L-SELECTIN-CARBOHYDRATE INTERACTIONS - RELEVANT MODIFICATIONS OF THE LEWIS-X TRISACCHARIDE

Protein-carbohydrate interactions are known to mediate cell-cell recog nition and adhesion events. Specifically, three carbohydrate binding p roteins termed selectins (E-, P-, and L-selectin) have been shown to b e essential for leukocyte rolling along the vascular endothelium, the first step in the recruitment of leukocytes from the blood into inflam matory sites or into secondary lymphoid organs. Although this phenomen on is well-established, little is known about the molecular-level inte ractions on which it depends. All three selectins recognize sulfated a nd sialylated derivatives of the Lewis x [Le(x): Gal beta 1-->4(Fuc al pha 1-->3)GlcNAc] and Lewis a [Le(a): Gal beta 1-->3(Fuc alpha 1-->4)G lcNAc] trisaccharide cores with affinities in the millimolar range, an d it is believed that variants of these structures are the carbohydrat e determinants of selectin recognition. Recently it was shown that the mucin GlyCAM-1, a secreted physiological ligand for L-selectin, is ca pped with sulfated derivatives of sialyl Lewis x [sLe(x): Sia alpha 2- ->3Gal beta 1--4(Fuc alpha 1-->3)GlcNAc] and that sulfation is require d for the high-affinity interaction between GlyCAM-1 and L-selectin. T o elucidate the important sites of sulfation on Le(x) with respect to L-selectin recognition, we have synthesized six sulfated Le(x) analogs and determined their abilities to block binding of a recombinant L-se lectLn-Ig chimera to immobilized GlyCAM-1. Our results suggest that 6- sulfo sLe(x) binds to L-selectin with higher affinity than does sLe(x) or 6'-sulfo sLe(x) and that sulfation of sLe(x) capping groups on Gly CAM-1 at the 6-position is important for L-selectin recognition.