Protein crystal content analysis by mass spectrometry and preliminary X-ray diffraction of a lectin from Canavalia grandiflora seeds with modulatory role in inflammation

ConA-Like Lectins: High Similarity Proteins as Models to Study Structure/Biological Activities Relationships

Lectins are a widely studied group of proteins capable of specific and reversible binding to carbohydrates. Undoubtedly, the best characterized are those extracted from plants of the Leguminosae family. Inside this group of proteins, those from the Diocleinae subtribe have attracted attention, in particular Concanavalin A (ConA), the best-studied lectin of the group. Diocleinae lectins, also called ConA-like lectins, present a high similarity of sequence and three-dimensional structure and are known to present inflammatory, vasoactive, antibiotic, immunomodulatory and antitumor activities, among others. This high similarity of lectins inside the ConA-like group makes it possible to use them to study structure/biological activity relationships by the variability of both carbohydrate specificity and biological activities results. It is in this context the following review aims to summarize the most recent data on the biochemical and structural properties, as well as biological activities, of ConA-like lectins and the use of these lectins as models to study structure/biological activity relationships.

Typhonium giganteum Lectin Exerts A Pro-Inflammatory Effect on RAW 264.7 via ROS and The NF-κB Signaling Pathway

Typhonii rhizoma, a widely used herb in traditional Chinese medicine, has acute irritating toxicity related to Typhonium giganteum lectin (TGL). TGL exhibits acute inflammatory effects, but the underlying molecular mechanisms are largely unknown. This paper is designed to assess the pro-inflammatory response of TGL on RAW 264.7 cells. RAW 264.7 treated with 6.25, 12.5, 25, and 50 µg/mL TGL showed elevated levels of inflammatory factors (TNF-α, IL-1β) and of p-IκB and p-p65, all dose-dependent, indicating that TGL had a substantial inflammatory effect and mobilized the nuclear factor-κB (NF-κB) pathway. All four TGL treatments also induced the up-regulation of reactive oxygen species (ROS) and cytosolic free Ca²⁺ and down-regulation of mitochondrial membrane potential (MMP). The production of cytokines and p-IκB, p-p65 were reduced by N-acetylcysteine (NAC), an ROS scavenger, which somewhat abrogated ROS production. The results showed the TGL-activated inflammatory signaling pathway NF-κB to be associated with the overproduction of ROS. Moreover, 50 μg/mL treatment with TGL led to cell apoptosis after 1 h and increased necrosis over time. These results provided potential molecular mechanisms for the observed inflammatory response to TGL including up-regulation of ROS and cytosolic free Ca²⁺, down-regulation of MMP, the mobilization of the NF-κB pathway, and the subsequent overproduction of pro-inflammatory factors resulting in apoptosis. Long-term stimulation with TGL resulted in strong toxic effects related to inflammation that induced necrosis in macrophages.

A novel N-acetyl-glucosamine lectin of Lonchocarpus araripensis attenuates acute cellular inflammation in mice

OBJECTIVE AND DESIGN

This study had investigated the anti-inflammatory activity of a seed lectin (LAL) isolated from Lonchocarpus araripensis.

MATERIAL/METHODS

LAL was purified by affinity chromatography (chitin column) and ion exchange chromatography (DEAE-Sephacel). In vitro LAL was tested for hemagglutinating activity against rabbit erythrocytes. In vivo LAL was assessed for the anti-inflammatory activity via intravenous injection (i.v.) in Swiss mice (25-30 g; n = 6/group) in models of paw edema and peritonitis.

STATISTICAL ANALYSIS

ANOVA (p < 0.05).

RESULTS

LAL revealed two bands of 30 and 60 kDa (SDS-PAGE) and exhibited hemagglutinating activity. LAL (10 mg/kg) inhibited the paw edema (77%) and vascular permeability (26%) induced by carrageenan, and the paw edema induced by serotonin (80%), bradykinin (49%), sodium nitroprusside (83%), TNF-α (75%) and PGE2 (64%). LAL also inhibited the neutrophil migration induced by fMLP (70%) or carrageenan (69%). The intravital microscopy showed that LAL inhibited rolling (83%) and adhesion (70%) of leukocytes. LAL anti-inflammatory effect was reversed by its association with N-acetyl-glucosamine. The nine-daily treatment with LAL (10 mg/kg; i.v.) showed no toxicity.

CONCLUSION

The novel N-acetyl-D-glucosamine-binding lectin isolated from L. araripensis seeds presents anti-inflammatory effect involving the lectin domain and the inhibition of 5-HT, BK, PGE2, NO, TNF-α and leukocyte rolling and adhesion.

The galactose-binding lectin isolated from Bauhinia bauhinioides Mart seeds inhibits neutrophil rolling and adhesion via primary cytokines

In this study, the amino acid sequence and anti-inflammatory effect of Bauhinia bauhinioides (BBL) lectin were evaluated. Tandem mass spectrometry revealed that BBL possesses 86 amino acid residues. BBL (1 mg/kg) intravenously injected in rats 30 min prior to inflammatory stimuli inhibited the cellular edema induced by carrageenan in only the second phase (21% - 3 h, 19% - 4 h) and did not alter the osmotic edema induced by dextran. BBL also inhibited carrageenan peritoneal neutrophil migration (51%), leukocyte rolling (58%) and adhesion (68%) and the neutrophil migration induced by TNF-α (64%). These effects were reversed by the association of BBL with galactose, demonstrating that the carbohydrate-binding domain is essential for lectin activity. In addition, BBL reduced myeloperoxidase activity (84%) and TNF-α (68%) and IL1-β (47%) levels. In conclusion, the present investigation demonstrated that BBL contains highly homologous isolectins, resulting in a total of 86 amino acid residues, and exhibits anti-inflammatory activity by inhibiting neutrophil migration by reducing TNF-α and IL1-β levels via the lectin domain.

