title: Saturation transfer difference NMR and computational modeling of a sialoadhesin-sialyl lactose complex.
abstract: The siglecs are a family of I-type lectins binding to sialic acids on the cell surface. Sialoadhesin (siglec-1) is expressed at much higher levels in inflammatory macrophages and specifically binds to alpha-2,3-sialylated N-acetyl lactosamine residues of glycan chains. The terminal disaccharide alpha-D-Neu5Ac-(2-->3)-beta-D-Gal is thought to be the main epitope recognized by sialoadhesin. To understand the basis of this biological recognition reaction we combined NMR experiments with a molecular modeling study. We employed saturation transfer difference (STD) NMR experiments to characterize the binding epitope of alpha-2,3-sialylated lactose, alpha-D-Neu5Ac-(2-->3)-beta-D-Gal-(1-->4)-D-Glc 1 to sialoadhesin at atomic resolution. The experimental results were compared to a computational docking model and to X-ray data of a complex of sialyl lactose and sialoadhesin. The data reveal that sialoadhesin mainly recognizes the N-acetyl neuraminic acid and a small part of the galactose moiety of 1. The crystal structure of a complex of sialoadhesin with sialyl lactose 1 was used as a basis for a modeling study using the FlexiDock algorithm. The model generated was very similar to the original crystal structure. Therefore, the X-ray data were used to predict theoretical STD values utilizing the CORCEMA-STD protocol. The good agreement between experimental and theoretical STD values indicates that a combined modeling/STD NMR approach yields a reliable structural model for the complex of sialoadhesin with alpha-D-Neu5Ac-(2-->3)-beta-D-Gal-(1-->4)-D-Glc 1 in aqueous solution.
authors.affiliation: Institute of Chemistry, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany.
authors.forename: Anirban
authors.initials: A
authors.lastname: Bhunia
authors.forename: V
authors.initials: V
authors.lastname: Jayalakshmi
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Benie
authors.forename: Oliver
authors.initials: O
authors.lastname: Schuster
authors.forename: Sørge
authors.initials: S
authors.lastname: Kelm
authors.forename: N
authors.initials: N
authors.lastname: Rama Krishna
authors.forename: Thomas
authors.initials: T
authors.lastname: Peters
mesh_terms: D002240:Carbohydrate Sequence; D003198:Computer Simulation; D007785:Lactose / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011485:Protein Binding; D011971:Receptors, Immunologic / Q000737:chemistry* / Q000378:metabolism*; D063267:Sialic Acid Binding Ig-like Lectin 1; D012794:Sialic Acids / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D008562:Membrane Glycoproteins; D011971:Receptors, Immunologic; D063267:Sialic Acid Binding Ig-like Lectin 1; D012794:Sialic Acids; C000020:N-acetylneuraminoyllactose; D007785:Lactose