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

Genetics and Pathogenicity Factors of Group C and G Streptococci

Of the eight phylogenetic groups comprising the genus Streptococcus , Lancefield group C and G streptococci (GCS and GGS, resp.) occupy four of them, including the Pyogenic, Anginosus, and Mitis groups, and one Unnamed group so far. These organisms thrive as opportunistic commensals in both humans and animals but may also be associated with clinically serious infections, often resembling those due to their closest genetic relatives, the group A streptoccci (GAS). Advances in molecular genetics, taxonomic approaches and phylogenomic studies have led to the establishment of at least 12 species, several of which being subdivided into subspecies. This review summarizes these advances, citing 264 early and recent references. It focuses on the molecular structure and genetic regulation of clinically important proteins associated with the cell wall, cytoplasmic membrane and extracellular environment. The article also addresses the question of how, based on the current knowledge, basic research and translational medicine might proceed to further advance our understanding of these multifaceted organisms. Particular emphasis in this respect is placed on streptokinase as the protein determining the host specificity of infection and the Rsh-mediated stringent response with its potential for supporting bacterial survival under nutritional stress conditions.

PEGylation of Truncated Streptokinase Leads to Formulation of a Useful Drug with Ameliorated Attributes

Streptokinase (SK) remains a favored thrombolytic agent in the developing world as compared to the nearly 10-fold more expensive human tissue-plasminogen activator (tPA) for the dissolution of pathological fibrin clots in myocardial infarction. However, unlike the latter, SK induces systemic activation of plasmin which results in a greater risk of hemorrhage. Being of bacterial origin, it elicits generation of unwanted antibody and has a relatively short half-life in vivo that needs to be addressed to make it more efficacious clinically. In order to address these lacunae, in the present study we have incorporated cysteine residues specifically at the N- and C-termini of partially truncated SK and these were then PEGylated successfully. Some of the obtained derivatives displayed enhanced plasmin resistance, longer half-life (upto several hours), improved fibrin clot-specificity and reduced immune-reactivity as compared to the native SK (nSK). This paves the way for devising next-generation SK-based thrombolytic agent/s that besides being fibrin clot-specific are endowed with an improved efficacy by virtue of an extended in vivo half-life.

Activity assessment of microbial fibrinolytic enzymes

Conversion of fibrinogen to fibrin inside blood vessels results in thrombosis, leading to myocardial infarction and other cardiovascular diseases. In general, there are four therapy options: surgical operation, intake of antiplatelets, anticoagulants, or fibrinolytic enzymes. Microbial fibrinolytic enzymes have attracted much more attention than typical thrombolytic agents because of the expensive prices and the side effects of the latter. The fibrinolytic enzymes were successively discovered from different microorganisms, the most important among which is the genus Bacillus. Microbial fibrinolytic enzymes, especially those from food-grade microorganisms, have the potential to be developed as functional food additives and drugs to prevent or cure thrombosis and other related diseases. There are several assay methods for these enzymes; this may due to the insolubility of substrate, fibrin. Existing assay methods can be divided into three major groups. The first group consists of assay of fibrinolytic activity with natural proteins as substrates, e.g., fibrin plate methods. The second and third groups of assays are suitable for kinetic studies and are based on the determination of hydrolysis of synthetic peptide esters. This review will deal primarily with the microorganisms that have been reported in literature to produce fibrinolytic enzymes and the first review discussing the methods used to assay the fibrinolytic activity.

Bacterial plasminogen receptors utilize host plasminogen system for effective invasion and dissemination

In order for invasive pathogens to migrate beyond the site of infection, host physiological barriers such as the extracellular matrix, the basement membrane, and encapsulating fibrin network must be degraded. To circumvent these impediments, proteolytic enzymes facilitate the dissemination of the microorganism. Recruitment of host proteases to the bacterial surface represents a particularly effective mechanism for enhancing invasiveness. Plasmin is a broad spectrum serine protease that degrades fibrin, extracellular matrices, and connective tissue. A large number of pathogens express plasminogen receptors which immobilize plasmin(ogen) on the bacterial surface. Surface-bound plasminogen is then activated by plasminogen activators to plasmin through limited proteolysis thus triggering the development of a proteolytic surface on the bacteria and eventually assisting the spread of bacteria. The host hemostatic system plays an important role in systemic infection. The interplay between hemostatic processes such as coagulation and fibrinolysis and the inflammatory response constitutes essential components of host defense and bacterial invasion. The goal of this paper is to highlight mechanisms whereby pathogenic bacteria, by engaging surface receptors, utilize and exploit the host plasminogen and fibrinolytic system for the successful dissemination within the host.

