An Immunological Investigation for the Presence of Lunasin, a Chemopreventive Soybean Peptide, in the Seeds of Diverse Plants.

Lunasin, a 43-amino acid bioactive peptide (SKWQHQQDSCRKQKQGVNLTPCEKHIMEKIQGRGDDDDDDDDD) derived from soybean, exhibits anti-cancer and anti-inflammatory properties. The C-terminal region of lunasin (EKHIMEKIQGRGDDDDDDDD) is essential for the chemopreventive effects associated with this bioactive peptide. All soybean varieties that have been examined contain lunasin. It has also been reported in few other plant species including Amaranthus, Solanum, wheat, barley, rye and triticale. Interestingly, detailed searches of available transcriptome and DNA sequence databases of cereals failed to identify lunasin-coding sequences raising questions about the authenticity of lunasin in cereals. In order to clarify the presence or absence of lunasin in cereals and other plant species, an immunological investigation was conducted utilizing polyclonal antibodies raised against the first 20 amino acid N-terminal peptide (SKWQHQQDSCRKQLQGVNLT) and a 15 amino acid C-terminal peptide (CEKHIMEKIQGRGDD) of lunasin.  Protein blot analyses revealed the presence of proteins from several plants that reacted against the lunasin N-terminal peptide antibodies.  However, the same proteins failed to react against the lunasin C-terminal peptide antibodies.   Our immunological studies reveal that some seeds contain peptides that have amino acid sequence similarity with the N-terminal region of the lunasin.  However, peptides that react against the C-terminal lunasin antibody were not detected in most of the seeds. Our results demonstrate that peptides identical to soybean lunasin are absent in seeds of diverse plants examined in our study.