Analyses of carbohydrate recognition by legume lectins: size of the combining site loops and their primary specificity

Effect of D-limonene on volatile fatty acidsproduction from anaerobic fermentation of waste activated sludge under pH regulation: Performance and mechanisms

D-limonene extracted from citrus peels possesses an inhibitory effect on methanogenic archaea. This study is aimed to bridge the research gap on the influence of D-limonene on volatile fatty acids (VFA) production from waste activated sludge (WAS) and to address the low VFA yield in standalone anaerobic fermentation of WAS. When the initial pH was not controlled, 1.00 g/g TSS D-limonene resulted in a VFA accumulation of 1175.45 ± 101.36 mg/L (174.45 ± 8.13 mgCOD/gVS). When the initial pH was controlled at 10 and the D-limonene concentration was 0.50 g/g TSS, the VFA accumulation reached 2707.44 ± 183.65 mg/L (445.51 ± 17.10 mgCOD/gVS). The pH-regulated D-limonene treatment enhanced solubilization and acidification, slightly inhibited hydrolysis, and significantly suppressed methanogenesis. D-limonene under alkaline conditions can increase the relative abundance of Clostridium_sensu_stricto, significantly enhancing acidification. Moreover, it markedly inhibited methanogenesis by particularly reducing the relative abundance of Methanothrix that was responsible for acetate consumption, thus favoring the accumulation of VFA. The research reveals the potential mechanism of pH regulation and D-limonene on anaerobic fermentation acid production, providing a theoretical basis for improving the acid production performance of the anaerobic fermentation of WAS.

Revisiting legume lectins: Structural organization and carbohydrate-binding properties

Legume lectins are a diverse family of carbohydrate-binding proteins that share significant similarities in their primary, secondary, and tertiary structures, yet exhibit remarkable variability in their quaternary structures and carbohydrate-binding specificities. The tertiary structure of legume lectins, characterized by a conserved β-sandwich fold, provides the scaffold for the formation of a carbohydrate-recognition domain (CRD) responsible for ligand binding. The structural basis for the binding is similar between members of the family, with key residues interacting with the sugar through hydrogen bonds, hydrophobic interactions, and van der Waals forces. Variability in substructures and residues within the CRD are responsible for the large array of specificities and enable legume lectins to recognize diverse sugar structures, while maintaining a consistent structural fold. Therefore, legume lectins can be classified into several specificity groups based on their preferred ligands, including mannose/glucose-specific, N-acetyl-d-galactosamine/galactose-specific, N-acetyl-d-glucosamine-specific, l-fucose-specific, and α-2,3 sialic acid-specific lectins. In this context, this review examined the structural aspects and carbohydrate-binding properties of representative legume lectins and their specific ligands in detail. Understanding the structure/binding relationships of lectins continues to provide valuable insights into their biological roles, while also assisting in the potential applications of these proteins in glycobiology, diagnostics, and therapeutics.

Fucose-binding lectins: purification, characterization and potential biomedical applications

The property of lectins to specifically recognize and bind carbohydrates makes them an excellent candidate in biomedical research. Among them are fucose-binding lectins possessing the capacity to bind fucose are taxonomically, evolutionarily and ecologically significant class of lectins that are identified in a wide range of taxa. Purification of fucose-binding lectins dates back to 1967 when L-fucose binding protein from Lotus tetragonolobus was isolated using a dye that contained three α-L-fucopyranosyl residues. Beginning with that, several FBLs were purified from various animals as well as plant sources that were structurally and functionally characterised. This review focuses on fucose-binding lectins, their occurrence and purification with special emphasis on various strategies adopted to purify them followed by molecular and functional characterization. The exclusive ability to recognize and bind to fucose-containing glycans endows these lectins with the potential to act as anti-cancer agents, diagnostic markers and mitogens for immune cells. Though they have been in research focus for more than half a century with their occurrence reported in various taxa, they still need to be explored for their prospective functions to develop them as a biological tool in biomedical research.

Isolation of Momordica charantia seed lectin and glycosidases from the protein bodies: Lectin-glycosidase (β-hexosaminidase) protein body membrane interaction reveals possible physiological function of the lectin

Momordica charantia seeds are known to contain a galactose specific lectin that has been well characterized. Seed extracts also contain glycosidases such as the β-hexosaminidase, α-mannosidase and α-galactosidase. In the present study, lectin was affinity purified from the seed extracts and protein bodies isolated by sucrose density gradient centrifugation. From the protein bodies, lectin was identified and β-hexosaminidase was isolated by lectin affinity chromatography and subsequently separated from other glycosidases by gel filtration. In the native PAGE, the purified β-hexosaminidase migrated as a single band with a molecular weight of ∼235 kDa and by zymogram analysis using 4-methylumbelliferyl N-acetyl-β-D-glucosaminide substrate it was confirmed as β-hexosaminidase. Under reducing conditions in SDS-PAGE, the purified enzyme dissociated into three bands (Mr 33, 20 and 15 kDa). The prominent bands (20 and 15 kDa) showed immunological cross-reactivity with the human Hexosaminidase B antibody in a western blot experiment. In gel digestion of the purified enzyme, followed by proteomic analysis using tandom MS/MS revealed sequence identity as compared to the genomic sequence of the Momordica charantia with a score of 57 (24% sequence coverage). Additionally, by CD analysis the purified β-hexosaminidase showed 39.1% of α-helix. Furthermore, secondary structure variations were observed in presence of substrate, lectin and at different pH values. Protein body membrane prepared from the isolated protein bodies showed a pH dependent interaction with the purified lectin and mixture of glycosidases.

Crystal structure of an L-type lectin domain from archaea

The crystal structures of an L-type lectin domain from Methanocaldococcus jannaschii in apo and mannose-bound forms have been determined. A thorough investigation of L-type lectin domains from several organisms provides insight into the differences in these domains from different kingdoms of life. While the overall fold of the L-type lectin domain is conserved, differences in the lengths of the carbohydrate-binding loops and significant variations in the Mn²⁺ -binding site compared to the Ca²⁺ -binding site are observed. Furthermore, the sequence and phylogenetic analyses suggest that the archaeal L-type lectin domain is evolutionarily closer to the plant legume lectins than to its bacterial or animal counterparts. This is the first report of the biochemical, structural, sequence, and phylogenetic analyses of an L-type lectin domain from archaea and serves to enhance our understanding of the species-specific differences and evolution of L-type lectin domains.

