Abstract
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.
Highlights
EXPERIMENTAL PROCEDURESMaterials—Oligomers consisting of 6, 9, 12, 15, or 18 residues of ␣2– 8-linked N-acetylneuraminic acid were purified by high performance liquid chromatography from colominic acid [11]
Polysialic acid is a developmentally regulated component in the neural cell adhesion molecule N-CAM which occurs as the capsular polysaccharide of bacteria causing meningitis
Atomic force microscopy revealed the presence of filamentous structures in samples of oligomers of 12 or more sialyl residues, whereas oligomers of 9 residues or shorter did not display these structures (Fig. 1)
Summary
Materials—Oligomers consisting of 6, 9, 12, 15, or 18 residues of ␣2– 8-linked N-acetylneuraminic acid were purified by high performance liquid chromatography from colominic acid [11]. The purity of the oligomers was assessed by gel electrophoresis [12] and staining with Alcian blue–silver. Embryonic polysialic acid-containing glycopeptides and normal sialylated embryonic glycopeptides without polysialyl units were isolated as described before [13]. Atomic Force Microscopy—Aliquots of 2 l containing 2 pmol of polysialic acid oligomer were applied together with 40 pmol of CaCl2 onto freshly cleaved mica surfaces and allowed to dry at 20 °C. Neuraminidase Digestion—Digestion of preformed filament networks bundles was carried out with 5 l of 0.1 milliunit/ml of Vibrio cholerae neuraminidase (Behringwerke AG) in 50 mM sodium acetate buffer, pH 5.5, containing 9 mM CaCl2 and 154 mM NaCl at 20 °C for 10 min. Control incubations were carried out under identical conditions but without enzyme
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