Amino acid sequence, glycan structure, and proteolytic processing of the lectin of Vatairea macrocarpa seeds

Multivalent lectin-carbohydrate interactions: Energetics and mechanisms of binding

The biological signaling properties of lectins, which are carbohydrate-binding proteins, are due to their ability to bind and cross-link multivalent glycoprotein receptors on the surface of normal and transformed cells. While the cross-linking properties of lectins with multivalent carbohydrates and glycoproteins are relatively well understood, the mechanisms of binding of lectins to multivalent glycoconjugates are less well understood. Recently, the thermodynamics of binding of lectins to synthetic clustered glycosides, a multivalent globular glycoprotein, and to linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules. Importantly, the mechanism of binding of lectins to mucins is similar to that for a variety of protein ligands binding to DNA. Recent analysis also shows that high-affinity lectin-mucin cross-linking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects which facilitate binding and subsequent complex formation including enzymology.

A galactoside-specific Dalbergieae legume lectin from seeds of Vataireopsis araroba (Aguiar) Ducke

The Dalbergieae lectin group encompasses several lectins with significant differences in their carbohydrate specificities and biological properties. The current work reports on the purification and characterization of a GalNAc/Gal-specific lectin from Vataireopsis araroba (Aguiar) Ducke, designated as VaL. The lectin was purified from the seeds in a single step using guar gum affinity chromatography. The lectin migrated as a single band of about 35 kDa on SDS-PAGE and, in native conditions, occurs as a homodimer. The purified lectin is stable at temperatures up to 60 °C and in a pH range from 7 to 8 and requires divalent cations for its activity. Sugar-inhibition assays demonstrate the lectin specificity towards N-acetyl-D-galactosamine, D-galactose and related sugars. Furthermore, glycan array analyses show that VaL interacts preferentially with glycans containing terminal GalNAc/Galβ1-4GlcNAc. Biological activity assays were performed using three insect cell lines: CF1 midgut cells from the spruce budworm Choristoneura fumiferana, S2 embryo cells from the fruit fly Drosophila melanogaster, and GutAW midgut cells from the corn earworm Helicoverpa zea. In vitro assays indicated a biostatic effect for VaL on CF1 cells, but not on S2 and GutAW cells. The lectin presented a biostatic effect by reducing the cell growth and inducing cell agglutination, suggesting an interaction with glycans on the cell surface. VaL has been characterized as a galactoside-specific lectin of the Dalbergieae tribe, with sequence similarity to lectins from Vatairea and Arachis.

Mechanism of Mucin Recognition by Lectins: A Thermodynamic Study

Isothermal titration microcalorimetry (ITC) can directly determine the thermodynamic binding parameters of biological molecules including affinity constant, binding stoichiometry, heat of binding (enthalpy) and indirectly the entropy, and free energy of binding. ITC has been extensively used to study the binding of lectins to mono- and oligosaccharides, but limitedly in applications to lectin-glycoprotein interactions. Inherent experimental challenges to ITC include sample precipitation during the experiment and relative high amount of sample required, but careful design of experiments can minimize these problems and allow valuable information to be obtained. For example, the thermodynamics of binding of lectins to multivalent globular and linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules leading to increased affinity. Importantly, the mechanism of binding of lectins to mucins appears similar to that for a variety of protein ligands binding to DNA. Recent results also show that high-affinity lectin-mucin cross-linking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects that facilitate binding interactions.

Lactose-binding lectin from Vatairea macrocarpa seeds induces in vivo angiogenesis via VEGF and TNF-ɑ expression and modulates in vitro doxorubicin-induced genotoxicity

