Carbohydrate binding, quaternary structure and a novel hydrophobic binding site in two legume lectin oligomers fromDolichos biflorus1 (original) (raw)
Related papers
Journal of Molecular Biology, 1999
The seed lectin (DBL) from the leguminous plant Dolichos bi¯orus has a unique speci®city among the members of the legume lectin family because of its high preference for GalNAc over Gal. In addition, precipitation of blood group A H substance by DBL is slightly better inhibited by a blood group A trisaccharide (GalNAc(a1-3)[Fuc(a1-2)]Gal) containing pentasaccharide, and about 40 times better by the Forssman disaccharide (GalNAc(a1-3)GalNAc) than by GalNAc. We report the crystal structures of the DBL-blood group A trisaccharide complex and the DBL-Forssman disaccharide complex.
Novel structures of plant lectins and their complexes with carbohydrates
Current Opinion in Structural Biology, 1999
Several novel structures of legume lectins have led to a thorough understanding of monosaccharide and oligosaccharide specificity, to the determination of novel and surprising quaternary structures and, most importantly, to the structural identification of the binding site for adenine and plant hormones. This deepening of our understanding of the structure/function relationships among the legume lectins is paralleled by advances in two other plant lectin families — the monocot lectins and the jacalin family. As the number of available crystal structures increases, more parallels between plant and animal lectins become apparent.
Structural Features of the Legume Lectins
The legume lectins are a family of carbohydrate binding proteins found in the Leguminosae plants and are used as a model system for studying protein-carbohydrate interactions. The different legume lectins show a remarkable range of sugar specificities, despite the high sequential and structural similarity of their subunits. Moreover, their subunits can associate into a number of different multimers. The unique variability of quaternary structure has implications for the formation of cross-linked lattices and binding of hydrophobic ligands.
Journal of Molecular Biology, 2001
The legume lectins are widely used as a model system for studying protein-carbohydrate and protein-protein interactions. They exhibit a fascinating quaternary structure variation, which becomes important when they interact with multivalent glycoconjugates, for instance those on cell surfaces. Recently, it has become clear that certain lectins form weakly associated oligomers. This phenomenon may play a role in the regulation of receptor crosslinking and subsequent signal transduction. The crystal structure of DB58, a dimeric lectin from the legume Dolichos bi¯orus reveals a separate dimer of a previously unobserved type, in addition to a tetramer consisting of two such dimers. This tetramer resembles that formed by DBL, the seed lectin from the same plant. A single amino acid substitution in DB58 affects the conformation and¯exibility of a loop in the canonical dimer interface. This disrupts the formation of a stable DBL-like tetramer in solution, but does not prohibit its formation in suitable conditions, which greatly increases the possibilities for the crosslinking of multivalent ligands. The non-canonical DB58 dimer has a buried symmetrical a helix, which can be present in the crystal in either of two antiparallel orientations. Two existing structures and datasets for lectins with similar quaternary structures were reconsidered. A central a helix could be observed in the soybean lectin, but not in the leucoagglutinating lectin from Phaseolus vulgaris. The relative position and orientation of the carbohydrate-binding sites in the DB58 dimer may affect its ability to crosslink mulitivalent ligands, compared to the other legume lectin dimers.
Journal of Molecular Biology, 2001
The legume lectins are widely used as a model system for studying protein-carbohydrate and protein-protein interactions. They exhibit a fascinating quaternary structure variation, which becomes important when they interact with multivalent glycoconjugates, for instance those on cell surfaces. Recently, it has become clear that certain lectins form weakly associated oligomers. This phenomenon may play a role in the regulation of receptor crosslinking and subsequent signal transduction. The crystal structure of DB58, a dimeric lectin from the legume Dolichos bi¯orus reveals a separate dimer of a previously unobserved type, in addition to a tetramer consisting of two such dimers. This tetramer resembles that formed by DBL, the seed lectin from the same plant. A single amino acid substitution in DB58 affects the conformation and¯exibility of a loop in the canonical dimer interface. This disrupts the formation of a stable DBL-like tetramer in solution, but does not prohibit its formation in suitable conditions, which greatly increases the possibilities for the crosslinking of multivalent ligands. The non-canonical DB58 dimer has a buried symmetrical a helix, which can be present in the crystal in either of two antiparallel orientations. Two existing structures and datasets for lectins with similar quaternary structures were reconsidered. A central a helix could be observed in the soybean lectin, but not in the leucoagglutinating lectin from Phaseolus vulgaris. The relative position and orientation of the carbohydrate-binding sites in the DB58 dimer may affect its ability to crosslink mulitivalent ligands, compared to the other legume lectin dimers.
Biochimica Et Biophysica Acta-protein Structure and Molecular Enzymology, 1998
The legume lectins are a large family of homologous carbohydrate binding proteins that are found mainly in the seeds of most legume plants. Despite their strong similarity on the level of their amino acid sequences and tertiary structures, their carbohydrate specificities and quaternary structures vary widely. In this review we will focus on the structural features of legume lectins and their complexes with carbohydrates. These will be discussed in the light of recent mutagenesis results when appropriate. Monosaccharide specificity seems to be achieved by the use of a conserved core of residues that hydrogen bond to the sugar, and a variable loop that determines the exact shape of the monosaccharide binding site. The higher affinity for particular oligosaccharides and monosaccharides containing a hydrophobic aglycon results mainly from a few distinct subsites next to the monosaccharide binding site. These subsites consist of a small number of variable residues and are found in both the mannose and galactose specificity groups. The quaternary structures of these proteins form the basis of a higher level of specificity, where the spacing between individual epitopes of multivalent carbohydrates becomes important. This results in homogeneous cross-linked lattices even in mixed precipitation systems, and is of relevance for their effects on the biological activities of cells such as mitogenic responses. Quaternary structure is also thought to play an important role in the high affinity interaction between some legume lectins and adenine and a series of adenine-derived plant hormones. The molecular basis of the variation in quaternary structure in this group of proteins is poorly understood. q 1997 Elsevier Science B.V.