Molecular Level Sucrose Quantification: A Critical Review

Sucrose is a primary metabolite in plants, a source of energy, a source of carbon atoms for growth and development, and a regulator of biochemical processes. Most of the traditional analytical chemistry methods for sucrose quantification in plants require sample treatment (with consequent tissue destruction) and complex facilities, that do not allow real-time sucrose quantification at ultra-low concentrations (nM to pM range) under in vivo conditions, limiting our understanding of sucrose roles in plant physiology across different plant tissues and cellular compartments. Some of the above-mentioned problems may be circumvented with the use of bio-compatible ligands for molecular recognition of sucrose. Nevertheless, problems such as the signal-noise ratio, stability, and selectivity are some of the main challenges limiting the use of molecular recognition methods for the in vivo quantification of sucrose. In this review, we provide a critical analysis of the existing analytical chemistry tools, biosensors, and synthetic ligands, for sucrose quantification and discuss the most promising paths to improve upon its limits of detection. Our goal is to highlight the criteria design need for real-time, in vivo, highly sensitive and selective sucrose sensing capabilities to enable further our understanding of living organisms, the development of new plant breeding strategies for increased crop productivity and sustainability, and ultimately to contribute to the overarching need for food security.

Advances in magnetic nanoparticles for the separation of foodborne pathogens: Recognition, separation strategy, and application

Foodborne pathogens contamination is one of the main sources of food safety problems. Although the existing detection methods have been developed for a long time, the complexity of food samples is still the main factor affecting the detection time and sensitivity, and the rapid separation and enrichment of pathogens is still an objective to be studied. Magnetic separation strategy based on magnetic nanoparticles (MNPs) is considered to be an effective tool for rapid separation and enrichment of foodborne pathogens in food. Therefore, this study comprehensively reviews the development of MNPs in the separation of foodborne pathogens over the past decade. First, various biorecognition reagents for identification of foodborne pathogens and their modifications on the surface of MNPs are introduced. Then, the factors affecting the separation of foodborne pathogens, including the size of MNPs, modification methods, separation strategies and separation forms are discussed. Finally, the application of MNPs in integrated detection methods is reviewed. Moreover, current challenges and prospects of MNPs for the analysis of foodborne pathogens are discussed. Further research should focus on the design of multifunctional MNPs, the processing of large-scale samples, the simultaneous analysis of multiple targets, and the development of all-in-one small analytical device with separation and detection.

A novel partial denitrification, anammox-biological phosphorus removal, fermentation and partial nitrification (PDA-PFPN) process for real domestic wastewater and waste activated sludge treatment

A novel process was developed for real domestic wastewater and waste activated sludge (WAS) treatment based on partial denitrification, anammox-biological phosphorus removal, fermentation and partial nitrification (PDA-PFPN). After 246 days of operation, the effluent concentrations of NH₄⁺-N, NO₂^--N and NO₃^--N were below detection limits (0.1 mg/L), and the effluent concentration of PO₄^3--P was 0.1 mg/L without the addition of external carbon source in PDA-PFPN system. Moreover, the sludge reduction efficiency reached 48.1% due to fermentation. The nitrite accumulation ratios by ammonia oxidation and nitrate reduction pathway were 60.6% and 87%, respectively. Intracellular metabolites measured by liquid chromatography mass spectrometer (LC-MS/MS) suggested that different intracellular amino acids were stored and consumed at different duration, and intracellular Valine, Glycine and Lysine were not utilized in oxic stage. Results of flow cytometry showed that the proportion of intact cells decreased from 94.7% to 82.9%, and necrotic cells increased from 5.3% to 17.1% with the increase of DNA content in sludge supernatant and cell decay rate, indicating the occurrence of cell death and lysis and leading to WAS reduction. Analysis of transcriptional community composition revealed that partial denitrification bacteria (Thauera), anammox bacteria (Candidatus Brocadia and Candidatus Kuenenia), simultaneous phosphorus removal and fermentation bacteria (Tetrasphaera) and partial nitrification bacteria (Nitrosomonas) coexisted and actually worked in PDA-PFPN system. The novel PDA-PFPN process simultaneously achieved highly efficient nitrogen and phosphorus removal and WAS reduction without the addition of external carbon source, which greatly reduced the operation cost of carbon source dosing and WAS treatment in wastewater treatment.

Intermittent pH control strategy in sludge anaerobic fermentation: Higher short-chain fatty acids production, lower alkali consumption, and simpler control

The pH control to promote short-chain fatty acids (SCFAs) production during anaerobic alkaline fermentation basically focused on constant pH control. In this study, a simple and consumption-reducing intermittent pH control strategy at moderate temperature (23 ± 2 °C) was investigated with adjusting pH to 10 when naturally reduced to 8. The intermittent pH control strategy could alleviate the inhibition of acid-producing bacteria by strong alkaline and high FA concentration. Meanwhile, microbial diversity promoted by 6% and 69% while the relative abundance of acid-producing bacteria increased by 36% and 61% compared to blank and constant pH fermenters. The relative genes abundance related to amino acid metabolism and fatty acid production were mostly promoted and led to enhanced SCFAs production. In the long-term fermenter, the intermittent pH control strategy could result in a 68% reduction in alkali consumption and a 37% increase in SCFAs production compared to that of the constant pH at 10.

Detection of Lectin Protein Allergen of Kidney Beans (Phaseolus vulgaris L.) and Desensitization Food Processing Technology

With the increase of food allergy events related to not properly cooked kidney beans (Phaseolus vulgaris L.), more and more researchers are paying attention to the sensitization potential of lectin, one of the major storage and defensive proteins with the specific carbohydrate-binding activity. The immunoglobulin E (IgE), non-IgE, and mixed allergic reactions induced by the lectins were inducted in the current paper, and the detection methods of kidney bean lectin, including the purification strategies, hemagglutination activity, specific polysaccharide or glycoprotein interactions, antibody combinations, mass spectrometry methods, and allergomics strategies, were summarized, while various food processing aspects, such as the physical thermal processing, physical non-thermal processing, chemical modifications, and biological treatments, were reviewed in the potential of sensitization reduction. It might be the first comprehensive review on lectin allergen detection from kidney bean and the desensitization strategy in food processing and will provide a basis for food safety control.

Achieving enhanced biological phosphorus removal utilizing waste activated sludge as sole carbon source and simultaneous sludge reduction in sequencing batch reactor

Achieving enhanced biological phosphorus removal dominated by Tetrasphaera utilizing waste activated sludge (WAS) as carbon source could solve the problems of insufficient carbon source and excessive discharge of WAS in biological phosphorus removal. Up to now, the sludge reduction ability of Tetrasphaera remained largely unknown. Furthermore, the difference between traditional sludge fermentation and sludge fermentation dominated by Tetrasphaera was still unclear. In this study, two different sequencing batch reactors (SBRs) were operated. WAS from SBR-parent was utilized as sole carbon source to enrich Tetrasphaera with the relative abundance of 91.9% in SBR-Tetrasphaera. PO₄^3--P removal and sludge reduction could simultaneously be achieved. The effluent concentration of PO₄^3--P was 0, and the sludge reduction efficiency reached about 44.14% without pretreatment of sludge. Cell integrity detected by flow cytometry, the increase of DNA concentration in the sludge supernatant and decrease of particle size of activated sludge indicated that cell death and lysis occurred in sludge reduction dominated by Tetrasphaera. Stable structure of activated sludge was also damaged in this process, which led to the sludge reduction. By analyzing the excitation-emission matrix spectra of extracellular polymeric substances and the changes of carbohydrate and protein concentration, this study proved that slowly biodegradable organics (e.g., soluble microbial byproduct, tyrosine and tryptophan aromatic protein) could be better hydrolyzed and acidized to volatile fatty acids (VFAs) in sludge fermentation dominated by Tetrasphaera than traditional sludge fermentation, which provided carbon source for biological nutrients removal and saved operation cost in wastewater treatment.

