Production and characterization of the B chains of mistletoe toxic lectins

Mistletoe toxic lectins consist of two polypeptide chains: an enzymatically active A chain, which is a toxic component, and a disulfide-bonded B chain, which confers the lectin properties on the total molecule. Mistletoe leaves contain three toxic lectins encoded by three genes. The B chains of these lectins were overproduced in Escherichia coli in a soluble form. The recombinant proteins bound with asialofetuin, but had substantially lower affinity for simple sugars D-galactose and N-acetyl-D-galactosamine as compared with the natural proteins. The functional properties of the B chains strongly depended on the storage conditions (salt concentration and the presence of galactose); the dependence was explained by structural instability of nonglycosylated recombinant proteins. The lectin activity of one of the recombinant B chains was close to that of the native protein, which was attributed to the lack of N-glycosylation sites in the latter.