Biosynthesis of DB58 Lectin in Cell Suspension Cultures of Dolichos biflorus

The stem and leaf lectin of the legume, Dolichos biflorus, was found to be expressed in cell suspension cultures derived from calli from this plant. The lectin is present at levels equivalent to the amount of lectin in the plant and its expression is correlated with the exponential growth phase of the cells. In vitro translation of mRNA isolated from these cultures, followed by immunoprecipitation with antibodies to the lectin, yields a single polypeptide precursor for this lectin. In vivo pulse chase labeling of the DB58 lectin yields a single glycosylated precursor that ultimately gives rise to the mature α and β subunits of this heterodimer. Chemical deglycosylation of the labeled precursors and products shows that the α and β subunits do not differ simply by their extent of glycosylation. Antibodies generated against a synthetic peptide representing the deduced COOH-terminus of the nascent protein react only with the α subunit. These data support a mechanism of lectin subunit generation involving differential carboxyl terminal modification of a single polypeptide precursor.