Concanavalin A

Concanavalin A is a member of a group of proteins called lectins which are proteins that react with specific sugar residues. It has broad applicability and is the most widely used lectin within molecular biology research. The conformation of concanavalin is pH-dependent. At pH 4.5-5.6 it exists as a dimer, above pH 7 it is predominantly tetrameric. Concanavalin A binds two metal ions per monomer: a transition metal at site S1 and Ca2+ at site S2. Both ions must be present for saccharide binding.

Concanavalin A (Con A) lectin is isolated from Jack beans (Canavalia ensiformis) and purified by affinity chromatography. The molecular weight is 104 kDa and the pI is 4.5-5.5. 

Con A binds specifically to α-Mannose, α-Galactose structures found in sugars, glycoproteins and glycolipids (2). The lectin has been utilized in hormone receptor studies, mitogenic assays and for characterizing normal and malignant cells (cancer cells are readily aggregated by Con A while normal cells are not). Con A can also initiate cell division (mitogenesis) principally acting on T-lymphocytes (3).

Immobilized Con A has been used in affinity chromatography purifications of a wide variety of glycoproteins and cellular structures.

Polyacrylamide gel electrophoresis in SDS of Con A from Jack beans yields three major bands corresponding to molecular weights 27, 13 and 10 kDa. One minor band is visible at 18 kDa. (4).

Con A is supplied as a white lyophilized powder from a buffer containing 0.5mM MnCl2, 0.5mM CaCl2, no preservatives are added. The identity is determined by SDS-PAGE and the protein content by spectrophotometry.

How to use Concanavalin A

The lectin may be reconstituted with 2mL of deionized water before use. Spin the vial gently until full dissolution. Aggregation is thought to occur in the presence of high concentrations of 2-mercaptoethanol. The solution may be reconstituted in this buffer to desired working concentration. In absence of lactose the lectin will polymerize and storage at pH 8.6–8.8 causes precipitation.

References

(1) John L. Wang, Bruce A. Cunningham and Gerald M. Edelman (1971) Unusual Fragments in the Subunit Structure of Concanavalin A (gelelectrophoresis/molecularweights) Proc. Nat. A cad. Sci. USA Vol. 68, No. 6, pp. 1130-1134, JuRm

(2) Ahmed, H.U., Blakeley, M.P., Cianci, M., Cruickshank, D.W.J., Hubbard, J.A., Helliwell, J.R. (2007) The Determination of Protonation States in Proteins. Acta Crystallogr.,Sect.D 63: 906.

(3) Liener I. E., Sharon N., Goldstein I. J., (1986) The Lectins – Properties, Functions and Applications in Biology and Medicine.

(4) Krauss S., Buttgereit F., (1999) Effects of the mitogen concanavalin A on pathways of thymocyte energy metabolism. BrandBiochim Biophys Acta 1412: 129–38.