About the Lectin

Tomato extracts have been shown to contain a potent hemagglutinin that is found in the juice and meat of the tomato. The lectin found in various extracts is not inhibited by monosaccharides. Inhibition experiments have shown that the tomato lectin is specific for oligomers of β–(1,4)-linked N-acetyl-D-glucosamine, with the binding site being able to accommodate up to 4 carbohydrate units. Comparisons have been made between several lectins that share a similar specificity, including WGA, DSA, STA, and OSA, showing that their reactivity with glycoproteins varies. Tamm-Horsfall glycoprotein and glycophorin are good inhibitors of LEA and WGA, but not of STA 1 . The tomato lectin does not seem to require that the GlcNAc residues be consecutive, a finding that has been noted for DSA, but not for WGA, STA, or OSA. Repeating units of GlcNAc and muramic acid, as found in the cell walls of Micrococcus luteus, are strong inhibitors of the lectin. DSA is also inhibited by the M. luteus cell wall polysaccharide. In contrast, DSA reacts with N-acetyllactosamine while LEA requires 3 consecutive LacNAc residues, making it specific for poly N-acetyllactosamine glycoproteins. 2 These findings serve to point out the subtle differences between lectins with very similar affinities. Purified LEA is heavily glycosylated, approximately 50% carbohydrate by weight. The pure lectin is actually a mixture of two isolectins, having a different isoelectric point5, but identical with regard to their carbohydrate specificity 3 . LEA is a very stable protein; it is stable at a pH of 1.5 and is fairly resistant to proteolytic enzymes, thus is able to survive passage through the gastrointestinal tract where it binds specifically to intestinal epithelium 4 , although a specific role of this lectin in the diet has not been determined1. Tomato lectin also binds to gastric H+/K+ATPase complex (proton pump) and is used for its specific purification 5 . It is also a specific marker for various glial cell populations 6,7 . The tomato lectin has been shown to depress the incorporation of tritium labeled thymidine into lymphocytes, essentially acting as an anti-mitogen. In fact, the lectin does inhibit the mitogenic response of both Con A and pokeweed. Polystyrene beads coated with LEA have been used for the specific agglutination of group B streptococci 8 . Although LEA is not blood group specific it shows a very strong preference for type O cells. Neuraminidase treated cells, regardless of blood type, are agglutinated more readily than untreated cells.

REFERENCES

  1. Nachbar, M. S., et al. (1980) J. Biol. Chem. 255 : 2056-2061.
  2. Kawashima, H., et al. (1990) Glycoconj. J. 7 : 323-334.
  3. Kilpatrick, D. C., et al. (1983) Anal. Biochem. 134 : 205-209.
  4. Lehr, C. M., et al. (1992) Pharmaceut. Res. 9 : 547-553.
  5. Callagham, J. M., et al. (1992) Biochem. J. 283 : 63-68.
  6. Acarin, L., et al. (1994) J. Histochem. Cytochem. 42 : 1033-1041.
  7. Velasco, A., et al. (1995) Brain Res. 705 : 315-324.
  8. Slifkin, M. and Cumbie, R. (1987) J. Clin. Micro. 25 : 1172.

Product Characteristics
Buffer 0.01M Phosphate – 0.15M NaCl, pH 7.2-7.4.
Blood Group Nonspecific. O > A, B.
Activity 50- 60 μg/ml will agglutinate type O human erythrocytes. 5-10 μg/ml will agglutinate neuraminidase treated cells.
Inhibitory Carbohydrate N‑acetyl‑D‑glucosamine β(1,4)N‑acetyl‑D-glucosamine oligomers up to 4 carbohydrate units. The N‑acetyl‑D‑glucosamine residues do not need to appear consecutively.
Molecular Weight Due to its high carbohydrate content, this lectin does not usually appear on SDS-PAGE gels under standard conditions.