Purification and characterization of abrin variants from three different varieties of Abrus precatorius seeds

Abrin is one of the most poisonous phytotoxins from the seeds of Abrus precatorius. In the present study, we purified abrin from three varieties (red and black, black and white) of Abrus seeds and further characterized through isoelectric focusing, MS analysis, binding assay and toxicity studies. The molecular masses of abrin variants (red and black, black and white seeds) were measured as 61.14, 60.85 and 61.24 kDa, respectively, by the MALDI-TOF/MS. Two-dimensional analysis of abrin variants showed differences in protein patterns and isoelectric point values ranging from 5.2 – 7.9. Immunological studies revealed that all the three anti-abrin antibodies are cross-reactive with all the three abrin variants. Estimated LD₅₀ values in mice showed that the abrin extracted from white seeds was 2 – 4 times more toxic than others. The levels of biochemical variables (SGOT, SGPT, ALP, bilirubin, urea, uric acid and creatinine) increased significantly in all treated groups. These variants decreased the level of glutathione, however increased the malondialdehyde level significantly in all treated animals. These effects were more prominent in animals treated with abrin from the white variety of seeds. Isoelectric focusing and MALDI-TOF/MS revealed microheterogeneity of abrin variants. Toxicity studies further confirmed the differences among the variants and also indicate that the abrin purified from white seeds is highly toxic and exhibits high lethal potency, which make it as an ideal candidate for immunotoxin studies.