L-Selectin−Carbohydrate Interactions: Relevant Modifications of the Lewis x Trisaccharide

Publisher Website
Google Scholar
Abstract
Protein−carbohydrate interactions are known to mediate cell−cell recognition and adhesion events. Specifically, three carbohydrate binding proteins termed selectins (E-, P-, and L-selectin) have been shown to be essential for leukocyte rolling along the vascular endothelium, the first step in the recruitment of leukocytes from the blood into inflammatory sites or into secondary lymphoid organs. Although this phenomenon is well-established, little is known about the molecular-level interactions on which it depends. All three selectins recognize sulfated and sialylated derivatives of the Lewis x [Lex: Galβ1→4(Fucα1→3)GlcNAc] and Lewis a [Lea: Galβ1→3(Fucα1→4)GlcNAc] trisaccharide cores with affinities in the millimolar range, and it is believed that variants of these structures are the carbohydrate determinants of selectin recognition. Recently it was shown that the mucin GlyCAM-1, a secreted physiological ligand for L-selectin, is capped with sulfated derivatives of sialyl Lewis x [sLex: Siaα2→3Galβ1→4(Fucα1→3)GlcNAc] and that sulfation is required for the high-affinity interaction between GlyCAM-1 and L-selectin. To elucidate the important sites of sulfation on Lex with respect to L-selectin recognition, we have synthesized six sulfated Lex analogs and determined their abilities to block binding of a recombinant L-selectin−Ig chimera to immobilized GlyCAM-1. Our results suggest that 6-sulfo sLex binds to L-selectin with higher affinity than does sLex or 6‘-sulfo sLex and that sulfation of sLex capping groups on GlyCAM-1 at the 6-position is important for L-selectin recognition.