

Native tissue plasminogen activator (ntPA) has a variable glycosylation site on its kringle-2 domain. We have examined the effects of kringle glycosylation on functional properties by studying the simplified tPA molecule, tPA-6. tPA-6 is composed of kringle-2 and the serine protease domains and, like ntPA, cells expressing tPA-6 process it into two glycoforms: the monoglycosylated tPA-6-primary (tPA-6P, type II) with N- linked glycosylation at Asn-448 in the serine protease domain and diglycosylated tPA-6-variant (tPA-6V, type I) with glycosylation at Asn- 448 and at Asn-184 in kringle-2. When the two glycoforms were separated, we found that purified tPA-6V had reduced fibrin-stimulated plasminogenolytic activity toward Glu-plasminogen when compared to purified tPA-6P. However, in the presence of fibrin, tPA-6V unexpectedly exhibited a sixfold increase in selectivity toward Lys- plasminogen. In addition, tPA-6V was less susceptible than tPA-6P to plasmin-mediated conversion to the two-chain form. By site-directed mutagenesis of tPA-6, we eliminated variable glycosylation at Asn-184 and engineered a new glycosylation signal at a remnant site in the kringle. This derivative, designated tPA-6D, was secreted with complete kringle glycosylation. Like the naturally occurring tPA-6V, tPA-6D had lower rates of fibrin-stimulated Glu-plasminogen activation, increased specificity toward Lys-plasminogen, and greater resistance to plasmin digestion. Although the activity of tPA-6D could be stimulated by fibrin, its activity was not stimulated significantly by fibrinogen, and in human plasma the rate of fibrinogen depletion was reduced threefold. Although fibrin binding to kringle-2 of tPA-6D was slightly improved, there was a substantial increase in the dissociation constant (kd) for lysine binding, demonstrating a lack of correlation between these ligand-binding sites. Overall, our data demonstrate the marked effect of kringle glycosylation on functional properties. In addition, we have generated a derivative with properties that potentially improve clot specificity and single-chain half-life and reduce the potential for plasminogen activation in the plasma.

Kringle Glycosylation in a Modified Human Tissue Plasminogen Activator Improves Functional Properties

Native tissue plasminogen activator (ntPA) has a variable glycosylation site on its kringle-2 domain. We have examined the effects of kringle glycosylation on functional properties by studying the simplified tPA molecule, tPA-6. tPA-6 is composed of kringle-2 and the serine protease domains and, like ntPA, cells expressing tPA-6 process it into two glycoforms: the monoglycosylated tPA-6-primary (tPA-6P, type II) with N-linked glycosylation at Asn-448 in the serine protease domain and diglycosylated tPA-6-variant (tPA-6V, type I) with glycosylation at Asn-448 and at Asn-184 in kringle-2. When the two glycoforms were separated, we found that purified tPA-6V had reduced fibrin-stimulated plasminogenolytic activity toward Glu-plasminogen when compared to purified tPA-6P. However, in the presence of fibrin, tPA-6V unexpectedly exhibited a sixfold increase in selectivity toward Lys-plasminogen. In addition, tPA-6V was less susceptible than tPA-6P to plasmin-mediated conversion to the two-chain form. By site-directed mutagenesis of tPA-6, we eliminated variable glycosylation at Asn-184 and engineered a new glycosylation signal at a remnant site in the kringle. This derivative, designated tPA-6D, was secreted with complete kringle glycosylation. Like the naturally occurring tPA-6V, tPA-6D had lower rates of fibrin-stimulated Glu-plasminogen activation, increased specificity toward Lys-plasminogen, and greater resistance to plasmin digestion. Although the activity of tPA-6D could be stimulated by fibrin, its activity was not stimulated significantly by fibrinogen, and in human plasma the rate of fibrinogen depletion was reduced threefold. Although fibrin binding to kringle-2 of tPA-6D was slightly improved, there was a substantial increase in the dissociation constant (kd) for lysine binding, demonstrating a lack of correlation between these ligand-binding sites. Overall, our data demonstrate the marked effect of kringle glycosylation on functional properties. In addition, we have generated a derivative with properties that potentially improve clot specificity and single-chain half-life and reduce the potential for plasminogen activation in the plasma.