Identification of a new quaternary association for legume lectins
Journal of Structural Biology, 2008
Lotus tetragonolobus lectin (LTA) is a fucose-specific legume lectin. Although several studies report a diverse combination of biological activities for LTA, little is known about the mechanisms involved in L-fucosyl oligosaccharide recognition. The crystal structure of LTA at 2.0 Å resolution reveals a different legume lectin tetramer. Its structure consists of a homotetramer composed of two back-to-back GS4-like dimers arranged in a new mode, resulting in a novel tetramer. The LTA N-linked carbohydrate at Asn4 and the unusual LTA dimer-dimer interaction are related to its particular mode of tetramerization. In addition, we used small angle X-ray scattering to investigate the quaternary structure of LTA in solution and to compare it to the crystalline structure. Although the crystal structure of LTA has revealed a conserved metal-binding site, its L-fucose-binding site presents some punctual differences. Our investigation of the new tetramer of LTA and its fucose-binding site is essential for further studies related to cross-linking between LTA and complex divalent L-fucosyl carbohydrates.
Journal of Molecular Biology, 1997
Recognition of cell-surface carbohydrates by lectins has wide implications in important biological processes. The ability of plant lectins to detect subtle variations in carbohydrate structures found on molecules, cells and organisms have made them a paradigm for protein-carbohydrate recognition. Legume lectins, one of the most well studied family of plant proteins, display a considerable repertoire of carbohydrate speci®cities owing perhaps to the sequence hypervariability in the loops constituting their combining site. However, lack of a rigorous framework to explain their carbohydrate binding speci®cities has precluded a rational approach to alter their ligand binding activity in a meaningful manner. This study reports an extensive analysis of sequences and structures of several legume lectins and shows that despite the hypervariability of their combining regions they exhibit within a signi®cant pattern of uniformity. The results show that the size of the binding site loop D is invariant in the Man/Glc speci®c lectins and is possibly a primary determinant of the monosaccharide speci®cities of the legume lectins. Analyses of size and sequence variability of loops reveal the existence of a common theme that subserves to de®ne their binding speci®cities. These results thus provide not only a framework for understanding the molecular basis of carbohydrate recognition by legume lectins but also a rationale for redesign of their ligand binding propensities.
Journal of Molecular Biology, 1997
Recognition of cell-surface carbohydrates by lectins has wide implications in important biological processes. The ability of plant lectins to detect subtle variations in carbohydrate structures found on molecules, cells and organisms have made them a paradigm for protein-carbohydrate recognition. Legume lectins, one of the most well studied family of plant proteins, display a considerable repertoire of carbohydrate speci®cities owing perhaps to the sequence hypervariability in the loops constituting their combining site. However, lack of a rigorous framework to explain their carbohydrate binding speci®cities has precluded a rational approach to alter their ligand binding activity in a meaningful manner. This study reports an extensive analysis of sequences and structures of several legume lectins and shows that despite the hypervariability of their combining regions they exhibit within a signi®cant pattern of uniformity. The results show that the size of the binding site loop D is invariant in the Man/Glc speci®c lectins and is possibly a primary determinant of the monosaccharide speci®cities of the legume lectins. Analyses of size and sequence variability of loops reveal the existence of a common theme that subserves to de®ne their binding speci®cities. These results thus provide not only a framework for understanding the molecular basis of carbohydrate recognition by legume lectins but also a rationale for redesign of their ligand binding propensities.
Journal of Biological Chemistry, 1984
The location and amino acid sequence surrounding a cysteine residue required for carbohydrate binding in the lima bean lectin (LBL) was determined. Following selective conversion of the sulfhydryl group to its Scyano derivative, LBL was cleaved at the essential cysteine residue to give two fragments, estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in two buffer systems to have molecular masses of 16.5-19 kDa and 10.5-11 kDa. The larger fragment, which contained the glycosyl moiety of the lectin, was shown by sequence analysis to contain the NH2terminal sequence of LBL. The smaller COOH-terminal fragment was found to contain the cysteine residue involved in the intersubunit disulfide bond of LBL. Digestion of LBL with pepsin and trypsin yielded four peptides containing the essential cysteine. Sequencing of the three major peptides gave a single concensus sequence, Val-Glu-Phe-Asp-Thr-Cys-His-Asn-Leu-Asp-, for the primary sequence surrounding the cysteine. The peptide sequence and site of cyanylation cleavage were used to predict alignment of the LBL peptide with the primary sequence of concanavalin A. Maximum homology was found with a sequence in concanavalin A beginning at valine 7. Implications of this alignment to the function of the cysteine in carbohydrate and metal ion binding of LBL, and for conservation of carbohydrate binding site residues in legume lectins are discussed. LBL' specifically binds glycoconjugates containing terminal nonreducing aD -GalNAc residues (1-3). In addition, sites were identified which bind Ca2+ and Mn2+ (3-5) and a variety of nonpolar ligands (6). Occupation of the divalent cation sites is required for Carbohydrate binding (3,4). LBL subunits contain two cysteine residues, one of which forms an intersubunit disulfide bond (7). The carbohydrate binding activity *This work was part of a dissertation submitted by D.D.R. in partial fulfillment of the requirements for the Doctor of Philosophy in the Horace H. Rackham School of Graduate Studies a t the University of Michigan. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.