Activity Regulation by Fibrinogen and Fibrin of Streptokinase from Streptococcus Pyogenes

Measuring Fibrinolysis

Physiological fibrinolysis under normal conditions progresses slowly, in contrast to coagulation which is triggered rapidly to stop bleeding and defend against microbial invasion. Methods to detect fibrinolysis abnormalities are less simple and poorly standardized compared with common coagulation tests. Fibrinolysis can be accelerated by preparing euglobulin from plasma to reduce endogenous inhibitors, or by adding plasminogen activators to normal plasma. However, these manipulations complicate interpretation of results and diagnosis of a "fibrinolysis deficit." Many observational studies on antigen levels of fibrinolysis inhibitors, plasminogen activator inhibitor 1 or thrombin-activatable fibrinolysis inhibitor, zymogen or active enzyme have been published. However, conclusions are mixed and there are clear problems with harmonization of results. Viscoelastic methods have the advantage of being rapid and are used as point-of-care tests. They also work with whole blood, allowing the contribution of platelets to be explored. However, there are no agreed protocols for applying viscoelastic methods in acute care for the diagnosis of hyperfibrinolysis or to direct therapy. The emergence of SARS-CoV-2 and the dangers of associated coagulopathy provide new challenges. A common finding in hospitalized patients is high levels of D-dimer fibrin breakdown products, indicative of ongoing fibrinolysis. Well-established problems with D-dimer testing standardization signal that we should be cautious in using results from such tests as prognostic indicators or to target therapies.

An international collaborative study to establish the WHO 4th International Standard for Streptokinase: Communication from the SSC of the ISTH

Streptokinase is used worldwide as a cost-effective treatment for acute myocardial infarction. Manufacturers use the World Health Organization (WHO) International Standard (IS) for Streptokinase to potency label their products, ensuring consistent, safe, and effective dosing. Stocks of the third IS for streptokinase (coded 00/464) are running low, and an international collaborative study was organized to calibrate a replacement. A total of 15 laboratories from nine countries took part, using chromogenic and/or fibrin clot lysis methods to determine the potency of two candidate preparations, coded 16/356 (sample B) and 16/358 (sample C), relative to the third IS (00/464). A third sample (88/824, sample A), which was used in the collaborative studies to establish the second and third IS, was also included. There was good agreement in potency estimates from different assay methods and low variability both within and between laboratories. Long-term stability modeling indicated the candidates are very stable. Comparison of potency estimates for 88/824 (sample A) with potencies calculated in previous studies revealed a variability of only 1.9% over the course of three collaborative studies spanning 30 years and more than 50 years of streptokinase standardization. This indicates excellent continuity of the International Unit (IU) and assay methods. Following agreement by study participants and Scientific and Standardization Committee experts of the International Society on Thrombosis and Haemostasis, the WHO Expert Committee on Biological Standardization established 16/358 (sample C) as the fourth IS for Streptokinase with a potency of 1013 IU per ampoule in October 2019.

In silico design and in vitro validation of a novel PCR-RFLP assay for determination of phylogenetic clusters of streptokinase gene alleles in streptococci groups

Streptokinase (SK), a heterogeneous plasminogen (Pg) activator protein secreted by groups A, C and G streptococci (GAS/GCS/GGS) is a virulence factor composed of three structural domains; SKα/SKβ/SKγ. Phylogenetic analysis of the major variable region of SKβ (sk-V1; nucleotides 448-791; 343bp) which classifies the SK alleles into SK1/SK2 clusters and SK2a/SK2b sub-clusters, is an approved assay to categorize clinical/natural streptococcal-isolates into co-related functional/pathogenesis groups. Herein, we describe a novel PCR-RFLP assay that in combination with Numerical Taxonomy and multivariate analysis System (NTSYS) resulted to dendrograms with complete adaption to that of the phylogenetic analysis of sk-V1-based clustering. In silico analyses by 30 restriction enzymes on GenBank-acquired sk-V1 sequences of known streptococcal clusters, resulted to the selection of "BsrI, MseI and Tsp45I″ enzymes that produced proper patterns to construct the expected dendrograms. In vitro analysis of the selected enzymes on clinical isolates of GAS/GCS/GGS validated the production of the same in silico-observed digestion patterns. Comparison of the constructed dendrogram and phylogenetic trees of selected GenBank and clinical isolates of streptococci indicated complete adaptation. Assessment of Pg-activation activity in selected clinical isolates indicated the expected co-related functionalities of the classified SK-clusters by the invented PCR-RFLP/NTSYS method. The simplicity of the assay relieves the need of sequencing/phylogenetic analyses for SK-clustering.

