A novel mode of carbohydrate recognition in jacalin, a Moraceae plant lectin with a beta-prism fold

Conformational analysis of champedak galactose-binding lectin under different urea concentrations

Conformational analysis of champedak galactose-binding (CGB) lectin under different urea concentrations was studied in phosphate-buffered saline (pH 7.2) using far-ultraviolet circular dichroism (far-UV CD), tryptophan (Trp) fluorescence and ANS fluorescence. In all cases, CGB lectin displayed a two-step, three-state transition. The first transition (from the native state to the intermediate state) started at ∼2.0 M urea and ended at ∼4.5 M urea, while the second transition (from the intermediate state to the completely denatured state) was characterized by the start- and end-points at ∼5.75 M and ∼7.5 M urea, respectively, when analyzed by the emission maximum of Trp fluorescence. A marked increase in the Trp fluorescence, ANS fluorescence and -CD values at 218 nm (-CD218 nm) represented the first transition, whereas a decrease in these parameters defined the second transition. On the other hand, emission maximum of the Trp fluorescence showed a continuous increase throughout the urea concentration range. Transformation of tetramer into monomer represented the first transition, whereas the second transition reflected the unfolding of monomer. Far-UV CD, Trp fluorescence and ANS fluorescence spectra were used to characterize the native, the intermediate and the completely denatured states of CGB lectin, obtained at 0.0 M, 5.0 M and 9.0 M urea, respectively. The intermediate state was characterized by the presence of higher secondary structures, increased ANS binding as well as increased Trp fluorescence intensity. A gradual decrease in the hemagglutination activity of CGB lectin was observed with increasing urea concentrations, showing complete loss at 4.0 M urea.

Transcriptome Analysis Revealed Highly Expressed Genes Encoding Secondary Metabolite Pathways and Small Cysteine-Rich Proteins in the Sclerotium of Lignosus rhinocerotis

Lignosus rhinocerotis (Cooke) Ryvarden (tiger milk mushroom) has long been known for its nutritional and medicinal benefits among the local communities in Southeast Asia. However, the molecular and genetic basis of its medicinal and nutraceutical properties at transcriptional level have not been investigated. In this study, the transcriptome of L. rhinocerotis sclerotium, the part with medicinal value, was analyzed using high-throughput Illumina HiSeq^TM platform with good sequencing quality and alignment results. A total of 3,673, 117, and 59,649 events of alternative splicing, novel transcripts, and SNP variation were found to enrich its current genome database. A large number of transcripts were expressed and involved in the processing of gene information and carbohydrate metabolism. A few highly expressed genes encoding the cysteine-rich cerato-platanin, hydrophobins, and sugar-binding lectins were identified and their possible roles in L. rhinocerotis were discussed. Genes encoding enzymes involved in the biosynthesis of glucans, six gene clusters encoding four terpene synthases and one each of non-ribosomal peptide synthetase and polyketide synthase, and 109 transcribed cytochrome P450 sequences were also identified in the transcriptome. The data from this study forms a valuable foundation for future research in the exploitation of this mushroom in pharmacological and industrial applications.

Interaction of sugar stabilized silver nanoparticles with the T-antigen specific lectin, jacalin from Artocarpus integrifolia

The advances in nanomedicine demonstrate the anticancer properties of silver nanoparticles (AgNPs) and considered as an alternative to the available chemotherapeutic agents. Owing to the preferential interaction of Artocarpus integrifolia lectin (jacalin) with Galβ1-3GalNAcα (a chemically well-defined tumor associated antigen), a study was undertaken to understand the interaction mechanism of AgNPs with jacalin in presence of specific sugar, galactose. Fluorescence spectroscopic analysis revealed that the AgNPs binding significantly quenched the intrinsic fluorescence of jacalin through a static quenching mechanism, and a non-radiative energy transfer occurred within the molecules. Association constants obtained from the interaction of different sugar-stabilized AgNPs with jacalin are in the order of 10(4)M(-1), this is in the same range as those obtained for the interaction of lectin with carbohydrate and hydrophobic ligand. Each subunit of the tetrameric jacalin binds one AgNPs, and the stoichiometry was unaffected by the presence of the specific sugar, galactose. Hemagglutination assay shows that sugar stabilized AgNPs interacts to jacalin at a site that is different from the saccharide-binding site. Analysis of the FTIR spectra of jacalin indicates that the binding of AgNPs does not alter the secondary structure of jacalin. More importantly, AgNPs exists in nano form even after interacting with the lectin. These results suggest that the development of lectin-AgNPs conjugate would be possible for diagnosis and treatment of cancer.

