Lectin-like glycoproteins

Several of the hydroxyproline-rich glycoproteins extracted from plant tissues have carbohydrate-binding activity these glycoproteins have the characteristics of lectins. These lectins or lectin-like glycoproteins have compositions which are similar to that of the cell wall hydroxyproline-rich glycoprotein. 

The content by weight of carbohydrate in glycoproteins may vary from only a few percent to over 50 percent in some proteins in mucous secretions. Although the function of the polysaccharide in most glycoproteins is unknown, in some cases it may provide hydrophilicity, recognition, and points of noncovalent interaction with other proteins through lectin-like affinity binding. 

Because avidin is a glycoprotein and has an isoelectric point (pi) of 10, it has a propensity to bind non-specifically to lectin-like and negatively charged tissue components at physiological pH. In contrast to avidin, streptavidin has a more neutral isoelectric point and lacks the carbohydrate moieties. These differences result in less nonspecific tissue binding. 

For instance, the liver Kupffer cells and macrophages probably have on their surfaces lectin-like components which recognize a manose determinant of lysosomal glycosidase (e.g. glycoprotein enzyme) and remove them from the blood circulation A similar effect which is applied in affinity chromatography... 

Lectins like concanavalin A and wheat germ agglntinin are nsed for selective glycoprotein emichment [21-22]. 

The property of conformational restriction in polysaccharides make them candidates for being the initial self-ordering molecules of prebiotic evolution. This same property in the complex carbohydrate moiety of glycoproteins is the basis of carbohydrate-mediated information transfer through cell surface oligosaccharides interacting with each other or with lectin-like proteins in cell-cell recognition processes. 

Selectins are transmembrane proteins with membrane-distal Ca +-dependent lectin domains. This family of cell adhesion molecules is involved in the tethering and rolling of leukocytes on the blood vessel endothelium. Nicholson and colleagues [10] published the analysis of leukocyte selectin, CD62L, binding to the mucin-like glycoprotein, Gly-CAM-1. 

Peterson, J.R., Ora, A., Van, P.N., and Helenius, A. Transient, Lectin-like Association of Calreticulin with Folding Intermediates of Cellular and Viral Glycoproteins Mol Biol Cell 1995 5, 1173-1184. 

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