Research advances and prospects of legume lectins

Lectins are widely distributed proteins having ability of binding selectively and reversibly with carbohydrates moieties and glycoconjugates. Although lectins have been reported from different biological sources, the legume lectins are the best-characterized family of plant lectins. Legume lectins are a large family of homologous proteins with considerable similarity in amino acid sequence and their tertiary structures. Despite having strong sequence conservation, these lectins show remarkable variability in carbohydrate specificity and quaternary structures. The ability of legume lectins in recognizing glycans and glycoconjugates on cells and other intracellular structures make them a valuable research tool in glycomic research. Due to variability in binding with glycans, glycoconjugates and multiple biological functions, legume lectins are the subject of intense research for their diverse application in different fields such as glycobiology, biomedical research and crop improvement. The present review specially focuses on structural and functional characteristics of legume lectins along with their potential areas of application.

Plant lectins and their many roles: Carbohydrate-binding and beyond

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 climate-resilient crops, or by regulating metabolic pathways by applications of plant growth regulators.

In silico analysis of carbohydrate-binding pockets in the lectin genes from various species of Canavalia

Legumes are endowed with an opulent class of proteins called lectins that can detect tenuous variations in carbohydrate structures and bind them reversibly with high affinity and specificity. The genus Canavalia, in the family of Leguminosae, is considered to be an affluent source of lectin. An effort has been made to analyse the sequences encoded by the lectin gene and its carbohydrate binding pockets from three species of Canavalia, including C. virosa, C. rosea, and C. pubescens. Crude seed extract showed highest haemagglutination titer against buffalo RBCs and has high affinity to mannose and trehalose. Amplification of the lectin gene by gene-specific primers showed the presence of an 870 bp amplicon. Physicochemical characterization using various bioinformatic tools showed that the isoelectric point was below 7, suggesting that lectin molecules were acidic. A high aliphatic index and high instability index were observed, which indicated that lectin molecules were stable towards a wide range of temperatures. The occurrence of N-glycosylation sites at two sites was also identified in all three species. Prediction of secondary structure showed that approximately 59.05 %, 56.76 % and 54.88 % of the elements were random coils in the case of C. virosa, C. pubescens and C. rosea, respectively. Comparative modelling of the proteins and docking of hypothetical models with sugar moieties that inhibited the agglutination activity suggested that asparagine, serine, alanine, valine, tyrosine and threonine were the major residues involved in hydrogen bonding and other stacking interactions. This can further provide insights on its prospective antibiosis property.

Novel insights into integrated fermentation and nitrogen removal by free nitrous acid (FNA) serving as treatment method

Free nitrous acid (FNA) has only been studied as the pretreatment of waste activated sludge (WAS). Integrated fermentation and nitrogen removal using FNA as a primary means of treatment are seldom investigated. WAS fermentation was characterized under various FNA concentration. The production of COD, protein, and carbohydrate increased with FNA concentration (in the range of 0.197-1.97 mg/L) before the denitrification process. Volatile fatty acids (VFA) were only produced after complete denitrification. Potential FNA impact on fermentation step found FNA facilitated both solubilization and hydrolysis but inhibited acidification, acetogenesis, and methanogenesis processes. The types of fermentation were determined using threedimensional excitation-emission matrix (EEM) fluorescence spectroscopy. Protein-like substances and Tyrosine/Tryptophan were the most dominant dissolved organic matters (DOMs). The cell decay rate increased from 0.044 to 0.102/d based on the nonlinear fitting for the FNA concentration of 0.197-1.97 mg/L. The microbial biomass mortality reached 92.7% when the FNA in tight extracellular polymeric substances (T-EPS) exceeded 0.04 mg/L. In addition, the microbial diversity and microbial structure were substantially reduced by FNA during long-term operation, while the bacterial abundance associated with hydrolysis and acidification increased significantly.

Enhancing the digestion of waste activated sludge through nitrite addition: insight on mechanism through profiles of extracellular polymeric substances (EPS) and microbial communities

Extracellular nitrite has been used to improve the digestion of waste activated sludge (WAS). However, the underlying mechanism remains largely unknown. In this study, WAS was treated with 0.2 gNO₂^--N/gVSS for 7 days and its performance was compared to that of aerobic and anaerobic treatments. The addition of nitrite had a distinct effect on the reduction of VSS/SS and the accumulation of soluble organics compared to the control reactors. As evident by the variations of extracellular polymeric substances (EPS), nitrite addition had a positive effect on decreasing protein. In particular, the decrease of protein mainly occurred in tightly bound EPS (TB-EPS), which caused sludge disintegration and enhanced sludge reduction. Additionally, the decrease of microbial diversity with nitrite addition was significant compared to the control reactors, accompany with a decrease of live/dead cells ratio and an increase of supernatant DNA concentration. This suggests that nitrite could cause cell death and lysis, resulting in sludge degradation. Thus, nitrite addition enhanced sludge treatment through the combined effect of TB-EPS disintegration and cell lysis. These findings will be useful for the optimization of sludge treatment process based on nitrite addition.

Crystal structure of the legume lectin-like domain of an ERGIC-53-like protein from Entamoeba histolytica

ERGIC-53-like proteins are type I membrane proteins that belong to the class of intracellular cargo receptors and are known to be indispensable for the intracellular transport of glycoproteins. They are implicated in transporting glycoproteins between the endoplasmic reticulum and the Golgi body. The crystal structure of the legume lectin-like domain of an ERGIC-53-like protein from Entamoeba histolytica has been determined at 2.4 Å resolution. Although the overall structure of the domain resembles those of its mammalian and yeast orthologs (ERGIC-53 and Emp46, respectively), there are significant changes in the carbohydrate-binding site. A sequence-based search revealed the presence of several homologs of ERGIC-53 in different species of Entamoeba. This is the first report of the structural characterization of a member of this class of proteins from a protozoan and serves to further knowledge and understanding regarding the species-specific differences.

Application of Concanavalin A-Linked Magnetic Beads for the Detection of Hepatitis A Virus

Prompt and inexpensive detection of hepatitis A virus (HAV) is essential to control acute hepatitis outbreaks associated with the consumption of contaminated raw or minimally processed food. In this study, various carbohydrate-binding lectins, including concanavalin A (Con A), wheat germ agglutinin, and soybean agglutinin, were compared for their binding affinity to HAV. Con A, which showed significantly higher binding affinity than other lectins, was used to develop an alternative and affordable method to conventional antibody-linked immunomagnetic separation prior to detection of HAV using reverse transcriptase PCR. This method, Con A-linked immunomagnetic separation combined with reverse transcriptase PCR, can detect HAV at a dilution concentration of 10^-4 of the virus stock (titer: 10⁴ median tissue culture infective dose per mL), indicating that Con A could be a promising candidate for concentrating HAV.

