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All cells are coated in either glycoproteins or glycolipids, both of which help determine cell types. [7] Lectins, or proteins that bind carbohydrates, can recognize specific oligosaccharides and provide useful information for cell recognition based on oligosaccharide binding. [citation needed]
Binding site location: In some proteins, the binding sites are located on the side surface of the β-barrel where three loops come together, in such a way they are partially wrapped by the binding partner. In others, the binding cleft at the side of the barrel opposite to the helix functions as binding site.
The saccharide of the glycolipid will bind to a specific complementary carbohydrate or to a lectin (carbohydrate-binding protein), of a neighboring cell. The interaction of these cell surface markers is the basis of cell recognitions, and initiates cellular responses that contribute to activities such as regulation, growth, and apoptosis. [7]
The binding of glycoproteins on the surface of parasitic cells also is believed to be a function. Several plant lectins have been found to recognize noncarbohydrate ligands that are primarily hydrophobic in nature, including adenine , auxins , cytokinin , and indole acetic acid , as well as water-soluble porphyrins .
The oligosaccharide chains also change the solubility and polarity of the proteins that they are bonded to. [4] For example, if the oligosaccharide chains are negatively charged, with enough density around the protein, they can repulse proteolytic enzymes away from the bonded protein. [4]
Generally, the carbohydrate part(s) play an integral role in the function of a glycoconjugate; prominent examples of this are neural cell adhesion molecule (NCAM) and blood proteins where fine details in the carbohydrate structure determine cell binding (or not) or lifetime in circulation.
An alternative definition is the entirety of carbohydrates in a cell. The glycome may in fact be one of the most complex entities in nature . " Glycomics , analogous to genomics and proteomics , is the systematic study of all glycan structures of a given cell type or organism" and is a subset of glycobiology .
This oligosaccharide content remains on the outside of the cell membrane where it is important for biological processes such as cell adhesion or cell–cell interactions. Glycosphingolipids also play an important role in oncogenesis and ontogenesis .