Antithrombotic Drugs-Pharmacology and Perspectives

Thrombosis, the localized clotting of blood that affects arterial or venous circulation, is one of the leading causes of death worldwide. Arterial thrombosis is commonly initiated by vascular endothelial injury, while venous thrombosis mainly stems from blood stasis. Despite these differences, platelet adhesion, activation and aggregation, and fibrin formation as a result of coagulation constitute the fundamental processes of thrombus formation. Antithrombotic drugs permitted on the clinical currently can dramatically reduce major adverse cardiovascular events; however, they can also increase the bleeding risk. Discovery of antithrombotic drugs that can effectively prevent thrombosis while sparing bleeding side effects remains unmet medical need. In this chapter, we provide an overview on the pathophysiology of thrombosis, followed by introduction of each class of antithrombotic drugs including their pharmacology, clinical applications and limitations. Practical challenges and future perspectives of antithrombotic drugs are discussed in the last part of this chapter.

Contribution of Streptokinase-Domains from Groups G and A (SK2a) Streptococci in Amidolytic/Proteolytic Activities and Fibrin-Dependent Plasminogen activation: A Domain-Exchange Study

BACKGROUND

Streptokinase (SK), a heterogeneous plasminogen activator (PA) protein from groups A, C, and G streptococci (GAS, GCS, GGS, respectively) contains three structural domains (SKα, SKβ, and SK). Based on the variable region of SKβ, GAS-SK (ska) are clustered as SK1 and SK2 (including cluster2-streptokinase (SK2a)/SK2b), which show low and high fibrinogen (FG)-dependent plasminogen (Plg) activation properties, respectively. Despite being co-clustered as SK2a, GCS/GGS-SK (skcg) variants display properties similar to SK1. Herein, by SKβ exchange between GGS (G88) and GAS-SK2a (STAB902) variants, the potential roles of SK domains in amidolytic/proteolytic activity and FG-bound-Plg activation are represented.

METHODS

Two parental SKG88 and SKSTAB902 genes were cloned into the NdeI/XhoI site of pET26b expression vector. The two chimeric SKβ-exchanged constructs (SKC1: αG88-βSTAB-γG88 and SKC2; αSTAB-βG88-γSTAB) were constructed by BstEII/BsiWI digestion/cross-ligation in parental plasmids. SK were expressed in E. coli and purified by nickel-nitriloacetic acid chromatography. PA potencies of SKs were measured by colorimetric assay.

RESULTS

SDS-PAGE and Western-blot analyses confirmed the proper expression of 47-kDa SK. Analyses indicated that the catalytic efficiency (Kcat/Km) for amidolytic and proteolytic activity were less and moderately dependent on SKβ, respectively. The increase of FG-bound-Plg activation for SKSTAB902/SKC1 containing SK2aβ was around six times, whereas for SKG88/SKC2 containing skcgβ, it was four times.

CONCLUSION

Although SKβ has noticeable contribution in FG-bound-Plg activation activity, it had minor contribution in fibrin-independent, amidolytic activity. These data might be of interest for engineering fibrin-specific versions of SK.

Structural Biology and Protein Engineering of Thrombolytics

Myocardial infarction and ischemic stroke are the most frequent causes of death or disability worldwide. Due to their ability to dissolve blood clots, the thrombolytics are frequently used for their treatment. Improving the effectiveness of thrombolytics for clinical uses is of great interest. The knowledge of the multiple roles of the endogenous thrombolytics and the fibrinolytic system grows continuously. The effects of thrombolytics on the alteration of the nervous system and the regulation of the cell migration offer promising novel uses for treating neurodegenerative disorders or targeting cancer metastasis. However, secondary activities of thrombolytics may lead to life-threatening side-effects such as intracranial bleeding and neurotoxicity. Here we provide a structural biology perspective on various thrombolytic enzymes and their key properties: (i) effectiveness of clot lysis, (ii) affinity and specificity towards fibrin, (iii) biological half-life, (iv) mechanisms of activation/inhibition, and (v) risks of side effects. This information needs to be carefully considered while establishing protein engineering strategies aiming at the development of novel thrombolytics. Current trends and perspectives are discussed, including the screening for novel enzymes and small molecules, the enhancement of fibrin specificity by protein engineering, the suppression of interactions with native receptors, liposomal encapsulation and targeted release, the application of adjuvants, and the development of improved production systems.

