J Biol Chem, Vol. 273, Issue 44, 28557-28559, October 30, 1998

COMMUNICATION
The Polysialic Acid Units of the Neural Cell Adhesion Molecule N-CAM Form Filament Bundle Networks

Jyri Toikka, Juha Aalto, Jukka Häyrinen^§, Lauri J. Pelliniemi^¶, and Jukka Finne

From the  Department of Medical Biochemistry, University of Turku, FIN-20520 Turku, Finland, the ^§ Department of Bio-Organic Chemistry, Bijvoet Research Center, University of Utrecht, NL-3584 CH Utrecht, The Netherlands, and the ^¶ Laboratory of Electron Microscopy, University of Turku, FIN-20520 Turku, Finland

Polysialic acid is a developmentally regulated component in the neural cell adhesion molecule N-CAM which also occurs as the capsular polysaccharide of bacteria causing meningitis. Polysialic acid has been considered as a repulsive element that regulates intermolecular and intercellular adhesion. Using atomic force microscopy we unexpectedly find that oligomers of polysialic acid assemble with each other into filament bundle networks. Filaments were formed from oligomers containing 12 or more N-acetylneuraminic acid residues, and they were sensitive to sialidase digestion. The networks were also formed by the polysialic acid-containing carbohydrate units of N-CAM. The formation of filament bundles is a novel and unexpected property of polysialic acid and of short carbohydrate oligomers in general and represents a previously unrecognized molecular interaction mechanism which impacts both eukaryotic and prokaryotic cell-cell adhesions.