Birth of plant proteomics in India: a new horizon

In the post-genomic era, proteomics is acknowledged as the next frontier for biological research. Although India has a long and distinguished tradition in protein research, the initiation of proteomics studies was a new horizon. Protein research witnessed enormous progress in protein separation, high-resolution refinements, biochemical identification of the proteins, protein-protein interaction, and structure-function analysis. Plant proteomics research, in India, began its journey on investigation of the proteome profiling, complexity analysis, protein trafficking, and biochemical modeling. The research article by Bhushan et al. in 2006 marked the birth of the plant proteomics research in India. Since then plant proteomics studies expanded progressively and are now being carried out in various institutions spread across the country. The compilation presented here seeks to trace the history of development in the area during the past decade based on publications till date. In this review, we emphasize on outcomes of the field providing prospects on proteomic pathway analyses. Finally, we discuss the connotation of strategies and the potential that would provide the framework of plant proteome research.

BIOLOGICAL SIGNIFICANCE

The past decades have seen rapidly growing number of sequenced plant genomes and associated genomic resources. To keep pace with this increasing body of data, India is in the provisional phase of proteomics research to develop a comparative hub for plant proteomes and protein families, but it requires a strong impetus from intellectuals, entrepreneurs, and government agencies. Here, we aim to provide an overview of past, present and future of Indian plant proteomics, which would serve as an evaluation platform for those seeking to incorporate proteomics into their research programs. This article is part of a Special Issue entitled: Proteomics in India.

Gene Expression, Protein Function and Pathways of Arabidopsis thaliana Responding to Silver Nanoparticles in Comparison to Silver Ions, Cold, Salt, Drought, and Heat

Silver nanoparticles (AgNPs) have been widely used in industry due to their unique physical and chemical properties. However, AgNPs have caused environmental concerns. To understand the risks of AgNPs, Arabidopsis microarray data for AgNP, Ag⁺, cold, salt, heat and drought stresses were analyzed. Up- and down-regulated genes of more than two-fold expression change were compared, while the encoded proteins of shared and unique genes between stresses were subjected to differential enrichment analyses. AgNPs affected the fewest genes (575) in the Arabidopsis genome, followed by Ag⁺ (1010), heat (1374), drought (1435), salt (4133) and cold (6536). More genes were up-regulated than down-regulated in AgNPs and Ag⁺ (438 and 780, respectively) while cold down-regulated the most genes (4022). Responses to AgNPs were more similar to those of Ag⁺ (464 shared genes), cold (202), and salt (163) than to drought (50) or heat (30); the genes in the first four stresses were enriched with 32 PFAM domains and 44 InterPro protein classes. Moreover, 111 genes were unique in AgNPs and they were enriched in three biological functions: response to fungal infection, anion transport, and cell wall/plasma membrane related. Despite shared similarity to Ag⁺, cold and salt stresses, AgNPs are a new stressor to Arabidopsis.

Spectroscopic investigation on the interaction of ruthenium complexes with tumor specific lectin, jacalin

Several ruthenium complexes are regarded as anticancer agents and considered as an alternative to the widely used platinum complexes. Owing to the preferential interaction of jacalin with tumor-associated T-antigen, we report the interaction of jacalin with four ruthenium complex namely, tris(1,10-phenanthroline)ruthenium(II)chloride, bis(1,10-phenanthroline)(N-[1,10]phenanthrolin-5-yl-pyrenylmethanimine)ruthenium(II)chloride, bis(1,10-phenanthroline)(dipyrido[3,2-a:2',3'-c]-phenazine)ruthenium(II)chloride, bis(1,10-phenanthroline)(11-(9-acridinyl)dipyrido[3,2-a:2',3'-c]phenazine)ruthenium(II) chloride. Fluorescence spectroscopic analysis revealed that the ruthenium complexes strongly quenched the intrinsic fluorescence of jacalin through a static quenching procedure, and a non-radiative energy transfer occurred within the molecules. Association constants obtained for the interaction of different ruthenium complexes with jacalin are in the order of 10(5) M(-1), which is in the same range as those obtained for the interaction of lectin with carbohydrate and hydrophobic ligand. Each subunit of the tetrameric jacalin binds one ruthenium complex, and the stoichiometry is found to be unaffected by the presence of the specific sugar, galactose. In addition, agglutination activity of jacalin is largely unaffected by the presence of the ruthenium complexes, indicating that the binding sites for the carbohydrate and the ruthenium complexes are different. These results suggest that the development of lectin-ruthenium complex conjugate would be feasible to target malignant cells in chemo-therapeutics.