Lactose-binding lectin from Vatairea macrocarpa seeds (VML) has attracted great attention due to its interesting biological activities, such as pro-inflammatory effects and macrophage activation. This study evaluated the cytotoxicity and genotoxicity/antigenotoxicity of VML in human lymphocytes using the CometChip assay, and angiogenic activity by the chick embryo chorioallantoic membrane (CAM) assay. In genotoxicity, lymphocytes were treated with different concentrations of VML (0.5, 2 and 8 μM). In antigenotoxicity, lymphocytes were treated with the same concentrations of VML concomitant doxorubicin (90 μM DXR). To evaluate angiogenesis, all CAM were treated with different concentrations of VML (0.5, 2 and 8 μM) alone or co-treated with lactose (0.1 M). Furthermore, the levels of vascular endothelial growth factor (VEGF) and tumor necrosis factor-alpha (TNF-α) in CAM were assessed by immunohistochemistry. The results showed that VML was cytotoxic to lymphocytes, genotoxic at the highest concentration (8 μM) and antigenotoxic at low concentrations (0.5, and 2 μM). Regarding the CAM assay and immunohistochemistry, VML was angiogenic and significantly increased VEGF and TNF-α levels. In contrast, co-treatment with lactose significantly reduced the angiogenic effect and VEGF levels. We propose that protein-carbohydrate interactions between VML and glycans in the cell membrane are probably the major events involved in these activities. It seems likely that VML elicits a pro-inflammatory response through VEGF and TNF-α expression, resulting in increased vascularization at the site of inflammation. Therefore, our results show novel information on the effects of VML on DNA, as well as provide data regarded the neovascularization process involving this lectin.

The Galactose-Binding Lectin Isolated from Vatairea macrocarpa Seeds Enhances the Effect of Antibiotics Against Staphylococcus aureus-Resistant Strain

The use of natural products together with standard antimicrobial drugs has recently received more attention as a strategy to combat infectious diseases caused by multidrug-resistant (MDR) microorganisms. This study aimed to evaluate the capacity of a galactose-binding lectin from Vatairea macrocarpa seeds (VML) to modulate antibiotic activity against standard and MDR Staphylococcus aureus and Escherichia coli bacterial strains. The minimum inhibitory concentration (MIC) obtained for VML against all strains was not clinically relevant (MIC ≥ 1024 μg/mL). However, when VML was combined with the antibacterial drugs gentamicin, norfloxacin and penicillin, a significant increase in antibiotic activity was observed against S. aureus, whereas the combination of VML and norfloxacin presented decreased and, hence, antagonistic antibiotic activity against E. coli. By its inhibition of hemagglutinating activity, gentamicin (MIC = 50 mM) revealed its interaction with the carbohydrate-binding site (CBS) of VML. Using molecular docking, it was found that gentamicin interacts with residues that constitute the CBS of VML with a score of - 120.79 MDS. It is this interaction between the antibiotic and the lectin's CBS that may be responsible for the enhanced activity of gentamicin in S. aureus. Thus, our results suggest that the VML can be an effective modulating agent against S. aureus. This is the first study to report the effect of lectins as modulators of bacterial sensitivity, and as such, the outcome of this study could lay the groundwork for future research involving the use of lectins and conventional antibiotics against such infectious diseases such as community-acquired methicillin-resistant S. aureus (MRSA).

A review of Vicieae lectins studies: End of the book or a story in the writing?

Vicieae tribe, Leguminosae family (Fabaceae), has been extensively studied. In particular, the study of lectins. The purification, physicochemical and structural characterizations of the various purified lectins and the analysis of their relevant biological activities are ongoing. In this review, several works already published about Vicieae lectins are addressed. Initially, we presented the purification protocols and the physicochemical aspects, such as specificity for carbohydrates, optimal activity in the face of variations in temperature and pH, as well metals-dependence. Following, structural characterization studies are highlighted and, finally, various biological activities already reported are summarized. Studies on lectins in almost all genera (Lathyrus, Lens, Pisum and Vicia) are considered, with the exception of Vavilovia which studies of lectins have not yet been reported. Like other leguminous lectins, Vicieae lectins present heterogeneous profiles of agglutination profiles for erythrocytes and other cells of the immune system, and glycoproteins. Most Vicieae lectins consist of two subunits, α and β, products of a single precursor protein derived from a single gene. The differences between the isoforms result from varying degrees of proteolytic processing. Along with the identification of these molecules and their characteristics, biological activities become very relevant and robust for both basic and applied research.

Is the orofacial antinociceptive effect of lectins intrinsically related to their specificity to monosaccharides?

