Structural analysis of the human galectin-9 N-terminal carbohydrate recognition domain reveals unexpected properties that differ from the mouse orthologue

J Mol Biol. 2008 Jan 4;375(1):119-35. doi: 10.1016/j.jmb.2007.09.060. Epub 2007 Sep 26.


Galectins are a family of beta-galactoside-binding lectins that contain a conserved carbohydrate recognition domain (CRD). They exhibit high affinities for small beta-galactosides as well as variable binding specificities for complex glycoconjugates. Structural and biochemical analyses of the mechanism governing specific carbohydrate recognition provide a useful template to elucidate the function of these proteins. Here we report the crystal structures of the human galectin-9 N-terminal CRD (NCRD) in the presence of lactose and Forssman pentasaccharide. Mouse galectin-9 NCRD, the structure of which was previously solved by our group, forms a non-canonical dimer in both the crystal state and in solution. Human galectin-9 NCRD, however, exists as a monomer in crystals, despite a high sequence identity to the mouse homologue. Comparative frontal affinity chromatography analysis of the mouse and human galectin-9 NCRDs revealed different carbohydrate binding specificities, with disparate affinities for complex glycoconjugates. Human galectin-9 NCRD exhibited a high affinity for Forssman pentasaccharide; the association constant for mouse galectin-9 NCRD was 100-fold less than that observed for the human protein. The combination of structural data with mutational studies demonstrated that non-conserved amino acid residues on the concave surface were important for determination of target specificities. The human galectin-9 NCRD exhibited greater inhibition of cell proliferation than the mouse NCRD. We discuss the biochemical and structural differences between highly homologous proteins from different species.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Animals
  • Binding Sites
  • Carbohydrate Sequence
  • Carbohydrates / chemistry*
  • Carbohydrates / pharmacology
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Conserved Sequence
  • Dose-Response Relationship, Drug
  • Galectins / chemistry*
  • Galectins / genetics
  • Galectins / metabolism
  • Glutathione Transferase / metabolism
  • Humans
  • Jurkat Cells
  • Lymphoma, B-Cell / pathology
  • Mice
  • Models, Chemical
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Conformation
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Valine / metabolism


  • Carbohydrates
  • Galectins
  • LGALS9 protein, human
  • Recombinant Fusion Proteins
  • galectin 9, mouse
  • Glutathione Transferase
  • Valine

Associated data

  • PDB/2EAK
  • PDB/2EAL