Structure--function studies on selectin carbohydrate ligands. Modifications to fucose, sialic acid and sulphate as a sialic acid replacement

Abstract

The selectins are a family of carbohydrate-binding proteins that have been implicated in the initial interaction between leukocytes and the vascular endothelium. The three members of this family will bind to the sialyl-Lewisx epitope [Sia alpha 2-3 Gal beta 1-4 (Fuc alpha 1-3) GlcNAc] and related oligosaccharides. In this report, we examine the molecular details of that recognition using synthesized carbohydrates with specific modifications on the sialyl-Lewisx epitope. E- and L-Selectin require hydroxyl groups at the 2, 3 and 4 positions of the fucose residue. P-Selectin, however, requires only the 3-position hydroxyl group, while tolerating removal of the oxygen at positions 2 or 4 of fucose residue. Modifications of the glycerol side chain or the N-acetyl group of the sialic acid have little effect on the binding of any of the selectins. All three selectins bind efficiently to an oligosaccharide with a sulphate replacement for the sialic acid [sulpho-Lewisx, or SO4-3Gal beta 1-4 (Fuc alpha 1-3) Glc-ceramide]. For E-Selectin, binding to sulpho-Lewisx appears to be equivalent to binding to sialyl-Lewisx, while for L- and P-Selectin binding to the sulphated structure shows characteristics distinct from sialyl-Lewisx recognition. Taken together, these data indicate that, while all three selectins can recognize sialyl-Lewisx, E-, L- and P-Selectin each display distinct carbohydrate ligand preferences.

L-selectin Interactions with Novel Mono- and Multisulfated Lewisx Sequences in Comparison with the Potent Ligand 3′-Sulfated Lewisa

“…Fourth, the presence of the 3Ј-linked fucose on 6-sulfo,3Ј-sialyl-Le x is essential for Lselectin binding. In accord with this finding is an earlier report that L-selectin binding is abolished by modification of the fucose in the 3Ј-sialyl-Le x sequence by removal of oxygen at position 2, 3, or 5 (18). The presence of the fucose is apparently less critical in the 3Ј-sulfo-Le x sequence as it has been observed that the defucosylated 3Ј-sulfo-Le x tri-and tetrasaccharides are bound by L-selectin, albeit less strongly than the 3Ј-fucosyl analogs (4,5).…”

Binding Specificities of the Sialoadhesin Family of I-type Lectins

“…5). These data are consistent with prior studies on the sensitivity of sialoadhesin and CD22 binding to modifications of the sialic acid residue (6, 33, 46 -48) and contrast with studies on selectins, in which extensive modifications of sialic acids have no effect (12,14,49). In fact, substitution of the entire sialic acid (e.g.…”

“…In certain sialic acid-dependent recognition systems, determinant stringency is low. For example, selectins bind to oligosaccharides bearing truncated sialic acids (12) or appropriately placed anionic groups (sulfates, carboxylic acids) otherwise unrelated to the sialic acid structure (13)(14)(15)(16). In contrast, sialoadhesins appear to have more stringent sialic acid specificities (see "Discussion") (9).…”

Regulation of selectin binding activity by cyclization of sialic acid moiety of carbohydrate ligands on human leukocytes

“…Binding of selectins to de-N-acetyl sialyl 6-sulfo Lewis X was also not unexpected because the amino residue at C-5 position is known not to be intimately involved in interaction with selectin; even KDN-Lewis X, which lacks the amino group at C-5, is known to bind to selectins, almost as equally as genuine sialyl Lewis X does (26,27). L-and P-selectins showed preferential binding to sialyl 6-sulfo Lewis X and de-N-acetyl sialyl 6-sulfo Lewis X rather than to classical sialyl Lewis X whereas E-selectin bound better to classical sialyl Lewis X.…”