This study examines the function and genetic structure of Momordica charantia lectin. A galactose-binding lectin (MCL1) was purified from M. charantia seeds. The MCL1 showed highest hemagglutinating activity toward human type-O(H) erythrocytes followed by A, B and Omh (para-Bombay phenotype, also known as H-deficient secretor) erythrocytes. Moreover, we observed that MCL1 inhibited the cell-free synthesis of luciferase in a rabbit reticulocyte lysate system. The N-terminal amino acid sequence of purified MCL1 was identified and used to design degenerate oligonucleotide primers. The 3' and 5' ends of the gene coding for this protein were amplified by rapid amplification of cDNA ends, cloned and sequenced. The coding region (1641 bp, 547 amino acid residues) consisted of a 23 amino acid N-terminal signal sequence preceding an A-chain of 263 amino acid residues encoding a ribosome-inactivating protein that was joined to the B-chain of 261 amino acid residues encoding a lectin. The transcript was detected only in embryos, but hemagglutinating activity was detected both in embryos and cotyledons. These results suggest that gene expression occurred only during embryogenesis and the product accumulated in embryos and cotyledons. The MCL1 was expressed in tobacco BY-2 cells and the supernatant fluid of disrupted cells showed higher hemagglutinating activity toward human type-O(H) erythrocyte than the other tested erythrocytes. Thus, transgenic tobacco suspension culture cells harboring the cloned cDNA encoding the lectin purified from M. charantia are expected to be useful for the production of MCL1.
H. Tanaka, J. Toyama and R. Akashi, 2009. Molecular Characterization of a Galactose-Binding Lectin from Momordica
charantia Seeds and Its Expression in Tobacco Cells. Asian Journal of Plant Sciences, 8: 544-550.