IDENTIFICATION OF THE SULFATED MONOSACCHARIDES OF GLYCAM-1, AN ENDOTHELIAL-DERIVED LIGAND FOR L-SELECTIN

L-Selectin, a receptor bearing a C-type lectin domain, mediates the initial attachment of lymphocytes to high endothelial venules of lymph nodes. One of the endothelial-derived ligands for L-selectin is GlyCAM-1 (previously known as Sgp50), a mucin-like glycoprotein with sulfated, sialylated, and fucosylated O-linked oligosaccharide chains. Sialylation, sulfation, and fucosylation appear to be required for the avid interaction of this ligand with L-selectin, but the exact carbohydrate structures involved in recognition remain undefined. In this study, we examine the nature of the sulfate-modified carbohydrates of GlyCAM-1. GlyCAM-1 was metabolically labeled in lymph node organ culture with (SO4)-S-35 and a panel of tritiated carbohydrate precursors. Mild hydrolysis conditions were established that released sulfated oligosaccharides without cleavage of sulfate esters. Low molecular weight and singly charged fragments, obtained by a combination of gel filtration and anion-exchange chromatography, were analyzed. The structural identification of the fragments relied on the use of a variety of radiolabeled sugar precursors, further chemical and enzymatic hydrolysis, and high-pH anion-exchange chromatography analysis. Sulfated constituents of GlyCAM-1 were identified as Gal-6-SO4, GlcNAc-6-SO4, (SO4-6)Gal beta 1-->4GlcNAc, and Gal beta 1-->4(SO4-6)GlcNAc. In the accompanying paper [Hemmerich, S., and Rosen, S.D. (1994) Biochemistry 33, 4830-4835] evidence is presented that (SO4-6)Gal beta 1-->4GlcNAc forms the core of a sulfated sialyl Lewis x structure that may comprise a recognition determinant on GlyCAM-1.