title: Isolectins I-A and I-B of Griffonia (Bandeiraea) simplicifolia. Crystal structure of metal-free GS I-B(4) and molecular basis for metal binding and monosaccharide specificity.
abstract: Seeds from the African legume shrub Griffonia simplicifolia contain several lectins. Among them the tetrameric lectin GS I-B(4) has strict specificity for terminal alpha Gal residues, whereas the closely related lectin GS I-A(4) can also bind to alpha GalNAc. These two lectins are commonly used as markers in histology or for research in xenotransplantation. To elucidate the basis for the fine difference in specificity, the amino acid sequences of both lectins have been determined and show 89% identity. The crystal structure of GS I-B(4), determined at 2.5-A resolution, reveals a new quaternary structure that has never been observed in other legume lectins. An unexpected loss of both Ca(2+) and Mn(2+) ions, which are necessary for carbohydrate binding in legume lectins, may be related to a particular amino acid sequence Pro-Glu-Pro in the metal binding loop. Comparison with demetallized concanavalin A reveals a different process for the loss of metal ions and for the subsequent loss of carbohydrate binding activity. The GS I-A x alpha GalNAc and GS I-B x alpha Gal complexes were constructed using homology modeling and docking approaches. The unusual presence of an aromatic amino acid at position 47 (Tyr in I-A and Trp in I-B) explains the strong preference for alpha-anomeric sugars in both isolectins. Alteration at one amino acid position, Ala(106) in I-A versus Glu(106) in I-B, is the basis for the observed specificities toward alpha GalNAc and alpha Gal.
authors.affiliation: Centre de Recherches sur les Macromolécules Végétales, CNRS, Université Joseph Fourier, BP 53, F-38041 Grenoble cedex 09, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Lescar
authors.forename: Remy
authors.initials: R
authors.lastname: Loris
authors.forename: Edward
authors.initials: E
authors.lastname: Mitchell
authors.forename: Catherine
authors.initials: C
authors.lastname: Gautier
authors.forename: Valérie
authors.initials: V
authors.lastname: Chazalet
authors.forename: Veronica
authors.initials: V
authors.lastname: Cox
authors.forename: Lode
authors.initials: L
authors.lastname: Wyns
authors.forename: Serge
authors.initials: S
authors.lastname: Pérez
authors.forename: Christelle
authors.initials: C
authors.lastname: Breton
authors.forename: Anne
authors.initials: A
authors.lastname: Imberty
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D037102:Lectins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008670:Metals / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D037121:Plant Lectins; D016133:Polymerase Chain Reaction; D020836:Protein Structure, Quaternary; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019685:Rosales / Q000737:chemistry*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D037102:Lectins; D008670:Metals; D037121:Plant Lectins