Frequent Occurrence of Pre-existing α2→8-Linked Disialic and Oligosialic Acids with Chain Lengths Up to 7 Sia Residues in Mammalian Brain Glycoproteins

Abstract

The pre-existence of ␣238-linked disialic acid (di-Sia) and oligosialic acid (oligo-Sia) structures with up to 7 Sia residues was shown to occur on a large number of brain glycoproteins, including neural cell adhesion molecules (N-CAMs), by two highly sensitive chemical methods (Sato, C., Inoue, S., Matsuda, T., and Kitajima, K. (1998) Anal. Biochem. 261, 191-197; Sato, C., Inoue, S., Matsuda, T., and Kitajima, K. (1999) Anal. Biochem. 266, 102-109). This unexpected finding was also confirmed using a newly developed antibody prepared using a copolymer of ␣238-linked N-acetylneuraminyl p-vinylbenzylamide and acrylamide as an immunogen and known antibodies whose immunospecificities were determined to be di-and oligo-Sia residues with defined chain lengths. The major significance of the new finding that di-and oligo-Sia chains exist on a large number of brain glycoproteins is 2-fold. First, it reveals a surprising diversity in the number and M r of proteins distinct from N-CAM that are covalently modified by these short sialyl glycotopes. Second, it suggests that synthesis of diand/or oligo-Sia units may be catalyzed by ␣238-sialyltransferase(s) that are distinct from the known polysialyltransferases, STX and PST, which are partially responsible for polysialylation of N-CAM.

A Small Region of the Natural Killer Cell Receptor, Siglec-7, Is Responsible for Its Preferred Binding to α2,8-Disialyl and Branched α2,6-Sialyl Residues

“…Di-or oligo-sialyl residues have been identified on several glycoproteins such as fetuin, ␣2-macroglobulin, and adipo Q in serum (29) and NCAM in the brain (30). An N-glycan containing a Gal␤1,3[Sia␣2,6]GlcNAc residue is found in serum transferrin (31).…”

Identification and Adipocyte Differentiation-dependent Expression of the Unique Disialic Acid Residue in an Adipose Tissue-specific Glycoprotein, Adipo Q

“…Rat anti-mouse IgM was purchased from Cappel (West Chester, PA). Monoclonal antibody S2-566, which recognizes Neu5Ac␣238Neu5Ac␣233Gal, was kindly provided by Dr. Koichi Furukawa (Nagoya University School of Medicine) and prepared as described (8). Monoclonal antibody 735, which recognizes polyNeu5Ac, and OL28, which recognizes oligoNeu5Ac and polyNeu5Ac, were kindly provided by Dr. Jü rgen Roth (University of Zü rich) and Dr. Karen Colley (University of Illinois, School of Medicine), respectively.…”

“…Monoclonal antibody 735, which recognizes polyNeu5Ac, and OL28, which recognizes oligoNeu5Ac and polyNeu5Ac, were kindly provided by Dr. Jü rgen Roth (University of Zü rich) and Dr. Karen Colley (University of Illinois, School of Medicine), respectively. Monoclonal antibody 1E6, which recognizes diNeu5Ac, was prepared as described previously (8). Bovine fat tissues were kindly provided by the Nagoya central wholesale market at Takahata station (Nagoya, Japan).…”

Siglec-7 Undergoes a Major Conformational Change When Complexed with the α(2,8)-Disialylganglioside GT1b

“…Importantly, Nicoll et al (21), have demonstrated that a b-series ganglioside, GD3, 3 when expressed on target cells, was able to mediate interactions with Siglec-7 expressed on NK cells, leading to the suppression of NK mediated cytolytic activity. This disialyl motif has also been identified on the serum glycoproteins fetuin, ␣2-macrogobulin, and adipo Q (23), neural cell adhesion molecule in the central nervous system (24), and a 70-kDa glycoprotein found on T cells (25). Previously, we have described the structure of Siglec-7 as a prototypic template for the CD33-related siglec subfamily and shown the mode of binding for the primary sialic acid (26,27).…”