Oriented Immobilization on Gold Nanoparticles of a Recombinant Therapeutic Zymogen

Direct immobilization of functional proteins on gold nanoparticles (AuNPs) affects their structure and function. Changes may vary widely and range from strong inhibition to the enhancement of protein function. More often though the outcome of direct protein immobilization results in protein misfolding and the loss of protein activity. Additional complications arise when the protein being immobilized is a zymogen which requires and relies on additional protein-protein interactions to exert its function. Here we describe molecular design of a glutathione-S-transferase-Staphylokinase fusion protein (GST-SAK) and its conjugation to AuNPs. The multivalent AuNP-(GST-SAK)n complexes generated show plasminogen activation activity in vitro. The methods described are transferable and could be adapted for conjugation and functional analysis of other plasminogen activators, thrombolytic preparations or other functional enzymes.

Engineered microparticles and nanoparticles for fibrinolysis

Fibrinolytic agents including plasmin and plasminogen activators improve outcomes in acute ischemic stroke and thrombosis by recanalizing occluded vessels. In the decades since their introduction into clinical practice, several limitations of have been identified in terms of both efficacy and bleeding risk associated with these agents. Engineered nanoparticles and microparticles address some of these limitations by improving circulation time, reducing inhibition and degradation in circulation, accelerating recanalization, improving targeting to thrombotic occlusions, and reducing off-target effects; however, many particle-based approaches have only been used in preclinical studies to date. This review covers four advances in coupling fibrinolytic agents with engineered particles: (a) modifications of plasminogen activators with macromolecules, (b) encapsulation of plasminogen activators and plasmin in polymer and liposomal particles, (c) triggered release of encapsulated fibrinolytic agents and mechanical disruption of clots with ultrasound, and (d) enhancing targeting with magnetic particles and magnetic fields. Technical challenges for the translation of these approaches to the clinic are discussed.

Exploring the potential of a structural alphabet-based tool for mining multiple target conformations and target flexibility insight

Protein flexibility is often implied in binding with different partners and is essential for protein function. The growing number of macromolecular structures in the Protein Data Bank entries and their redundancy has become a major source of structural knowledge of the protein universe. The analysis of structural variability through available redundant structures of a target, called multiple target conformations (MTC), obtained using experimental or modeling methods and under different biological conditions or different sources is one way to explore protein flexibility. This analysis is essential to improve the understanding of various mechanisms associated with protein target function and flexibility. In this study, we explored structural variability of three biological targets by analyzing different MTC sets associated with these targets. To facilitate the study of these MTC sets, we have developed an efficient tool, SA-conf, dedicated to capturing and linking the amino acid and local structure variability and analyzing the target structural variability space. The advantage of SA-conf is that it could be applied to divers sets composed of MTCs available in the PDB obtained using NMR and crystallography or homology models. This tool could also be applied to analyze MTC sets obtained by dynamics approaches. Our results showed that SA-conf tool is effective to quantify the structural variability of a MTC set and to localize the structural variable positions and regions of the target. By selecting adapted MTC subsets and comparing their variability detected by SA-conf, we highlighted different sources of target flexibility such as induced by binding partner, by mutation and intrinsic flexibility. Our results support the interest to mine available structures associated with a target using to offer valuable insight into target flexibility and interaction mechanisms. The SA-conf executable script, with a set of pre-compiled binaries are available at http://www.mti.univ-paris-diderot.fr/recherche/plateformes/logiciels.

[Streptokinase and Staphylokinase: Differences in the Kinetics and Mechanism of Their Interaction with Plasminogen, Inhibitors and Fibrin]

Comparative in vitro study of the kinetics of various reactions involved in the process of thrombolysis initiated by streptokinase (SK) and staphylokinase (STA) was carried out. It was shown that at the interaction of an equimolar ratio of plasminogen (Pg) with SK or STA the rate of formation and the specific esterase activity of the complex plasmin (Pm) · SK are higher than those of the complex Pm · STA. The catalytic efficiency (kcat/Km) of hydrolysis of the chromogenic plasmin substrates by Pm · SK complex was 2 times higher than by Pm · STA complex. In the absence of fibrin catalytic efficiency (kPg/K(Pg)) of activation of Glu-plasminogen and Lys-plasminogen glycoform II by Pm · SK complex was higher than by Pm · STA complex, but the pres- ence of fibrin increased kPg/K(Pg)) activation of both plasminogens by Pm · STA complex significantly stronger than by Pm · SK complex due to the decrease in K(Pg)). In contrast to STA (15.5 kDa), SK molecule (47 kDa) creates significant steric hindrances for the interaction of plasmin in Pm · SK complex with protein inhibi- tors. In addition, SK caused greater fibrinogen degradation than STA. It is shown that Pm · SK and Pm · STA complexes lyse fibrin clots in buffer with similar rates, while the rate of lysis of plasma clots, immersed in plas- ma, by Pm · STA complex are significantly higher than those by Pm · SK complex. It was revealed that the species specificity of STA and S K is determined mainly by the rate of formation and the efficiency of Pm · SK and Pm · STA complexes in the activation of autologous plasminogen. The lysis efficiency of plasma clots of mammals fell in the series: human > dog > rabbit for SK and the dog > human > rabbit for STA. The results show that in the purified system SK is a more effective activator of plasminogen than STA. In the system con- taining fibrin and α2-AP, the activator and fibrinolytic activities of STA are higher than those of SK, due to the increased stability in plasma and fibrin specificity of STA, the fast reaction of the complex Pm · STA with α2AP and the ability of the STA to recyclization in the presence of α2AP.

Fibrinolytic and procoagulant activities of Yersinia pestis and Salmonella enterica

Pla of the plague bacterium Yersinia pestis and PgtE of the enteropathogen Salmonella enterica are surface-exposed, transmembrane β-barrel proteases of the omptin family that exhibit a complex array of interactions with the hemostatic systems in vitro, and both proteases are established virulence factors. Pla favors fibrinolysis by direct activation of plasminogen, inactivation of the serpins plasminogen activator inhibitor-1 and α2-antiplasmin, inactivation of the thrombin-activable fibrinolysis inhibitor, and activation of single-chain urokinase. PgtE is structurally very similar but exhibits partially different functions and differ in expression control. PgtE proteolysis targets control aspects of fibrinolysis, and mimicry of matrix metalloproteinases enhances cell migration that should favor the intracellular spread of the bacterium. Enzymatic activity of both proteases is strongly influenced by the environment-induced variations in lipopolysaccharide that binds to the β-barrel. Both proteases cleave the tissue factor pathway inhibitor and thus also express procoagulant activity.

[Screening of Producers of Proteinases with Fibrinolytic and Collagenolytic Activities among Micromycetes]

Screening for producers of proteinases with fibrinolytic (plasmin-like and plasminogen-activating) and collagenolytic activities-was carried out among 83 strains of microscopic fungi belonging to various ecological groups. Entomopathogenic micromycetes secreted proteinases with higher fibrinolytic and collagenolytic activity than saprotrophic, potentially phytopathogenic, and epiphytic strains. Micromycete strains possessing proteolytic enzymes with collagenase activity were revealed, as well as the strains producing proteinases with plasmin-like activity. None of the strains studied secreted proteinases possessing only plasminogen-activating activity. Tolypocladium inflatum k1 was found to be a producer of extracellular proteinases with high plasminogen-activating, plasmin-like, and collagenolytic activities. The specific plasminogen-activating activity of T. inflatum k1 was shown to be 20% higher than its plasmin-like activity.

Desmoteplase in the treatment of acute ischemic stroke

Desmoteplase, developed by Paion, Forest and Lundbeck, is a novel plasminogen activator that selectively activates fibrin-bound plasminogen and is currently being investigated for the treatment of acute ischemic stroke within the time window of 3-9 h after symptom onset. Desmoteplase is believed to offer pharmacologic advantages over currently approved treatment options. To date, two published Phase II perfusion imaging-based clinical trials have reported the safety and potential efficacy of desmoteplase in ischemic stroke. Results from a recently completed Phase III trial in Europe, Asia and the USA are awaited. This article reviews the available data on desmoteplase, including discussion of its favorable features and potential benefit beyond the 3-h time window in the treatment of ischemic stroke.