Jacalin-carbohydrate interactions: distortion of the ligand molecule as a determinant of affinity

Jacalin is among the most thoroughly studied lectins. Its carbohydrate-binding site has also been well characterized. It has been postulated that the lower affinity of β-galactosides for jacalin compared with α-galactosides is caused by steric interactions of the substituents in the former with the protein. This issue has been explored energetically and structurally using different appropriate carbohydrate complexes of jacalin. It turns out that the earlier postulation is not correct. The interactions of the substituent with the binding site remain essentially the same irrespective of the anomeric nature of the substitution. This is achieved through a distortion of the sugar ring in β-galactosides. The difference in energy, and therefore in affinity, is caused by a distortion of the sugar ring in β-galactosides. The elucidation of this unprecedented distortion of the ligand as a strategy for modulating affinity is of general interest. The crystal structures also provide a rationale for the relative affinities of the different carbohydrate ligands for jacalin.

Genome-based proteomic analysis of Lignosus rhinocerotis (Cooke) Ryvarden sclerotium

Lignosus rhinocerotis (Cooke) Ryvarden (Polyporales, Basidiomycota), also known as the tiger milk mushroom, has received much interest in recent years owing to its wide-range ethnobotanical uses and the recent success in its domestication. The sclerotium is the part with medicinal value. Using two-dimensional gel electrophoresis coupled with mass spectrometry analysis, a total of 16 non-redundant, major proteins were identified with high confidence level in L. rhinocerotis sclerotium based on its genome as custom mapping database. Some of these proteins, such as the putative lectins, immunomodulatory proteins, superoxide dismutase, and aegerolysin may have pharmaceutical potential; while others are involved in nutrient mobilization and the protective antioxidant mechanism in the sclerotium. The findings from this study provide a molecular basis for future research on potential pharmacologically active proteins of L. rhinocerotis.

Protein characterisation of Brosimum gaudichaudii Trécul latex and study of nanostructured latex film formation

Brosimum gaudichaudii Tréc. (Moraceae) is a common Brazilian Cerrado plant known by its pharmaceutical industry relevance. The authors investigated the latex protein components and potential biotechnological applications. Some protein fragments had their sequences elucidated, presenting similarities to jacalin and Kunitz-type trypsin inhibitors. Amino acid residue modifications were found, such as glutamine N-terminal residue cyclisation into pyroglutamic acid residue, and mass differences corresponding to hexoses and N-acetylhexosamine presence. The latex was used to produce a nanoscale structured film, which presented an increased attraction and reduced adhesion behaviours. The film presented high homogeneity, as observed by low nanoroughness values, probably because of its intrinsic components, such as the jacalin-like protein that has known agglutination properties. The immobilised Kunitz-type trypsin inhibitor presence in the latex film allow us to point out to applications related to this inhibition, as in active food packaging, since these peptidase inhibitors are able to inhibit pests and microorganism proliferation.

Banana lectin: a brief review

Lectins are a group of proteins of non-immune origin that recognize and bind to carbohydrates without modifying them. Banana is the common name for both herbaceous plants of the genus Musa and for the fruit they produce. They are indeed a promising source for many medicinal applications. Banana lectins have the potential for inhibiting HIV-1 reverse transcriptase activity, suppressing cancer cell proliferation and stimulating macrophage activities. Nevertheless, compared to other plant lectins, there is relatively little information in the literature on banana lectins, particularly with respect to their structure and biological functions. Herein we focus our review on the structure, functions and exploitable properties of banana lectins.

Structural diversity and ligand specificity of lectins. The Bangalore effort

Structural studies in this laboratory encompass four of the five major classes of plant lectins, including the one discovered by us. In addition to addressing issues specific to individual lectins, the work provided insights into protein folding, quaternary association and generation of ligand specificity. Legume and β-prism fold lectins constitute families of proteins in which small alterations in essentially the same tertiary structure lead to large variations in quaternary structure, including that involving an open structure. Strategies for generating ligand specificity include water bridges, variation in loop length, post translational modification and oligomerization. Three of the structural classes investigated have subunits with three-fold symmetry. The symmetry in the structure is reflected in the sequence to different extents in different sub-classes. The evolutionary implications of this observation have been explored. The work on lectins has now been extended to those from mycobacteria.

Structural insights into Bacillus thuringiensis Cry, Cyt and parasporin toxins

Since the first X-ray structure of Cry3Aa was revealed in 1991, numerous structures of B. thuringiensis toxins have been determined and published. In recent years, functional studies on the mode of action and resistance mechanism have been proposed, which notably promoted the developments of biological insecticides and insect-resistant transgenic crops. With the exploration of known pore-forming toxins (PFTs) structures, similarities between PFTs and B. thuringiensis toxins have provided great insights into receptor binding interactions and conformational changes from water-soluble to membrane pore-forming state of B. thuringiensis toxins. This review mainly focuses on the latest discoveries of the toxin working mechanism, with the emphasis on structural related progress. Based on the structural features, B. thuringiensis Cry, Cyt and parasporin toxins could be divided into three categories: three-domain type α-PFTs, Cyt toxin type β-PFTs and aerolysin type β-PFTs. Structures from each group are elucidated and discussed in relation to the latest data, respectively.