Biochemical and structural characterization of a mannose binding jacalin-related lectin with two-sugar binding sites from pineapple (Ananas comosus) stem

A mannose binding jacalin-related lectin from Ananas comosus stem (AcmJRL) was purified and biochemically characterized. This lectin is homogeneous according to native, SDS-PAGE and N-terminal sequencing and the theoretical molecular mass was confirmed by ESI-Q-TOF-MS. AcmJRL was found homodimeric in solution by size-exclusion chromatography. Rat erythrocytes are agglutinated by AcmJRL while no agglutination activity is detected against rabbit and sheep erythrocytes. Hemagglutination activity was found more strongly inhibited by mannooligomannosides than by D-mannose. The carbohydrate-binding specificity of AcmJRL was determined in some detail by isothermal titration calorimetry. All sugars tested were found to bind with low affinity to AcmJRL, with K_a values in the mM range. In agreement with hemagglutination assays, the affinity increased from D-mannose to di-, tri- and penta-mannooligosaccharides. Moreover, the X-ray crystal structure of AcmJRL was obtained in an apo form as well as in complex with D-mannose and methyl-α-D-mannopyranoside, revealing two carbohydrate-binding sites per monomer similar to the banana lectin BanLec. The absence of a wall separating the two binding sites, the conformation of β7β8 loop and the hemagglutinating activity are reminiscent of the BanLec His84Thr mutant, which presents a strong anti-HIV activity in absence of mitogenic activity.

Insight into Erythrina Lectins: Properties, Structure and Proposed Physiological Significance

The genus Erythrina, collectively known as “coral tree”, are pantropical plants, comprising of more than 112 species. Since the early 1980s, seven of these have been found to possess hemagglutinating activity, although not yet characterized. However, around two dozen galactose-binding lectins have been isolated and fully characterized with respect to their sugar specificity, glycoconjugates agglutination, dependence of activity on metal ions, primary and secondary structures and stability. Three lectins have been fully sequenced and the crystal structures of the two proteins have been solved with and without the haptenic sugar. Lectins isolation and characterization from most of these species usually originated from the seeds, although the proteins from other vegetative tissues have also been reported. The main objective of this review is to summarize the physicochemical and biological properties of the reported purified Erythrina lectins to date. Structural comparisons, based on available lectins sequences, are also made to relate the intrinsic physical and chemical properties of these proteins. Particular attention is also given to the proposed biological significance of the lectins from the genus Erythrina.

Legume Lectins: Proteins with Diverse Applications

Lectins are a diverse class of proteins distributed extensively in nature. Among these proteins; legume lectins display a variety of interesting features including antimicrobial; insecticidal and antitumor activities. Because lectins recognize and bind to specific glycoconjugates present on the surface of cells and intracellular structures; they can serve as potential target molecules for developing practical applications in the fields of food; agriculture; health and pharmaceutical research. This review presents the current knowledge of the main structural characteristics of legume lectins and the relationship of structure to the exhibited specificities; provides an overview of their particular antimicrobial; insecticidal and antitumor biological activities and describes possible applications based on the pattern of recognized glyco-targets.

The Distribution of Lectins across the Phylum Nematoda: A Genome-Wide Search

Nematodes are a very diverse phylum that has adapted to nearly every ecosystem. They have developed specialized lifestyles, dividing the phylum into free-living, animal, and plant parasitic species. Their sheer abundance in numbers and presence in nearly every ecosystem make them the most prevalent animals on earth. In this research nematode-specific profiles were designed to retrieve predicted lectin-like domains from the sequence data of nematode genomes and transcriptomes. Lectins are carbohydrate-binding proteins that play numerous roles inside and outside the cell depending on their sugar specificity and associated protein domains. The sugar-binding properties of the retrieved lectin-like proteins were predicted in silico. Although most research has focused on C-type lectin-like, galectin-like, and calreticulin-like proteins in nematodes, we show that the lectin-like repertoire in nematodes is far more diverse. We focused on C-type lectins, which are abundantly present in all investigated nematode species, but seem to be far more abundant in free-living species. Although C-type lectin-like proteins are omnipresent in nematodes, we have shown that only a small part possesses the residues that are thought to be essential for carbohydrate binding. Curiously, hevein, a typical plant lectin domain not reported in animals before, was found in some nematode species.

Novel interactions of complex carbohydrates with peanut (PNA), Ricinus communis (RCA-I), Sambucus nigra (SNA-I) and wheat germ (WGA) agglutinins as revealed by the binding specificities of these lectins towards mucin core-2 O-linked and N-linked glycans and related structures

Plant lectins through their multivalent quaternary structures bind intrinsically flexible oligosaccharides. They recognize fine structural differences in carbohydrates and interact with different sequences in mucin core 2 or complex-type N-glycan chain and also in healthy and malignant tissues. They are used in characterizing cellular and extracellular glycoconjugates modified in pathological processes. We study here, the complex carbohydrate-lectin interactions by determining the effects of substituents in mucin core 2 tetrasaccharide Galβ1-4GlcNAcβ1-6(Galβ1-3)GalNAcα-O-R and fetuin glycopeptides on their binding to agarose-immobilized lectins PNA, RCA-I, SNA-I and WGA. Briefly, in mucin core 2 tetrasaccharide (i) structures modified by α2-3/6-Sialyl LacNAc, LewisX and α1-3-Galactosyl LacNAc resulted in regular binding to PNA whereas compounds with 6-sulfo LacNAc displayed no-binding; (ii) strucures bearing α2-6-sialyl 6-sulfo LacNAc, or 6-sialyl LacdiNAc carbohydrates displayed strong binding to SNA-I; (iii) structures with α2-3/6-sialyl, α1-3Gal LacNAc or LewisX were non-binder to RCA-I and compounds with 6-sulfo LacNAc only displayed weak binding; (iv) structures containing LewisX, 6-Sulfo LewisX, α2-3/6-sialyl LacNAc, α2-3/6-sialyl 6-sulfo LacNAc and GalNAc Lewis-a were non-binding to WGA, those with α1-2Fucosyl, α1-3-Galactosyl LacNAc, α2-3-sialyl T-hapten plus 3'/6'sulfo LacNAc displayed weak binding, and compounds with α2-3-sialyl T-hapten, α2.6-Sialyl LacdiNAc, α2-3-sialyl D-Fucβ1-3 GalNAc and Fucα-1-2 D-Fucβ-1-3GalNAc displaying regular binding and GalNAc LewisX and LacdiNAc plus D-Fuc β-1-3 GalNAcα resulting in tight binding. RCA-I binds Fetuin triantennary asialoglycopeptide 100 % after α-2-3 and 25 % after α-2-6 sialylation, 30 % after α-1-2 and 100 % after α-1-3 fucosylation, and 50 % after α-1-3 galactosylation. WGA binds 3-but not 6-Fucosyl chitobiose core. Thus, information on the influence of complex carbohydrate chain constituents on lectin binding is apparently essential for the potential application of lectins in glycoconjugate research.