Lectins are proteins of non-immunological origin that may play several biological applications, of which we can highlight the anti-inflammatory and antinociceptive activities. In this work, we evaluated the possible effect of orofacial antinociceptive activity of three plant lectins, Dioclea violacea (DVL - Man/Glc-binding), Vatairea macrocarpa (VML - Gal-binding) and PPL (Parkia platycephala - Man/Glc-binding) in adult zebrafish. Acute nociception was induced by menthol (1.2 μM), or capsaicin (4.93 μM) applied into in the upper lip (5.0 μL) of adult wild zebrafish. Zebrafish were pretreated by intraperitoneal injection (20 μL) with vehicle (Control) or lectins (0.025; 0.05 or 0.1 mg/mL) 30 min before induction. The effect of lectins on zebrafish locomotor behavior was evaluated with the open field test. Naive groups (n = 8) were included in all tests. Our results indicate that only PPL presented antinociceptive induced by capsaicin, suggesting the potential clinical application of PPL as inhibitor of orofacial nociception and that this effect may be due to the modulation of TRPV1 channel. In conclusion, lectins that exhibit affinity to the same or different carbohydrates do not necessarily have an antinociceptive effect on the orofacial nociception model, indicating that the glycan carbohydrate binding pattern may be related to the effect on nociception inhibition.

Dalbergieae lectins: A review of lectins from species of a primitive Papilionoideae (leguminous) tribe

Lectins are (glyco)proteins capable of reversibly binding to specific carbohydrates, thus having various functions and applications. Plant lectins are the best studied, and the Leguminoseae family is highlighted in a number of published works, especially species of the Papilionoideae subfamily. Dalbergieae is one of the tribes in this subfamily comprising 49 genera and over 1300 species. From this tribe, about 26 lectins were studied, among which we can highlight the Arachis hypogaea lectin, widely used in cancer studies. Dalbergieae lectins demonstrate various carbohydrate specificities and biological activities including anti-inflammatory, vasorelaxant, nociceptive, antibacterial, antiviral among others. Structurally, these lectins are quite similar in their three-dimensional folding but present significant differences in oligomerization patterns and in the conservation of carbohydrate-recognition domain. Despite the existence of structural data from some lectins, only sparse literature has reported on this tribe's diversity, not to mention the range of biological effects, determined through specific assays. Therefore, this work will review the most important studies on Dalbergieae lectins and their potential biomedical applications.

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.

Purification and primary structure of a novel mannose-specific lectin from Centrolobium microchaete Mart seeds

This study aimed to purify and characterize a novel mannose-binding lectin from the seeds of Centrolobium microchaete. Centrolobium microchaete lectin (CML) was purified by affinity chromatography in mannose-Sepharose-4B column. CML agglutinated rabbit erythrocytes and was inhibited by D-mannose, α-methyl-D-mannoside, D-glucose, N-Acetyl-D-glucosamine and sucrose. The lectin was stable at pH 7.0 and 8.0 and temperatures up to 60°C. The monomeric form of CML showed approximately 28kDa, and its native form is probably a homodimer, as determined by gel filtration chromatography. The primary structure of CML was determined by tandem mass spectrometry that showed CML as a protein with two distinct forms (isolectins CML-1 and CML-2) with 246 and 247 residues, respectively. CML-2 possesses one residue of Asn more than CML-1 in C-terminal. The primary structure of CML agrees with the molecular weights found by electrospray ionization mass spectrometry: 27,224 and 27,338Da for CML-1 and CML-2, respectively. CML is a metal-dependent glycoprotein. Moreover, the glycan composition of CML and its structure were predicted.

Probing lectin-mucin interactions by isothermal titration microcalorimetry

Isothermal titration microcalorimetry (ITC) can directly determine the thermodynamic binding parameters of biological molecules including affinity constant, binding stoichiometry, and heat of binding (enthalpy) and indirectly the entropy and free energy of binding. ITC has been extensively used to study the binding of lectins to mono- and oligosaccharides, but limited applications to lectin-glycoprotein interactions. Inherent experimental challenges to ITC include sample precipitation during the experiment and relative high amount of sample required, but careful design of experiments can minimize these problems and allow valuable information to be obtained. For example, the thermodynamics of binding of lectins to multivalent globular and linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules leading to increased affinity. Importantly, the mechanism of binding of lectins to mucins appears similar to that for a variety of protein ligands binding to DNA. Recent results also show that high affinity lectin-mucin cross-linking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects that facilitate binding interactions.

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.

