CHARACTERIZATION OF A NOVEL SULFATED CARBOHYDRATE UNIT IMPLICATED IN THE CARBOHYDRATE-CARBOHYDRATE-MEDIATED CELL-AGGREGATION OF THE MARINE SPONGE MICROCIONA-PROLIFERA

Species-specific cell reaggregation in the marine sponge Microciona pr olifera is mediated by an adhesion proteoglycan. Two interactions are involved in the process: a Ca2+-dependent hemophilic binding between p roteoglycan molecules and a Ca2+-independent binding between the molec ule and cells. Both interactions are mediated by the glycan moieties o f the proteoglycan. The interaction of the proteoglycan with itself ha s been characterized as a carbohydrate-carbohydrate interaction of mul tiple low affinity sites. The monoclonal antibodies Block 1 and Block 2 raised against the purified aggregation proteoglycan and selected fo r inhibition of aggregation bind to these glycans. In a previous repor t the structure, Pyr<(6)(4)>Gal beta 1-4GlcNAc beta 1-3Fuc STRUCTURE 1 was assigned to the oligosaccharide reacting with Block 1 antibody (S pillmann, D., Hard, K., Thomas-Gates, J., Vliegenthart, J. F. G., Mise vic, G., Burger, M. M., and Finne, J. (1993) J. Biol, Chem. 268, 13378 -13387), By the technique of attaching the water-soluble acid-degraded fragments to a lipid carrier for immunochemical detection and by chem ical, enzymatic and spectroscopic methods the structure, GlcNAc beta 1 -3Fuc \ 3SO(3) STRUCTURE 2 was assigned to the oligosaccharide reactin g with the aggregation- blocking monoclonal antibody Block 2. The stru cture, Gal alpha 1-2Gal beta 1-4GlcNAc beta 1-3Fuc \ 3SO(3) was assign ed to a major nonreactive oligosaccharide, which outlined the molecula r requirements of antibody binding of the two aggregation-associated e pitopes. These data demonstrate that two different functional sites wi th distinct structural characteristics and antibody reactivities are i nvolved in the reaggregation of sponge cells, a model of carbohydrate carbohydrate-mediated cell interactions.