Thrombolytic therapy (clot-busting) aims to dissolve acute arterial or venous thrombi and restore blood flow to ischaemic tissues, most critically in acute myocardial infarction (heart attack) and acute ischaemic stroke. The ideal thrombolytic agent activates the fibrinolytic system — specifically converting the inactive zymogen plasminogen to active plasmin, which then proteolytically degrades the fibrin network of the clot. Streptokinase was one of the first thrombolytics used clinically and remains in use in resource-limited settings due to its relatively low cost. Other thrombolytics include tissue plasminogen activator (t-PA) and its recombinant forms (alteplase, tenecteplase, reteplase) which are more fibrin-specific (activating plasminogen preferentially at the clot surface rather than systemically) and have largely replaced streptokinase in high-resource settings due to their superior efficacy and reduced risk of systemic bleeding complications and allergic reactions.

Streptokinase is a protein of approximately 47 kDa produced naturally by Group C beta-haemolytic streptococci, where it likely functions to help the bacteria escape fibrin clots formed around them during infection (providing a bacterial survival advantage by dissolving clot barriers). Streptokinase itself is not an enzyme but works as an activator of the fibrinolytic system: it forms a stoichiometric complex with plasminogen (at a 1:1 molar ratio), inducing a conformational change that confers proteolytic activity on the plasminogen molecule, essentially creating an active streptokinase-plasminogen complex with plasmin-like activity. This complex then converts additional free plasminogen to plasmin, which degrades fibrin, fibrinogen, and other clotting factors throughout the blood — the systemic nature of streptokinase-induced fibrinolysis (not limited to the clot surface) explains why it carries a significant risk of bleeding complications at other sites. Recombinant streptokinase (produced by expressing the streptokinase gene in E. coli) has the same mechanism but offers more consistent quality and purity compared to streptokinase purified from bacterial cultures.

Streptokinase exemplifies the broader category of biotechnology-derived therapeutic proteins that have transformed medicine over the past four decades. The ability to produce biologically active proteins in large quantities using recombinant DNA technology has enabled treatments for conditions that were previously untreatable or required dangerous extraction from limited biological sources. Key categories of biotechnology-derived therapeutics: Thrombolytics: streptokinase, t-PA (alteplase) — produced recombinantly for treating heart attacks and strokes. Hormones: insulin, growth hormone, erythropoietin (EPO), follicle stimulating hormone (FSH) — all produced recombinantly at scale. Clotting factors: recombinant Factor VIII (haemophilia A), Factor IX (haemophilia B) — replacing plasma-derived factors that previously carried blood-borne pathogen risks. Monoclonal antibodies: trastuzumab (Herceptin, breast cancer), infliximab (Remicade, autoimmune diseases), bevacizumab (Avastin, cancer) — a rapidly growing class of highly specific therapeutics. Vaccines: recombinant hepatitis B vaccine (HBsAg produced in yeast), HPV vaccines (virus-like particles). Enzymes: imiglucerase (Gaucher disease), laronidase (MPS I) — enzyme replacement therapies for lysosomal storage disorders.

The pharmaceutical industry has extracted enormous value from the natural chemical diversity produced by microorganisms, which evolved these bioactive compounds over billions of years primarily for ecological functions (antibiosis, competition, signalling) that happen to have therapeutic applications in humans. Antibiotics from fungi: Penicillin (Penicillium chrysogenum/notatum) — the first antibiotic, discovered by Fleming in 1928; Cephalosporins (Acremonium chrysogenum). Antibiotics from bacteria: Streptomycin (Streptomyces griseus, Waksman 1943) — first antibiotic effective against tuberculosis; Erythromycin (Streptomyces erythraeus); Chloramphenicol (Streptomyces venezuelae); Vancomycin (Streptomyces orientalis) — last-resort antibiotic for MRSA. Immunosuppressants: Cyclosporin A (Tolypocladium inflatum) — revolutionised organ transplantation by making long-term graft survival routine. Cholesterol-lowering drugs: Lovastatin (Monascus purpureus, also Aspergillus terreus) — first statin drug; led to discovery of the entire statin drug class. Anti-cancer agents: Vincristine and vinblastine (Catharanthus roseus, a plant); Taxol/paclitaxel (originally from Taxus brevifolia bark, now from fungal endophytes Taxomyces andreanae).