Two jacalin-related lectins from seeds of the African breadfruit (Treculia africana L.)

Two jacalin-related lectins (JRLs) were purified by mannose-agarose and melibiose-agarose from seeds of Treculia africana. One is galactose-recognizing JRL (gJRL), named T. africana agglutinin-G (TAA-G), and another one is mannose-recognizing JRL (mJRL), TAA-M. The yields of the two lectins from the seed flour were approximately 7.0 mg/g for gJRL and 7.2 mg/g for mJRL. The primary structure of TAA-G was determined by protein sequencing of lysyl endopeptic peptides and chymotryptic peptides. The sequence identity of TAA-G to other gJRLs was around 70%. Two-residue insertion was found around the sugar-binding sites, compared with the sequences of other gJRLs. Crystallographic studies on other gJRLs have shown that the primary sugar-binding site of gJRLs can accommodate Gal, GalNAc, and GalNAc residue of T-antigen (Galβ1-3GalNAcα-). However, hemagglutination inhibition and glycan array showed that TAA-G did not recognize GalNAc itself and T-antigen. TAA-G preferred melibiose and core 3 O-glycan.

Thermal, chemical and pH induced unfolding of turmeric root lectin: modes of denaturation

Curcuma longa rhizome lectin, of non-seed origin having antifungal, antibacterial and α-glucosidase inhibitory activities, forms a homodimer with high thermal stability as well as acid tolerance. Size exclusion chromatography and dynamic light scattering show it to be a dimer at pH 7, but it converts to a monomer near pH 2. Circular dichroism spectra and fluorescence emission maxima are virtually indistinguishable from pH 7 to 2, indicating secondary and tertiary structures remain the same in dimer and monomer within experimental error. The tryptophan environment as probed by acrylamide quenching data yielded very similar data at pH 2 and pH 7, implying very similar folding for monomer and dimer. Differential scanning calorimetry shows a transition at 350.3 K for dimer and at 327.0 K for monomer. Thermal unfolding and chemical unfolding induced by guanidinium chloride for dimer are both reversible and can be described by two-state models. The temperatures and the denaturant concentrations at which one-half of the protein molecules are unfolded, are protein concentration-dependent for dimer but protein concentration-independent for monomer. The free energy of unfolding at 298 K was found to be 5.23 Kcal mol⁻¹ and 14.90 Kcal mol⁻¹ for the monomer and dimer respectively. The value of change in excess heat capacity upon protein denaturation (ΔC_p) is 3.42 Kcal mol⁻¹ K⁻¹ for dimer. The small ΔC_p for unfolding of CLA reflects a buried hydrophobic core in the folded dimeric protein. These unfolding experiments, temperature dependent circular dichroism and dynamic light scattering for the dimer at pH 7 indicate its higher stability than for the monomer at pH 2. This difference in stability of dimeric and monomeric forms highlights the contribution of inter-subunit interactions in the former.

Glycan specificity of the Vibrio vulnificus hemolysin lectin outlines evolutionary history of membrane targeting by a toxin family

Pore-forming toxins (PFTs) are a class of pathogen-secreted molecules that oligomerize to form transmembrane channels in cellular membranes. Determining the mechanism for how PFTs bind membranes is important in understanding their role in disease and for developing possible ways to block their action. Vibrio vulnificus, an aquatic pathogen responsible for severe food poisoning and septicemia in humans, secretes a PFT called V. vulnificus hemolysin (VVH), which contains a single C-terminal targeting domain predicted to resemble a β-trefoil lectin fold. In order to understand the selectivity of the lectin for glycan motifs, we expressed the isolated VVH β-trefoil domain and used glycan-chip screening to identify that VVH displays a preference for terminal galactosyl groups including N-acetyl-d-galactosamine and N-acetyl-d-lactosamine. The X-ray crystal structure of the VVH lectin domain solved to 2.0Å resolution reveals a heptameric ring arrangement similar to the oligomeric form of the related, but inactive, lectin from Vibrio cholerae cytolysin. Structures bound to glycerol, N-acetyl-d-galactosamine, and N-acetyl-d-lactosamine outline a common and versatile mode of recognition allowing VVH to target a wide variety of cell-surface ligands. Sequence analysis in light of our structural and functional data suggests that VVH may represent an earlier step in the evolution of Vibrio PFTs.

