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The sialoadhesins are a distinct subgroup of the immunoglobulin superfamily, comprising sialoadhesin, CD22, the myelin-associated glycoprotein, and CD33. They can all mediate sialic acid-dependent binding to cells with distinct specificities. Sialoadhesin is a murine macrophage-restricted cell-surface molecule with 17 extracellular immunoglobulin-like domains that recognizes NeuAc alpha 2-3Gal in N- and O-glycans and interacts preferentially with cells of the granulocytic lineage. Its sialic acid-binding site is located within the NH2-terminal (membrane-distal) V-set domain. Here we have carried out site-directed mutagenesis in an attempt to identify the binding site of sialoadhesin. A subset of nonconservative mutations disrupted sialic acid-dependent binding without affecting binding of three monoclonal antibodies directed to two distinct epitopes of sialoadhesin. A CD8 alpha-based molecular model predicts that these residues form a contiguous binding site on the GFCC'C" beta-sheet of the V-set domain centered around an arginine in the F strand. A conservative mutation of this arginine to lysine also abolished binding. This amino acid is conserved among all members of the sialoadhesin family and is therefore likely to be a key residue in mediating sialic acid-dependent binding of sialoadhesins to cells.

Type

Journal article

Journal

J Biol Chem

Publication Date

19/04/1996

Volume

271

Pages

9267 - 9272

Keywords

Amino Acid Sequence, Animals, Antibodies, Monoclonal, Antigens, CD8, Arginine, Binding Sites, Carbohydrate Conformation, Carbohydrate Sequence, Cell Adhesion Molecules, Cell Line, Conserved Sequence, Epitopes, Erythrocytes, Humans, Membrane Glycoproteins, Mice, Models, Structural, Molecular Sequence Data, Mutagenesis, Site-Directed, Point Mutation, Polymerase Chain Reaction, Polysaccharides, Protein Structure, Secondary, Receptors, Immunologic, Recombinant Proteins, Sequence Homology, Amino Acid, Sialic Acid Binding Ig-like Lectin 1, Sialic Acids, Transfection