Cytosolic and nuclear localization of the cytolytic and insecticidal plant protein enterolobin

Enterolobin is a 52 905 Da cytolytic, inflammatory and insecticidal protein obtained from seeds of the Brazilian tree Enterolobium contortisiliquum. It shares structural and functional similarities with aerolysins, pore-forming toxins from Aeromonas bacteria. These characteristics suggest that enterolobin might play a defence role in the plant. In order to determine the localization and distribution of this phytocytolysin in the seed cells, immunocytochemical labelling experiments were carried out using rabbit anti-enterolobin serum and colloidal gold conjugated with goat antirabbit IgG. Light microscopy results indicated that labelling was widely distributed in the cytosol (33%) of cotyledon cells and in the nucleus (67%). Electron microscopy results confirmed the presence of enterolobin in both the cytosol and nucleus. Putative nuclear localization signals (NLS) were found in the sequence of enterolobin.