The β-prism lectin domain of Vibrio cholerae hemolysin promotes self-assembly of the β-pore-forming toxin by a carbohydrate-independent mechanism

Vibrio cholerae cytolysin/hemolysin (VCC) is an amphipathic 65-kDa β-pore-forming toxin with a C-terminal β-prism lectin domain. Because deletion or point mutation of the lectin domain seriously compromises hemolytic activity, it is thought that carbohydrate-dependent interactions play a critical role in membrane targeting of VCC. To delineate the contributions of the cytolysin and lectin domains in pore formation, we used wild-type VCC, 50-kDa VCC (VCC(50)) without the lectin domain, and mutant VCC(D617A) with no carbohydrate-binding activity. VCC and its two variants with no carbohydrate-binding activity moved to the erythrocyte stroma with apparent association constants on the order of 10(7) M(-1). However, loss of the lectin domain severely reduced the efficiency of self-association of the VCC monomer with the β-barrel heptamer in the synthetic lipid bilayer from ∼83 to 27%. Notably, inactivation of the carbohydrate-binding activity by the D617A mutation marginally reduced oligomerization to ∼77%. Oligomerization of VCC(50) was temperature-insensitive; by contrast, VCC self-assembly increased with increasing temperature, suggesting that the process is driven by entropy and opposed by enthalpy. Asialofetuin, the β1-galactosyl-terminated glycoprotein inhibitor of VCC-induced hemolysis, promoted oligomerization of 65-kDa VCC to a species that resembled the membrane-inserted heptamer in stoichiometry and morphology but had reduced global amphipathicity. In conclusion, we propose (i) that the β-prism lectin domain facilitated toxin assembly by producing entropy during relocation in the heptamer and (ii) that glycoconjugates inhibited VCC by promoting its assembly to a water-soluble, less amphipathic oligomer variant with reduced ability to penetrate the bilayer.

Synthesis and characterization of jacalin-gold nanoparticles conjugates as specific markers for cancer cells

New nanobiocomposites that combine nanoparticles and biomolecules have been shown very relevant for medical applications. Recently, cancer diagnostics and treatment have benefited from the development of nanobiocomposites, in which metallic or magnetic nanoparticles are conjugated with specific biomolecules for selective cell uptake. Despite recent advances in this area, the biomedical applications of these materials are still limited by the low efficiency of functionalization, low stability, among other factors. In this study, we report the synthesis of jacalin-conjugated gold nanoparticles, a nanoconjugate with potential application in medical areas, especially for cancer diagnosis. Jacalin is a lectin protein and it was employed due to its ability to recognize the Galβ1-3GalNAc disaccharide, which is highly expressed in tumor cells. Gold nanoparticles (AuNPs) were synthesized in the presence of generation 4 polyamidoamine dendrimer (PAMAM G4) and conjugated with fluorescein isothiocyanate (FITC)-labeled jacalin. The AuNPs/jacalin nanoconjugates were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS) and vibrational spectroscopy (FTIR). We also performed an investigation using isothermal titration calorimetry (ITC) and fluorescence quenching measurements to understand the interactions occurring between the AuNPs and jacalin, which revealed that the nanoconjugate formation is driven by an entropic process with good affinity. Furthermore, in vitro tests revealed that the AuNPs/jacalin-FITC nanoconjugates exhibited higher affinity for leukemic K562 cells than for healthy mononuclear blood cells, which could be useful for biomedical applications, including cancer cells imaging.

The sequence and structure of snake gourd (Trichosanthes anguina) seed lectin, a three-chain nontoxic homologue of type II RIPs

The sequence and structure of snake gourd seed lectin (SGSL), a nontoxic homologue of type II ribosome-inactivating proteins (RIPs), have been determined by mass spectrometry and X-ray crystallography, respectively. As in type II RIPs, the molecule consists of a lectin chain made up of two β-trefoil domains. The catalytic chain, which is connected through a disulfide bridge to the lectin chain in type II RIPs, is cleaved into two in SGSL. However, the integrity of the three-dimensional structure of the catalytic component of the molecule is preserved. This is the first time that a three-chain RIP or RIP homologue has been observed. A thorough examination of the sequence and structure of the protein and of its interactions with the bound methyl-α-galactose indicate that the nontoxicity of SGSL results from a combination of changes in the catalytic and the carbohydrate-binding sites. Detailed analyses of the sequences of type II RIPs of known structure and their homologues with unknown structure provide valuable insights into the evolution of this class of proteins. They also indicate some variability in carbohydrate-binding sites, which appears to contribute to the different levels of toxicity exhibited by lectins from various sources.

