A liquid‐phase binding analysis for L‐selectin: A strong dependency on highly clustered sulfate groups

L‐selectin, together with E‐ and P‐selectins, forms a newer group of cell adhesion molecules which are believed to interact with carbohydrate ligands [Lasky, L. A., Singer, M. S., Yednoch, T. A., Dowbenko, D., Fennie, C., Rodriguez, H., Nguyen, T., Stachel, S. & Rosen, S. D. (1989) Cell 56, 1045–1055]. Using radiolabeled fucoidan as a reference ligand, we have developed a new liquid‐phase microcentrifugation assay where fine differences in binding affinity can be compared accurately. We found that glucan sulfates strongly inhibited the binding of fucoidan by murine L‐selectin‐IgG chimera. The efficacy of inhibition is extremely dependent on the size (up to 12 kDa) and the sulfate density (up to two sulfate groups/glucose molecule) of the glucan sulfates. The nature of the inter‐glucose linkages is also important. These data suggest that the binding by L‐selectin prefers certain clustering and proper spatial arrangement of the anionic groups.