Evaluation of the proteolytic susceptibility of three lectins from subtribe Diocleinae using enzymatic action, heat treatment and molecular modeling

The enzymatic digestion of the lectins fi om Canavalia brasiliensis, Diocle a grandiflora and Cratylia floribunda seeds was investigated by heat treatm ent and gelfiltration chromatography. The potential sites of lectin cleavag e by pepsin and trypsin was then determined by molecular modelling of the t hree-dimensional structure ofD.grandiflora lectin. The lectins were shown t o be susceptible to proteolytic cleavage using peptide mapping with the FPL C system. However, new peptides arose when hydrolysis was followed by hear treatment at 73C. According to the molecular model of D. grandiflora lectin , there are numerous sites for pepsin and trypsin proteolysis on the surfac e of the protein. It is suggested that when subjected to enzymatic action, the resulting peptides interact in order to retain the general folding of t he protein. This is attributed, at least in part, to the numerous hydrogen bonds and hydrophobic interactions occurring within the inner protein struc ture. After heat treatment the additional cleavage sites become available a nd the lectins become completely inactivated.