Fast and simple detection of Yersinia pestis applicable to field investigation of plague foci

Yersinia pestis, the plague bacillus, has a rodent-flea-rodent life cycle but can also persist in the environment for various periods of time. There is now a convenient and effective test (F1-dipstick) for the rapid identification of Y. pestis from human patient or rodent samples, but this test cannot be applied to environmental or flea materials because the F1 capsule is mostly produced at 37°C. The plasminogen activator (PLA), a key virulence factor encoded by a Y. pestis-specific plasmid, is synthesized both at 20°C and 37°C, making it a good candidate antigen for environmental detection of Y. pestis by immunological methods. A recombinant PLA protein from Y. pestis synthesized by an Escherichia coli strain was used to produce monoclonal antibodies (mAbs). PLA-specific mAbs devoid of cross-reactions with other homologous proteins were further cloned. A pair of mAbs was selected based on its specificity, sensitivity, comprehensiveness, and ability to react with Y. pestis strains grown at different temperatures. These antibodies were used to develop a highly sensitive one-step PLA-enzyme immunoassay (PLA-EIA) and an immunostrip (PLA-dipstick), usable as a rapid test under field conditions. These two PLA-immunometric tests could be valuable, in addition to the F1-disptick, to confirm human plague diagnosis in non-endemic areas (WHO standard case definition). They have the supplementary advantage of allowing a rapid and easy detection of Y. pestis in environmental and flea samples, and would therefore be of great value for surveillance and epidemiological investigations of plague foci. Finally, they will be able to detect natural or genetically engineered F1-negative Y. pestis strains in human patients and environmental samples.

Model thrombi formed under flow reveal the role of factor XIII-mediated cross-linking in resistance to fibrinolysis

BACKGROUND

Activated factor XIII (FXIIIa), a transglutaminase, introduces fibrin-fibrin and fibrin-inhibitor cross-links, resulting in more mechanically stable clots. The impact of cross-linking on resistance to fibrinolysis has proved challenging to evaluate quantitatively.

METHODS

We used a whole blood model thrombus system to characterize the role of cross-linking in resistance to fibrinolytic degradation. Model thrombi, which mimic arterial thrombi formed in vivo, were prepared with incorporated fluorescently labeled fibrinogen, in order to allow quantification of fibrinolysis as released fluorescence units per minute.

RESULTS

A site-specific inhibitor of transglutaminases, added to blood from normal donors, yielded model thrombi that lysed more easily, either spontaneously or by plasminogen activators. This was observed both in the cell/platelet-rich head and fibrin-rich tail. Model thrombi from an FXIII-deficient patient lysed more quickly than normal thrombi; replacement therapy with FXIII concentrate normalized lysis. In vitro addition of purified FXIII to the patient's preprophylaxis blood, but not to normal control blood, resulted in more stable thrombi, indicating no further efficacy of supraphysiologic FXIII. However, addition of tissue transglutaminase, which is synthesized by endothelial cells, generated thrombi that were more resistant to fibrinolysis; this may stabilize mural thrombi in vivo.

CONCLUSIONS

Model thrombi formed under flow, even those prepared as plasma 'thrombi', reveal the effect of FXIII on fibrinolysis. Although very low levels of FXIII are known to produce mechanical clot stability, and to achieve γ-dimerization, they appear to be suboptimal in conferring full resistance to fibrinolysis.

L-arginine hydrochloride increases the solubility of folded and unfolded recombinant plasminogen activator rPA

L-arginine hydrochloride (L-ArgHCl) was found to be an effective enhancer for in vitro protein refolding more than two decades ago. A detailed understanding of the mechanism of action, by which L-ArgHCl as co-solvent is capable to effectively suppress protein aggregation, while protein stability is preserved, has remained elusive. Concepts for the effects of co-solvents, which have been established over the last decades, were found to be insufficient to completely explain the effects of L-ArgHCl on protein refolding. In this article, we present data, which clearly establish that L-ArgHCl acts on the equilibrium solubility of the native model protein recombinant plasminogen activator (rPA), while for S-carboxymethylated rPA (IAA-rPA) that served as a model protein for denatured protein states, equilibrium solubilities could not be obtained. Solid to solute free transfer energies for native rPA were lowered by up to 14 kJ mol(-1) under the tested conditions. This finding is in marked contrast to a previously proposed model in which L-ArgHCl acts as a neutral crowder which exclusively has an influence on the stability of the transition state of aggregation. The effects on the apparent solubility of IAA-rPA, as well as on the aggregation kinetics of all studied protein species, that were observed in the present work could tentatively be explained within the framework of a nucleation-aggregation scheme, in which L-ArgHCl exerts a strong effect on the pre-equilibria leading to formation of the aggregation seed.

[Study on the effect of GDG on secondary structure of plasminogen and plasminogen activators by circular dichroism]

To investigate the effect of GDG on the secondary structure of plasminogen and plasminogen activators, circular dichroism and SDS-PAGD were applied. The results show that the secondary structures of prourokinase and streptokinase were changed by GDG. The amount of alpha-helix, beta-sheet, beta-turn and random coil of fibrinolytic factors relates with the different concentrations of GDG in the study. GDG has no effects on the secondary structure of plasmin and plasminogen. GDG enhancing the interactivation of plasminogen and prourokinase was indicated by SDS-PAGE. It was found that GDG significantly affected the activity of prourokinase and streptokinase, and increased intrinsic fluorescence of prourokinase.

Substrate specificity and screening of the integral membrane protease Pla

This paper reports a study to find small peptide substrates for the important virulence factor of Yersinia pestis, plasminogen activator, Pla. The method used to find small substrates for this protease is reported along with studies examining the ability of these peptides to inhibit activity of the enzyme. Through the use of parallel synthesis and positional scanning, small tripeptides were identified that are viable substrates for the protease.

Isolation and absolute configuration of SMTP-0, a simplest congener of the SMTP family nonlysine-analog plasminogen modulators

SMTP-0, a new simple congener of the SMTP nonlysine-analog plasminogen modulators, was isolated from a culture of Stachybotrys microspora. Based on the physico-chemical data, SMTP-0 was shown to be an enantiomer of the antimicrobial compound stachybotrin B. The absolute configuration of SMTP-0 was determined by the modified Mosher method. The stereochemistry was further confirmed using an epimer of SMTP-0. Unlike most SMTPs with an amino acid side chain linked to the nitrogen atom of the lactam moiety, SMTP-0, which lacks the N-linked side chain, showed no plasminogen modulator activity.

Regulation of Nonproteolytic Active Site Formation in Plasminogen

Streptokinase may be less effective at saving lives in patients with heart attacks because it explosively generates plasmin in the bloodstream at sites distant from fibrin clots. We hypothesized that this rapid plasmin generation is due to SK's singular capacity to nonproteolytically generate the active protease SK x Pg*, and we examined whether the kringle domains regulate this process. An SK mutant lacking Ile-1 (deltaIle1-SK) does not form SK x Pg*, although it will form complexes with plasmin that can activate plasminogen. When compared to SK, deltaIle1-SK diminished the generation of plasmin in plasma by more than 30-fold, demonstrating that the formation of SK x Pg* plays an important role in SK activity in the blood. The rate of SK x Pg* formation (measured by an active site titrant) was much slower in Glu-Pg, which contains five kringle domains, than in Pg forms containing one kringle (mini-Pg) or no kringles (micro-Pg). In a similar manner, Streptococcus uberis Pg activator (SUPA), an SK-like molecule, generated SUPA x Pg* much slower with bovine Pg than bovine micro-Pg. The velocity of SK x Pg* formation was regulated by agents that influence the conformation of Pg through interactions with the kringle domains. Chloride ions, which maintain the compact Pg conformation, hindered SK x Pg* formation. In contrast, epsilon-aminocaproic acid, fibrin, and fibrinogen, which induce an extended Pg conformation, accelerated the formation of SK x Pg*. In summary, the explosive generation of plasmin in blood or plasma, which diminishes SK's therapeutic effects, is attributable to the formation of SK x Pg*, and this process is governed by kringle domains.