Computational Analysis of the Ligand Binding Site of the Extracellular ATP Receptor, DORN1

DORN1 (also known as P2K1) is a plant receptor for extracellular ATP, which belongs to a large gene family of legume-type (L-type) lectin receptor kinases. Extracellular ATP binds to DORN1 with strong affinity through its lectin domain, and the binding triggers a variety of intracellular activities in response to biotic and abiotic stresses. However, information on the tertiary structure of the ligand binding site of DORN1is lacking, which hampers efforts to fully elucidate the mechanism of receptor action. Available data of the crystal structures from more than 50 L-type lectins enable us to perform an in silico study of molecular interaction between DORN1 and ATP. In this study, we employed a computational approach to develop a tertiary structure model of the DORN1 lectin domain. A blind docking analysis demonstrated that ATP binds to a cavity made by four loops (defined as loops A B, C and D) of the DORN1 lectin domain with high affinity. In silico target docking of ATP to the DORN1 binding site predicted interaction with 12 residues, located on the four loops, via hydrogen bonds and hydrophobic interactions. The ATP binding pocket is structurally similar in location to the carbohydrate binding pocket of the canonical L-type lectins. However, four of the residues predicted to interact with ATP are not conserved between DORN1 and the other carbohydrate-binding lectins, suggesting that diversifying selection acting on these key residues may have led to the ATP binding activity of DORN1. The in silico model was validated by in vitro ATP binding assays using the purified extracellular lectin domain of wild-type DORN1, as well as mutated DORN1 lacking key ATP binding residues.

Structural analysis of Centrolobium tomentosum seed lectin with inflammatory activity

A glycosylated lectin (CTL) with specificity for mannose and glucose has been detected and purified from seeds of Centrolobium tomentosum, a legume plant from Dalbergieae tribe. It was isolated by mannose-sepharose affinity chromatography. The primary structure was determined by tandem mass spectrometry and consists of 245 amino acids, similar to other Dalbergieae lectins. CTL structures were solved from two crystal forms, a monoclinic and a tetragonal, diffracted at 2.25 and 1.9 Å, respectively. The carbohydrate recognition domain (CRD), metal-binding site and glycosylation site were characterized, and the structural basis for mannose/glucose-binding was elucidated. The lectin adopts the canonical dimeric organization of legume lectins. CTL showed acute inflammatory effect in paw edema model. The protein was subjected to ligand screening (dimannosides and trimannoside) by molecular docking, and interactions were compared with similar lectins possessing the same ligand specificity. This is the first crystal structure of mannose/glucose native seed lectin with proinflammatory activity isolated from the Centrolobium genus.

Mutated Leguminous Lectin Containing a Heparin-Binding like Motif in a Carbohydrate-Binding Loop Specifically Binds to Heparin

We previously introduced random mutations in the sugar-binding loops of a leguminous lectin and screened the resulting mutated lectins for novel specificities using cell surface display. Screening of a mutated peanut agglutinin (PNA), revealed a mutated PNA with a distinct preference for heparin. Glycan microarray analyses using the mutated lectin fused to the Fc region of human immunoglobulin, revealed that a particular sulfated glycosaminoglycan (GAG), heparin, had the highest binding affinity for mutated PNA among 97 glycans tested, although wild-type PNA showed affinity towards Galβ1-3GalNAc and similar galactosylated glycans. Further analyses of binding specificity using an enzyme-linked immunoadsorbent assay demonstrated that the mutated PNA specifically binds to heparin, and weakly to de-2-O-sulfated heparin, but not to other GAG chains including de-6-O-sulfated and de-N-sulfated heparins. The mutated PNA had six amino acid substitutions within the eight amino acid-long sugar-binding loop. In this loop, the heparin-binding like motif comprised three arginine residues at positions 124, 128, and 129, and a histidine at position 125 was present. Substitution of each arginine or histidine residue to alanine reduced heparin-binding ability, indicating that all of these basic amino acid residues contributed to heparin binding. Inhibition assay demonstrated that heparin and dextran sulfate strongly inhibited mutated PNA binding to heparin in dose-dependent manner. The mutated PNA could distinguish between CHO cells and proteoglycan-deficient mutant cells. This is the first report establishing a novel leguminous lectin that preferentially binds to highly sulfated heparin and may provide novel GAG-binding probes to distinguish between heterogeneous GAG repeating units.

Mammalian Cell Surface Display as a Novel Method for Developing Engineered Lectins with Novel Characteristics

Leguminous lectins have a conserved carbohydrate recognition site comprising four loops (A–D). Here, we randomly mutated the sequence and length of loops C and D of peanut agglutinin (PNA) and expressed the proteins on the surface of mouse green fluorescent protein (GFP)-reporter cells. Flow cytometry, limiting dilution, and cDNA cloning were used to screen for several mutated PNAs with distinct properties. The mutated PNA clones obtained using NeuAcα2-6(Galβ1-3)GalNAc as a ligand showed preference for NeuAcα2-6(Galβ1-3)GalNAc rather than non-sialylated Galβ1-3GlcNAc, whereas wild-type PNA binds to Galβ1-3GlcNAc but not sialylated Galβ1-3GalNAc. Sequence analyses revealed that for all of the glycan-reactive mutated PNA clones, (i) loop C was eight amino acids in length, (ii) loop D was identical to that of wild-type PNA, (iii) residue 127 was asparagine, (iv) residue 125 was tryptophan, and (v) residue 130 was hydrophobic tyrosine, phenylalanine, or histidine. The sugar-binding ability of wild-type PNA was increased nine-fold when Tyr125 was mutated to tryptophan, and that of mutated clone C was increased more than 30-fold after His130 was changed to tyrosine. These results provide an insight into the relationship between the amino acid sequences of the carbohydrate recognition site and sugar-binding abilities of leguminous lectins.

