CRYSTAL-STRUCTURE OF THE N-TERMINAL DOMAIN OF SIALOADHESIN IN COMPLEXWITH 3'-SIALYLLACTOSE AT 1.85 ANGSTROM RESOLUTION

The structure of the functional N-terminal domain from the extracellul ar region of the cell surface receptor sialoadhesin has been determine d in complex with the oligosaccharide 3' sialyllactose. This provides structural information for the siglec family of proteins. The structur e conforms to the V-set immunoglobulin-like fold but contains several distinctive features, including an intra-beta sheet disulphide and a s plitting of the standard beta strand G into two shorter strands. These novel features appear important in adapting the V-set fold for sialic acid-mediated recognition. Analysis of the complex with 3' sialyllact ose highlights three residues, conserved throughout the siglec family, as key features of the sialic acid-binding template. The complex is r epresentative of the functional recognition interaction with carbohydr ate and as such provides detailed information for a heterotypic cell a dhesion interaction.