Mechanism of action of θ-amino acids on plasminogen activation and fibrinolysis induced by staphylokinase

Stimulation of Lys-plasminogen (Lys-Pg) and Glu-plasminogen (Glu-Pg) activation under the action of staphylokinase and Glu-Pg activation under the action of preformed plasmin-staphylokinase activator complex (Pm-STA) by low concentrations and inhibition by high concentrations of omega-amino acids (>90-140 mM) were found. Maximal stimulation of the activation was observed at concentrations of L-lysine, 6-aminohexanoic acid (6-AHA), and trans-(4-aminomethyl)cyclohexanecarboxylic acid 8.0, 2.0, and 0.8 mM, respectively. In contrast, the Lys-Pg activation rate by Pm-STA complex sharply decreased when concentrations of omega-amino acids exceeded the above-mentioned values. It was found that formation of Pm-STA complex from a mixture of equimolar concentrations of staphylokinase and Glu-Pg or Lys-Pg is stimulated by low concentrations (maximal at 10 mM) of 6-AHA. Negligible increase in the specific activities of plasmin and Pm-STA complex was detected at higher concentrations of 6-AHA (to maximal at 70 and 50 mM, respectively). Inhibitory effects of omega-amino acids on the rate of fibrinolysis induced by staphylokinase, Pm-STA complex, and plasmin were compared. It was found that inhibition of staphylokinase-induced fibrinolysis by omega-amino acids includes blocking of the reactions of Pm-STA complex formation, plasminogen activation by this complex, and lysis of fibrin by forming plasmin as a result of displacement of plasminogen and plasmin from the fibrin surface. Thus, the slow stage of Pm-STA complex formation plays an important role in the mechanism of action of omega-amino acids on Glu-Pg activation and fibrinolysis induced by staphylokinase. In addition to alpha-->beta change of Glu-Pg conformation, stimulation of Pm-STA complex formation leads to increase in Glu-Pg activation rate in the presence of low concentrations of omega-amino acids. Inhibition of Pm-STA complex formation on fibrin surface by omega-amino acids is responsible for appearance of long lag phases on curves of fibrinolysis induced by staphylokinase.

Zoonotic focus of plague, Algeria

After an outbreak of human plague, 95 Xenopsylla cheopis fleas from Algeria were tested for Yersinia pestis with PCR methods. Nine fleas were definitively confirmed to be infected with Y. pestis biovar orientalis. Our results demonstrate the persistence of a zoonotic focus of Y. pestis in Algeria.

Biochemical characterization and molecular cloning of a plasminogen activator proteinase (LV-PA) from bushmaster snake venom

The protein (LV-PA) from bushmaster (Lachesis muta muta) venom is a serine proteinase which specifically activates the inactive proenzyme plasminogen. LV-PA is a single chain glycoprotein with an apparent molecular mass of 33 kDa that fell to 28 kDa after treatment with N-Glycosidase F (PNGase F). Approximately 93% of its protein sequence was determined by automated Edman degradation of various fragments derived from a digestion with trypsin. A cDNA library of L. m. muta was constructed to generate expressed sequence tags (ESTs) and the plasminogen activator precursor cDNA was sequenced. The complete amino acid sequence of the enzyme was deduced from the cDNA sequence. LV-PA is composed of 234 residues and contains a single asparagine-linked glycosylation site, Asn-X-Ser, bearing sugars that account for approximately 10% of the enzyme's total molecular mass of 33 kDa. The sequence of LV-PA is highly similar to the plasminogen activators (PAs) TSV-PA from Trimeresurus stejnegeri venom and Haly-PA from Agkistrodon halys. Furthermore, the mature protein sequence of LV-PA exhibits significant similarity with other viperidae venom serine proteinases which affect many steps of hemostasis, ranging from the blood coagulation cascade to platelet function. The Michaelis constant (Km) and the catalytic rate constant (kcat) of LV-PA on four chromogenic substrates were obtained from Lineweaver-Burk plots. In addition, we used an indirect enzyme-linked immunoabsorbent assay (ELISA) to explore the phylogenetic range of immunological cross-reactivity (using antibodies raised against LV-PA) with analogous serine proteinases from two viperidae venoms and mammals.

A novel plasminogen activator from Agkistrodon blomhoffii Ussurensis venom (ABUSV-PA): Purification and characterization

A plasminogen activator with arginine ester hydrolysis activity (ABUSV-PA) has been identified and purified to homogeneity from Chinese Agkistrodon blomhoffii Ussurensis snake venom. ABUSV-PA, a monomeric protein with molecular mass of 27815.2 Da, was purified 180-fold with 0.02% recovery for protein and 3.6% recovery for esterase activity. ABUSV-PA reacts optimally with its substrate N(alpha)-tosyl-l-arginine-methyl ester (TAME) at approximately pH 7.5 and at 51 degrees C. Measurement from inductively coupled plasma-atomic emission spectroscopy (ICP-AES) reveals that ABUSV-PA is a Zn(2+)-containing protein with a stoichiometry of 1:1 [Zn(2+)]:[ABUSV-PA]. Analyses of esterase hydrolysis and UV absorption and CD spectra indicate that Zn(2+) plays an important role in maintaining the structural integrity rather than the esterase activity of ABUSV-PA. Divalent metal ions, including Ca(2+), Mg(2+), Cu(2+), Ni(2+), Mn(2+), and Co(2+), increase the TAME hydrolysis activity of ABUSV-PA. A red-shift of the emission wavelengths of the synchronous fluorescence of ABUSV-PA, compared to those of free Tyr and Trp, indicates a conformation where the Tyr and Trp residues are in exposed hydrophilic environments. The presence of zinc increases the hydrophobicity of the conformational environments surrounding the Trp residues of ABUSV-PA and affects the secondary structure of ABUSV-PA, as proved by UV absorption and CD spectroscopy.

Adhesive properties of the purified plasminogen activator Pla ofYersinia pestis

The beta-barrel outer membrane protease Pla from Yersinia pestis is an important virulence factor in plague and enables initiation of the bubonic plague. Pla is a multifunctional protease whose expression also enhances bacterial adherence to extracellular matrix. It has remained uncertain whether the increase in cellular adhesiveness results from modification of the bacterial surface by Pla, or whether the Pla molecule is an adhesin. Pla was purified as a His6-fusion protein from Escherichia coli and reconstituted with lipopolysaccharide to an enzymatically active form. Purified His6-Pla was coated onto fluorescent micro-particles (FMPs) that expressed plasminogen activity. Pla-coated FMPs also bound to laminin and to reconstituted basement membrane (Matrigel) immobilized on permanox slides, whereas only poor activity was seen with lipopolysaccharide-coated FMPs or bovine serum albumin-coated FMPs. The results show that the Pla molecule has intrinsic adhesive properties and that purified transmembrane proteins coated onto FMPs can be used for functional assays.

Influence of homocysteine on fibrin network lysis

To elucidate some of the links between homocysteine and vascular disease, we have evaluated the effect of the amino acid on the formation (by kinetics studies), structure (by electron microscopy) and lysis of the fibrin network, using tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). We have studied whether homocysteine could alter the activity of the components involved in fibrinolysis (by amidolytic and thrombolytic methods). The results showed that homocysteine-associated networks were more compact and branched than controls (52 +/- 6 vs 44 +/- 5 fibers/field, P = 0.008), and were formed by shorter and thicker fibers. This clot proved to be more resistant to fibrinolysis with u-PA than control [lysis time 50%: 257 +/- 16 (homocysteine) vs 187 +/- 6 min (control); P < 0.004], but there were no differences with t-PA. Homocysteine did not affect the biological activities of plasmin, or plasminogen activation by t-PA and u-PA. Defective fibrinolysis with u-PA was therefore associated with homocysteine-fibrin structural alterations rather than the homocysteine effect on the biological activities of the fibrinolytic components evaluated. Results suggest that hyperhomocysteinemic patients could produce tight clots, were more resistant to lysis, and generated a procoagulant environment in situ. We believe that our findings may contribute to understanding the mechanisms involved in the homocysteine harmful effect.

