MOLECULAR-CLONING OF 2 DIFFERENT MANNOSE-BINDING LECTINS FROM TULIP BULBS

Two lectins were isolated from the bulbs of Tulipa cv. Apeldoorn and t heir corresponding cDNA clones analyzed. The first, called TxLMII (sec ond mannose-binding Tulipa hybrid lectin), is a novel mannose-binding tulip lectin. Based on its molecular structure, carbohydrate-binding s pecificity and amino acid sequence, TxLMII belongs to the superfamily of mannose-binding monocot lectins which are also found in representat ives of the plant families Amaryllidaceae, Alliaceae, Orchidaceae and Araceae. Molecular cloning of the second lectin, called TxLCI (first T ulipa hybrid lectin with complex specificity), allowed determination u nambiguously of the molecular structure of this previously described p rotein. In addition, evidence is presented that each TxLCI subunit pos sesses a mannose-binding site and an N-acetylgalactosamine-binding sit e, which act independently of each other. Both binding sites are locat ed in a separate domain of the lectin polypeptide. Since the first dom ain of TxLCI shows sequence similarity to TxLMII, it is suggested that their genes evolved from a common ancestor.