A bioconjugated polyglycerol dendrimer with glucose sensing properties

In this work, the biological and electrochemical properties of glucose biosensor based on polyglycerol dendrimer (PGLD) is presented. Streptokinase (SK), glucose oxidase (GOx) and phosphorylcholine (PC) were immobilized onto PGLD to obtain a blood compatible bioconjugate with glucose sensing properties. The bioconjugated PGLD was entrapped in polyaniline nanotubes (PANINT's) through template electrochemical polymerization of aniline. PANINT's were used as electron mediator due to their high ability to promote electron-transfer reactions involving GOx. Platelet adhesion, fibrinolytic activity and protein adsorption were studied by in vitro experiments to examine the interaction of blood with PGLD biosensor. The PGLD biosensor exhibits a strong and stable amperometric response to glucose. The enzyme affinity for the substrate (K (M) (app) ) indicates that the enzyme activity was not significantly altered after the bioconjugation of GOx with PGLD dendrimer. The bioelectrochemical properties suggest that the bioconjugated PGLD developed in this work appears to be a good candidate for providing interfaces for implantable biosensors, especially oxidoreductase-based sensors.

Cloning and overexpression of active recombinant fusion streptokinase: a new approach to facilitate purification

Streptokinase is a common fibrinolytic drug and included in the World Health Organization (WHO) Model List of Essential Medicines. Comparative clinical trails such as cost-effectiveness suggest that streptokinase can be the drug of choice for thrombolytic therapy. To reach the highest amount of the protein and production of active form of streptokinase in bacteria need to modify and optimize methods. In the present study, chromosomal DNA was extracted from S. equisimilis H46A and used for amplification of streptokinase gene (skc) (mature section: 1245 bp) by cloning into pGEX-4T-2 vector which contains a tac promoter. The cloning results were controlled by PCR, double digestion and sequencing. The expression level of the protein in different strain of E. coli was optimized and reached up to 50% of the total cell protein. The function of the fusion protein as active fibrinolytic protein was confirmed by plasmin hydrolysis of chromogenic peptidyl anilide substrate assay.

Structural consideration of the formation of the activation complex between the staphylokinase-like streptococcal plasminogen activator PadA and bovine plasminogen

The characteristics of a streptococcal plasminogen activator (PA) displaying specificity for ruminant plasminogen (Plg) were defined using molecular approaches. The 16-kDa secreted protein PadA was found to be prevalent in Streptococcus dysgalactiae subspecies dysgalactiae isolated from cases of bovine mastitis and septic arthritis in lambs. PadA was able to activate bovine, ovine and caprine Plg, but not human Plg. Amino acid sequence analysis identified a limited level of homology to other streptococcal PAs, including streptokinase; however, PadA was found to align well with and match in size the staphylococcal PA, staphylokinase. Recombinant PadA was used to investigate interaction with bovine Plg, leading to formation of an activator complex that was capable of recruiting and converting further substrate Plg into plasmin. Individual non-overlapping peptides of PadA or bovine microplasminogen were found to block the interaction between PadA and bovine Plg, preventing the formation of the activation complex. Homology modelling based upon structures of staphylokinase complexed with human microplasminogen supported these findings by placing critical residues in close proximity to the plasmin component of the activation complex.

Streptokinase—the drug of choice for thrombolytic therapy

Thrombosis, the blockage of blood vessels with clots, can lead to acute myocardial infarction and ischemic stroke, both leading causes of death. Other than surgical interventions to remove or by pass the blockage, or the generation of collateral vessels to provide a new blood supply, the only treatment available is the administration of thrombolytic agents to dissolve the blood clot. This article describes a comprehensive review of streptokinase (SK). We discuss the biochemistry and molecular biology of SK, describing the mechanism of action, structures, confirmational properties, immunogenecity, chemical modification, and cloning and expression. The production and physico-chemical properties of this SK are also discussed. In this review, considering the properties and characteristics of SK that make it the drug of choice for thrombolytic therapy.

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.

Survey of the year 2003 commercial optical biosensor literature

In the year 2003 there was a 17% increase in the number of publications citing work performed using optical biosensor technology compared with the previous year. We collated the 962 total papers for 2003, identified the geographical regions where the work was performed, highlighted the instrument types on which it was carried out, and segregated the papers by biological system. In this overview, we spotlight 13 papers that should be on everyone's 'must read' list for 2003 and provide examples of how to identify and interpret high-quality biosensor data. Although we still find that the literature is replete with poorly performed experiments, over-interpreted results and a general lack of understanding of data analysis, we are optimistic that these shortcomings will be addressed as biosensor technology continues to mature.

Streptokinase—a clinically useful thrombolytic agent

A failure of hemostasis and consequent formation of blood clots in the circulatory system can produce severe outcomes such as stroke and myocardial infraction. Pathological development of blood clots requires clinical intervention with fibrinolytic agents such as urokinase, tissue plasminogen activator and streptokinase. This review deals with streptokinase as a clinically important and cost-effective plasminogen activator. The aspects discussed include: the mode of action; the structure and structure-function relationships; the structural modifications for improving functionality; recombinant streptokinase; microbial production; and recovery of this protein from crude broths.