Isolation of a cDNA encoding a protease from Perinereis aibuhitensis Grube

The cDNA encoding a protease of Perinereis aibuhitensis Grube (PPA) was cloned. The deduced amino acid sequence analysis showed that the protein had 49% identity to the C-terminal amino acid 169-246 of serine protease of Heterodera glycines. Northern blotting analysis indicated that the cDNA could hybridize with mRNA of approximately 260 bases isolated from the marine earthworm. The cDNA was amplified by polymerase chain reaction and cloned into pMAL-p2 to construct expression vector pMAL-PPA. pMAL-PPA was introduced into Escherichia coli BL21(DE3) and overexpression of PPA fused with maltose binding protein was achieved by isopropyl-beta-D-thiogalactopyranoside induction. The fusion protein was purified by affinity chromatography on an amylose resin column and ion-exchange chromatography on a diethylaminoethyl-Sepharose 4B column. Rabbits were immunized with the purified protein and antiserum was prepared. The antibody could react with a protein of approximately 9 kDa extracted from the marine earthworm as shown by Western blotting analysis. The activity analysis of the recombinant PPA suggested that it was probably a plasminogen activator.

Regulation of serine protease inhibitor-E2 and plasminogen activator expression and secretion by follicle stimulating hormone and growth factors in non-luteinizing bovine granulosa cells in vitro

During ovarian follicle growth, there is expansion of the basal lamina and changes in the follicular extracellular matrix (ECM) that are mediated in part by proteolytic enzyme cascades regulated by tissue-type plasminogen activator (tPA) and urokinase plasminogen activator (uPA). One PA inhibitor, serine protease inhibitor-E2 (SERPINE2) is expressed in granulosa but not theca cells, and expression changes with follicle development. In this study, we hypothesized that PA and SERPINE2 expression/secretion by granulosa cells are regulated by FSH and growth factors. SERPINE2 mRNA and protein levels, tPA gene expression and uPA secretion were stimulated by FSH. Insulin-like growth factor-I stimulated SERPINE2 secretion and uPA activity, and decreased secreted tPA activity and gene expression. Bone morphogenetic protein-7 increased SERPINE2 secretion and expression and tPA secretion. In contrast, fibroblast growth factor-2 inhibited tPA secretion and SERPINE2 secretion and expression. Epidermal growth factor inhibited SERPINE2 secretion and expression, but increased secreted tPA activity. Estradiol and SERPINE2 secretion were highly positively correlated, but estradiol did not alter SERPINE2 expression. These data demonstrate that SERPINE2 expression and protein secretion are regulated by FSH and growth factors in non-luteinizing bovine granulosa cells. As estradiol is a known marker of follicle health, and SERPINE2 is an anti-apoptotic factor, we propose that SERPINE2 is involved in the regulation of atresia in bovine follicles.

Design of a novel plasminogen activator based on the structure of hirudin

Using a phage library, seven peptide sequences with high affinity to human microplasminogen were obtained. Caseinolytic assay indicated that only the synthesized peptide P07 had slight fibrinolytic activity. To enhance its plasminogen activation ability, peptide P07 was fused into loop 32-35 of hirudin. In vitro assay demonstrated that this hirudin-like fusion protein can activate human plasminogen and retain the function of thrombin inhibition. Fusing the sequence ''SPDASRL'' into hirudin generated a plasminogen activation activity 100 times higher than peptide P07 in chromogenic and radial caseinolytic assay. This significant functional improvement might originate from a more specific active structure due to the hirudin scaffold.

Binding of the COOH-terminal lysine residue of streptokinase to plasmin(ogen) kringles enhances formation of the streptokinase.plasmin(ogen) catalytic complexes

Streptokinase (SK) activates human fibrinolysis by inducing non-proteolytic activation of the serine proteinase zymogen, plasminogen (Pg), in the SK.Pg* catalytic complex. SK.Pg* proteolytically activates Pg to plasmin (Pm). SK-induced Pg activation is enhanced by lysine-binding site (LBS) interactions with kringles on Pg and Pm, as evidenced by inhibition of the reactions by the lysine analogue, 6-aminohexanoic acid. Equilibrium binding analysis and [Lys]Pg activation kinetics with wild-type SK, carboxypeptidase B-treated SK, and a COOH-terminal Lys414 deletion mutant (SKDeltaK414) demonstrated a critical role for Lys414 in the enhancement of [Lys]Pg and [Lys]Pm binding and conformational [Lys]Pg activation. The LBS-independent affinity of SK for [Glu]Pg was unaffected by deletion of Lys414. By contrast, removal of SK Lys414 caused 19- and 14-fold decreases in SK affinity for [Lys]Pg and [Lys]Pm binding in the catalytic mode, respectively. In kinetic studies of the coupled conformational and proteolytic activation of [Lys]Pg, SKDeltaK414 exhibited a corresponding 17-fold affinity decrease for formation of the SKDeltaK414.[Lys]Pg* complex. SKDeltaK414 binding to [Lys]Pg and [Lys]Pm and conformational [Lys]Pg activation were LBS-independent, whereas [Lys]Pg substrate binding and proteolytic [Lys]Pm generation remained LBS-dependent. We conclude that binding of SK Lys414 to [Lys]Pg and [Lys]Pm kringles enhances SK.[Lys]Pg* and SK.[Lys]Pm catalytic complex formation. This interaction is distinct structurally and functionally from LBS-dependent Pg substrate recognition by these complexes.

Synthesis of 1,4-Diphenylbutadiene Derivatives: Novel Inducer of Tissue-Type Plasminogen Activator (t-PA) in Cultured Bovine Endothelial Cells

(E,E)-1,4-Diphenylbutadiene derivatives were synthesized by utilizing the Stobbe reaction of dimethyl succinate as a key step. Their stereoisomers were also synthesized stereoselectively by means of the cross-coupling reaction of the vinylstannanes and the vinylbromides, which were obtained from the propiolic acid esters by stereoselective hydrostannation, as a key step. To discover novel stimulators of fibrinolysis in vascular endothelial cells, the synthesized compounds were added to cultured bovine endothelial cells to determine the activity of the plasminogen activator in the conditioned medium. Of the synthesized compounds, three compounds were found to stimulate the activity of the plasminogen activator in endothelial cells. In addtition, these compounds inhibited thrombus formation in a rat model of venous thrombosis.

Thermodynamic Characteristics of Plasminogen Activation by Indirect Activators

Several indirect plasminogen (Pg) activators are known including streptokinase and the monoclonal antibody IV-Ic, whose mechanism of activation is well studied. To characterize thermodynamically the activation of Pg by streptokinase (SK) and the monoclonal antibody (mAB) IV-Ic, the activation energies were calculated for various reaction stages. Activation energy of 7.4 kcal/mol was determined for the interaction of the chromogenic substrate S-2251 with plasmin (Pm) and activated equimolar complexes Pm-SK and Pg*SK at the steady-state reaction stage, and 18.7 kcal/mol with the complexes Pg*IV-Ic. A 2.5-fold increase in the energy of activation for the Pg*IV-Ic complex suggests a more intricate mechanism of its interaction with the substrate. At the stage of increasing active center concentrations and the formation of activated complexes Pg*SK and Pg*mAB IV-Ic, the activation energy was found to be 10.5 and 38 kcal/mol, respectively. At this reaction stage the conformational rearrangement of Pg molecule with the formation of active center is the limiting stage determining the reaction rate. Unexpectedly high energy of activation at the second stage of interaction between mAB IV-Ic and Pg suggests several simultaneous reactions and complexity of conformation rearrangement in the Pg molecule in activated complexes, thus requiring large energy expense. Formation of the active center is probably accompanied by its transition within a narrow temperature range into another conformation state with the change in activation parameters of the reaction. Quantitative evaluation of the studied reactions from the perspective of thermodynamics of the enzymatic reactions gives more comprehensive characteristics of the activation mechanism.

Identification of laminin-binding motifs of plasminogen activator by phage display

Yersinia pestis plasminogen activator (Pla), a surface virulence factor contributes to the highly invasive nature of the pathogen by binding various tissue matrix components. In this study we characterised the laminin-binding site(s) of Pla via phage display and alanine-scanning mutagenesis. Previously we isolated 18 different heptamer peptide sequences from a phage display library with biopanning on laminin, and have shown that two of them with sequences of WSLLTPA or YPYIPTL completely inhibited laminin binding of a Pla-expressing recombinant Escherichia coli strain. These phages themselves strongly bound laminin in an ELISA assay utilising horseradish peroxidase-labelled anti-M 13 antibody. In the present study, with the application of synthetic peptides, a 55% and a 33% inhibition was demonstrated using WSLLTPA and YPYIPTL, respectively. Peptide pattern alignment showed two homologous regions for WSLLTPA and one for YPYIPTL inside the Pla sequence. Amino acids were changed for alanine in one of the WSLLTPA regions and in the YPYIPTL region in order to prove the role of the LTP/PTL motifs in laminin binding. Of the four constructed mutants, the triple mutant L65A-T66A-L67A in the WSLLTPA region and the double mutant G178A-L179A in the YPYIPTL region decreased the laminin binding capacity of the Pla-expressing recombinant E. coli by about 50%.

