Determination of the Amino Acid Sequence of the Plant Cytolysin Enterolobin

The cytolytic seed protein enterolobin from seeds ofEnterolobium contortisiliquumwas purified by using FPLC on a Mono Q column giving a single peak in capillary electrophoresis. The complete amino acid sequence of the plant cytolysin was determined by an automated method, yielding a molecular mass of 54,806 Da. Databank searches and sequence alignment demonstrated a high degree of sequence identity and similarity between enterolobin and bacterial aerolysins fromAeromonas hydrophilaandA. sobria.Several key residues involved in oligomerization ofA. hydrophilaaerolysin are conserved in enterolobin. Circular dichroism measurements and structural predictions revealed that enterolobin is very rich in β sheet, like aerolysin. Light-scattering studies revealed that enterolobin oligomerizes as a hexamer at pH levels below 7.0. NaCl concentrations above 50 mM caused dimerization of enterolobin. Dithiothreitol did not cause oligomerization.