Sialyl-Lewis(x) sequence 6-O-sulfated at N-acetylglucosamine rather than at galactose is the preferred ligand for L-selectin and de-N-acetylation of the sialic acid enhances the binding strength.
Oligosaccharide sequences based on sialyl-Lewis(x) with 6-O-sulfation at galactose (6'-sulfo) or at N-acetylglucosamine (6-sulfo) and expressed on high endothelial venules are considered likely endogenous ligands for the leukocyte adhesion molecule, L-selectin. In the course of high performance TLC of three hexaglycosylceramides 6'-sulfo sialyl Lewis(x), 6-sulfo sialyl Lewis(x), and 6',6-bis-sulfo sialyl Lewis(x), synthesized chemically for selectin recognition studies, two minor byproducts were detected and isolated from each parent compound. By liquid secondary ion mass spectrometry these were identified as isomers containing a de-N-acetylated sialic acid or having a modified carboxyl group. Binding experiments with the parent compounds and the non-sulfated sialyl Lewis(x) glycolipid show that 6-sulfation potentiates, whereas 6'-sulfation virtually abolishes L-selectin binding. Thus the hierarchy of binding strengths were 6-sulfo sialyl > sialyl = 6',6-bis-sulfo sialyl >> 6'-sulfo sialyl Lewis(x). Whereas modification of the sialic acid carboxyl group markedly impaired L-selectin binding, de-N-acetylation resulted in enhanced binding. The natural occurrence on high endothelial venules of this 'super-active' de-N-acetylated form of 6-sulfo sialyl Lewis(x), and related structures, now deserves investigation.
Galustian
C
C
Glycosciences Laboratory, Imperial College School of Medicine, Northwick Park Hospital, Harrow, Middx, United Kingdom.
Lawson
A M
AM
Komba
S
S
Ishida
H
H
Kiso
M
M
Feizi
T
T
D000107:Acetylation; D000117:Acetylglucosamine / Q000737:chemistry* / Q000378:metabolism; D002240:Carbohydrate Sequence; D002518:Ceramides / Q000737:chemistry / Q000378:metabolism; D004730:Endothelium, Vascular / Q000737:chemistry; D005690:Galactose / Q000737:chemistry* / Q000378:metabolism; D019041:L-Selectin / Q000378:metabolism*; D008024:Ligands; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid / Q000737:chemistry* / Q000378:metabolism; D009844:Oligosaccharides / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D000080506:Sialyl Lewis X Antigen; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism
D002518:Ceramides; D008024:Ligands; D009844:Oligosaccharides; D011994:Recombinant Proteins; D000080506:Sialyl Lewis X Antigen; D013431:Sulfates; D019041:L-Selectin; D019158:N-Acetylneuraminic Acid; D000117:Acetylglucosamine; D005690:Galactose