Transient Expression of Lumbrokinase (PI239) in Tobacco Using a Geminivirus-Based Single Replicon System Dissolves Fibrin and Blood Clots

Lumbrokinases， a group of fibrinolytic enzymes extracted from earthworm， have been widely used to prevent and treat various cardiovascular diseases. They specifically target fibrin to effectively degrade thrombi without major side effects. Plant expression systems are becoming potential alternative expression platforms for producing pharmaceutical proteins. In this work， a lumbrokinase (PI239) was produced from a plant system. Both wild-type (WT) and plant codon-optimized (OP) gene sequences were synthesized and cloned into a geminivirus-based single-vector DNA replicon system. Both vectors were independently expressed in tobacco leaves transiently by agroinfiltration. Overexpressed PI239 resulted in sudden tissue necrosis 3 days after infiltration. Remaining proteins were purified through His-tag affinity chromatography and analyzed with SDS-PAGE and Western blot methods. Purified PI239 successfully degraded artificial fibrin with relative activity of 13，400 U/mg when compared with commercial lumbrokinase product. tests demonstrated that plant-derived PI239 dissolved human blood clots and that the plant expression system is capable of producing functional PI239.