Abstract
Polysialylation of the neural cell adhesion molecule (N‐CAM) is known to destabilize cell‐cell adhesion and to promote plasticity in cell–cell interactions. To gain more insights into the molecular mechanisms regulating the selective expression of polysialic acid on distinct glycan chains, the underlying core structures of polysialylated N‐CAM glycans from newborn mouse brain were examined. Starting from low picomolar amounts of oligosaccharides, a multistep approach was used that was based on various mass spectrometric techniques with minimized sample consumption. Evidence could be provided that polysialylated murine N‐CAM glycans comprise diantennary, triantennary and tetraantennary core structures carrying, in part, type‐1 N‐acetyllactosamine antennae, sulfate groups linked to terminal galactose or subterminal N‐acetylglucosamine residues and, as a characteristic feature, a sulfated glucuronic acid unit which was bound exclusively to C3 of terminal galactose in Manα3‐linked type‐2 antennae. Hence, our results reveal that part of the murine N‐CAM carbohydrates are modified within a single oligosaccharide by polysialic acid plus a HSO3‐GlcA‐moiety, which is likely to represent a HNK1‐epitope. As HNK1‐carbohydrates are also known to modulate cell–cell interactions, the simultaneous presence of both carbohydrate epitopes may reflect a new mechanism involved in the fine‐tuning of N‐CAM functions.