Vibrio cholerae cytolysin recognizes the heptasaccharide core of complex N-glycans with nanomolar affinity

Pathogens selectively target host cells using adhesion molecules and secreted virulence factors that may utilize protein, lipid, or carbohydrate ligands on the cell surface. The human intestinal pathogen Vibrio cholerae secretes a pore-forming toxin, V.cholerae cytolysin (VCC), which contains two domains that are structurally similar to known carbohydrate-binding proteins. These tandem domains are attached to the carboxy-terminus of the cytolytic domain and contain a β-trefoil fold and a β-prism fold. VCC has been shown to bind glycosylated proteins, and removal of the β-prism domain leads to a large decrease in lytic activity against rabbit erythrocytes. Despite these clues, the identity of the glycan receptors of VCC and the role of glycan binding in toxin activity remain unknown. To better understand this specificity, we used a combination of structural and functional approaches to characterize the carbohydrate-binding activity of the VCC toxin. We first probed the monosaccharide-binding activity of VCC and demonstrated that the toxin exhibits millimolar affinity for aldohexoses. To understand this specificity, we solved the crystal structure of the VCC β-prism domain bound to methyl-α-mannose. Next, we utilized a mammalian glycan screen to determine that the β-prism domain preferentially binds complex N-glycans with a heptasaccharide GlcNAc(4)Man(3) core (NGA2). Fluorescence anisotropy and surface plasmon resonance indicated an approximately 100-nM affinity of the β-prism domain for the heptasaccharide core. Our results suggest that carbohydrate-binding domains on the VCC toxin facilitate high-affinity targeting of mammalian cell membranes, which may contribute to the ability of VCC to lyse cells at picomolar concentrations.

Functional mapping of the lectin activity site on the β-prism domain of vibrio cholerae cytolysin: implications for the membrane pore-formation mechanism of the toxin

Vibrio cholerae cytolysin (VCC) is a prominent member in the family of β-barrel pore-forming toxins. It induces lysis of target eukaryotic cells by forming transmembrane oligomeric β-barrel channels. VCC also exhibits prominent lectin-like activity in interacting with β1-galactosyl-terminated glycoconjugates. Apart from the cytolysin domain, VCC harbors two lectin-like domains: the β-Trefoil and the β-Prism domains; however, precise contribution of these domains in the lectin property of VCC is not known. Also, role(s) of these lectin-like domains in the mode of action of VCC remain obscure. In the present study, we show that the β-Prism domain of VCC acts as the structural scaffold to determine the lectin activity of the protein toward β1-galactosyl-terminated glycoconjugates. Toward exploring the physiological implication of the β-Prism domain, we demonstrate that the presence of the β-Prism domain-mediated lectin activity is crucial for an efficient interaction of the toxin toward the target cells. Our results also suggest that such lectin activity may act to regulate the oligomerization ability of the membrane-bound VCC toxin. Based on the data presented here, and also consistent with the existing structural information, we propose a novel mechanism of regulation imposed by the β-Prism domain's lectin activity, implicated in the process of membrane pore formation by VCC.

Ipomoelin, a jacalin-related lectin with a compact tetrameric association and versatile carbohydrate binding properties regulated by its N terminus

Many proteins are induced in the plant defense response to biotic stress or mechanical wounding. One group is lectins. Ipomoelin (IPO) is one of the wound-inducible proteins of sweet potato (Ipomoea batatas cv. Tainung 57) and is a Jacalin-related lectin (JRL). In this study, we resolved the crystal structures of IPO in its apo form and in complex with carbohydrates such as methyl α-D-mannopyranoside (Me-Man), methyl α-D-glucopyranoside (Me-Glc), and methyl α-D-galactopyranoside (Me-Gal) in different space groups. The packing diagrams indicated that IPO might represent a compact tetrameric association in the JRL family. The protomer of IPO showed a canonical β-prism fold with 12 strands of β-sheets but with 2 additional short β-strands at the N terminus. A truncated IPO (ΔN10IPO) by removing the 2 short β-strands of the N terminus was used to reveal its role in a tetrameric association. Gel filtration chromatography confirmed IPO as a tetrameric form in solution. Isothermal titration calorimetry determined the binding constants (K(A)) of IPO and ΔN10IPO against various carbohydrates. IPO could bind to Me-Man, Me-Glc, and Me-Gal with similar binding constants. In contrast, ΔN10IPO showed high binding ability to Me-Man and Me-Glc but could not bind to Me-Gal. Our structural and functional analysis of IPO revealed that its compact tetrameric association and carbohydrate binding polyspecificity could be regulated by the 2 additional N-terminal β-strands. The versatile carbohydrate binding properties of IPO might play a role in plant defense.

Purification, crystallization and preliminary X-ray crystallographic analysis of MIL, a glycosylated jacalin-related lectin from mulberry (Morus indica) latex

A quantitatively major protein has been purified from the latex of Morus indica. The purified previously uncharacterized protein, M. indica lectin (MIL), was further shown to be a glycosylated tetramer and belongs to the family of jacalin-related lectins. Crystallization of MIL was also accomplished and the tetragonal crystals diffracted synchrotron X-rays to a resolution of 2.8 Å.

