THE MAJOR TUBER STORAGE PROTEIN OF ARACEAE SPECIES IS A LECTIN - CHARACTERIZATION AND MOLECULAR-CLONING OF THE LECTIN FROM ARUM-MACULATUM L

A new lectin was purified from tubers of Arum maculatum L. by affinity chromatography on immobilized asialofetuin. Although this lectin is a lso retained on mannose-Sepharose 48, under the appropriate conditions free mannose is a poor inhibitor of its agglutination activity. Pure preparations of the Arum lectin apparently yielded a single polypeptid e band of approximately 12 kD upon sodium dodecyl sulfate-polyacrylami de gel electrophoresis. However, N-terminal sequencing of the purified protein combined with molecular cloning of the lectin have shown that the lectin is composed of two different 12-kD lectin subunits that ar e synthesized on a single large precursor translated from an mRNA of a pproximately 1400 nucleotides. Lectins with similar properties were al so isolated from the Araceae species Colocasia esculenta (L.) Schott, Xanthosoma sagittifolium (L.) Schott, and Dieffenbachia sequina Schott . Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel fi ltration of the different Araceae lectins have shown that they are tet rameric proteins composed of lectin subunits of l2 to 14 kD. Interesti ngly, these lectins are the most prominent proteins in the tuber tissu e. Evidence is presented that a previously described major storage pro tein of Colocasia tubers corresponds to the lectin.