N-glycan analysis of mannose/glucose specific lectin from Dolichos lablab seeds

An affinity purified mannose/glucose specific lectin from the seeds of Dolichos lablab (Indian bean/lablab bean) resolves into five subunits upon SDS-PAGE in the range of Mr 12-20kDa. Partial de novo sequencing of subunits resulted in 88% and 73% sequence coverage for α and β subunits of the cDNA derived FRIL (Flt3 receptor interacting lectin) sequence, respectively and suggested that four bands correspond to the α-subunits while the band of lowest molecular mass is designated as β. It was proposed in an earlier study on FRIL that the difference in molecular mass of α-subunits is due to differences in C-terminal processing and differential N-glycosylation i.e. numbers of N-glycans present (Colucci et al., 1999). Thus, differential N-glycosylation of the purified mannose/glucose specific lectin was unravelled by in-gel trypsin/chymotrypsin digestion of the α-subunits followed by desalting and ZIC-HILIC enrichment of N-glycopeptides. Subsequently, analyses by nano electrospray ionisation quadrupole time of flight mass spectrometry and low-energy collision-induced dissociation experiments revealed the presence of a typical paucimannose type N-glycan (Man2(Xyl)GlcNAc2(Fuc)) in α subunits 2-4.

Effect of algae and plant lectins on planktonic growth and biofilm formation in clinically relevant bacteria and yeasts

This study aimed to evaluate the abilities of plant and algae lectins to inhibit planktonic growth and biofilm formation in bacteria and yeasts. Initially, ten lectins were tested on Staphylococcus epidermidis, Staphylococcus aureus, Klebsiella oxytoca, Pseudomonas aeruginosa, Candida albicans, and C. tropicalis at concentrations of 31.25 to 250 μg/mL. The lectins from Cratylia floribunda (CFL), Vatairea macrocarpa (VML), Bauhinia bauhinioides (BBL), Bryothamnion seaforthii (BSL), and Hypnea musciformis (HML) showed activities against at least one microorganism. Biofilm formation in the presence of the lectins was also evaluated; after 24 h of incubation with the lectins, the biofilms were analyzed by quantifying the biomass (by crystal violet staining) and by enumerating the viable cells (colony-forming units). The lectins reduced the biofilm biomass and/or the number of viable cells to differing degrees depending on the microorganism tested, demonstrating the different characteristics of the lectins. These findings indicate that the lectins tested in this study may be natural alternative antimicrobial agents; however, further studies are required to better elucidate the functional use of these proteins.

Vatairea macrocarpa lectin (VML) induces depressive-like behavior and expression of neuroinflammatory markers in mice

Lectins are proteins capable of reversible binding to the carbohydrates in glycoconjugates that can regulate many physiological and pathological events. Galectin-1, a β-galactoside-binding lectin, is expressed in the central nervous system (CNS) and exhibits neuroprotective functions. Additionally, lectins isolated from plants have demonstrated beneficial action in the CNS. One example is a lectin with mannose-glucose affinity purified from Canavalia brasiliensis seeds, ConBr, which displays neuroprotective and antidepressant activity. On the other hand, the effects of the galactose-binding lectin isolated from Vatairea macrocarpa seeds (VML) on the CNS are largely unknown. The aim of this study was to verify if VML is able to alter neural function by evaluating signaling enzymes, glial and inflammatory proteins in adult mice hippocampus, as well as behavioral parameters. VML administered by intracerebroventricular (i.c.v) route increased the immobility time in the forced swimming test (FST) 60 min after its injection through a carbohydrate recognition domain-dependent mechanism. Furthermore, under the same conditions, VML caused an enhancement of COX-2, GFAP and S100B levels in mouse hippocampus. However, phosphorylation of Akt, GSK-3β and mitogen-activated protein kinases named ERK1/2, JNK1/2/3 and p38(MAPK), was not changed by VML. The results reported here suggest that VML may trigger neuroinflammatory response in mouse hippocampus and exhibit a depressive-like activity. Taken together, our findings indicate a dual role for galactose binding lectins in the modulation of CNS function.

