A small region of the natural killer cell receptor, Siglec-7, is responsible for its preferred binding to alpha 2,8-disialyl and branched alpha 2,6-sialyl residues. A comparison with Siglec-9.
Siglec-7 is a sialic acid-binding lectin recently identified as an inhibitory receptor on natural killer cells. Here we characterize the sugar-binding specificity of Siglec-7 expressed on Chinese hamster ovary cells using polyvalent streptavidin-based glyco-probes. Glyco-probes carrying unique oligosaccharide structures such as GD3 (NeuAc alpha 2,8NeuAc alpha 2,3Gal beta 1,4Glc) and LSTb (Gal beta 1,3[NeuAc alpha 2,6]GlcNAc beta 1,3Gal beta 1,4Glc) oligosaccharides bound to Siglec-7 better than those carrying LSTc (NeuAc alpha 2,6Gal beta 1,4GlcNAc beta 1,3Gal beta 1,4Glc) or GD1a (NeuAc alpha 2,3Gal beta 1,3GalNAc beta 1,4[NeuAc alpha 2,3]Gal beta 1,4Glc) oligosaccharides. In contrast, Siglec-9, which is 84% identical to Siglec-7, did not bind to the GD3 and LSTb probes but did bind to the LSTc and GD1a probes. To identify a region(s) responsible for their difference in binding specificity, we prepared a series of V-set domain chimeras between Siglecs-7 and -9. Substitution of a small region, Asn(70)-Lys(75), of Siglec-7 with the equivalent region of Siglec-9 resulted in loss of Siglec-7-like binding specificity and acquisition of Siglec-9-like binding properties. In comparison, a Siglec-9-based chimera, which contains Asn(70)-Lys(75) with additional amino acids derived from Siglec-7, exhibited Siglec-7-like specificity. These results, combined with molecular modeling, suggest that the C-C' loop in the sugar-binding domain plays a major role in determining the binding specificities of Siglecs-7 and -9.
Yamaji
Toshiyuki
T
Glyco-chain Functions Laboratory, Supra-biomolecular System Group, Frontier Research System, RIKEN Institute, Saitama 351-0198, Japan.
Teranishi
Takane
T
Alphey
Magnus S
MS
Crocker
Paul R
PR
Hashimoto
Yasuhiro
Y
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism*; D016466:CHO Cells; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D006224:Cricetinae; D005732:Gangliosides / Q000378:metabolism; D006801:Humans; D037102:Lectins / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; D012794:Sialic Acids / Q000378:metabolism*; D013379:Substrate Specificity; D014162:Transfection
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D005732:Gangliosides; D037102:Lectins; D009844:Oligosaccharides; D011994:Recombinant Proteins; C402206:SIGLEC7 protein, human; C412227:SIGLEC9 protein, human; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; D012794:Sialic Acids