Cloning, expression, purification, crystallization and preliminary X-ray studies of the mannose-binding lectin domain of MSMEG_3662 from Mycobacterium smegmatis

The mannose-binding lectin domain of MSMEG_3662 from Mycobacterium smegmatis has been cloned, expressed, purified and crystallized and the crystals have been characterized using X-ray diffraction. The Matthews coefficient suggests the possibility of two lectin domains in the triclinic cell. The amino-acid sequence of the domain indicates structural similarity to well characterized β-prism II fold lectins.

Interaction of aromatic imino glycoconjugates with jacalin: experimental and computational docking studies

Altering the lectin properties by chemically modified glycoconjugates can have profound effect on their biological applications. In the present case, jacalin has been chosen to study the binding aspects toward glycoconjugates modified by connecting aromatic moieties through imine conjugation at their C-1- or C-2-positions. Out of 10 glycoconjugates, the galactosyl-naphthyl imine (1c) was found to be most effective toward agglutination inhibition (260 times better than galactose), quenching fluorescence intensity, and exhibiting greater binding (K(a), 1.3 × 10(4)M(-1)) with jacalin. The specific binding of galactose conjugates and the nonspecific binding of other conjugates have been demonstrated based on ITC. Changes in the secondary structures have been addressed by far- and near-UV CD spectroscopy. The present studies demonstrated that galactose-based conjugates bind at carbohydrate recognition domain (CRD) mainly through polar interactions in addition to exhibiting some nonpolar/hydrophobic interactions, whereas the conjugates other than galactose primarily interact through hydrophobic interactions. Binding of galactosyl conjugates at CRD has been further demonstrated by rigid docking.

Characterization of the secondary binding sites of Maclura pomifera agglutinin by glycan array and crystallographic analyses

The Maclura pomifera agglutinin (MPA) recognizes the T-antigen disaccharide Galβ1,3GalNAc mainly through interaction of the α-GalNAc moiety with its primary site, but the interactions of the two flanking subsites A and B with aglycones and substituents other than Gal, respectively, are not well understood. We therefore characterized the specificity of MPA in more detail by glycan microarray analysis and determined the crystal structures of MPA without ligand and in complexes with Galβ1,3GalNAc and p-nitrophenyl α-GalNAc. In both sugar complexes, pairs of ligands created inter-tetramer hydrogen-bond bridging networks. While subsite A showed increased affinity for hydrophobic aglycones, it also accommodated several sugar substituents. Notably, a GalNAc-O-tripeptide, a Tn-antigen mimic, showed lower affinity than these compounds in surface plasmon resonance (SPR) experiments. The glycan array data that showed subsite B accepted compounds in which the O3 position of the GalNAc was substituted with various sugars other than Gal, but substitutions at O6 led to inactivity. Additions to the Gal moiety of the disaccharide also had only small effects on reactivity. These results are all compatible with the features seen in the crystal structures.

Deletion of the N-terminal dirigent domain in maize beta-glucosidase aggregating factor and its homolog sorghum lectin dramatically alters the sugar-specificities of their lectin domains

Maize beta-glucosidase aggregating factor (BGAF) and its homolog Sorghum Lectin (SL) are modular proteins consisting of an N-terminal dirigent domain and a C-terminal jacalin-related lectin (JRL) domain. BGAF is a polyspecific lectin with a monosaccharide preference for galactose, whereas SL displays preference for GalNAc. Here, we report that deletion of the N-terminal dirigent domain in the above lectins dramatically changes their sugar-specificities. Deletions in the N-terminal region of the dirigent domain of BGAF abolished binding to galactose/lactose, but binding to mannose was unaffected. Glucose, which was a poor inhibitor of hemagglutinating activity of BGAF, displayed higher inhibitory effect on the hemagglutinating activity of deletion mutants. Deletion of the dirigent domain in SL abolished binding to GalNAc, but binding to mannose was not affected. Surprisingly, fructose, an extremely poor inhibitor (minimum inhibitory concentration (MIC) = 125 mM) of SL hemagglutinating activity, was found to be a very potent inhibitor (MIC = 1 mM) of hemagglutinating activity of its JRL domain. These results indicate that the dirigent domain in this class of modular lectins, at least in the case of maize BGAF and SL, influences sugar specificity.

