THE POLYSIALIC ACID UNITS OF THE NEURAL CELL-ADHESION MOLECULE N-CAM FORM FILAMENT BUNDLE NETWORKS

Polysialic acid is a developmentally regulated component in the neural cell, adhesion molecule N-CAM which also occurs as the capsular polys accharide of bacteria causing meningitis. Polysialic acid has been con sidered as a repulsive element that regulates intermolecular and inter cellular adhesion. Using atomic force microscopy we unexpectedly find that oligomers of polysialic acid assemble with each other into filame nt 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 a cid-containing carbohydrate units of N-CAM. The formation of filament bundles is a novel and unexpected property of polysialic acid and of s hort carbohydrate oligomers in general and represents a previously unr ecognized molecular interaction mechanism which impacts both eukaryoti c and prokaryotic cell-cell adhesions.