Sialic acids (Sia) are involved in many biological activities and are commonly
present as monosialyl residues at the non-reducing terminal end of glycoconjugates.
Occasionally, polymerized structures in the form of disialic acid (diSia), oligosialic acid
(oligoSia), and polysialic acid (polySia) appear in glycoconjugates. In particular, polySia is
known to be a common epitope from bacteria to humans and is one of the most famous,
biologically-important glycotopes in vertebrates. The biological functions of polySia,
especially on neural cell adhesion molecules (NCAMs), have been well studied and an indepth
body of knowledge concerning polySia has been accumulated. However, considerably
less attention has been paid to glycoproteins containing di- and oligoSia groups. As the
analytical methods used to detect oligo/polymerized structures have been improved,
glycoproteins containing di/oligo/polySia chains have been identified with an increasing
frequency in nature. In addition, more sophisticated genetic techniques have helped elucidate
the underlying mechanisms of polySia-mediated activities. In this chapter, the recent
advances in the study of di-, oligo- and polySia residues on glycoproteins, including their
distribution, chemical properties, biosynthetic pathways, and functions are described.
Keywords: Sialic acid, disialic acid, oligosialic acid, polysialic acid,
polysialyltransferase, neural cell adhesion molecule, polysialoglycoprotein,
flagellasialin, neurotrohic factor, growth factor, neurotransmitter, salmonid fish,
neuroinvasive bacteria, sea urchin, helical structure, fertilization, neurogenesis,
anti-adehesive field, attractive field, schizophrenia, cancer.