Jatropha curcas L. Seed Cake Residue as an Alternative Source for Obtaining Curcin: A Type 1 Ribosome-Inactivating Protein

Abstract

Jatropha curcas seed cake is a byproduct of oil extraction from biodiesel industry. Although it has high protein content, its valorization is hampered by its toxicity. Curcin is a type 1 ribosome-inactivating protein (type 1 RIP) that contributes to the Jatropha seed cake toxicity. The present study aimed to evaluate the feasibility of using Jatropha seed cake as an alternative source to obtain bioactive curcin. Extracts from the seed cake stored for 15, 30, 45, 60, 75, and 90 days were used to produce protein fractions (JcPFC15, JcPFC30, JcPFC45, JcPFC60, JcPFC75, and JcPFC90), which were further used in purifying curcin via size exclusion chromatography. All JcPFCs comprised curcin. The purified JcPFC curcins apparently had a molecular mass of 28 kDa, which was similar to the seed curcin. Western blot using antibody anti-curcin revealed a single band, corresponding to curcin. No significant differences were observed in the curcin concentrations in all JcPFCs throughout storage. Furthermore, JcPFCs’ curcins presented conformational similarities to those of seed curcin, on evaluation by circular dichroism and intrinsic fluorescence spectroscopy. The RIP characteristic activity was assayed by rRNA-N-glycosidase activity test and in vitro protein synthesis inhibition assay, which revealed that the enzymatic activity was maintained in all JcPFCs’ curcins. Moreover, the toxicity test did not indicate significant differences between JcPFCs’ curcins and seed curcin. Accordingly, based on the results obtained, it is possible to affirm that J. curcas seed cake is a viable source of active curcin even after 90 days of storage.