Purification and partial characterization of a new mannose/glucose-specific lectin from Dialium guineense Willd seeds that exhibits toxic effect

A new mannose/glucose-specific lectin, named DigL, was purified from seeds of Dialium guineense by a single step using a Sepharose 4b-Mannose affinity chromatography column. DigL strongly agglutinated rabbit erythrocytes and was inhibited by d-mannose, d-glucose, and derived sugars, especially α-methyl-d-mannopyranoside and N-acetyl-d-glucosamine. DigL has been shown to be a stable protein, maintaining its hemagglutinating activity after incubation at a wide range of temperature and pH values and after incubation with EDTA. DigL is a glycoprotein composite by approximately 2.9% of carbohydrates by weight. By sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis, the purified DigL exhibited an electrophoretic profile consisting of a broad band of 28-30 kDa. Analysis using electrospray ionization mass spectrometry indicated that purified DigL possesses a molecular average mass of 28 452 ± 2 Da and shows the presence of possible glycoforms. In addition, DigL exhibited an intermediary toxic effect on Artemia sp. nauplii, and this effect was both dependent on native structure and mediated by a carbohydrate-binding site.

Purification and characterization of a mannose/N-acetyl-D-glucosamine-specific lectin from the seeds of Platymiscium floribundum Vogel

Platymiscium floribundum lectin (PFL), a mannose/N-acetyl-D-glucosamine-specific lectin, was isolated from P. floribundum seeds using Sepharose-mannose affinity media chromatography. PFL is a glycoprotein that is a potent agglutinin for rabbit erythrocytes. In addition, PFL is highly stable because it is able to maintain its hemagglutinating activity after exposure to temperatures of up to 60 °C for 1 h and exposure to a wide pH range. The PFL purification process was monitored using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the results showed that the purified lectin consists of a single band with a molecular mass of approximately 29 kDa in either the presence or the absence of a reducing agent. The analysis of purified PFL by electrospray ionization-mass spectrometry showed that most ions had a molecular weight of 27,053 ± 2 Da, and other less abundant ions had similar molecular weights. Gel filtration shows that the lectin exists as a dimer in solution with mass at approximately 65 kDa. Sixteen peptides were sequenced, and as a result, a total of 130 amino acids were identified and resulted in a coverage of approximately 65% of the PFL sequence. The partial sequence of PFL was aligned with sequences of other lectins from evolutionarily related species, and PFL showed considerable similarity to the other lectins.

Multivalent lectin-carbohydrate interactions energetics and mechanisms of binding

The biological signaling properties of lectins, which are carbohydrate-binding proteins, are due to their ability to bind and cross-link multivalent glycoprotein receptors on the surface of normal and transformed cells. While the crosslinking properties of lectins with multivalent carbohydrates and glycoproteins are relatively well understood, the mechanisms of binding of lectins to multivalent glycoconjugates are less well understood. Recently, the thermodynamics of binding of lectins to synthetic clustered glycosides, a multivalent globular glycoprotein, and to linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules. Importantly, the mechanism of binding of lectins to mucins is similar to that for a variety of protein ligands binding to DNA. Recent analysis also shows that high-affinity lectin-mucin crosslinking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects which facilitate binding and subsequent complex formation including enzymology.

Renal effects induced by the lectin from Vatairea macrocarpa seeds

Lectins are glycoproteins that interact reversibly and specifically with carbohydrates. The renal effects of the galactose-binding lectin from the seeds of Vatairea macrocarpa were investigated. Isolated kidneys from Wistar rats (240–280 g) were perfused with Krebs-Henseleit solution containing 6% bovine serum albumin. The V. macrocarpa lectin (10 μg mL−1) increased the perfusion pressure, renal vascular resistance, urinary flow and glomerular filtration rate. However, V. macrocarpa lectin did not change the percentage sodium, potassium or chloride tubular transport. Pretreatment with lectin-galactose complex significantly blocked the increase in perfusion pressure, renal vascular resistance, urinary flow and glomerular filtration rate. The control group showed a small amount of a proteinaceous material in the urinary space, although no alteration in the renal tubules was detected. The administration of galactose alone did not modify the functional parameters of the kidney. Kidneys perfused with V. macrocarpa lectin showed moderate deposits of a proteinaceous material in the tubules and urinary space. Those pre-treated with lectin-galactose complex had only small amount of a proteinaceous material in the urinary space. No abnormalities were seen in renal tubules. The results suggest that lectin from V. macrocarpa seeds has important effects on the carbohydrate-binding sites of the renal system, given the reversal of renal effects with the use of that specific inhibitor.

An anti-inflammatory lectin from Luetzelburgia auriculata seeds inhibits adhesion and rolling of leukocytes and modulates histamine and PGE2 action in acute inflammation models

OBJECTIVES

To study and characterize the in vivo effect of the lectin from Luetzelburgia auriculata seed on acute inflammation models.