The interaction of N-trifluoroacetylgalactosamine and its derivatives with winged bean (Psophocarpus tetragonolobus) basic agglutinin reveals differential mechanism of their recognition: a fluorine-19 nuclear magnetic resonance study

Here, we show the binding results of a leguminosae lectin, winged bean basic agglutinin (WBA I) to N-trifluoroacetylgalactosamine (NTFAGalN), methyl-α-N-trifluoroacetylgalactosamine (MeαNTFAGalN) and methyl-β-tifluoroacetylgalactosamine (MeβNTFAGalN) using (19) F NMR spectroscopy. No chemical shift difference between the free and bound states for NTFAGalN and MeβNTFAGalN, and 0.01-ppm chemical shift change for MeαNTFAGalN, demonstrate that the MeαNTFAGalN has a sufficiently long residence time on the protein binding site as compared to MeβNTFAGalN and the free anomers of NTFAGalN. The sugar anomers were found in slow exchange with the binding site of agglutinin. Consequently, we obtained their binding parameters to the protein using line shape analyses. Aforementioned analyses of the activation parameters for the interactions of these saccharides indicate that the binding of α and β anomers of NTFAGalN and MeαNTFAGalN is controlled enthalpically, while that of MeβNTFAGalN is controlled entropically. This asserts the sterically constrained nature of the interaction of the MeβNTFAGalN with WBA I. These studies thus highlight a significant role of the conformation of the monosaccharide ligands for their recognition by WBA I.

Isolation and biochemical characterization of Apios tuber lectin

Apios tuber lectin, named ATL, was isolated from Apios americana Medikus by two chromatography steps, hydrophobic chromatography and anion-exchange chromatography. The minimum concentration required for the hemagglutination activity toward rabbit erythrocytes of ATL was 4 μg/mL. ATL was composed of a homodimer of 28.4 kDa subunits. The amino acid sequence of ATL was similar to those of other legume lectins. The lectin showed moderate stability toward heating and acidic pH, and the binding affinity against several monosaccharides, such as D-glucosamine and D-galactosamine. ATL also bound to desialylated or agalactosylated glycoproteins such as asialo and agalacto transferrin. ATL decreased the transepithelial electrical resistance across human intestinal Caco-2 cell monolayers, suggesting the effect on the tight junction-mediated paracellular transport.

Insights into animal and plant lectins with antimicrobial activities

Lectins are multivalent proteins with the ability to recognize and bind diverse carbohydrate structures. The glyco -binding and diverse molecular structures observed in these protein classes make them a large and heterogeneous group with a wide range of biological activities in microorganisms, animals and plants. Lectins from plants and animals are commonly used in direct defense against pathogens and in immune regulation. This review focuses on sources of animal and plant lectins, describing their functional classification and tridimensional structures, relating these properties with biotechnological purposes, including antimicrobial activities. In summary, this work focuses on structural-functional elucidation of diverse lectin groups, shedding some light on host-pathogen interactions; it also examines their emergence as biotechnological tools through gene manipulation and development of new drugs.

High-resolution structure of a new Tn antigen-binding lectin from Vatairea macrocarpa and a comparative analysis of Tn-binding legume lectins

Plant lectins have been studied as histological markers and promising antineoplastic molecules for a long time, and structural characterization of different lectins bound to specific cancer epitopes has been carried out successfully. The crystal structures of Vatairea macrocarpa (VML) seed lectin in complex with GalNAc-α-O-Ser (Tn antigen) and GalNAc have been determined at the resolution of 1.4Å and 1.7Å, respectively. Molecular docking analysis of this new structure and other Tn-binding legume lectins to O-mucin fragments differently decorated with this antigen provides a comparative binding profile among these proteins, stressing that subtle alterations that may not influence monosaccharide binding can, nonetheless, directly impact the ability of these lectins to recognize naturally occurring antigens. In addition to the specific biological effects of VML, the structural and binding similarities between it and other lectins commonly used as histological markers (e.g., VVLB4 and SBA) strongly suggest VML as a candidate tool for cancer research.

Structural basis of ConM binding with resveratrol, an anti-inflammatory and antioxidant polyphenol

Resveratrol can also inhibit the activation of proinflammatory mediators and cytokines at the early gene expression stage. It is well known that lectins are sugar-binding proteins that act as both pro- and anti-inflammatory molecules. Thus, the objective of this work was to verify the binding of a polyphenol compound with a lectin of Canavalia maritima (ConM) based on their ability to inhibit pro-inflammatory processes. To accomplish this, ConM was purified and crystallized, and resveratrol was soaked at 5mM for 2h of incubation. The crystal belongs to the monoclinic space group C2, the final refinement resulted in an Rfactor of 16.0% and an Rfree of 25.5%. Resveratrol binds in the rigid β-sheet through H-bonds and hydrophobic interaction with amino acids that compose the fifth and sixth β-strands of the rigid β-sheet of ConM. The ConM and resveratrol inhibited DPPH oxidation, showing synergic activity with the most effective ratio of 2:3 and carbohydrate binding site is not directly related to antioxidant activity. It is the interaction between ConM and resveratrol that indicates the synergism of these two molecules in acting as free radicals scavengers and in reducing the inflammatory process through the inhibition of many pro-inflammatory events.

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.

Effects of jacalin and follicle-stimulating hormone on in vitro goat primordial follicle activation, survival and gene expression

This study aims to investigate the effects of jacalin and follicle-stimulating hormone (FSH) on activation and survival of goat primordial follicles, as well as on gene expression in cultured ovarian tissue. Ovarian fragments were cultured for 6 days in minimum essential medium (MEM) supplemented with jacalin (10, 25, 50 or 100 μg/ml – Experiment 1) or in MEM supplemented with jacalin (50 μg/ml), FSH (50 ng/ml) or both (Experiment 2). Non-cultured and cultured tissues were processed for histological and ultrastructural analysis. Cultured tissues from Experiment 2 were also stored to evaluate the expression of BMP-15, KL (Kit ligand), c-kit, GDF-9 and proliferating cell nuclear antigen (PCNA) by real-time polymerase chain reaction (PCR). The results of Experiment 1 showed that, compared with tissue that was cultured in control medium, the presence of 50 μg/ml of jacalin increased both the percentages of developing follicles and viability. In Experiment 2, after 6 days, higher percentages of normal follicles were observed in tissue cultured in presence of FSH, jacalin or both, but no synergistic interaction between FSH and jacalin was observed. These substances had no significant effect on the levels of mRNA for BMP-15 and KL, but FSH increased significantly the levels of mRNA for PCNA and c-kit. On the other hand, jacalin reduced the levels of mRNA for GDF-9. In conclusion, jacalin and FSH are able to improve primordial follicle activation and survival after 6 days of culture. Furthermore, presence of FSH increases the expression of mRNA for PCNA and c-kit, but jacalin resulted in lower GDF-9 mRNA expression.

Purification and cDNA cloning of a lectin and a lectin-like protein from Apios americana Medikus tubers

An Apios americana lectin (AAL) and a lectin-like protein (AALP) were purified from tubers by chromatography on Butyl-Cellulofine, ovomucoid-Cellulofine, and DEAE-Cellulofine columns. AAL showed strong hemagglutinating activity toward chicken and goose erythrocytes, but AALP showed no such activity toward any of the erythrocytes tested. The hemagglutinating activity of AAL was not inhibited by mono- or disaccharides, but was inhibited by glycoproteins, such as asialofetuin and ovomucoid, suggesting that AAL is an oligosaccharide-specific lectin. The cDNAs of AAL and AALP consist of 1,093 and 1,104 nucleotides and encode proteins of 302 and 274 amino acid residues, respectively. Both amino acid sequences showed high similarity to known legume lectins, and those of their amino acids involved in carbohydrate and metal binding were conserved.

