Purification, characterization, and molecular cloning of lectin from winter buds of Lysichiton camtschatcensis (L.) Schott.

A novel lectin was purified to homogeneity from winter buds of Lysichiton camtschatcensis (L.) Schott of the Araceae family. It was a tetramer composed of two non-covalently associated polypeptides with small subunits (11 kDa) and large subunits (12 kDa). Sequencing of both subunits yielded unique N-terminal sequences. A cDNA encoding the lectin was cloned. The isolated cDNA contained an open reading frame that encoded 267 amino acids. It encoded both subunits, indicating that the lectin is synthesized as a single precursor protein that is post-translationally processed into two different subunits with 45% sequence identity. Each subunit contained a mannose-binding motif known to be conserved in monocot mannose-binding lectins, but its activity was not inhibited by monosaccharides, including methyl α-mannoside. Asialofetuin and yeast invertase were potent inhibitors. Lectin activity was detected in the buds formed during the winter season but not in the expanded leaves.