Production of Desmodus rotundus salivary plasminogen activator alpha1 (DSPAalpha1) in tobacco is hampered by proteolysis

The high fibrin specificity of Desmodus rotundus salivary plasminogen activator alpha1 (DSPAalpha1 or desmoteplase (INN)) makes it a promising candidate for the treatment of acute ischemic stroke. In the current study we explored the use of transgenic tobacco plants and BY-2 suspension cells as alternative production platforms for this drug. Four different N-terminal signal peptides, from plants and animals, were used to translocate the recombinant DSPAalpha1 protein to the endomembrane system. Intact recombinant DSPAalpha1 was produced in transgenic plants and BY-2 cells, although a certain degree of degradation was observed in immunoblotted extracts. The choice of signal peptide had no major influence on the degradation pattern or recombinant protein accumulation, which reached a maximum level of 38 microg/g leaf material. N-terminal sequencing of purified, His6-tagged DSPAalpha1 revealed only minor changes in the position of signal peptide cleavage compared to the same protein expressed in Chinese hamster ovary cells. However, correctly processed recombinant DSPAalpha1 was also detected. The enzymatic activity of the recombinant protein was confirmed using an in vitro assay with unpurified and purified samples, demonstrating that plants are suitable for the production of functional DSPAalpha1. In contrast to whole plant cell extracts, no recombinant DSPAalpha1 was detected in the culture supernatant of transgenic BY-2 cells. Further analysis showed that recombinant DSPAalpha1 is subject to proteolysis and that endogenous secreted BY-2 proteases are responsible for DSPAalpha1 degradation in the culture medium. The addition of a highly concentrated protease inhibitor mixture or 5 mM EDTA reduced DSPAalpha1 proteolysis, improving the accumulation of intact product in the culture medium. Strategies to improve the plant cell suspension system for the production of secreted recombinant proteins are discussed.

Molecular detection of Yersinia pestis isolates of Indian origin by using Pla specific monoclonal antibodies

Monoclonal antibodies (MAbs) were generated against the recombinant plasminogen activator (Pla) protein of Yersinia pestis. These MAbs detected Pla in all the 18 isolates of Y. pestis obtained from the sputum of pneumonic plague patients and from the liver and spleen of rodents from plague-affected areas of India during 1994-1995 as well as in seven of the eight isolates obtained from rodents in the surveillance regions of Hosur and Palmner in India during 1998 by simple dot-ELISA. In immunoblotting, the MAbs reacted with the Pla antigen only in Y. pestis isolates at 37 and 35kDa region. These monoclonal antibodies, being strictly specific, can be used for detecting Y. pestis isolates that are Fraction 1 antigen-negative. Also, the radiolabelled pla fragment hybridized specifically to the representative DNA samples of Y. pestis isolates.

Regulation of urokinase receptor proteolytic function by the tetraspanin CD82

The high affinity interaction between the urokinase-type plasminogen activator (uPA) and its glycolipid-anchored cellular receptor (uPAR) promotes plasminogen activation and the efficient generation of pericellular proteolytic activity. We demonstrate here that expression of the tetraspanin CD82/KAI1 (a tumor metastasis suppressor) leads to a profound effect on uPAR function. Pericellular plasminogen activation was reduced by approximately 50-fold in the presence of CD82, although levels of components of the plasminogen activation system were unchanged. uPAR was present on the cell surface and molecularly intact, but radioligand binding analysis with uPA and anti-uPAR antibodies revealed that it was in a previously undetected cryptic form unable to bind uPA. This was not due to direct interactions between uPAR and CD82, as they neither co-localized on the cell surface nor could be co-immunoprecipitated. However, expression of CD82 led to a redistribution of uPAR to focal adhesions, where it was shown by double immunofluorescence labeling to co-localize with the integrin alpha(5)beta(1), which was also redistributed in the presence of CD82. Co-immunoprecipitation experiments showed that, in the presence of CD82, uPAR preferentially formed stable associations with alpha(5)beta(1), but not with a variety of other integrins, including alpha(3)beta(1). These data suggest that CD82 inhibits the proteolytic function of uPAR indirectly, directing uPAR and alpha(5)beta(1) to focal adhesions and promoting their association with a resultant loss of uPA binding. This represents a novel mechanism whereby tetraspanins, integrins, and uPAR, systems involved in cell adhesion and migration, cooperate to regulate pericellular proteolytic activity and may suggest a mechanism for the tumor-suppressive effects of CD82/KAI1.

Thrombolytic activity of BB-10153, a thrombin-activatable plasminogen

BACKGROUND

BB-10153 is an engineered variant of human plasminogen, modified to be activated to plasmin by thrombin. Thrombin-activatable plasminogen was designed as a novel thrombolytic agent which would persist in the blood as a prodrug and be activated to plasmin only at fresh or forming thrombi by the thrombin that is tightly localized there. We previously described the construction of several thrombin-activatable plasminogens and their in vitro clot lysis activity.

OBJECTIVES AND METHODS

The current study was an examination of the thrombolytic properties of BB-10153 in vivo; comparison was made with tissue-type plasminogen activator (t-PA) in a femoral artery copper coil thrombosis model in the anesthetized dog and rabbit. Heparin was not coadministered so that the fundamental activity of the agents could be compared.

RESULTS

BB-10153, administered as an intravenous bolus of 5 mg kg(-1) in the dog and 10 mg kg(-1) in the rabbit, produced a comparable incidence of reperfusion to 3 mg kg(-1) t-PA. Reocclusion at these doses occurred in 4/4 dogs and 5/7 rabbits treated with t-PA and in 2/6 dogs and 0/10 rabbits treated with BB-10153. There was no reocclusion in three dogs dosed with 10 mg kg(-1) BB-10153. BB-10153 did not affect plasma alpha2-antiplasmin levels or the bleeding time, whereas 3 mg kg(-1) t-PA caused marked depletion of alpha2-antiplasmin and fibrinogen and increased the bleeding time. The plasma half-life of BB-10153 was 3-4 h.

CONCLUSIONS

The long half-life and thrombus-selective thrombolytic activity of BB-10153 might allow it to overcome the bleeding and reocclusion shortfalls in the performance of current thrombolytics.

Analysis of five streptokinase formulations using the euglobulin lysis test and the plasminogen activation assay

Streptokinase, a 47-kDa protein isolated and secreted by most group A, C and G ss-hemolytic streptococci, interacts with and activates human protein plasminogen to form an active complex capable of converting other plasminogen molecules to plasmin. Our objective was to compare five streptokinase formulations commercially available in Brazil in terms of their activity in the in vitro tests of euglobulin clot formation and of the hydrolysis of the plasmin-specific substrate S-2251. Euglobulin lysis time was determined using a 96-well microtiter plate. Initially, human thrombin (10 IU/ml) and streptokinase were placed in individual wells, clot formation was initiated by the addition of plasma euglobulin, and turbidity was measured at 340 nm every 30 s. In the second assay, plasminogen activation was measured using the plasmin-specific substrate S-2251. Streptase was used as the reference formulation because it presented the strongest fibrinolytic activity in the euglobulin lysis test. The Unitinase and Solustrep formulations were the weakest, showing about 50% activity compared to the reference formulation. All streptokinases tested activated plasminogen but significant differences were observed. In terms of total S-2251 activity per vial, Streptase (75.7 +/- 5.0 units) and Streptonase (94.7 +/- 4.6 units) had the highest activity, while Unitinase (31.0 +/- 2.4 units) and Strek (32.9 +/- 3.3 units) had the weakest activity. Solustrep (53.3 +/- 2.7 units) presented intermediate activity. The variations among the different formulations for both euglobulin lysis test and chromogenic substrate hydrolysis correlated with the SDS-PAGE densitometric results for the amount of 47-kDa protein. These data show that the commercially available clinical streptokinase formulations vary significantly in their in vitro activity. Whether these differences have clinical implications needs to be investigated.

