Glycobiology of di- and oligosialyl glycotopes

alpha 2->8-linked di- and oligosialic acid (diSia and oligoSia) chains with DP 2,3 Sia residues are known to be common structural units of gangliosides, and to be 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 oligomers on glycoproteins. However, it has recently been shown that glycoproteins containing di- and oligoSia groups occur in nature more frequently than was ever recognized, as analytical methods to detect di- and oligoSia structures have improved. It is thus hypothesized that these di- and oligoSia moieties on glycoproteins may have similar important functions in common with those proposed for the gangliosides. In this review, we describe the recent advances in the study of di- and oligoSia residues on glycoproteins, including analytical methods, occurrence, functions, and biosynthetic pathways.