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.

TitleIsolectins 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.
Publication TypeJournal Article
Year of Publication2002
AuthorsLescar, J., R. Loris, E. Mitchell, C. Gautier, V. Chazalet, V. Cox, L. Wyns, S. PĂ©rez, C. Breton, and A. Imberty
JournalJ Biol Chem
Volume277
Issue8
Pagination6608-14
Date Published2002 Feb 22
ISSN0021-9258
KeywordsAmino Acid Sequence, Binding Sites, Cloning, Molecular, Crystallography, X-Ray, Lectins, Metals, Models, Molecular, Molecular Sequence Data, Plant Lectins, Polymerase Chain Reaction, Protein Structure, Quaternary, Reverse Transcriptase Polymerase Chain Reaction, Rosales, Sequence Alignment, Sequence Homology, Amino Acid
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.

DOI10.1074/jbc.M109867200
Alternate JournalJ. Biol. Chem.
PubMed ID11714720