A novel screening system for yeast strains capable of secreting tissue plasminogen activator.

We have developed a simple screening procedure that allowed us to identify Saccharomyces cerevisiae strains able to secrete human tissue plasminogen activator (tPA) into the culture medium. The screen can be used to isolate more efficient secretor strains and to look for novel tPA analogs. Employing one of these strains to study the effect of glycosylation on secretion, we show that glycosylation in the catalytic domain of tPA plays an important role in folding and/or secretion of the molecule. Removing this glycosylation site resulted in a 3-5-fold reduction in the level of tPA secretion. We anticipate that this system will prove useful in studying yeast secretory pathway as well as structure-function relationships in the tPA molecule.

Effect of Peptides on the Inactivation of Tissue Plasminogen Activator by Plasminogen Activator Inhibitor-1 and on the Binding of Tissue Plasminogen Activator to Endothelial Cells

The effectiveness of tissue plasminogen activator (tPA) in thrombolytic therapy is dependent upon the rate at which therapeutically administered tPA reaches the clot site and the proportion of that tPA which is enzymatically active. Interactions between tPA and its main plasma inhibitor (PAI-1) and between tPA and the endothelial cells lining blood vessels are two factors which may limit efficacy. In an attempt to identify the regions of the tPA molecule involved in these interactions, we have examined a series of synthetic peptides with amino acid sequences corresponding to different regions of the tPA molecule for their ability to protect tPA from inactivation by PAI-1 and for their ability to reduce the binding of tPA to endothelial cells. Three peptides were identified which were especially effective at maintaining tPA activity in the presence of PAI-1 and three others were found which had a lesser effect. These same peptides were also found to inhibit the binding of tPA to endothelial cells. This suggests that the same regions of the tPA molecule are involved in both processes. None of the peptides inhibited the binding of tPA to fibrin. These peptides may serve as models for the development of agents for enhancing the activity of both endogenous tPA and of tPA administered in thrombolytic therapy.

The Conformation Changes of the Finger Domain of Tissue Type Plasminogen Activator during the Activator-lnhibitor Reaction

A peptide fragment of tissue plasminogen activator (tPA) corresponding to amino acid residues 4-8 (tPA4-8) was synthesized, coupled to thyroglobulin and injected into rabbits. Antibodies specific to the peptide tPA4-8 were purified immunochemically on the pentapeptide coupled to CNBr-Sepha rose 4B. Anti-tPA4-8 antibodies, reacted with iodinated peptide tPA4-8, showing a relatively high binding affinity (KD = 2.3 x 10(-8) M). There was no interaction between anti-tPA4-8 antibodies and native one- or two-chain tPA. However, reduction of disulfide bonds unmasked the epitope on the heavy chain of tPA which became accessible to anti-tPA4-8 antibodies. Similarly, complexing of tPA with alpha 1-antitrypsin inhibitor resulted in unmasking of the epitope formed by amino acid residues in the positions 4-8. Presented data suggest that complexing of tPA with inhibitors results in conformational changes occurring in the "finger" domain of tPA molecule and such conformational transition can be detected by antipeptide antibodies. Therefore, anti-tPA4-8 antibodies may be employed as sequence-specific reporter molecules to monitor local conformational changes in tPA molecule.

Functional characterization of monoclonal antibodies directed against fibrin binding domains of tissue-type plasminogen activator

