Lectins are protein covalently linked with monosaccharide found in both plants and animals. They reversibly bind carbohydrate on the surface of cells without causing any conformational changes. They bind to any substance or cell that has glycoprotein or glycolipid on its surface, this include the erythrocyte, yeasts and several bacteria. Lectins are very specific in their action so they have some specific carbohydrate that they bind and will not bind to any other one.
There are many types of Lectins depending on the source and they all share some general characteristics like the site by which they use to bind to the carbohydrate called carbohydrate binding domain (CRD). Lectins have quaternary structure consisting of two to four polypeptide chains and usually with one binding site per chain. Some forms of Lectins require metals like calcium or magnesium to bind to a specific carbohydrate, while others requires thiol groups.
Since different blood group have some unique carbohydrates, Lectins bind to these carbohydrate causing fusing together of the blood. Thus Lectins can be use to differentiate between different blood types. Also, they are use to stop blood from bleeding. They are also used to remove some certain glycoprotein that can be dangerous from the circulation.
References
Lectin: http://www. cs. stedwards. edu/chem/Chemistry/CHEM43/CHEM43/Lectin/STRUCTURE. html Reference Date: May 24, 2008