Biochemistry of carbohydrate-protein interaction

Recognition of glycoconjugates is an important event in biological systems, and is frequently in the form of carbohydrate-protein interactions. To thoroughly understand these interactions, well-defined carbohydrate ligands must be available. Naturally derived glycoconjugates can be highly purified, and their structures (including conformational structures) can be elucidated to provide such ligands. This requires highly effective methods of separation, such as various forms of high-performance liquid chromatography. Alternatively, structurally well-defined glycoconjugates can be synthesized for this purpose. These include conjugates of carbohydrate derivatives to proteins, lipids, and nonbiological carriers and polymers. The efficacy of these conjugates is amply demonstrated in the studies of carbohydrate-binding proteins from animals. Hepatic carbohydrate receptors, requiring calcium for binding, recognize only the terminal sugar residues. Although different sugar specificities are manifested by different species, there is some commonality in the requirement of the substituents of the sugar rings. Clustering of the target sugars in proper geometric arrangement greatly enhances the binding by these proteins. Some other animal carbohydrate-binding proteins, however, may require penultimate sugars for optimal binding.