Characterization of Two Non-Fetuin-Binding Lectins from Tepary Bean (Phaseolus acutifolius) Seeds with Differential Cytotoxicity on Colon Cancer Cells

Two non-fetuin-binding lectins from tepary bean (Phaseolus acutifolius) seeds were purified and characterized. Both lectins LA and LB showed by two dimensional gel electrophoresis very similar apparent molecular mass, and their isoelectric point for both lectins were also very close. Mass spectrometry analysis confirmed these similarities showing high sequence homology among them, and when these sequences were compared to the Mirkov´s deduced sequence of the phyto-hemagglutinin from Phaseolus acutifolius, LA showed higher homology than LB. On the other hand, when their biological activity was determined, only LA possessed affinity to type A erythrocytes, and when these lectins using a semi pure fraction were measured for their cytotoxic effect on colon cancer cells, they showed a differential effect. In the semi pure protein fraction tested, the rest of no-lectin proteins separated by electrophoresis presented no activity. Our results indicate that despite the high homology in their sequence, isoelectric point, and apparent molecular mass, these two structurally closely related lectins, showed differences in their biological behaviour, represented by their agglutinatination activity, as well as, in their cytotoxic effect on human colon cancer cells.