Artocarpus: a review of its traditional uses, phytochemistry and pharmacology

The genus Artocarpus (Moraceae) comprises about 50 species of evergreen and deciduous trees. Economically, the genus is of appreciable importance as a source of edible fruit, yield fairly good timber and is widely used in folk medicines. The aim of the present review is to present comprehensive information of the chemical constituents, biological and pharmacological research on Artocarpus which will be presented and critically evaluated. The close connection between traditional and modern sources for ethnopharmacological uses of Artocarpus species, especially for treatment against inflammation, malarial fever, diarrhoea, diabetes and tapeworm infection. Artocarpus species are rich in phenolic compounds including flavonoids, stilbenoids, arylbenzofurons and Jacalin, a lectin. The extracts and metabolites of Artocarpus particularly those from leaves, bark, stem and fruit possess several useful bioactive compounds and recently additional data are available on exploitation of these compounds in the various biological activities including antibacterial, antitubercular, antiviral, antifungal, antiplatelet, antiarthritic, tyrosinase inhibitory and cytotoxicity. Several pharmacological studies of the natural products from Artocarpus have conclusively established their mode of action in treatment of various diseases and other health benefits. Jacalin, a lectin present in seeds of this plant has a wide range of activities. Strong interdisciplinary programmes that incorporate conventional and new technologies will be critical for the future development of Artocarpus as a promising source of medicinal products. In the present review, attempts on the important findings have been made on identification; synthesis and bioactivity of metabolites present in Artocarpus which have been highlighted along with the current trends in research on Artocarpus.

Group epitope mapping considering relaxation of the ligand (GEM-CRL): including longitudinal relaxation rates in the analysis of saturation transfer difference (STD) experiments

In the application of saturation transfer difference (STD) experiments to the study of protein-ligand interactions, the relaxation of the ligand is one of the major influences on the experimentally observed STD factors, making interpretation of these difficult when attempting to define a group epitope map (GEM). In this paper, we describe a simplification of the relaxation matrix that may be applied under specified experimental conditions, which results in a simplified equation reflecting the directly transferred magnetisation rate from the protein onto the ligand, defined as the summation over the whole protein of the protein-ligand cross-relaxation multiplied by with the fractional saturation of the protein protons. In this, the relaxation of the ligand is accounted for implicitly by inclusion of the experimentally determined longitudinal relaxation rates. The conditions under which this "group epitope mapping considering relaxation of the ligand" (GEM-CRL) can be applied were tested on a theoretical model system, which demonstrated only minor deviations from that predicted by the full relaxation matrix calculations (CORCEMA-ST) [7]. Furthermore, CORCEMA-ST calculations of two protein-saccharide complexes (Jacalin and TreR) with known crystal structures were performed and compared with experimental GEM-CRL data. It could be shown that the GEM-CRL methodology is superior to the classical group epitope mapping approach currently used for defining ligand-protein proximities. GEM-CRL is also useful for the interpretation of CORCEMA-ST results, because the transferred magnetisation rate provides an additional parameter for the comparison between measured and calculated values. The independence of this parameter from the above mentioned factors can thereby enhance the value of CORCEMA-ST calculations.

Structure, dynamics, and interactions of jacalin. Insights from molecular dynamics simulations examined in conjunction with results of X-ray studies

Molecular dynamics simulations have been carried out on all the jacalin-carbohydrate complexes of known structure, models of unliganded molecules derived from the complexes and also models of relevant complexes where X-ray structures are not available. Results of the simulations and the available crystal structures involving jacalin permit delineation of the relatively rigid and flexible regions of the molecule and the dynamical variability of the hydrogen bonds involved in stabilizing the structure. Local flexibility appears to be related to solvent accessibility. Hydrogen bonds involving side chains and water bridges involving buried water molecules appear to be important in the stabilization of loop structures. The lectin-carbohydrate interactions observed in crystal structures, the average parameters pertaining to them derived from simulations, energetic contribution of the stacking residue estimated from quantum mechanical calculations, and the scatter of the locations of carbohydrate and carbohydrate-binding residues are consistent with the known thermodynamic parameters of jacalin-carbohydrate interactions. The simulations, along with X-ray results, provide a fuller picture of carbohydrate binding by jacalin than provided by crystallographic analysis alone. The simulations confirm that in the unliganded structures water molecules tend to occupy the positions occupied by carbohydrate oxygens in the lectin-carbohydrate complexes. Population distributions in simulations of the free lectin, the ligands, and the complexes indicate a combination of conformational selection and induced fit.

Molecular characterization of a wheat protein induced by vernalisation

Using a PCR strategy we isolated from winter wheat (Triticum aestivum L. cv. Bolero) the ver2 gene coding for a modular protein constituted by an N-terminal domain called "dirigent", found in several defence-related genes, and a C-terminal domain related to jacalin-related lectin (JRL). ver2 transcript as well as native Ver2 levels increased during vernalisation and upon methyl jasmonate treatment of young seedlings. ver2 transcript levels were kept constant either in infected tissues or in wounded samples indicating that Ver2 is not directly involved in plant defence mechanisms. The Ver2 protein was expressed in bacteria as a recombinant GST-Ver2 fusion protein. The purified recombinant protein was further characterized using an affinity chromatography approach based on its interaction with mannose-agarose beads. GST-Ver2 tightly bound to the matrix. Molecular modelling of the jacalin domain and mannose docking confirmed that Ver2 possesses D: -mannose binding capacity.