Enhancing multiple disulfide bonded protein folding in a cell-free system

A recombinant plasminogen activator (PA) protein with nine disulfide bonds was expressed in our cell-free protein synthesis system. Due to the unstable and reducing environment in the initial E. coli-based cell-free system, disulfide bonds could not be formed efficiently. By treating the cell extract with iodoacetamide and utilizing a mixture of oxidized and reduced glutathione, a stabilized redox potential was optimized. Addition of DsbC, replacing polyethylene glycol with spermidine and putrescine to create a more natural environment, adding Skp, an E. coli periplasmic chaperone, and expressing PA at 30 degrees C increased the solubility of the protein product as well as the yield of active PA. Taken together, the modifications enabled the production of more than 60 microg/mL of bioactive PA in a simple 3-h batch reaction.

Monolithic peptidyl sorbents for comparison of affinity properties of plasminogen activators

Plasminogen activators are the proteases which convert plasminogen into plasmin dissolving, in its turn, the major component of blood clots, fibrin. They are extremely useful in heart attack therapy. Modern and most appropriate way of scaled up production of these valuable proteins is gene engineering. In this case, a separation and a purification of target product become the important steps of the whole process. Recently developed affinity chromatography on short monolithic columns seems to be a very attractive method for these purposes. High speed of a process prevents the protein's denaturation due to temperature or/and solvents influence. The better mass transfer mechanism (convection rather than diffusion) allows considering only biospecific complexing as time limiting step. Specificity of several synthetic peptides to plasminogen activators have been studied by affinity chromatography on short monolithic columns. Peptide ligands were synthesized by conventional solid phase peptide synthesis (SPPS). The immobilization procedure was carried out as a one step process at static conditions. The results of quantitative evaluation of such affinity interactions were compared with those established for plasminogen that is the natural affinity counterpart to both proteases. Additionally, some of investigated peptides were synthesized directly on GMA-EDMA disks and their affinity properties were compared with those established for the case of immobilized ligands. The possibility of using of synthetic peptidyl ligands for plasminogen activators isolation from native cell supernatant and model protein mixtures has been demonstrated.

Clot penetration and fibrin binding of amediplase,a chimeric plasminogen activator (K2 tu-PA)

Amediplase (K(2) tu-PA) is a hybrid plasminogen activator, consisting of the kringle 2 domain of alteplase and the protease domain of urokinase. The objective of this study was to determine the in vitro clot penetration of amediplase in relation to its fibrin binding and to compare the properties with those of alteplase. The clot lysis activity of amediplase in internal clot lysis models (both purified system and plasma system) was about 10 times less than that of alteplase. The clot lysis activity of amediplase in an external clot lysis model (plasma system) was similar to that of alteplase at therapeutic concentrations around 1 micro g/ml. The fibrin-clot binding properties of amediplase and alteplase were studied in a purified system as well as in a plasma system. In both systems amediplase bound to fibrin although to a significantly lower extent than alteplase. The binding of amediplase or alteplase did not increase during plasmin-mediated degradation of fibrin. The binding of amediplase was fully inhibited by epsilon-aminocaproic acid, indicating that the observed binding was specific and occurred via the lysine binding site in the kringle of amediplase. Clot penetration was studied during pressure-driven fluid permeation using syringes containing plasma clots. Amediplase was able to enter the clot without significant hindrance, while alteplase was concentrated on the top of the plasma clot and hardly entered into the inner parts of the clot. Diffusion-driven clot penetration was studied during clot lysis using confocal microscopy. Alteplase was detected on or close to the clot surface, while two-chain urokinase, which has no affinity to fibrin, was also detected deep inside the clot. Amediplase showed a penetration behaviour, which was distinct from that of alteplase and similar to that of two-chain urokinase. We concluded that the fibrin binding of amediplase is moderate and does not hinder clot penetration under permeation-driven or diffusion-driven transport conditions. Enhanced clot penetration, especially in large clots, could allow a more efficient lysis during thrombolytic therapy.

Functional properties of a recombinant chimeric plasminogen activator with platelet-targeted fibrinolytic and anticoagulant potential

The construction, purification, and characterization of dscuPA33khC, a bifunctional protein designed for thrombosis treatment is described. The chimera was designed to consist of a decorsin (platelet aggregation inhibitor), a low molecular mass (33kDa) single-chain urokinase (scuPA-33k), and a thrombin inhibitory domain. We have successfully produced this recombinant protein in the Escherichia coli expression system, in which the target protein exists in the form of inclusion bodies. After refolding by dilution in vitro, the chimeric protein was purified to homogeneity by immobilized metal affinity chromatography, ion-exchange chromatography, and gel filtration chromatography. The dscuPA33khC could directly activate plasminogen following Michaelis-Menten kinetics with K(m) = 1.52 microM and K(2) = 0.0024 s(-1). The specific activity of the chimera detected by fibrin plate determination was 11,000 IU/mg, which suggested a high thrombolysis effect. However, the chimeric dscuPA33khC bound the activated platelet and significantly increased affinity to platelet clots as compared to fibrin clots. It was found to inhibit ADP-induced platelet aggregation in a concentration-dependent manner as well as it exhibits antithrombin activity. These results suggest that the chimeric protein not only has platelet-targeted thrombolytic activity but also obtains anti-thrombus function.

A proposed reference method for plasminogen activators that enables calculation of enzyme activities in SI units

A method has been developed for accurately and precisely measuring the activity of a range of plasminogen activators (PAs) used as thrombolytic agents, including streptokinase, tissue plasminogen activator (tPA) and variants, and urokinase (uPA), both single and two chain forms. Plasminogen activation is monitored in a transparent, solid fibrin matrix but uses chromogenic substrate hydrolysis, rather than changes in fibrin, to quantitate the activity of PAs. The method has been tested in two recent international collaborative studies involving tPA and streptokinase where it has been shown to perform very well. Furthermore, the method is based on sound enzymological principles and once correction for the competitive inhibition of fibrin(ogen) is made, the generation of plasmin can be determined in molar terms and hence the activity of PAs can be expressed and compared in SI units (rate of increase in molar concentration of plasmin) as well as International Units. The assay is also arranged in such a way to reflect the behavior of PAs in vivo during thrombolytic therapy and it is shown that the specific activity of streptokinase and tPA in this system reflects plasmin generation capacity of these thrombolytics for doses given in infusions for treatment of myocardial infarction. The method would make a suitable reference method for PAs and provides a rigorous means of studying and modeling the enzymology of fibrinolysis and will be helpful in the rational design of third generation thrombolytic agents.

International collaborative study to establish the 3rd International Standard for Streptokinase

An international collaborative study was organized to calibrate a replacement for the current (2nd) International Standard (IS) for Streptokinase, stocks of which are almost exhausted. Two candidate preparations were assayed against the 2nd IS in a study involving 16 laboratories in 12 countries: preparation 88/824 (coded B), and preparation 00/464 (C and D, coded duplicates). Laboratories could use two methods provided, either a fibrin clot lysis assay or a solution chromogenic method, or an in-house method. Laboratories were encouraged to perform more than one method if possible. With the exception of one laboratory which gave outlying results for preparation 00/464, there was good agreement within and between laboratories and no significant differences between potencies using the different methods employed. This study demonstrates that a solution chromogenic assay is an acceptable format for potency determination of the streptokinase preparations in this study and fibrin is not necessary. It has now been agreed that a solution chromogenic plasminogen activation assay replace the current euglobulin reference method for streptokinase activity determination in the European Pharmacopoeia. Study participants, SSC of the International Society on Thrombosis and Haemostasis and the Expert Committee on Biological Standardization (ECBS) at the World Health Organization approved preparation 00/464 (C,D in the study) as the 3rd IS for Streptokinase with a potency of 1030 IU per ampoule.

