Phaseolus lunatus

About the Lectin

The first demonstration of a blood group specific lectin was that of Phaseolus lunatus, or LBA 1 . LBA has been purified using a variety of techniques. Regardless of the technique used, LBA consists of three different but related components. Component III is made up of four subunits while component II is made up of eight subunits. Component I is the largest of the three and is still made up of the same subunit; however, this component is not active and is only present in low concentrations 2 . The basic subunit for each of these components has a MW=30,000, The subunit is heterogeneous by isoelectric focusing, appearing as three distinct species 3 . The primary structure of the LBA was determined by cloning the gene encoding the lectin 4 . Component II and III are immunologically identical, but they do differ with regard to blood group activity. Component II is a more potent agglutinin of type A erythrocytes than component III. Component II will also agglutinate type B erythrocytes, while component III will not. LBA is a metalloprotein containing Mn ++ and Ca ++ . Treatment of the lectin with a chelating agent, such as EDTA, will abolish activity. The activity can be restored by removal of the chelating agent and the addition of various divalent cations, including Mn ++ and Ca ++ . LBA is nominally specific for N-acetyl-D-galactosamine and is more specific for the fucose containing type A blood group trisaccharide, GalNAcα(1,3)[L-fuc α(1,2)]Gal, than any of the other GalNAc specific lectins tested 5 . Each subunit of LBA binds one molecule of GalNAc 6 , as well as hydrophobic ligand, e.g. 1,8-anilino-1-napthalene-sulfonic acid 7 . Additionally, LBA component III binds one molecule of adenine and its N6 derivatives related to cytokinins 6 . LBA is mitogenic for human peripheral T lymphocytes but not B lymphocytes. Polymeric forms of the lectin are reported to be even more potent mitogens than the unpolymerized lectin 5 .

REFERENCES

  1. Boyd, W. C. and Reguera, R. M. (1949) J. Immunol. 62: 333-339.
  2. Galbraith, W. and Goldstein, I. J. (1972) Meth. Enzymol. 28 (part B): 318-323.
  3. Roberts, D. D., et al. (1982) J. Biol. Chem. 257: 9198-9204.
  4. Jordan, E. and Goldstein, I. J. (1994) J. Biol. Chem. 269 : 7674-7681.
  5. Roberts, D. D. and Goldstein, I. J. (1984) J. Biol. Chem. 259: 903-908.
  6. Roberts, D.D. and Goldstein, I. J. (1983) J. Biol. Chem 258 : 13820-13824.
  7. Roberts, D.D. and Goldstein, I. J. (1982) J. Biol. Chem 257 : 11274-11277.
  8. Kraut, H., et al. (1980) Protides Biol. Fluids. 27: 619-622.

Product Characteristics

Buffer 0.01M Phosphate – 0.15M NaCl, pH 7.2-7.4.
Blood Group A1 > A2 >>B.
Activity Less than 60 μg/ml will agglutinate type A1 erythrocytes. More than 200 μg/ml is required to agglutinate type A2 cells.
Inhibitory Carbohydrate N-acetyl‑D‑galactosamine.
Molecular Weight Subunit MW=30,000. Component II has a MW=120,000. Component III has a MW=245,000.