About the Lectin

Concanavalin A (Con A) is the most widely known and used plant lectin, as well as the first to be purified. In 1936 Con A was reported to precipitate certain carbohydrates such as glycogen and starch from corn and rice, and to agglutinate various erythrocytes. More recent research has shown that Con A can also precipitate various other polysaccharides such as dextrans and fructans, various glycoproteins such as immunoglobulins and blood group substances, as well as pneumococcal polysaccharides. Con A also reacts with a variety of bacterial and animal cells, can distinguish between certain normal and tumor cells, and can initiate cell division (mitogenesis). The native lectin is composed of four identical subunits. The association of these subunits is pH dependent: below pH 5.6 the subunits associate to form a dimer, above pH 5.6 the dimers associate to form a tetramer. The dimer retains its carbohydrate binding specificity below pH 5.0 but loses its ability to precipitate polysaccharides ¹ . Con A has been used successfully in the past to initiate differentiation and cell division ^2,3 . More recently Con A has been used to stimulate T-cells to produce IL 1-like factors ⁴ . It has also been used in the proliferation of spleen cells ⁵ and to study ligand/receptor interactions required for activation ⁶ . Using histochemical techniques, Con A has been used for the demonstration of macrophage histiocytes in pathological specimens ⁷ , as well as to differentiate between normal ACTH producing pituitary cells and ACTH producing adenomas ⁸ . Con A potentiates the response of glutamate neurotransmitter receptors, and has been used in studies on the role of glycosylation in ion channel modulation ^9,10 . While temperature and pH are known to alter the equilibrium between the subunits, it is also possible to chemically modify the protein.

Succinylated Con A is a dimeric protein that can stimulate DNA synthesis in mouse splenocytes. In addition to altering the subunit composition of the lectin, succinylation also lowers the isoelectric point of the protein. The succinylated form maintains the specific carbohydrate binding properties of the native lectin, and is substantially more soluble. High concentrations of Con A are not stable for long term storage in the recommended buffer. Increasing the NaCl concentration to 1.0 M seems to help stabilize the lectin. The addition of calcium or manganese ions has been recommended in the past since they are required for lectin binding. However, these ions are not removed from the protein during the purification process and are therefore not required in the working buffer. Some research groups have had success using PBS for reconstitution and dilution of the lectin. Almost all preparations of the purified lectin will contain a small percentage of aggregates upon reconstitution. EY Laboratories has found that the material supplied by some other manufacturers may contain salts in the lyophilized preparation. This tends to lead to a greater degree of aggregate formation after reconstitution. The lyophilized preparation supplied by EY Laboratories is essentially salt free.

REFERENCES

1. Goldstein, I. J. and Poretz, R. D. (1986). The Lectins: Properties, Functions, and Applications in Biology and Medicine. Academic Press.
2. Wecksler, M., et al. (1968). Acta Cient. Venezo. 19 : 154.
3. Powell, A. E. and Leon, M. A. (1970). Exp. Cell. Res.62 : 315.
4. Yamashita, U., et al. (1987). J. Immunol. 138 : 3284-3289.
5. Murray, H. W., et al. (1987). J. Immunol. 138 : 2290.
6. Weiss, A., et al. (1987). J. Immunol. 138 : 2169-2176.
7. Ree, H. J. (1983). Cancer. 51 : 1639-1646.
8. Hori, T., et al. (1985). Acta Neuropath. (Berlin). 66 : 177.
9. Partin, K. M., et al. (1993) Neuron 11 : 1069-1082.
10. Everts, I., et al. (1997) Mol. Pharm. 52 : 861-873.