Localization of plasminogen activator activity within normal and injured lungs by in situ zymography

During inflammatory lung injury, the fibrinolytic activity that is normally present within bronchoalveolar lavage (BAL) fluid (BALF) is often suppressed due to increased levels of inhibitors, including plasminogen activator inhibitor (PAI)-1. Despite this suppression, BALF frequently contains fibrin degradation products, indicating persistence of fibrinolytic activity within the lung. To address this discrepancy and determine the sites where plasminogen activation is occurring, we developed an in situ zymographic technique for frozen sections of lung tissue that localizes plasminogen activator activity at the cellular level. After validating the method using enzyme inhibitors and mice with genetic manipulations of their plasminogen system genes, we applied the technique to lungs of normal and bleomycin-exposed mice. In normal mice, plasminogen activator activity was localized to bronchial epithelial cells, cells of the alveolar walls, and alveolar macrophages. After bleomycin exposure, in situ zymography showed that, despite loss of fibrinolytic activity within BALF, abundant enzymatic activity was associated with aggregates of inflammatory cells. PAI-1-deficient mice that are protected from bleomycin-induced fibrosis had preserved plasminogen activator activity in BALF and increased tissue activity, as determined by in situ zymography. We conclude that analysis of BALF does not adequately reflect the fibrinolytic activity that persists within microenvironments of the lung during inflammation.

Enhanced expression of an antibody-targeted plasminogen activator in Escherichia coli by fusion to decorsin

To improve the thrombolytic specificity of plasminogen activators, an antibody-targeted plasminogen activator was constructed consisting of a single-chain variable fragment of a monoclonal antibody SZ-51 raised specifically against human P-selectins on activated platelets and a low molecular weight single-chain urokinase. After fusion to the 3' end of the gene coding for decorsin, originally isolated from the leech Macrobdella decora, expression of the antibody-targeted plasminogen activator gene in E. coli strain Rosetta (DE3) pLysS was greatly enhanced.

Nonlysine-analog plasminogen modulators promote autoproteolytic generation of plasmin(ogen) fragments with angiostatin-like activity

We recently discovered several nonlysine-analog conformational modulators for plasminogen. These include SMTP-6, thioplabin B and complestatin that are low molecular mass compounds of microbial origin. Unlike lysine-analog modulators, which increase plasminogen activation but inhibit its binding to fibrin, the nonlysine-analog modulators enhance both activation and fibrin binding of plasminogen. Here we show that some nonlysine-analog modulators promote autoproteolytic generation of plasmin(ogen) derivatives with its catalytic domain undergoing extensive fragmentation (PMDs), which have angiostatin-like anti-endothelial activity. The enhancement of urokinase-catalyzed plasminogen activation by SMTP-6 was followed by rapid inactivation of plasmin due to its degradation mainly in the catalytic domain, yielding PMD with a molecular mass ranging from 68 to 77 kDa. PMD generation was observed when plasmin alone was treated with SMTP-6 and was inhibited by the plasmin inhibitor aprotinin, indicating an autoproteolytic mechanism in PMD generation. Thioplabin B and complestatin, two other nonlysine-analog modulators, were also active in producing similar PMDs, whereas the lysine analog 6-aminohexanoic acid was inactive while it enhanced plasminogen activation. Peptide sequencing and mass spectrometric analyses suggested that plasmin fragmentation was due to cleavage at Lys615-Val616, Lys651-Leu652, Lys661-Val662, Lys698-Glu699, Lys708-Val709 and several other sites mostly in the catalytic domain. PMD was inhibitory to proliferation, migration and tube formation of endothelial cells at concentrations of 0.3-10 microg.mL(-1). These results suggest a possible application of nonlysine-analog modulators in the treatment of cancer through the enhancement of endogenous plasmin(ogen) fragment formation.

Domain-dependent action of urokinase on smooth muscle cell responses

BACKGROUND

Single-chain urokinase-type plasminogen activator (sc-uPA) is one of the key serine proteases involved in modulating cellular and extracellular matrix responses during tissue remodeling. Sc-uPA is composed of three domains: aminoterminal fragment (ATF), kringle domain, and carboxyterminal fragment (CTF). sc-uPA is readily cleaved into these three domain fragments in vitro, each of which is biologically active; however, their roles in the microenvironment of the vessel wall are poorly understood.

PURPOSE

The purpose of this study was to determine the role of each domain of sc-uPA on vascular smooth muscle cell (SMC) proliferation and migration.

METHODS

SMCs were cultured in vitro. Assays of DNA synthesis, cell proliferation, and migration were performed in response to sc-uPA, ATF, kringle, and CTF in the presence and absence of the plasmin inhibitors epsilon-aminocaproic acid (EACA) and aprotinin, the Galphai inhibitor pertussis toxin, and the mitogen-activated protein kinase 1 (the upstream regulator of the extracellular-signal regulated kinase [ERK]) inhibitor PD98059.

RESULTS

sc-uPA produced dose-dependent increases in DNA synthesis and cell proliferation. These responses were dependent on the CTF domain and were sensitive to plasmin inhibitors, pertussis toxin, and PD98059. Sc-uPA also induced SMC migration, which could be elicited by both ATF and kringle. Migration to sc-uPA, ATF, and kringle was both pertussis toxin and PD98059 sensitive, but importantly was plasmin-independent.

CONCLUSION

sc-uPA induces SMC proliferation and migration, which are domain-dependent and mediated in part by Galphai-linked, ERK-dependent processes, while only the mitogenic response is protease dependent. These findings suggest that migration is linked to a G-protein coupled nonprotease receptor, while proliferation is associated with a G-protein coupled protease receptor.

SMTP-4D, -5D, -6D, -7D and -8D, a new series of the non-lysine-analog plasminogen modulators with a D-amino acid moiety

Staplabin and SMTPs, triprenyl phenol metabolites of the fungus Stachybotrys microspora, are a family of non-lysine-analog plasminogen modulators that enhance both activation and fibrin binding of plasminogen by modulating plasminogen conformation. These compounds, including SMTP-4, -5, -6, -7 and -8, have an amino acid or an amino alcohol moiety in their structure, and precursor amine feeding greatly increases the biosynthesis of a metabolite of interest. In the present study, we have isolated five novel SMTPs (designated SMTP-4D, -5D, -6D, -7D and -8D) from precursor D-amino acid-fed cultures. Physico-chemical properties as well as chromatographic behavior were distinct from those of the corresponding L-amino acid analogs, which are selectively accumulated in L-amino acid-fed cultures and share common properties with corresponding natural products. The D-series SMTPs enhanced urokinase-catalyzed plasminogen activation by 10-fold at 80 approximately 180 microM.

Tissue expression, protease specificity, and Kunitz domain functions of hepatocyte growth factor activator inhibitor-1B (HAI-1B), a new splice variant of HAI-1

Hepatocyte growth factor activator inhibitor-1 (HAI-1) is an integral membrane protein expressed on epithelial cells and contains two extracellular Kunitz domains (N-terminal KD1 and C-terminal KD2) known to inhibit trypsin-like serine proteases. In tumorigenesis and tissue regeneration, HAI-1 regulates the hepatocyte growth factor (HGF)/c-Met pathway by inhibiting the activity of HGF activator (HGFA) and matriptase, two serine proteases that convert pro-HGF into its biologically active form. By screening a placental cDNA library, we discovered a new splice variant of HAI-1 designated HAI-1B that contains an extra 16 amino acids adjacent to the C terminus of KD1. To investigate possible consequences on Kunitz domain function, a soluble form of HAI-1B (sHAI-1B) comprising the entire extracellular domain was produced. First, we found that sHAI-1B displayed remarkable enzyme specificity by potently inhibiting only HGFA (IC50 = 30.5 nm), matriptase (IC50 = 16.5 nm), and trypsin (IC50 = 2.4 nm) among 16 serine proteases examined, including plasminogen activators (urokinase- and tissue-type plasminogen activators), coagulation enzymes thrombin, factors VIIa, Xa, XIa, and XIIa, and activated protein C. Relatively weak inhibition was found for plasmin (IC50 = 399 nm) and plasma kallikrein (IC50 = 686 nm). Second, the functions of the KD1 and KD2 domains in sHAI-1B were investigated using P1 residue-directed mutagenesis to show that inhibition of HGFA, matriptase, trypsin, and plasmin was due to KD1 and not KD2. Furthermore, analysis by reverse transcription-PCR demonstrated that HAI-1B and HAI-1 were co-expressed in normal tissues and various epithelial-derived cancer cell lines. Both isoforms were up-regulated in eight examined ovarian carcinoma specimens, three of which had higher levels of HAI-1B RNA than of HAI-1 RNA. Therefore, previously demonstrated roles of HAI-1 in various physiological and pathological processes likely involve both HAI-1B and HAI-1.

