Protein–carbohydrate interactions
Carbohydrate–protein interactions are the intermolecular and intramolecular interactions between protein and carbohydrate moieties. These interactions form the basis of specific recognition of carbohydrates by lectins. Carbohydrates are important biopolymers and have a variety of functions. Often carbohydrates serve a function as a recognition element. That is, they are specifically recognized by other biomolecules. Proteins which bind carbohydrate structures are known as lectins. Compared to the study of protein–protein and protein–DNA interaction, it is relatively recent that scientists get to know the protein–carbohydrate binding.
Many of these interactions involved carbohydrates found at the cell surface, as part of a membrane glycoprotein or glycolipid. These interactions can play a role in cellular adhesion and other cellular recognition events. Intramolecular carbohydrate–protein interactions refer to interactions between glycan and polypeptide moieties in glycoproteins or the glycosylated proteins.
Generally, there are two types of protein carbohydrate binding important in biological processes: Lectin and antibody.
Lectin is a kind of protein that can bind to carbohydrate with their carbohydrate recognition domains (CRDs). We could use different CRD to classify them.
Ca2+ is required to activate the binding. Ca2+ binds to the protein and carbohydrate by non covalent bond. Mannose-binding protein (MBP) contains the C-type CRD.
Two types mannose-6-phosphate can recognize phosphorylated saccharide. One is cation-dependent and the other does not require cation to activate.
I-type lectin named from the immunoglobulin-like domain. Sialoadhesin is one of the I-type lectin, which binds specifically to sialic acid.
Most antibodies have the similar structure except the hypervariable region which is called the antigen binding site. This region is constituted by the combination of various amino acids. When the antigen is a kind of carbohydrate (Polysaccharide), the binding could be regarded as a protein-carbohydrate interaction.
Protein–carbohydrate interactions play an important role in biological function.
Just like other organic molecule study, X-ray crystallography is a very useful tool to know the detail information on the interaction between carbohydrate and protein.
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