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Synthetic bifunctional sialic acid analog. Image: Feng et al. 2013
Researchers have synthesized synthetic sialic acid containing two functionalities that can be incorporated into the sialylated glycans. This process is called as metabolic glycan labeling that has emerged as a tool to study the sialylation of various types of glycosylation.
Sialic acid is a common term for neuraminic acid with substituent either at N- or O-. Sialic acid is a monosaccharide having 9-C backbone. There are two major types of sialic acids; N-acetylneuraminic acid (Neu5Ac) in which an acetamide is attached through its N to the carbon-5 and 2-keto-3-deocynonic acid (Kdn) in which there is no such substituent but an extra hydroxyl group is present at carbon-5.
types of sialic acid; N-acetylneuraminic acid and 2-Keto-3-deoxynonic acid. Image: glycoform via Common Wikimedia
Sialic acids are not normally present in a free form but are usually found to be incorporated into glycoproteins and glycolipids called as glycoconjugates. Sialic acids have a special affinity for certain types of proteins called as sialic acid binding proteins or lectins (not the glycoproteins; carbohydrate containing proteins). The process of interaction between sialic acid and lectin is called as oligosaccharide-lectin interaction in which sialic acid plays an important role in the recognition by the lectin.
Naturally occurring sialic acids have only single functionality (a group that can be used for labeling) that is N-acetyl group present at the carbon-5. However, researchers have synthesized sialic acid derivative that has two distinct functionalities both of which can be used to label the sialic acid for metabolic glycan labeling. The one functionality is located at the N-acetyl grout at carbon-5 while the second one is located at the carbon-9.
Thus, synthesized bifunctional sialic acid analog can be incorporated into the cellular glycans in the same way as the naturally occurring sialic acids. This approach increases the possibility of metabolic glycan labeling to study the sialylation and glycan-protein interactions.
Reference: Journal of the American Chemical Society (Bifunctional Unnatural Sialic Acids for Dual Metabolic Labeling of Cell-Surface Sialylated Glycans)
Article doi: 10.1021/ja402326z
