Proteases regulate important pathophysiological processes in human body such as homeostasis, blood coagulation, fibrinolysis, tumor progression, etc. These biological effects of proteases largely attribute to their applicability as therapeutic agents. Imbalance in blood coagulation and fibrinolysis, two important physiological processes in human body, leads to thrombosis, a leading cause of cardiovascular complications including myocardial infarction, stroke, etc. The enzymes used to dissolve thrombus (blood clot) are known as thrombolytic agents and among them, the enzymes involving hydrolysis of fibrin called fibrinolytic agents. Thrombolytic agents can be classified according to generation, mechanism of action, source and active site of the enzymes. Among the commercially available thrombolytic agents, uPA and tPA are generally safe but are very expensive. On the other hand, the bacterial streptokinase is a relatively cheap thrombolytic agent but causes undesirable side effects such as bleeding complications. For this reason, worldwide research for potent thrombolytic agents to prevent and treat cardiovascular diseases have been continuing. Microbes are considered as a potential source of as well as safe vectors for expressing thrombolytic and fibrinolytic enzymes. Bacilli are one of the largest groups for this purpose. They have been collected from different traditional fermented foods or have been produced by solid state fermentation using appropriate nutrient substrates including different agro-industrial wastes such as rice straw, molasses, soybean curd residues, etc. This review focuses on different bacterial proteases reported to have potential thrombolytic and fibrinolytic activities.

Investigations were performed to find out new microbial enzymes as thrombolytics having better efficacy and specificity. Mutant strain of Bacillus species, B. licheniformis MZK05M9 was cultured in modified urea-glucose media followed by purification using ammonium sulphate precipitation and ultrafiltration through centricon tube of specific MWCO value. The production method yielded 823.42 units/mg of the crude enzyme from mutant strain MZK05M9 and after purification 37695.64 units/mg. The molecular weight of the purified enzyme was estimated as 27.2 kDa and purification increased its specific activity to 16.5 fold with a recovery of 10%. The purified proteases were identified as serine proteases by irreversible inhibition of activity with phenylmethylsulfonyl fluoride (PMSF) and it exhibited 32.84% thrombolytic activity, by in vitro clot lysis assay. Stability studies showed that crude enzyme from mutant strain MZK05M9 remained stable up to a temperature of 45˚C and showed maximum stability at pH range 7.5 to 8.5. Our observation indicates that proteases produced by Bacillus licheniformis mutant have the potential to be developed as a viable thrombolytic agent.