Subsets of sialylated, sulfated mucins of diverse origins are recognized by L-selectin. Lack of evidence for unique oligosaccharide sequences mediating binding.
Previous studies have shown that the mucin-type polypeptides GlyCAM-1, CD34, and MAdCAM-1 can function as ligands for L-selectin only when they are synthesized by the specialized high-endothelial venules (HEV) of lymph modes. Since sialylation, sulfation, and possibly fucosylation are required for generating recognition, we reasoned that other mucins known to have such components might also bind L-selectin. We show here that soluble mucins secreted by human colon carcinoma cells, as well as those derived from human bronchial mucus can bind to human L-selectin in a calcium-dependent manner. As with Gly-CAM-1 synthesized by lymph node HEV, alpha 2-3 linked sialic acids and sulfation seem to play a critical role in generating this L-selectin binding. In each case, only a subset of the mucin molecules is recognized by L-selectin. Binding is not destroyed by boiling, suggesting that recognition may be based primarily upon carbohydrate structures. Despite this, O-linked oligosaccharide chains released from these ligands by beta-elimination do not show any detectable binding to L-selectin. Following protease treatment of the ligands, binding persists in a subset of the resulting fragments, indicating that specific recognition is determined by certain regions of the original mucins. However, O-linked oligosaccharides released from the subset of non-binding mucin fragments do not show very different size and charge profiles compared to those that do bind. Furthermore, studies with polylactosamine-degrading endoglycosidases suggest that the core structures involved in generating binding can vary among the different ligands. Taken together, these data indicate that a single unique oligosaccharide structure may not be responsible for high-affinity binding. Rather, diverse mucins with sialylated, sulfated, fucosylated lactosamine-type O-linked oligosaccharides can generate high-affinity L-selectin ligands, but only when they present these chains in unique spacing and/or clustered combinations, presumably dictated by the polypeptide backbone.
Crottet
P
P
UCSD Cancer Center, La Jolla, 92093, USA.
Kim
Y J
YJ
Varki
A
A
D000606:Amino Sugars / Q000378:metabolism; D001980:Bronchi / Q000378:metabolism; D002240:Carbohydrate Sequence; D002460:Cell Line; D003110:Colonic Neoplasms / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D019041:L-Selectin / Q000378:metabolism*; D008969:Molecular Sequence Data; D009077:Mucins / Q000737:chemistry / Q000378:metabolism*; D009093:Mucus / Q000378:metabolism; D019158:N-Acetylneuraminic Acid; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D012794:Sialic Acids / Q000378:metabolism
D000606:Amino Sugars; D009077:Mucins; D009844:Oligosaccharides; D011134:Polysaccharides; D012794:Sialic Acids; C066929:polylactosamine; D019041:L-Selectin; D006026:Glycoside Hydrolases; D019158:N-Acetylneuraminic Acid