Effects of Canavalia lectins on acute inflammation in sensitized and non-sensitized rats

The anti-inflammatory activity of Canavalia seed lectins (Canavalia gladiata [CGL], Canavalia maritima [ConM] and Canavalia brasiliensis [ConBr]) was evaluated by intravenous administration in rats. In non-sensitized rats, cellular edema elicited by carrageenan was reduced (45-51 %) by ConM and (44-59 %) by CGL. Osmotic edema elicited by dextran was reduced by ConM and CGL in 27 % and 29 %. ConM and CGL reduced the edema elicited by L-arginine in 53 % and that of prostaglandin E2 in 48 % and 36 %. Leukocyte migration elicited by carrageenan was reduced in 49 % by ConM and in 55 % by CGL (attenuated in 4× by glucose) and peritoneal TNF-α content in 82 %. In rats sensitized, ConM inhibited the paw edema and leukocyte migration elicited by ovalbumin in 34 % and 70 %. ConM and CGL are anti-inflammatory, mainly in cellular events mediated by prostaglandin E₂, nitric oxide and TNF-α in non-sensitized rats. However, only ConM is anti-inflammatory in sensitized rats. CGL effect involves the lectin domain.

Molecular modeling of lectin-like protein from Acacia farnesiana reveals a possible anti-inflammatory mechanism in Carrageenan-induced inflammation

Acacia farnesiana lectin-like protein (AFAL) is a chitin-binding protein and has been classified as phytohaemagglutinin from Phaseolus vulgaris (PHA). Legume lectins are examples for structural studies, and this family of proteins shows a remarkable conservation in primary, secondary, and tertiary structures. Lectins have ability to reduce the effects of inflammation caused by phlogistic agents, such as carrageenan (CGN). This paper explains the anti-inflammatory activity of AFAL through structural comparison with anti-inflammatory legume lectins. The AFAL model was obtained by molecular modeling and molecular docking with glycan and carrageenan were performed to explain the AFAL structural behavior and biological activity. Pisum sativum lectin was the best template for molecular modeling. The AFAL structure model is folded as a β sandwich. The model differs from template in loop regions, number of β strands and carbohydrate-binding site. Carrageenan and glycan bind to different sites on AFAL. The ability of AFAL binding to carrageenan can be explained by absence of the sixth β -strand (posterior β sheets) and two β strands in frontal region. AFAL can inhibit pathway inflammatory process by carrageenan injection by connecting to it and preventing its entry into the cell and triggers the reaction.

Expression of soybean lectin in transgenic tobacco results in enhanced resistance to pathogens and pests

Lectins are proteins of non-immune origin that specifically interact with carbohydrates, known to play important roles in the defense system of plants. In this study, in order to study the function of a new soybean lectin (SBL), the corresponding encoding gene lec-s was introduced into tobacco plants via Agrobacterium-mediated transformation. Southern blot analyses had revealed that the lec-s gene was stable integrated into the chromosome of the tobacco. The results of the reverse transcription polymerase chain reaction (RT-PCR) also indicated that the lec-s gene in the transgenic tobacco plants could be expressed under the control of the constitutive CaMV35S promoter. Evaluation agronomic of the performance had showed that the transgenic plants could resist to the infection of Phytophthora nicotianae. Insect bioassays using detached leaves from transgenic tobacco plants demonstrated that the ectopically expressed SBL significantly (P.0.05) reduced the weight gain of larvae of the beet armyworm (Spodoptera exigua). Further on, the lectins retarded the development of the larvae and their metamorphosis. These findings suggest that soybean lectins have potential as a protective agent against pathogens and insect pests through a transgenic approach.

Plant as a plenteous reserve of lectin

Lectins are clusters of glycoproteins of nonimmune foundation that combine specifically and reversibly to carbohydrates, mainly the sugar moiety of glycoconjugates, resulting in cell agglutination and precipitation of glycoconjugates. They are universally distributed in nature, being established in plants, fungi, viruses, bacteria, crustacea, insects, and animals, but leguminacae plants are rich source of lectins. The present review reveals the structure, biological properties, and application of plant lectins.

Phytohemagglutinin improves the development and ultrastructure of in vitro-cultured goat (Capra hircus) preantral follicles

The objective this study was to determine the effect of phytohemagglutinin (PHA) on survival, growth and gene expression in caprine secondary follicles cultured in vitro. Secondary follicles (∼0.2 mm) were isolated from the cortex of caprine ovaries and cultured individually for 6 days in α-MEM⁺ supplemented with PHA (0, 1, 10, 50, 100, or 200 µg/mL). After 6 days of culture, follicle diameter and survival, antrum formation, ultrastructure and expression of mRNA for FSH receptors (FSH-R), proliferating cell nuclear antigen (PCNA), and neuronal nitric oxide synthase were determined. All treatments maintained follicular survival [α-MEM⁺ (94.59%); 1 µg/mL PHA (96.43%); 10 µg/mL PHA (84.85%); 50 µg/mL PHA (85.29%); 100 µg/mL PHA (88.57%), and 200 µg/mL PHA (87.50)], but the presence of 10 µg/mL PHA in the culture medium increased the antrum formation rate (21.21%) when compared with control (5.41%, P < 0.05) and ensured the maintenance of oocyte and granulosa cell ultrastructures after 6 days of culture. The expression of mRNA for FSH-R (2.7 ± 0.1) and PCNA (4.4 ± 0.2) was also significantly increased in follicles cultured with 10 µg/mL PHA in relation to those cultured in α-MEM⁺ (1.0 ± 0.1). In conclusion, supplementation of culture medium with 10 µg/mL PHA maintains the follicular viability and ultrastructure, and promotes the formation of antral cavity after 6 days of culture in vitro.

Expression of antigen tf and galectin-3 in fibroadenoma

Background

Fibroadenomas are benign human breast tumors, characterized by proliferation of epithelial and stromal components of the terminal ductal unit. They may grow, regress or remain unchanged, as the hormonal environment of the patient changes. Expression of antigen TF in mucin or mucin-type glycoproteins and of galectin-3 seems to contribute to proliferation and transformations events; their expression has been reported in ductal breast cancer and in aggressive tumors.