Domain truncation studies reveal that the streptokinase-plasmin activator complex utilizes long range protein-protein interactions with macromolecular substrate to maximize catalytic turnover

To explore the interdomain co-operativity during human plasminogen (HPG) activation by streptokinase (SK), we expressed the cDNAs corresponding to each SK domain individually (alpha, beta, and gamma), and also their two-domain combinations, viz. alphabeta and betagamma in Escherichia coli. After purification, alpha and beta showed activator activities of approximately 0.4 and 0.05%, respectively, as compared with that of native SK, measured in the presence of human plasmin, but the bi-domain constructs alphabeta and betagamma showed much higher co-factor activities (3.5 and 0.7% of native SK, respectively). Resonant Mirror-based binding studies showed that the single-domain constructs had significantly lower affinities for "partner" HPG, whereas the affinities of the two-domain constructs were remarkably native-like with regards to both binary-mode as well as ternary mode ("substrate") binding with HPG, suggesting that the vast difference in co-factor activity between the two- and three-domain structures did not arise merely from affinity differences between activator species and HPG. Remarkably, when the co-factor activities of the various constructs were measured with microplasminogen, the nearly 50-fold difference in the co-factor activity between the two- and three-domain SK constructs observed with full-length HPG as substrate was found to be dramatically attenuated, with all three types of constructs now exhibiting a low activity of approximately 1-2% compared to that of SK.HPN and HPG. Thus, the docking of substrate through the catalytic domain at the active site of SK-plasmin(ogen) is capable of engendering, at best, only a minimal level of co-factor activity in SK.HPN. Therefore, apart from conferring additional substrate affinity through kringle-mediated interactions, reported earlier (Dhar et al., 2002; J. Biol. Chem. 277, 13257), selective interactions between all three domains of SK and the kringle domains of substrate vastly accelerate the plasminogen activation reaction to near native levels.

Amediplase: CGP 42935, K2tu-PA, MEN 9036

Amediplase [CGP 42935, MEN 9036, K2tu-PA] is a recombinant chimeric plasminogen activator, consisting of the kringle 2 domain from the A-chain of tissue plasminogen activator (t-PA) and the carboxy terminal region of pro-urokinase. Amediplase was the outcome of a collaborative project with Ciba Geigy (now Novartis), but subsequent preclinical and clinical development has been completed by Menarini. Menarini is currently investigating amediplase in phase III clinical trials in Europe as a thrombolytic given as a single bolus to patients with myocardial infarction. In June 2002, Prometic Life Sciences announced that its collaboration with Menarini Biotech had resulted in the discovery of a scaleable manufacturing process for amideplase, based on Prometic's Mimetic Ligand- technology; amideplase manufactured by this process is expected to be used in the phase III studies.

Noncatalytic domain of uPA stimulates human extravillous trophoblast migration by using phospholipase C, phosphatidylinositol 3-kinase and mitogen-activated protein kinase

The serine protease urokinase-type plasminogen activator (uPA) promotes matrix degradation by many cell types, including the invasive extravillous trophoblast (EVT) of the human placenta. The noncatalytic amino-terminal end of uPA binds to uPA receptors (uPARs) expressed by these cells. A highly polarized expression of uPAR-bound uPA at the migration front of EVT cells in situ suggests a functional role of uPA:uPAR interaction in EVT cell migration. The present study examined whether uPA stimulates EVT cell migration, independent of proteolytic function, and investigated some of the signaling pathways involved. Using in vitro-propagated EVT cells in Transwell migration assays, both uPA and its noncatalytic amino-terminal fragment (ATF) were shown to stimulate migration through multiporous polycarbonate (pore size 8 microm) membranes. A uPAR-blocking antibody inhibited basal and ATF-stimulated migration. Migration was found to be stimulated by hypoxic conditions, which upregulates uPAR expression; this stimulation was abrogated with the uPAR-blocking antibody, indicating the role of endogenous uPA in EVT cell migration. Spectrofluorometric measurement of cytosolic calcium in cells treated with uPA and ATF demonstrated a rapid rise in [Ca2+](i), which was prevented by pretreatment of cells with thapsigargin, indicating a release from intracellular stores. Both basal and ATF-mediated migratory responses were suppressed in the presence of selective pharmacological inhibitors LY294002, U73122, and U0126, implicating the respective roles of phosphatidinylinositol 3-kinase (PI 3-K), phospholipase C (PLC), and MEK1/2 in basal and ATF-stimulated migratory capacity. Taken together, these results demonstrate that uPA:uPAR interaction stimulates EVT cell migration, independent of uPA enzymatic activity, using the mitogen-activated protein kinase pathway and calcium signaling events including the participation of PI 3-K and PLC. These findings are relevant to clinical conditions of aberrant trophoblast migration, including spontaneous abortion, preeclampsia, and choriocarcinoma.

Functional roles of streptokinase C-terminal flexible peptide in active site formation and substrate recognition in plasminogen activation

The bacterial protein streptokinase (SK) activates human plasminogen (Pg) into the fibrinolytic protease plasmin (Pm). Roughly 40 residues from the SK C-terminal domain are mobile in the crystal structure of SK complexed with the catalytic domain of Pm, and the functions of this C-tail remain elusive. To better define its roles in Pg activation, we constructed and characterized three C-terminal truncation mutants containing SK residues 1-378, 1-386, and 1-401, respectively. They exhibit gradually reduced amidolytic activity and Pg-activator activity, as well as marginally decreased binding affinity toward Pg, as more of the C-terminus is deleted. As compared with full-length SK, the shortest construct, SK(1-378), exhibits an 80% decrease in amidolytic activity (k(cat)/K(M)), an 80% decrease in Pg-activator activity, and a 30% increase in the dissociation constant toward the Pg catalytic domain. The C-terminal truncation mutations did not attenuate the resistance of the SK-Pm complex to alpha(2)-antiplasmin. Attempts at using a purified C-tail peptide to rescue the activity loss of the truncation mutants failed, suggesting that the integrity of the SK C-terminal peptide is important for the full function of SK.

Alteplase: stability and bioactivity after dilution in normal saline solution

PURPOSE

To characterize the biochemical stability and bioactivity of reconstituted alteplase when diluted to a concentration of 0.01 mg/mL in normal saline solution and stored at ambient temperature for as long as 24 hours in commercial saline solution bags.

MATERIALS AND METHODS

Two commercially available formulations of lyophilized alteplase (2-mg and 50-mg vials, respectively) were reconstituted with sterile water to a final concentration of 1 mg/mL. For each vial configuration, 5 mg of alteplase (5 mL) was added to a commercial 500-mL bag of normal saline solution to achieve a 0.01-mg/mL targeted concentration. Solutions were assayed for optical clarity, pH, protein concentration, and in-vitro clot lysis activity. Assays of the solutions were performed at time points of 0 (control), 4, 8, and 24 hours at ambient room temperature and compared to controls.

RESULTS

On visual inspection, aliquots of the diluted protein solutions in clear glass vials remained clear/colorless after 24 hours. Bioactivity (clot lysis assay) over the course of 24 hours at ambient temperature remained essentially unchanged relative to control (2-mg vial: mean of 98.3%, range of 93.7%-103.3%; 50-mg vial: mean of 103.1%, range of 100.6%-108.3%). The mean protein recovery rates (relative to targeted concentration) over a 24-hour period were 43% (range, 39%-46%) and 42% (range, 40%-45%) for the 2-mg and 50-mg vial configurations, respectively.

CONCLUSIONS

Alteplase diluted in normal saline solution at a concentration of 0.01 mg/mL is biochemically stable and active at ambient temperature for as long as 24 hours as assessed by in vitro clot lysis assays. Alteplase appears to have a bimodal solubility profile in normal saline solution and further studies are required to determine the activity and solubility of alteplase concentrations lower than 0.01 mg/mL.