Fibrin interacts with tissue-type plasminogen activator (tPA) via the finger and the kringle 2 domains. Three monoclonal antibodies against tPA, designated MPW3VPA, MPW6VPA, and MPW7VPA, which react with epitopes in the tPA molecule involved in fibrin binding, were characterized. The IgM monoclonal antibody MPW6VPA, directed against an epitope close to the finger and epidermal growth factor domains, stimulated plasminogen activation only in the absence of CNBr-fibrinogen fragments by increasing kcat in a dose-dependent fashion, an effect which was not restricted to the intact molecule. These results suggest that MPW6VPA mimics the initial effect of fibrin bound to the tPA molecule, which results in a change of kcat values. The MPW6VPA effect was reversed by another antibody, MPW3VPA, also directed against epidermal growth factor and finger domains. The latter antibody also inhibited plasminogen activation by tPA in the presence of CNBr-fibrinogen fragments in a dose-dependent, apparently noncompetitive way. No effect of MPW3VPA was seen in the absence of CNBr-fibrinogen fragments. MPW7VPA directed against kringle 2 of tPA inhibited plasminogen activation by tPA only when CNBr-fibrinogen fragments were present. This inhibition was apparently competitive and dose-dependent. These data suggest that MPW3VPA interferes with the first phase of fibrin binding to tPA, whereas MPW7VPA interferes with the second phase of fibrin binding to the tPA molecule via kringle 2, resulting in Km changes.

Construction of a tissue plasminogen activator gene having unique restriction sites to facilitate domain manipulation: a model for the analysis of multi-domain proteins

We have designed and constructed a DNA sequence encoding human tissue plasminogen activator (tPA) with convenient restriction sites that flank each of the domains of the heavy chain. To accomplish this, the first 1095 bases of the gene coding for the mature protein were synthesized with unique restriction sites engineered into the interdomainal regions. This synthetic construction was then ligated to a cDNA fragment of the tPA gene that encoded the active site, thus generating a full-length tPA gene. The gene products produced by Chinese hamster ovary (CHO) cells transfected with either the tPA cassette gene or the tPA cDNA gene were then compared with the tPA produced by Bowes melanoma cells to determine whether or not synthetic interdomainal amino acid changes had an effect on the biochemical characteristics of the molecule. Specifically, molecular weight, specific activity, enhancement by fibrinogen fragments and kinetic constants were analysed. None of the properties examined were significantly different from those of the native melanoma tPA. Therefore, the cassette gene described herein should provide considerable versatility and precision in the construction of tPA mutants by facilitating the manipulation of the finger, growth factor and kringle domains, and likewise should be useful in assessing the function of these domains within the tPA molecule. We present this cassette gene system as a model for the analysis of protein domain function applicable to other multi-domain proteins.

Structure–function analysis of tissue-type plasminogen activator by linker-insertion, point and deletion mutagenesis

We undertook a structure--function analysis of human tissue plasminogen activator (tPA) using linker-scanning and deletion mutagenesis. Synthetic oligonucleotide linkers were introduced into the tPA cDNA at pre-existing restriction enzyme sites. This generated a series of tPA variants which contained small primary sequence alterations consisting of point mutations, deletions or insertions. The majority of the linker-insertion variants demonstrate a significant reduction in amidolytic and fibrinolytic activity in comparison to wild-type tPA. The exceptions are the variants with linker-inserts placed at the BglII(115) and StyI(277) sites of the tPA cDNA (4SLEG5 and 57LEA58 respectively), which encode insertions at the boundaries of the finger domain. The variants with linker-inserts in the light chain (protease domain) of tPA are the lowest in enzymatic activity. Particularly sensitive to mutation are highly conserved amino acids. Heavy chain deletion variants were constructed from point mutants at the domain boundaries of tPA. Deletion of the kringle domains lowers the fibrinolytic activity to a greater extent than deletion of the finger or growth factor domains. We conclude that alterations in any domain of the tPA molecule, and particularly in the highly conserved residues within these domains, can affect fibrinolytic activity.

Kinetic analysis of the interactions between plasminogen activator inhibitor 1 and both urokinase and tissue plasminogen activator

