Probing Sialic Acid Binding Ig-like Lectins (Siglecs) with Sulfated Oligosaccharides

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Soluble siglecs-1,-4,-5,-6,-7,-8,-9, and-10 were probed with polyacrylamide glycoconjugates in which: 1) the Neu5Ac residue was substituted by a sulfate group (Su); 2) glycoconjugates contained both Su and Neu5Ac; 3) sialoglycoconjugates contained a tyrosine-O-sulfate residue. It was shown that sulfate derivatives of LacNAc did not bind siglecs-1,-4,-5,-6,-7,-8,-9, and-10; binding of 6′-O-Su-LacNAc to siglec-8 was stronger than binding of 3′SiaLacNAc. The relative affinity of 3′-O-Su-TF binding to siglecs-1,-4, and-8 was similar to that of 3′SiaTF. 3′-O-Su-Lec displayed two-fold weaker binding to siglec-1 and siglec-4 than 3′SiaLec. The interaction of soluble siglecs with sulfated oligosaccharides containing sialic acid was also studied. It was shown that siglecs-1,-4,-5,-6,-7,-9, and-10 did not interact with these compounds; binding of 6-O-Su-3′SiaLacNAc and 6-O-Su-3′SiaTF to siglec-8 was weaker than that of the corresponding sulfate-free sialoside probes. Siglec-8 displayed affinity to 6′-O-Su-LacNAc and 6′-O-Su-SiaLex, and defucosylation of the latter compound led to an increase in the binding. Sialoside probes containing tyrosine-O-sulfate residue did not display increased affinity to siglecs-1 and-5 compared with glycoconjugates containing only sialoside. Cell-bound siglecs-1,-5,-7, and-9 did not interact with 6-O-Su-3′SiaLacNAc, whereas the sulfate-free probe 3′SiaLacNAc demonstrated binding. In contrast, the presence of sulfate in 6-O-Su-6′SiaLacNAc did not affect binding of the sialoside probe to siglecs. 6′-O-Su-SiaLex displayed affinity to cell-bound siglecs-1 and-5; its isomer 6-O-Su-SiaLex bound more strongly to siglecs-1,-5, and-9 than SiaLex.

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