ISOLATION AND CHARACTERIZATION OF A NEW CLASS OF ACIDIC GLYCANS IMPLICATED IN SEA-URCHIN EMBRYONAL CELL-ADHESION

Three major glycan fractions of 580 kDa (g580), 150 kDa (g150), and 2 kDa (g2) were isolated and purified from Lytechinus pictus sea urchin embryos at the mesenchyme blastula stage by gel filtration and high pr essure liquid chromatography. Chemical analysis, by gas chromatography , revealed that g580 is highly sulfated and rich in N-acetylglucosamin e, N-acetylgalactosamine, glucuronic acid, and fucose. The g150 fracti on is less acidic than g580 and contains high amounts of amino sugars, xylose, and mannose. The g2 fraction is neutral, rich in N-acetylgluc osamine, mannose, and galactose. The g580 and g150 fractions are resis tant to glycosaminoglycan-degrading enzymes, indicating that they are distinct from the glycosaminoglycans. The g580 fraction resembles, wit h respect to chemical composition, a previously characterized 200 kDa sponge adhesion glycan (g200). The binding of the monoclonal antibody Block 2, which recognizes a repetitive epitope on g200, as well as of the anti-g580 polyclonal antibodies to both g580 and g200 indicated th at these two glycans share similar antigenic determinants. The Fab fra gments of the Block 2 antibody, which previously have been shown to in hibit cell adhesion in sponges, also blocked the reaggregation of diss ociated sea urchin mesenchyme blastula cells. These results indicate t hat g580 carries a carbohydrate epitope, similar to the sponge adhesio n epitope of g200, which is involved in sea urchin embryonal cell adhe sion. (C) 1993 Wiley-Liss, Inc.