The β-domain of streptokinase affects several functionalities, including specific/proteolytic activity kinetics

Streptokinase (SK) is a plasminogen activator which converts inactive plasminogen (Pg) to active plasmin (Pm), which cleaves fibrin clots. SK secreted by groups A, C, and G Streptococcus (SKA/SKC/SKG) is composed of three domains: SKα, SKβ and SKγ. Previous domain-swapping studies between SK1/SK2b-cluster variants revealed that SKβ plays a major role in the activation of human Pg. Here, we carried out domain-swapping between skcg-SK/SK2-cluster variants to determine the involvement of SKβ in several SK functionalities, including specific/proteolytic activity kinetics, fibrinogen-bound Pg activation and α2 -antiplasmin resistance. Our results indicate that SKβ has a minor to determining role in these diverse functionalities for skcg-SK and SK2b variants, which might potentially be accompanied by few critical residues acting as hot spots. Our findings enhance our understanding of the roles of SKβ and hot spots in different functional characteristics of SK clusters and may aid in the engineering of fibrin-specific variants of SK for breaking down blood clots with potentially higher efficacy and safety.

Evaluation of Activity Kinetic Parameters of SK319cys, As a New Cysteine Variant of Streptokinase: A Comparative Study

BACKGROUND

Despite the extensive use of streptokinase in thrombolytic therapy, its administration may have some shortcomings like allergic reactions and relatively low half life. Specific PEGylation on cysteine at desired sites of streptokinase may alleviate these deficiencies and improve the quality of treatment.

OBJECTIVE

This study was carried out to create a new cystein variant of streptokinase and compare its activity with formerly mutated SK263cys, SK45cys and intact streptokinase (Ski) to introduce superior candidates for specific PEGylation.

METHOD

In silico study was carried out to select appropriate amino acid for cysteine substitution and accordingly mutagenesis was carried out by SOEing PCR. The mutated gene was cloned in E. coli, expressed, and purified by affinity chromatography. Activity of the purified proteins was assayed and kinetic parameters of enzymatic reaction were analyzed.

RESULTS

According to in silico data, Arginine319 was selected for substitution with cysteine. SK319cys was achieved with 98% purity after cloning, expression and purification. It was shown that the enzymatic efficiency of SK319Cys and SK263cys was increased 18 and 21%, respectively, when compared to SKi (79.4 and 81.3 vs. 67.1µM-1min-1), while SK45cys showed 7% activity decrease (62.47µM-1min-1) compared to SKi. According to time-based activity assay, SK319Cys and SK263cys exhibited higher activity at lower substrate concentrations (100 and 200 µM), but at higher concentrations of substrate (400 and 800 µM), the proteins showed a very close trend of activity.

CONCLUSION

SK319cys, as the new cysteine variant of streptokinase, together with SK263cys and SK45cys can be considered as appropriate molecules for specific PEGylation.

Design of a DNA-Programmed Plasminogen Activator

Although the functional specificity and catalytic versatility of enzymes have been exploited in numerous settings, controlling the spatial and temporal activity of enzymes remains challenging. Here we describe an approach for programming the function of streptokinase (SK), a protein that is clinically used as a blood "clot buster" therapeutic. We show that the fibrinolytic activity resulting from the binding of SK to the plasma proenzyme plasminogen (Pg) can be effectively regulated (turned "OFF" and "ON") by installing an intrasteric regulatory feature using a DNA-linked protease inhibitor modification. We describe the design rationale, synthetic approach, and functional characterization of two generations of intrasterically regulated SK-Pg constructs and demonstrate dose-dependent and sequence-specific temporal control in fibrinolytic activity in response to short predesignated DNA inputs. The studies described establish the feasibility of a new enzyme-programming approach and serves as a step toward advancing a new generation of programmable enzyme therapeutics.

Measuring fibrinolysis: from research to routine diagnostic assays

Development and standardization of fibrinolysis methods have progressed more slowly than coagulation testing and routine high-throughput screening tests for fibrinolysis are still lacking. In laboratory research, a variety of approaches are available and are applied to understand the regulation of fibrinolysis and its contribution to the hemostatic balance. Fibrinolysis in normal blood is slow to develop. For practical purposes plasminogen activators can be added to clotting plasma, or euglobulin prepared to reduce endogenous inhibitors, but results are complicated by these manipulations. Observational studies to identify a 'fibrinolysis deficit' have concluded that excess fibrinolysis inhibitors, plasminogen activator inhibitor 1 (PAI-1) or thrombin-activatable fibrinolysis inhibitor (TAFI), zymogen or active enzyme, may be associated with an increased risk of thrombosis. However, results are not always consistent and problems of adequate standardization are evident with these inhibitors and also for measurement of fibrin degradation products (D-dimer). Few methods are available to investigate fibrinolysis under flow, or in whole blood, but viscoelastic methods (VMs) such as ROTEM and TEG do permit the contribution of cells, and importantly platelets, to be explored. VMs are used to diagnose clinical hyperfibrinolysis, which is associated with high mortality. There is a debate on the usefulness of VMs as a point-of-care test method, particularly in trauma. Despite the difficulties of many fibrinolysis methods, research on the fibrinolysis system, taking in wider interactions with hemostasis proteins, is progressing so that in future we may have more complete models and better diagnostic methods and therapeutics.