Background: Parasporin, a new crystal protein derived from non-insecticidal and non-hemolytic Bacillus thuringiensis , recognizes and kills human colon cancer cells as well as some classes of human cultured cells. Here we report that a novel cytotoxic protein was isolated from the crystal produced by B. thuringiensis subsp. thuringiensis S9 strain.
Methods: Fifty soil samples were collected from different Iranian provinces, and characterization was performed based on protein crystal morphology by phase-contrast microscope and variations of Cry protein toxin using SDS-PAGE. After parasporin process with proteinase K, the active form was produced and protein activity on the cell line was evaluated.
Results: Parasporal inclusion proteins showed different cytotoxicity against human colon cancer cell line (HCT-116), but not against normal lymphocyte. Isolated parasporin demonstrated no hemolytic activity against human erythrocyte. It appears that these proteins have the ability to differentiate between normal lymphocytes and leukemia cells and have specific receptors on specific cancer cell lines.
Conclusion: The 37-kDa protein from S9 exhibited various degrees of cytocidal activity toward human colon cancer cells and caused cell swelling or the formation of blebs in the surface of the cells. Thus, parasporin acts as a cytolysin, which targets cell specificity and subsequently induces cell decay.