Carbohydrate-carbohydrate interactions of a novel acidic glycan can mediate sponge cell adhesion

Cell recognition and adhesion were first demonstrated in marine sponges. These phenomena were later shown in Microciona prolifera sponge to be mediated by a Ca(2+)-dependent self-association of adhesion proteoglycans (APs) attached in a species-specific manner to cell-surface receptors. Using the same experimental system we now provide three lines of evidence that highly polyvalent Ca(2+)-dependent carbohydrate-carbohydrate interactions of a novel AP glycan represent the basis of AP-AP self-binding and thus of cell adhesion. 1) A specific monoclonal antibody which blocks cell aggregation and AP bead adhesion identified a highly repetitive novel carbohydrate epitope (2500 sites) in an acidic glycan of M(r) = 200 x 10(3) (g200) from AP. 2) Reconstitution of the Ca(2+)-dependent self-interaction activity of AP was achieved by cross-linking the purified protein-free g200 glycan into polymers of similar valency as the native AP. 3) Beads coated with the protein-free g200 glycan showed a Ca(2+)-dependent aggregation equivalent to that of AP beads. Carbohydrate and amino acid analyses of the g200 glycan purified by gel electrophoresis, high performance liquid chromatography gel filtration, and ion exchange chromatography yielded six components in the following proportions; 68 fucose, 32 glucuronic acid, 2 mannose, 18 galactose, 19 N-acetylglucosamine, and 1 asparagine residue. These unique chemical features together with immunological and enzymological analyses suggest that the g200 glycan is a large highly fucosylated, acidic, N-linked polysaccharide with a novel structure distinct from that of other known glycosaminoglycans.