Fine tuning of cell signals by glycosylation.

Carbohydrates on the glycoproteins and glycosphingolipids expressed on the cell surface membrane play crucial roles in the determination of cell fates by being involved in the fine tuning of cell signalling as reaction molecules in the front line to various extrinsic stimulants. In glycoproteins, modification of proteins is performed by substitution of sugar chains to one or multiple sites of individual proteins, leading to quantitative and qualitative changes of receptor functions in the cell membrane. As for glycosphingolipids, majority of them consist of two moieties, i.e. carbohydrates and ceramides, and are localized in the microdomains such as lipid rafts or detergent-resistant microdomains. They generate and/or modulate cell signals to determine the cell fates by interacting with various carbohydrate-recognizing proteins. Modes of glycosylation and mechanisms by which glycosylation is involved in the regulation of cell signals are now hot subjects in glycobiology.