title: Structural characterization of human galectin-4 C-terminal domain: elucidating the molecular basis for recognition of glycosphingolipids, sulfated saccharides and blood group antigens.
abstract: Human galectin-4 is a lectin that is expressed mainly in the gastrointestinal tract and exhibits metastasis-promoting roles in some cancers. Its tandem-repeat nature exhibits two distinct carbohydrate recognition domains allowing crosslinking by simultaneous binding to sulfated and non-sulfated (but not sialylated) glycosphingolipids and glycoproteins, facilitating stabilization of lipid rafts. Critically, galectin-4 exerts favourable or unfavourable effects depending upon the cancer. Here we report the first X-ray crystallographic structural information on human galectin-4, specifically the C-terminal carbohydrate recognition domain of human (galectin-4C) in complex with lactose, lactose-3'-sulfate, 2'-fucosyllactose, lacto-N-tetraose and lacto-N-neotetraose. These structures enable elucidation of galectin-4C binding fine-specificity towards sulfated and non-sulfated lacto- and neolacto-series sphingolipids as well as to human blood group antigens. Analysis of the lactose-3'-sulfate complex structure shows that galectin-4C does not recognize the sulfate group using any specific amino acid, but binds the ligand nonetheless. Complex structures with lacto-N-tetraose and lacto-N-neotetraose displayed differences in binding interactions exhibited by the non-reducing-end galactose. That of lacto-N-tetraose points outward from the protein surface whereas that of lacto-N-neotetraose interacts directly with the protein. Recognition patterns of human galectin-4C towards lacto- and neolacto-series glycosphingolipids are similar to those of human galectin-3; however, detailed scrutiny revealed differences stemming from the extended binding site that offer distinction in ligand profiles of these two galectins. Structural characterization of the complex with 2'-fucosyllactose, a carbohydrate with similarity to the H antigen, and molecular dynamics studies highlight structural features that allow specific recognition of A and B antigens, whilst a lack of interaction with the 2'-fucose of blood group antigens was revealed.
  4YLZ, 4YM0, 4YM1, 4YM2, 4YM3.
authors.affiliation: Institute for Glycomics, Griffith University, Australia.
authors.forename: Khuchtumur
authors.initials: K
authors.lastname: Bum-Erdene
authors.affiliation: Section MIG, Department of Laboratory Medicine, Lund University, Sweden.
authors.forename: Hakon
authors.initials: H
authors.lastname: Leffler
authors.affiliation: Centre for Analysis and Synthesis, Department of Chemistry, Lund University, Sweden.
authors.forename: Ulf J
authors.initials: UJ
authors.lastname: Nilsson
authors.affiliation: Institute for Glycomics, Griffith University, Australia.
authors.forename: Helen
authors.initials: H
authors.lastname: Blanchard
mesh_terms: D001665:Binding Sites; D001789:Blood Group Antigens / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D037541:Galectin 4 / Q000737:chemistry* / Q000235:genetics; D015870:Gene Expression; D006023:Glycoproteins / Q000737:chemistry*; D006028:Glycosphingolipids / Q000737:chemistry*; D006801:Humans; D006860:Hydrogen Bonding; D007785:Lactose / Q000031:analogs & derivatives / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D009844:Oligosaccharides / Q000737:chemistry; D011485:Protein Binding; D017510:Protein Folding; D054730:Protein Interaction Domains and Motifs; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D013463:Sulfuric Acid Esters / Q000737:chemistry; D013816:Thermodynamics; D014312:Trisaccharides / Q000737:chemistry
chemical_list: D001789:Blood Group Antigens; D037541:Galectin 4; D006023:Glycoproteins; D006028:Glycosphingolipids; D009844:Oligosaccharides; D011994:Recombinant Proteins; D013463:Sulfuric Acid Esters; D014312:Trisaccharides; C122022:lactose 3'-sulfate; C013084:lacto-N-neotetraose; D007785:Lactose; C031420:2'-fucosyllactose
keywords: blood group antigen; crystal structure; galectin-4; glycosphingolipid; oligosaccharide