METHODS

The lectin was purified from the crude saline extract by affinity chromatography on a guar-gum matrix. Native, heat-treated, and digested lectin was evaluated for anti-inflammatory activity by using peritonitis and paw edema models. The anti-inflammatory activity was characterized by intravital microscopy, nitric oxide production, and myeloperoxidase activity.

RESULTS

The lectin exhibited anti-inflammatory activity (2 mg/kg) on both models, reducing local myeloperoxidase activity. Galactose or heat treatment (100 degrees C, 10 min) reduced anti-inflammatory action. Anti-inflammation involves the inhibition of adhesion and rolling of leukocytes along with augmentation of nitric oxide in serum. The lectin inhibited the edematogenic effect of histamine and prostaglandins (PGE2) but did not alter the chemoattractant effect of IL-8.

CONCLUSIONS

The results indicate that this lectin is a potent anti-inflammatory molecule. Its effects engage diverse modulatory events.

Binding studies of alpha-GalNAc-specific lectins to the alpha-GalNAc (Tn-antigen) form of porcine submaxillary mucin and its smaller fragments

Isothermal titration microcalorimetry (ITC) and hemagglutination inhibition measurements demonstrate that a chemically and enzymatically prepared form of porcine submaxillary mucin that possesses a molecular mass of approximately 10(6) daltons and approximately 2300 alpha-GalNAc residues (Tn-PSM) binds to the soybean agglutinin (SBA) with a K(d) of 0.2 nm, which is approximately 10(6)-fold enhanced affinity relative to GalNAcalpha1-O-Ser (Tn), the pancarcinoma carbohydrate antigen. The enzymatically derived 81 amino acid tandem repeat domain of Tn-PSM containing approximately 23 alpha-GalNAc residues binds with approximately 10(3)-fold enhanced affinity, while the enzymatically derived 38/40 amino acid cleavage product(s) of Tn-PSM containing approximately 11-12 alpha-GalNAc residues shows approximately 10(2)-fold enhanced affinity. A natural carbohydrate decorated form of PSM (Fd-PSM) containing 40% of the core 1 blood group type A tetrasaccharide, and 58% peptide-linked GalNAcalpha1-O-Ser/Thr residues, with 45% of the peptide-linked alpha-GalNAc residues linked alpha-(2,6) to N-glycolylneuraminic acid, shows approximately 10(4) enhanced affinity for SBA. Vatairea macrocarpa lectin (VML), which is also a GalNAc binding lectin, displays a similar pattern of binding to the four forms of PSM, although there are quantitative differences in its affinities as compared with SBA. The higher affinities of SBA and VML for Tn-PSM relative to Fd-PSM indicate the importance of carbohydrate composition and epitope density of mucins on their affinities for lectins. The higher affinities of SBA and VML for Tn-PSM relative to its two shorter chain analogs demonstrate that the length of a mucin polypeptide and hence total carbohydrate valence determines the affinities of the three Tn-PSM analogs. The results suggest a binding model in which lectin molecules "bind and jump" from alpha-GalNAc residue to alpha-GalNAc residue along the polypeptide chain of Tn-PSM before dissociating. The complete thermodynamic binding parameters for these mucins including their binding stoichiometries are presented. The results have important implications for the biological activities of mucins including those expressing the Tn cancer antigen.

Proteomic identification of actin-derived oligopeptides in dry-cured ham

An intense proteolysis of muscle proteins, mainly due to the action of endogenous proteolytic enzymes, has been reported to occur during the processing of dry-cured ham. This gives rise to an important generation of free amino acids and peptides of small size that contribute directly or indirectly to flavor characteristics of the final product. The nature and properties of the free amino acids generated during postmortem proteolysis have been well established. However, little is known about the identity of peptides generated during the processing of dry-cured ham. In the present paper, we describe the isolation (by ethanol precipitation followed by size exclusion and reverse phase chromatographies) and identification (by matrix-assisted laser desorption/ionization time-of-flight MS and collision-induced dissociation MS/MS) in a Spanish dry-cured ham of the following four oligopeptides: (A) TKQEYDEAGPSIVHR, (B) ITKQEYDEAGPSIVHRK, (C) DSGDGVTHNVPIYE, and (D) DSGDGVTHNVPIYEG. This is the first time that these peptide fragments have been reported in dry-cured ham at the end of processing. Sequence homology analysis revealed that the four peptides originated from muscle actin, indicating an extensive hydrolysis of this protein during dry-curing. Some of the cleavage sites corresponding to these fragments in actin were reproduced by other authors through the incubation of this myofibrillar protein in the presence of cathepsin D (EC 3.4.23.5), thus supporting a relevant action of this enzyme during the processing of dry-cured ham.