Findings

Lectin histochemistry, immunohistochemistry, and immunofluorescence were used to examine the expression and distribution of antigen TF and galectin-3. We used lectins from Arachis hypogaea, Artocarpus integrifolia, and Amaranthus lecuocarpus to evaluate TF expression and a monoclonal antibody to evaluate galectin-3 expression. We used paraffin-embedded blocks from 10 breast tissues diagnosed with fibroadenoma and as control 10 healthy tissue samples. Histochemical and immunofluorescence analysis showed positive expression of galectin-3 in fibroadenoma tissue, mainly in stroma, weak interaction in ducts was observed; whereas, in healthy tissue samples the staining was also weak in ducts. Lectins from A. leucocarpus and A. integrifolia specificaly recognized ducts in healthy breast samples, whereas the lectin from A. hypogaea recognized ducts and stroma. In fibroadenoma tissue, the lectins from A. integrifolia, A. Hypogaea, and A. leucocarpus recognized mainly ducts.

Conclusions

Our results suggest that expression of antigen TF and galectin-3 seems to participate in fibroadenoma development.

The enzymatic lectin of field bean (Dolichos lablab): salt assisted lectin-sugar interaction

Field bean seed contains a Gal/GalNAc lectin (DLL-II) that exhibits associated polyphenol oxidase (PPO) activity and does not bind to its sugar specific affinity matrix. The molecular basis for this lack of binding is not known. The DLL-II gene was therefore cloned and its sequence analyzed. A conserved aromatic residue in the sugar binding site required for a stacking interaction with the apolar backbone of Gal is replaced by His in DLL-II, which explains the lack of binding. However, specific sugar binding is achieved by including (NH₄)₂SO₄ in the buffer. Interestingly two other salts of the Hofmeister series, K₂HPO₄ and Na₂SO₄ also assist binding to immobilized galactose. In the presence of (NH₄)₂SO₄ the surface hydrophobicity of DLL-II and dissociation constant for 8-anilino 1-naphthalene sulfonic acid were enhanced three fold. This increased surface hydrophobicity in the presence of salt is probably the cause for assisted sugar binding in legume lectins that lack aromatic stacking interactions. Accordingly, two other lectins which lack the conserved aromatic residue show similar salt assisted binding. The salt concentrations required for Gal/GalNAc binding are not physiologically relevant in vivo, suggesting that the role of DLL-II per se in the seed is primarily that of a PPO purportedly for plant defense.

A lectin from Platypodium elegans with unusual specificity and affinity for asymmetric complex N-glycans

Lectin activity with specificity for mannose and glucose has been detected in the seed of Platypodium elegans, a legume plant from the Dalbergieae tribe. The gene of Platypodium elegans lectin A has been cloned, and the resulting 261-amino acid protein belongs to the legume lectin family with similarity with Pterocarpus angolensis agglutinin from the same tribe. The recombinant lectin has been expressed in Escherichia coli and refolded from inclusion bodies. Analysis of specificity by glycan array evidenced a very unusual preference for complex type N-glycans with asymmetrical branches. A short branch consisting of one mannose residue is preferred on the 6-arm of the N-glycan, whereas extensions by GlcNAc, Gal, and NeuAc are favorable on the 3-arm. Affinities have been obtained by microcalorimetry using symmetrical and asymmetrical Asn-linked heptasaccharides prepared by the semi-synthetic method. Strong affinity with K(d) of 4.5 μm was obtained for both ligands. Crystal structures of Platypodium elegans lectin A complexed with branched trimannose and symmetrical complex-type Asn-linked heptasaccharide have been solved at 2.1 and 1.65 Å resolution, respectively. The lectin adopts the canonical dimeric organization of legume lectins. The trimannose bridges the binding sites of two neighboring dimers, resulting in the formation of infinite chains in the crystal. The Asn-linked heptasaccharide binds with the 6-arm in the primary binding site with extensive additional contacts on both arms. The GlcNAc on the 6-arm is bound in a constrained conformation that may rationalize the higher affinity observed on the glycan array for N-glycans with only a mannose on the 6-arm.

The D-galactose specific lectin of field bean (Dolichos lablab) seed binds sugars with extreme negative cooperativity and half-of-the-sites binding

The field bean (Dolichos lablab) lectin designated as PPO-haemagglutinin (DLL-II) is bifunctional, exhibiting both polyphenol oxidase and haemagglutinating activity. The lectin is unusual in that it binds galactose (Gal), lactose (Lac) and N-acetylgalactosamine (GalNAc) only in the presence of (NH₄)₂SO₄ and exhibits negative cooperativity and half-of-the-sites binding. Circular dichroism, isothermal titration calorimetry and fluorescence quenching were used to assess the sugar binding in the presence of (NH₄)₂O₄. Comparison of the near-UV CD spectra with and without bound sugar revealed ligand induced conformational changes. The intrinsic fluorescence quenching data indicate that DLL-II exhibits weak binding to Gal in the presence of (NH₄)₂SO₄ with a stoichiometry of one bound ligand per dimer. ITC data fitted using a two sets of sites binding model presented a similar picture. The K(a)'s for Gal, Lac and GalNAc in the presence of (NH₄)₂SO₄ were 0.16±0.002, 0.21±0.004 and 8.45±0.78 (×10⁻³) M⁻¹ respectively. The Hill plot for the binding of these sugars to DLL-II was curvilinear with a tangent slope <1.0 indicating negative cooperativity. DLL-II thus exhibits half-of-the-site binding, an extreme form of negative cooperativity in which the second ligand does not bind at all. This is the first report of a legume lectin, exhibiting half-of-the-sites binding.

Identification and characterization of a novel legume-like lectin cDNA sequence from the red marine algae Gracilaria fisheri

A legume-type lectin (L-Lectin) gene of the red algae Gracilaria fisheri (GFL) was cloned by rapid amplification of cDNA ends (RACE). The full-length cDNA of GFL was 1714 bp and contained a 1542 bp open reading frame encoding 513 amino acids with a predicted molecular mass of 56.5 kDa. Analysis of the putative amino acid sequence with NCBI-BLAST revealed a high homology (30-68%) with legume-type lectins (L-lectin) from Griffithsia japonica, Clavispora lusitaniae, Acyrthosiphon pisum, Tetraodon nigroviridis and Xenopus tropicalis. Phylogenetic relationship analysis showed the highest sequence identity to a glycoprotein of the red algae Griffithsia japonica (68%) (GenBank number AAM93989). Conserved Domain Database analysis detected an N-terminal carbohydrate recognition domain (CRD), the characteristic of L-lectins, which contained two sugar binding sites and a metal binding site. The secondary structure prediction of GFL showed a beta-sheet structure, connected with turn and coil. The most abundant structural element of GFL was the random coil, while the alpha-helixes were distributed at the N- and C-termini, and 21 beta-sheets were distributed in the CRD. Computer analysis of three-dimensional structure showed a common feature of L-lectins of GFL, which included an overall globular shape that was composed of a beta-sandwich of two anti-parallel beta-sheets, monosaccharide binding sites, were on the top of the structure and in proximity with a metal binding site. Northern blot analysis using a DIG-labelled probe derived from a partial GFL sequence revealed a hybridization signal of (approx.) 1.7 kb consistent with the length of the full-length GFL cDNA identified by RACE. No detectable band was observed from control total RNA extracted from filamentous green algae.