About the Lectin

The jackfruit, Artocarpus integrifolia (also known as A. heterophyllus), contains a lectin which is specific for D-galactose. The lectin is composed of four α and α’ monomers of 14,000 – 16,000 Da, which vary slightly in amino acid sequence, as well as degree of glycosylation, and four small β subunits having 20 amino acid residue (at least 3 variants), to give a complex mixture of isolectins of approximately 65,000 Da 1-3 . Its structure and sequences are very similar to those of Maclura pomifera, which is also a galactose-binding lectin for the family Moraceae. The lectin is also a potent mitogen for T-cells and induces immunoglobulin secretion by B-cells 4 . Initially the lectin was used in crude form and was found to bind to human serum proteins, specifically IgA 5 . The specificity of the lectin for IgA is due to the presence of a terminal galactose residue. Although IgG contains similar sugars, the presence of a terminal sialic acid residue is sufficient to prevent binding of the lectin. Further purification of the lectin, followed by carbohydrate inhibition studies, indicates that the lectin is primarily specific for α-D-galactose and oligosaccharides terminating with this sugar 6 . Of special note is the fact that the lectin is also highly specific for the T-antigen, Gal- β(1,3)GalNAc. It is more specific for this structure than the anti-T lectin from peanut since Jacalin is not inhibited by other β-galactose containing oligosaccharides such as lactose (see Arachis hypogaea – PNA). Jacalin appears to vary in its reactivity with immunoglobulins, depending on the geographic source of the seeds 7-11 , possibly reflecting different isolectin makeup of different genetic pools. Most sources, however, react with IgA and IgD 11 . In addition, extracts from seeds of Artocarpus altilis (breadfruit) also exhibit properties similar to jacalin 12 . It is therefore important to know the seed source for the lectin before making any conclusions about specificity. Currently, EY Laboratories is supplying a lectin isolated from the Brazilian jackfruit. Immobilized Jacalin is useful in the purification of O-linked glycoproteins 13 . While many lectins with a specificity for N-linked glycoproteins have been purified, Jacalin is one of the few lectins to exhibit such a strong preference for Olinked structures. Jacalin isolated from a Vietnamese str. of jackfruit reacts with mouse T-cell lymphoma (Eb) having low metastatic potential, but not with its high metastatic potential mutant, ESb. Nor does it react with human colon carcinoma also with high metastatic potential 14 . Jacalin also interacts with the CD4 cell surface glycoprotein, a target of HIV on T lymphocytes. It inhibits HIV infectivity, but does not block HIV attachment, nor CD4 mAb binding to CD4+ T-cells 15,16 . However, the interaction appears to be via a protein-protein interaction not involving the carbohydrate binding site of Jacalin nor the glycan moiety of CD4 17 .

REFERENCES

  1. Young, N. M., et al. (1991) FEBS Lett. 282 : 382-284.
  2. Mahanta, S.K.., et al. (1992) Biochem. J. 284 : 95-100.
  3. Ruffet, E., et. al. (1992) Biochem. J. 286 : 131-134.
  4. Bunn-Moreno, M. and Campos-Neto, A. (1981). J. Imm.127 : 427- 429.
  5. Roque-Barreira, M. and Campos-Neto, A. (1985). J. Imm.134 : 1740-1743.
  6. Hagiwari, K., et al. (1988). Mol. Immunol. 25 : 69-83.
  7. Aucouturier, P., et al. (1987). Mol. Immunol. 24 : 503-511.
  8. Kobayashi, K., et al. (1988). Mol. Immunol. 25 : 1037-1038. Letter to the Editor – Jacalin: Chaos in its Immunoglobulin- Binding Specificity.
  9. Kondoh, H., et al. (1987). Mol. Immunol. 24 : 1219-1222.
  10. Zehr, B. D. and Litwin, S. D. (1987). Scand. J. Imm. 26 : 229-236.
  11. Aucouturier, P., et al. (1989) J. Clin. Lab. Anal. 3 : 244-251.
  12. Pekelharing, J. M. and Animashaun, T. (1988). Lectin: Biology, Biochemistry, Clinical Biochemistry. 17 : 131-132.
  13. Hortin, G. L. and Trimpe, B. L. (1990). Anal. Biochem.188 : 271- 277.
  14. Fischer, E., et al. (1997) Biochem, Cell. Biol. 75 : 171-175.
  15. Corbeau, P., et al. (1994) Mol. Immunol. 31 : 569-575.
  16. Favero, J., et al. (1993) Eur. J. Immunol. 23 : 179-185.
  17. Lafont, V., et al. (1996) J. Leukocyte Biol. 59 : 691-696.

Product Characteristics
Buffer 0.01M Phosphate -0.15M Nacl, pH 7.2-7.4
Blood Group Non-specific after neuraminidase treatment.
Activity Less than 0.5μg/ml will agglutinate neuraminidase treated human erythrocytes.
Inhibitory Carbohydrate α-D-Galactose.
Molecular Weight Normally 65,000 Da. A low molecular weight smear below 18,000 Da appears when analysed by SDS-PAGE. Occasionally a band of MW = 100,000 is visible.
Caution The purified, lyophilized lectin is not very soluble at neutral pH. It is recommended that the powder be resuspended in a small quantity of PBS at pH 9-10. After it has been solubilized, it may be further diluted with PBS, pH 7.2-7.4.