Structural basis of carbohydrate recognition by a Man(alpha1-2)Man-specific lectin from Bowringia milbraedii

The crystal structure of the seed lectin from the tropical legume Bowringia milbraedii was determined in complex with the disaccharide ligand Man(alpha1-2)Man. In solution, the protein exhibits a dynamic dimer-tetramer equilibrium, consistent with the concanavalin A-type tetramer observed in the crystal. Contacts between the tetramers are mediated almost exclusively through the carbohydrate ligand, resulting in a crystal lattice virtually identical to that of the concanavalin-A:Man(alpha1-2)Man complex, even though both proteins have less than 50% sequence identity. The disaccharide binds exclusively in a "downstream" binding mode, with the non-reducing mannose occupying the monosaccharide-binding site. The reducing mannose is bound in a predominantly polar subsite involving Tyr131, Gln218, and Tyr219.

Snake venomics: Comparative analysis of the venom proteomes of the Tunisian snakesCerastes cerastes, Cerastes vipera andMacrovipera lebetina

The protein composition of the crude venoms of the three most important vipers of Tunisia was analyzed by RP-HPLC, N-terminal sequence analysis, MALDI-TOF mass determination, and in-gel tryptic digestion followed by PMF and CID-MS/MS of selected peptide ions in a quadrupole-linear IT instrument. Our results show that the venom proteomes of Cerastes cerastes, Cerastes vipera, and Macrovipera lebetina are composed of proteins belonging to a few protein families. However, each venom showed distinct degree of protein composition complexity. The three venoms shared a number of protein classes though the relative occurrence of these toxins was different in each snake species. On the other hand, the venoms of the Cerastes species and Macrovipera lebetina each contained unique components. The comparative proteomic analysis of Tunisian snake venoms provides a comprehensible catalogue of secreted proteins, which may contribute to a deeper understanding of the biological effects of the venoms, and may also serve as a starting point for studying structure-function correlations of individual toxins.

Determinants of quaternary association in legume lectins

It is well known that the sequence of amino acids in proteins code for its tertiary structure. It is also known that there exists a relationship between sequence and the quaternary structure of proteins. The question addressed here is whether the nature of quaternary association can be predicted from the sequence, similar to the three-dimensional structure prediction from the sequence. The class of proteins called legume lectins is an interesting model system to investigate this problem, because they have very high sequence and tertiary structure homology, with diverse forms of quaternary association. Hence, we have used legume lectins as a probe in this paper to (1) gain novel insights about the relationship between sequence and quaternary structure; (2) identify the sequence motifs that are characteristic of a given type of quaternary association; and (3) predict the quaternary association from the sequence motif.

The galactose-binding lectin from Vatairea macrocarpa seeds induces in vivo neutrophil migration by indirect mechanism

To explore the pathways by which lectins induce an inflammatory response, the lectin from Vatairea macrocarpa (VML) seeds was used to induce neutrophil migration in rats. The lectin was shown to cause cell migration, with the effect partially blocked when galactose was added to inhibit lectin activity. Neutrophil migration was also reduced when peritoneal cavity of the animals was depleted of their resident cells beforehand, suggesting that neutrophil migration was mediated by an indirect mechanism. Pre-treatment of rats with thioglycollate increased recruitment of neutrophils while depletion of mast cells by the addition of compound 48/80 had little effect on neutrophil infiltration, suggesting the involvement of macrophages in the inflammatory process induced by the lectin. Inhibition of the cyclooxigenase, leukotriene and PAF activities by indomethacin, MK886 and BN50730, respectively, did not modify the pro-inflammatory effect previously observed. However, dexamethasone and thalidomide significantly reduced the population of neutrophils in the peritoneal cavity after lectin injection. The present study suggests that the effects produced by a galactose-binding lectin do not involve lipoxygenase, cyclooxygenase or PAF mediators that are well known to be involved in the inflammatory process. The blocking actions of dexamethasone and thalidimide suggest that as yet unidentified pro-inflammatory mediators are involved.

