Purification and characterization of two lectins from calllus of Helianthus tuberosus

Two lectins were purified from Helianthus tuberosus callus by maltose affinity chromatography and subsequent preparative electrophoresis. The lectins were designated HTA I and HTA II and their molecular masses were about 34 kDa by gel-filtration chromatography. A single band of 17 kDa and bands of 17 kDa and 18 kDa were detected after SDS-PAGE of HTA I and HTA II, respectively, indicating that HTA I is a homodimer while HTA II is a heterodimer. The amino acid compositions of the two lectins were very similar; they were rich in glycine residues, lacking detectable amounts of methionine, cysteine, and histidine. A hapten-inhibition assay showed that HTA I and HTA II had identical saccharide-binding specificity to the extent tested and belonged to the group of so-called mannose/glucose-binding lectins. They had high affinity for alpha-linked manno-oligosaccharides. Each HTA completely lost its hemagglutinating activity at pH 5.0, as a result of its dissociation to monomers, but it did not lose its ability to bind to oligosaccharides.