Visualization of sialyl LewisX glycosphingolipid microdomains in model membranes as selectin recognition motifs using a fluorescence label

Selectin-induced leukocyte rolling along the endothelial surface is an essential step in the cellular immune response. For efficient recognition, the relevant carbohydrate epitope sialyl LewisX (sLeX; α-Neup5Ac-(2→3)-β-Galp-(1→4)-[α-Fucp-(1→3)]GlcpNAc) has to be arranged in clusters. We describe the synthesis of the sLeX-glycosphingolipid (sLeX-GSL) with a NBD fluorescence label in the tail region, which allows the direct visualization of sLeX-GSL microdomains to very low concentrations (0.01 mol %) in various planar phosphocholine matrices by fluorescence microscopy. Cell rolling experiments of E-selectin expressing cells along these membranes confirmed that the fluorescence analog behaves similar to the naturally occuring sLeX-GSL. This is direct evidence for recent hypotheses on multivalent sLeX binding as molecular basis for selectin-mediated cell rolling.

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