Plasminogen activator inhibitor 1 (PAI-1) was purified from medium conditioned by cultured bovine aortic endothelial cells by successive chromatography on concanavalin A Sepharose, Sephacryl S-200, Blue B agarose, and Bio-Gel P-60. As shown previously for conditioned media ( C. M. Hekman and D. J. Loskutoff (1985) J. Biol Chem. 260, 11581–11587 ) the purified PAI-1 preparation contained latent inhibitory activity which could be stimulated 9.4-fold by sodium dodecyl sulfate and 45-fold by guanidine-HCl. The specific activity of the preparation following treatment with 0.1% sodium dodecyl sulfate was 2.5 × 10 3 IU/mg. The reaction between purified, guanidine-activated PAI-1 and both urokinase and tissue plasminogen activator (tPA) was studied. The second-order rate constants (pH 7.2, 35 °C) for the interaction between guanidine-activated PAI-1 and urokinase (UK), and one- and two-chain tPA are 1.6 × 10 8, 4.0 × 10 7, and 1.5 × 10 8 M −1 s −1, respectively. The presence of CNBr fibrinogen fragments had no affect on the rate constants of either one- or two-chain tPA. Steady-state kinetic analysis of the effect of PAI-1 on the rate of plasminogen activation revealed that the initial UK PAI-1 interaction can be competed with plasminogen suggesting that the UK PAI-1 interaction may involve a competitive type of inhibition. In contrast, the initial tPA PAI-1 interaction can be competed only partially with plasminogen, suggesting that the tPA PAI-1 interaction may involve a mixed type of inhibition. The results indicate that PAI-1 interacts more rapidly with UK and tPA than any PAI reported to date and suggest that PAI-1 is the primary physiological inhibitor of single-chain tPA. Moreover, the interaction of PAI-1 with tPA differs from its interaction with UK, and may involve two Sites on the tPA molecule.

Neutralization by plasminogen activator inhibitor-1 of mutants of tissue plasminogen activator.

Deletion mutants of human tissue plasminogen activator (tPA) were expressed in Chinese hamster ovary cells. These cells had been transfected with genes that encoded tPA but included restriction sites that allowed the deletion of DNA encoding specific structural domains of the tPA molecule's heavy chain. Purified, two-chain mutant tPAs, or analogues of tPA, lacking one or several structural domains, along with Bowes melanoma tPA were studied in order to determine their susceptibility to inhibition by plasminogen activator inhibitor-1 (PAI-1). The full-length analogue of tPA, designated by its domains FGK1K2P, as well as analogues GK1K2P, FK2P, and FGK1P were treated with various amounts of PAI-1. When the amounts of added tPA and analogues were standardized so that each generated the same absorbance in a chromogenic assay containing S-2251, plasminogen, and fibrinogen fragments, there was a significant difference in the way in which the analogues were titrated by the inhibitor. The melanoma tPA and FGK1K2P were the most susceptible, FK2P slightly less sensitive, and GK1K2P and FGK1P the least sensitive to inhibition. In contrast, when the amounts of enzyme used were standardized on the basis of absorbance generated in a direct assay employing the chromogenic substrate S-2288 and then titrated with PAI-1, these differences in susceptibility to inhibition were not observed. Based on these data, the differential susceptibility to inhibition observed in the plasminogen-dependent assay was attributed to the extent to which the activity of a given analogue is enhanced by fibrinogen fragments, and thus reflected the different amounts of enzymes added in order to standardize the assay on the basis of absorbance.(ABSTRACT TRUNCATED AT 250 WORDS)

Co-carcinogens or modulators of carcinogenesis. New aspects of the etiology of human tumors and of the molecular mechanisms of carcinogenesis

Within the last 10 years numerous new and typical exogenous cocarcinogens were identified chemically as well as biologically and characterized biochemically as initiation or tumor promoters. They are highly irritant diterpene esters of plant origin. Promoters of this type were recently detected also in the Euphorbiacea Croton flavens L., the multiple use of which for stimulants according to local habits was previously held responsible for the unusually high rate of esophageal cancer on Curacao. This detection confirms for the first time that in the etiology of human cancer besides solitary carcinogens (first-order carcinogenic risk factors) also cocarcinogens of the promoter type have to be considered (second-order carcinogenic risk factors). -- The active principles of the diterpene ester type are the strongest promoters known so far; they are noninitiators and nonmutagens. Of the manyfold biochemical activities of these promoters the three most actual are: the TPA molecule does not require activation by metabolic alteration, it releases very rapidly prostaglandin E2 from cellular membranes and it activates latent DNA-viral genoms.