Purification and physicochemical characterization of a cotyledonary lectin from Luetzelburgia auriculata

A lectin was purified from the cotyledons of Luetzelburgia auriculata (Fr. All) Ducke by affinity chromatography on agarose-N-acetyl-D-galactosamine. The lectin is a potent agglutinin for rabbit erythrocytes, reacts with human red cells, but is inactive against cow, sheep, and goat erythrocytes. Hemagglutination of rabbit erythrocytes was inhibited by either 0.39 mM N-acetyl-neuraminic acid or N-acetyl-D-galactosamin, 12.5 mM D-lactose or D-melibiose, 50 mM D-galactose or raffinose. Its hemagglutinating activity was lost at 80 degrees C, 5 min, and the activation energy required for denaturation was 104.75 kJ mol(-1). Chromatography on Sephadex G-100, at pH 7.6, showed that at this hydrogenic ionic concentration the native lectin was a homotetramer (123.5 kDa). By denaturing SDS-PAGE, LAA seemed to be composed of a mixture of 29 and 15 kDa polypeptide subunits. At acidic and basic pHs it assumed different conformations, as demonstrated by exclusion chromatography on Superdex 200 HR 10/30. The N-terminal sequence of the 29 kDa band was SEVVSFSFTKFNPNQKDII and the 15 kDa band contained a mixture of SEVVSFSFTKFNPNQKDII and KFNQIVAVEEDTDXESQPQ sequences, indicating that these bands may represent full-length and its endogenous fragments, respectively. The lectin is a glycoprotein having 3.2% neutral carbohydrate, with a pI of 5.8, containing high levels of Asp+Asn and Glu+Gln and hydroxy amino acids, and low amount or absence of sulfur amino acids. Its absorption spectrum showed a maximum at 280 nm and a epsilon (1%) x (1cm) of 5.2. Its CD spectrum was characterized by minima near 228 nm, maxima near 196 nm and a negative to positive crossover at 210 nm. The secondary structure content was 6% alpha-helix, 8% parallel beta-sheet, 38% antiparallel beta-sheet, 17% beta-turn, 31% unordered and others contribution, and 1% RMS (root mean square). In the fluorescence spectroscopy, excitation of the lectin solution at 280 nm gave an emission spectrum in the 285-445 nm range. The wavelength maximum emission was in 334.5 nm, typical for tryptophan residues buried inside the protein.

Biochemical and functional characterization of the Tn-specific lectin from Salvia sclarea seeds

SSL, the lectin isolated from Salvia sclarea seeds, recognizes the Tn antigen (GalNAcalpha-O-Ser/Thr), a specific marker of many human carcinomas. Two-dimensional electrophoresis, amino-acid and amino-sugar analysis, and MALDI-TOF MS showed that SSL is an acidic (pI 5.5), 60-61-kDa dimeric glycoprotein composed of apparently identical subunits linked by a single disulfide bond. The apparent molecular mass of SSL in solution determined by equilibrium sedimentation analytical ultracentrifugation was 59 +/- 9 kDa. This value did not change in the pH range 2.5-8.5, indicating that SSL does not associate into higher order structures. Tandem mass spectrometry and methylation analysis of N-glycans released from SSL by hydrazinolysis indicated that SSL possesses 2-3 glycosylation sites occupied with the typical plant glycans Manalpha1-6[(Manalpha1-3)(Xylbeta1-2)]Manbeta1-4 -GlcNAcbeta1-4(Fucalp ha1-3)GlcNAc and [(Manalpha1-3/6)(Xylbeta1-2)]Manbeta1-4-GlcNAcbeta1 -4(Fucalpha1-3)Glc NAc. The influence of adjacent Tn structures on the binding of two Tn-specific lectins (SSL and the isolectin B4 from Vicia villosa) and an anti-Tn monoclonal antibody (mAb 83D4) was evaluated using synthetic Tn glycopeptides. The binding of both lectins to the synthetic Tn glycopeptides was independent of the density of Tn structures. On the other hand, mAb 83D4 only reacted with glycopeptides displaying two or three consecutive Tn structures.