Multiplicity of carbohydrate-binding sites in β-prism fold lectins: occurrence and possible evolutionary implications (original) (raw)
Related papers
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.
Plant lectins and their many roles: Carbohydrate-binding and beyond
Journal of Plant Physiology, 2021
Lectins are ubiquitous proteins that reversibly bind to specific carbohydrates and, thus, serve as readers of the sugar code. In photosynthetic organisms, lectin family proteins play important roles in capturing and releasing photosynthates via an endogenous lectin cycle. Often, lectin proteins consist of one or more lectin domains in combination with other types of domains. This structural diversity of lectins is the basis for their current classification, which is consistent with their diverse functions in cell signaling associated with growth and development, as well as in the plant's response to biotic, symbiotic, and abiotic stimuli. Furthermore, the lectin family shows evolutionary expansion that has distinct clade-specific signatures. Although the function(s) of many plant lectin family genes are unknown, studies in the model plant Arabidopsis thaliana have provided insights into their diverse roles. Here, we have used a biocuration approach rooted in the critical review of scientific literature and information available in the public genomic databases to summarize the expression, localization, and known functions of lectins in Arabidopsis. A better understanding of the structure and function of lectins is expected to aid in improving agricultural productivity through the manipulation of candidate genes for breeding climateresilient crops, or by regulating metabolic pathways by applications of plant growth regulators.
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.
Structure-function relationship of monocot mannose-binding lectins
PLANT PHYSIOLOGY, 1996
The monocot mannose-binding lectins are an extended superfamily of structurally and evolutionarily related proteins, which until now have been isolated from species of the Amaryllidaceae, Alliaceae, Araceae, Orchidaceae, and Liliaceae. To explain the obvious differences in biological activities, the structure-function relationships of the monocot mannose-binding lectins were studied by a combination of glycan-binding studies and molecular modeling using the deduced amino acid sequences of the currently known lectins. Molecular modeling indicated that the number of active mannose-binding sites per monomer varies between three and zero. Since the number of binding sites is fairly well correlated with the binding activity measured by surface plasmon resonance, and is also in good agreement with the results of previous studies of the biological activities of the mannose-binding lectins, molecular modeling is of great value for predicting which lectins are best suited for a particular application. Plant lectins are an extended group of proteins that, according to a recently updated definition, comprise all plant proteins possessing at least one noncatalytic domain that binds reversibly to specific mono-or oligosaccharides (Peumans and Van Damme, 1995). Due to advances in the biochemistry and molecular biology of plant lectins during the last decade, the structural and evolutionary relationships between the different members of this apparently very , heterogeneous group of proteins have become increasingly evident. At present, the majority of all currently known plant lectins can be classified into four groups of evolutionarily related proteins: the legume lectins (Sharon and Lis, 1990), the chitin-binding lectins containing hevein domains (Raikhel and Broekaert, 1993), the type 2 ribosome-inactivating proteins (Barbieri et al., 1993), and the so-called monocot Man-binding lectins. Legume lectins are confined to species of the Leguminoseae, whereas the chitin-binding lectins and type 2 ribosome-inactivating
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.
Related lectins from snowdrop and maize differ in their carbohydrate-binding specificity
Biochemical and Biophysical Research Communications, 2009
Searches in an EST database from maize revealed the expression of a protein related to the Galanthus nivalis (GNA) agglutinin, referred to as GNA maize . Heterologous expression of GNA maize in Pichia pastoris allowed characterisation of the first nucleocytoplasmic GNA homolog from plants. GNA maize is a tetrameric protein which shares 64% sequence similarity with GNA. Glycan microarray analyses revealed important differences in the specificity. Unlike GNA, which binds strongly to high-mannose N-glycans, the lectin from maize reacts almost exclusively with more complex glycans. Interestingly, GNA maize prefers complex glycans containing β1-2 GlcNAc residues. The obvious difference in carbohydrate-binding properties is accompanied by a 100-fold reduced anti-HIV activity. Although the sequences of GNA and GNA maize are clearly related they show only 28% sequence identity. Our results indicate that gene divergence within the family of GNA-related lectins leads to changes in carbohydrate binding specificity, as shown on N-glycan arrays.
The structure of basic Winged Bean Agglutinin (WBAI) with two dimeric molecules complexed with methyl-a-D-galactopyranoside in the asymmetric unit, has been determined by the molecular replacement method and re®ned with 2.5 A Ê X-ray intensity data. The polypeptide chain of each monomer has the characteristic legume lectin tertiary fold. The structure clearly de®nes the lectin-carbohydrate interactions. It reveals how the unusually long variable loop in the binding region endows the lectin with its characteristic sugar speci®city. The lectin forms non-canonical dimers of the type found in Erythrina corallodendron lectin (EcorL) even though glycosylation, unlike in EcorL, does not prevent the formation of canonical dimers. The structure thus further demonstrates that the mode of dimerisation of legume lectins is not necessarily determined by the covalently bound carbohydrate but is governed by features intrinsic to the protein. The present analysis and our earlier work on peanut lectin (PNA), show that legume lectins are a family of proteins in which small alterations in essentially the same tertiary structure lead to wide variations in quaternary association. A relationship among the non-canonical modes of dimeric association in legume lectins is presented.
Glycoconjugate Journal, 2000
During the last few years compelling evidence has been presented for the occurrence of cytoplasmic/nuclear plant lectins that are not detectable in normal plants but are only induced upon application of well-defined stress conditions. Since both the regulation of the expression and the subcellular location indicate that these 'non-classical lectins' are good candidates to play a physiologically important role as mediators of specific protein-carbohydrate-interactions within the plant cell, a critical assessment is made of the impact of these findings on the development of novel concepts about the role of plant lectins. Based on an analysis of the biochemical, molecular and evolutionary data of a jasmonate-induced chitinbinding lectin from tobacco leaves and a salt/jasmonate-induced leaf lectin from rice it is concluded that these lectins most probably interact with endogenous glycans located within the cytoplasmic/nuclear compartment of the plant cell. Several working mechanisms are proposed to explain how these inducible lectins may fulfill an important regulatory or structural role in stressed cells. In addition, the question of the evolutionary relationship(s) between the newly discovered inducible lectins and their 'classical' constitutively expressed homologs is addressed. Evidence is presented that the 'non-classical lectins' represent the main evolutionary line and that some of their corresponding genes were used as templates for genes encoding storage protein-like 'classical' homologs.
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.