Plant Lectin on Blood Agglutination

Lectin is a protein that is commonly found in certain plants such as grains  (wheat), legumes (soybeans and peanuts), and also can be found in potato, tomato, eggplant and pepper. It is found to be toxic, especially if the food containing it is undercooked. It causes damage to the gut wall in the stomach. Lectin’s toxicity may even cause rapid death.
Lectin is a glycoprotein. As a glycoprotein, it is capable of binding to carbohydrate. It tends to bind to carbohydrates in specific and reversible manner. It is a protein that has binding site specific to carbohydrate. Because of this ability of lectin, it can cause agglutination of red blood cells. It does so by interaction with the sugar moieties of the cell wall leading to the clumping together of the cells.
In blood agglutination by lectin, its active sites are the ones that bind to the sugar moieties present in the cell wall of the red blood cells These active sites are consists of certain amino acid residues. It was suggested that there are two or more amino acid residues that are present in the active site of lectin (cited in Sharon, 2007). Some of these amino acid forms hydrogen bonds with the hydroxyl group of the sugar or carbohydrate moiety.

The other amino acids interact hydrophobically. Aside from these interactions, other kinds of interactions such as coordination with the metal, like interaction with the iron compound of the hemoglobin in the red blood cells, and electrostatic interaction might occur as well.  Further interaction of these active sites to other carbohydrate part of the blood cells results to large mass, then the clumping of cells occurs.
Specificity of lectin towards carbohydrates depends on the kind of amino acid present in its active site. This made plant lectin found its usefulness in the field of medicine. One application of plant lectin is in determining blood group. Lectin can agglutinate specific types of erythrocytes. Different sources of lectin may have different active sites, therefore may dictate the kind of carbohydrate it binds with.
Plant lectins, despite of the danger it may pose in our health, can be still useful in our life. As the study and research on lectin progresses, more benefits that we can derive from these compounds are revealed.
Reference
Sharon, N. (2007). Lectins: Carbohydrate-specific Reagents and Biological Recognition
Molecules. Journal of Biological Chemistry, 282, 5, 2753-2764. Retrieved December 9,  2007 from, http://www.jbc.org/cgi/content/full/282/5/2753