Molecular Cloning and the cDNA-Derived Amino Acid Sequence of Narcissus tazetta Isolectins

Recently several complete cDNAs encoding the Narcissus tazetta lectins (NTL) were cloned. The sequence analyses of the cloned DNAs reveal that there are at least three unidentical positive clones for NTLs. The primary structure of the three NTL clones contains a mature polypeptide consisting of 105 amino acids and a C-terminal peptide extension beyond the C-terminal amino acids Thr-Gly. There are two fixed-position cysteines within the protein domain (amino acids 29 and 52), which are probably involved in the disulfide-bond linkage within the molecules to confer the secondary structure of the mature lectin. One third of the deduced amino acid composition consisted of glycine, leucine, and asparagine. From the cDNA-derived amino acid sequences the three NTL clones are not identical and are suggested to be isolectins present in N. tazetta var. chinensis. This study further confirms the previous isolation of mannose-specific isolectins from Chinese daffodil leaves [Ooi et al. (2000), J. Protein Chem.19, 163-168].