Structural Analysis of Polysialic Acid
Polysialic acid is the polymerized structure of sialic acid, and its degree of polymerization (DP) varies from 8 to 200. Polysialic acid was first identified in the glycocalyx of neuroinvasive bacteria. Five glycoproteins, fish egg polysialoglycoprotein (PSGP), neural cell adhesion molecule (NCAM), a voltage-gated sodium channel of eel, CD36 in human milk, and neuropilin-2 have been identified as polysialic acid-containing glycoproteins until recently (Sato 2004). By virtue of their net negative charge at physiological pH, they serve as regulators of ligand-receptor and cell-cell interactions via anti-adhesive effect (Bonfanti 2006). Polysialylation occurs in some tumors and is involved in metastasis. Since polysialic acid is directly involved in the biologic function, it is important to analyze the precise structure of polysialic acid. When samples containing di- oligoand polysialic acid structures at 10–100 µg are analyzed, conventional methods including methylation analysis, NMR, and mild acid hydrolysis-TLC (Sato et al. 1993) can be applied. However, the amount of these types of glycoproteins is often too small to be analyzed by the conventional methods. The fact that di/oligo/polysialic acid-modification of glycoproteins have not been reported so often suggests the rare occurrence of polysialic acid in an organism. As highly sensitive chemical and immunochemical methods to analyze minute amounts of di-, oligo-, and polysialic acid have been developed (Sato et al. 1998, 1999; Sato 2004), studies on di/oligo/polysialic acid have gradually emerged. As chemical detection methods are described in the Chapter by C. Sato this volume, immunochemical methods to detect and determine the polysialic acid structures with specific antibodies and enzymes are introduced as powerful tools in this chapter.
KeywordsSialic Acid Neural Cell Adhesion Molecule Clostridium Perfringens Sialic Acid Residue Sensitive Chemical
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