Chain Length Diversity of Sialic Acids and Its Biological Significance

Abstract

Sialic acids are commonly present as monosialyl residues at the non-reducing terminal end of glycoconjugates. In some cases, α2→8 linked di/oligosialic acid chains with DP 2 or 3 sialic acid residues are common structural units of gangliosides, and involved in various biological processes, such as cell adhesion, cell differentiation, signal transduction, and surface expression of stage specific antigen. In contrast, little attention has been paid to the occurrence and functions of such short sialyl di/oligomers on glycoproteins, while polysialic acid (DP≥8) in embryonic NCAM has been extensively studied as a regulator of cell adhesion in neurogenesis. As analytical methods to detect di/oligosialic acid structures have been improved, several glycoproteins containing di/oligo/polysialic acid chains have been identified. It is thus hypothesized that these di/oligosialic acid residues on glycoproteins may have similar important functions in common with those proposed for the gangliosides or may have new functions. Currently, several studies showing the importance of di/oligosialic acid-containing glycoproteins have emerged. In this review, recent advances in such studies of di/oligosialic acid residues on glycoproteins, including analytical methods, occurrence, biosynthetic pathways, and functions, are described.