About the Lectin

The lectin purified from seeds of the asparagus pea has been used as an O(H) specific reagent. As with the other L-fucose specific lectins, AAA and UEA-I, Lotus has an affinity for certain glycosidic linkages of fucose. The purified lectin reacts most strongly with terminal α-L-fucose. Lectin activity is decreased if the fucose residue is linked to an internal carbohydrate unit. Consistent with this is the finding that the asparagine linked disaccharide Fucα(1,6)GlcNAc is a potent inhibitor of the lectin ¹ . However, internal α(1,6)-linked fucose residues are not reactive with the lectin. Immobilized Lotus lectin strongly retards Lewis X [Le(x)] glycans or glycopeptides (Galβ1,4[Fucα1,3] GlcNAcβ-OR), but not the isomeric oligosaccharide Galβ1,3[Fucα1,4]GlcNAc, nor sialylLe(x). Although 2’fucosyllactose (Fucα1,2Galβ1,4Glc) also reacts with the immobilized lectin, glycans containing the H antigen Fucα1,2Galβ1,3(4)GlcNAc-OR are very poorly reactive ² . Although Lotus shows a preference for α-linked fucose residues, it reacts with methyl β-L-fucose as well as it reacts with L-fucose alone. The carbohydrate binding site has been reported to be relatively small ³ , however the glycosidic linkages of the subterminal carbohydrates play an important role in lectin binding. Peptides contained in Asp-N or Lys-C endopeptidase digests of lotus lectin are retarded by columns of fucose-gels ⁴ . Purified Lotus is a mixture of three isolectins ⁵ which have been separated by ion exchange chromatography on DEAE-cellulose. Each of the isolectins has a similar subunit size and the same complex specificity for L-fucose residues. In spite of these similarities, the isolectins differ with respect to their aggregate molecular weight, their isoelectric point, and the binding constant for fucose residues ⁶ . Isolectin B (Mr~58,000) was isolated and sequenced. The sequence possesses a high degree of homology with other legume lectin sequences, especially in the putative carbohydrate binding regions ⁷ . These workers also noted that the larger and smaller aggregates (isolectins A and C) were not present in their extracts, suggesting genetic or physiological differences between batchs of seeds. In addition to its use as an anti-O(H) specific reagent, and in the purification of fucose containing glycopeptides by affinity chromatography, the Lotus lectin has been used in other areas as well. Purified Lotus has been used in studies on the inhibition of macrophage migration and in comparison to macrophage inhibition factor (MIF) ⁸ . It has been used to help distinguish between pathogenic and non-pathogenic Trypanosomes by lectin agglutination ⁹ . It has also been used to study development of chick thymus ¹⁰ . The presence of high levels of binding sites for lotus lectin in transitional cell carcinoma of human urinary bladder is corelated with increased metastatic potential and poor patient survival time ¹¹ .

REFERENCES

1. Susz, J. P. and Dawson, G. (1979) J. Neurochem. 32 : 1009-1013.
2. Yan, L., et al. (1997) Glycoconj. J. 14 : 45-55.
3. Allen, H. J., et al. (1977) Immun. Comm. 6 : 585-602.
4. Konami, Y., et al. (1992) J. Chromatography 597 : 213-219.
5. Kalb, A. J. (1968) Biochem. Biophys. Acta. 168 : 532-536.
6. Pereira, M. E. A. and Kabat, E. A. (1974) Biochemistry. 13: 3184-3192.
7. Konami, Y., et al. (1990) FEBS Lett. 268 : 281-286.
8. Leu, R. W., et al. (1980) Cell. Immunol. 52 : 414-428.
9. Miranda Santos, I. K. F. and Pereira, M. E. A. (1985) Am. J. Trop. Med. Hyg. 33 : 839.
10. Fernandez, J.G., et al. (1994) J. Anatomy 184 : 137-145.
11. Shirahawa, T., et al. (1993) Cancer 72 : 1329-1334.