Purification and characterization of two lectins from Caragana arborescens seeds

A glycoprotein fraction with hemagglutinating activity was purified by affinity chromatography from seeds of the pea tree, Caragana arborescens. Subsequent fractionation resolved two components, which could be separated on a preparative scale using different affinity matrices. The major component binds to N-acetylgalactosamine coupled to Sepharose 4B. It is a glycoprotein with high hemagglutinating activity. It is composed of two types of polypeptides, present in nonstoichiometric amounts, with apparent molecular weights near 30,000. In the native molecule, the subunits are cross-linked by disulfide bonds to form dimers, which in turn appear to be in rapid equilibrium with tetramers. The minor component binds to underivatized Sepharose 4B. It too, is a glycoprotein but has low hemagglutinating activity. It is composed of three types of polypeptides which, although they have apparent molecular weights near 30,000 are distinguished from the subunits of the major hemagglutinin by a number of physical and chemical properties. The native molecule is dimeric, with a mass of 60,000 daltons. The major component has high affinity (K = 0.1 mM) for the haptenic sugar, N-acetylgalactosamine, but will also bind D-galactose. Neither lectin has ABO blood group specificity, nor are they transformed mouse fibroblasts to the same extent.