About the Lectin

In addition to being a source of the tubulin binding drug colchicine, tubers of the meadow saffron, Colchicum autumnale, contain a lectin with some unusual biochemical properties. Purified CA agglutinates both human and rabbit erythrocytes. The reaction with human cells can be inhibited by lactose, galactosamine, GalNAc, and galactose, but the reaction with rabbit cells is not inhibited by any simple carbohydrates ¹ . Agglutination of rabbit erythrocytes is inhibited by complex glycoproteins such as fetuin. Although sialic acid alone is not inhibitory, desialylated fetuin is a much stronger inhibitor of the lectin than native fetuin. This finding would indicate that CA has a preference for terminal β-galactose residues. The lectin exhibits stronger reactivity with trypsin treated erythrocytes than with untreated cells. CA is not blood group specific, but the agglutination reaction is stronger with O cells than with A or B cells. Purified CA is a stable protein, retaining activity between pH 4-12 and when heated to 60°C. The two most interesting components found in meadow saffron tubers exhibit competing activities. Colchicine binds free tubulin in solution, preventing their assembly into microtubules². This activity inhibits mitosis and the drug has been successfully used to produce polyploid cells. In contrast, purified CA is a potent mitogen for human lymphocytes. Unlike other mitogens, however, CA induces proliferation of only a fraction of CD4+ and CD8+ mouse T-lymphocytes, although it induces activation markers (CD69 and CD44) in all such cells ³ .

REFERENCES

1. Peumans, W. J., et al. (1986) Plant Physiol. 82 : 1036-1039.
2. Borisy, B. G. and Taylor, E. W. (1967) J. Cell. Biol. 34 : 525-533.
3. Bemer, V., et al. (1996) Cellular Immunology. 172 : 60-69.