Structural studies of an anti-inflammatory lectin from Canavalia boliviana seeds in complex with dimannosides

Plant lectins, especially those purified from species of the Leguminosae family, represent the best-studied group of carbohydrate-binding proteins. Lectins purified from seeds of the Diocleinae subtribe exhibit a high degree of sequence identity notwithstanding that they show very distinct biological activities. Two main factors have been related to this feature: variance in key residues influencing the carbohydrate-binding site geometry and differences in the pH-dependent oligomeric state profile. In this work, we have isolated a lectin from Canavalia boliviana (Cbol) and solved its x-ray crystal structure in the unbound form and in complex with the carbohydrates Man(α1-3)Man(α1-O)Me, Man(α1-4)Man(α1-O)Me and 5-bromo-4-chloro-3-indolyl-α-D-mannose. We evaluated its oligomerization profile at different pH values using Small Angle X-ray Scattering and compared it to that of Concanavalin A. Based on predicted pKa-shifts of amino acids in the subunit interfaces we devised a model for the dimer-tetramer equilibrium phenomena of these proteins. Additionally, we demonstrated Cbol anti-inflammatory properties and further characterized them using in vivo and in vitro models.

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.

Vasorelaxant activity of Canavalia grandiflora seed lectin: A structural analysis

Lectins are comprised of a large family of proteins capable of the specific and reversible recognition of carbohydrates. Legume lectins, the most studied plant lectins, show high structural similarity, but with modifications that imply a variation in the intensity of some biological activities. In this work, the primary and tertiary structures of Canavalia grandiflora (ConGF) were determined. ConGF, a lectin isolated from C. grandiflora seeds, is able to induce relaxant activity in rat aortic rings. The complete sequence of ConGF comprises 237 amino acids. This particular protein has primary sequence variations commonly found in lectins from Dioclea and Canavalia genera. The protein structure was solved at 2.3 Å resolution by X-ray crystallography. An X-Man molecule was modeled into the carbohydrate recognition domain. Still, ConGF (30 and 100 μg mL(-1)) elicited 25% of vasorelaxation (IC50=34.48 ± 5.07 μg mL(-1)) in endothelialized aortic rings. A nonselective inhibitor of nitric oxide blocked ConGF relaxant effect, showing mediation by nitric oxide. Key distances between ConGF carbohydrate recognition domain residues were determined in order to explain this effect, in turn revealing some structural aspects that could differentiate lectins from the Canavalia genera with respect to different efficacy in vasorelaxant effect.

Lectin from Crataeva tapia Bark Improves Tissue Damages and Plasma Hyperglycemia in Alloxan-Induced Diabetic Mice

Crataeva tapia is a plant popularly used for diabetes treatment, in Brazil. Progressive decline in renal and hepatic functions has been described in patients with diabetes mellitus, and mortality rate is increased in patients with chronic liver and renal disease. This study aimed to evaluate whether Crataeva tapia bark lectin (CrataBL) improves hyperglycemia and renal and hepatic damage in diabetic mice. CrataBL was purified by ion exchange chromatography on CM-cellulose, and intraperitoneal administration of CrataBL to alloxan-induced diabetic mice at dose of 10 mg/Kg/day and 20 mg/Kg/day for 10 days significantly reduced serum glucose levels by 14.9% and 55.9%, respectively. Serum urea, creatinine, aspartate aminotransferase, and alanine aminotransferase were also significantly reduced after treatment with both doses of CrataBL. Furthermore, histological analysis of liver, kidney, and pancreas revealed an improvement in the tissue morphology upon treatment with CrataBL. The results suggest that CrataBL has a beneficial hypoglycemic activity and improves the renal and hepatic complications of diabetes. Therefore, this lectin may be a promising agent for the treatment of diabetes, and this might be the basis for its use in the folk medicine as an alternative treatment to manage diabetes-related complications such as hyperglycemia and tissue damage.

Holothuria grisea agglutinin (HGA): the first invertebrate lectin with anti-inflammatory effects

Holothuria grisea agglutinin (HGA) is a dimeric lectin of molecular mass 228 kDa by gel filtration with monomers of 105 kDa by SDS-PAGE. The lectin is highly thermostable as it retains full activity for 1 h at 70 °C. Unlike other lectins purified from marine invertebrates, the hemagglutination activity of HGA does not require any divalent metal ions. The affinity analysis of HGA showed that only mucin was able to inhibit the hemagglutinating activity. HGA administered intravenously was tested in classical models of nociception and inflammation. HGA was able to inhibit neutrophil migration into the peritoneal cavity induced by carrageenan. This inhibitory effect was 68% at a dose of 1 mg/kg. In acetic acid-induced writhing tests, a significant antinociceptive effect was observed by treatment with HGA (0.1; 1 or 10 mg/kg) reducing constrictions by 27, 90 and 84%, respectively. In formalin tests, HGA at a dose of 10 mg/kg showed antinociceptive effect only in the inflammatory phase (phase 2). Nevertheless, in hot-plate tests, HGA did not show any nociceptive effect. In rota-rod and open-field tests, HGA did not alter the animals' behavior. The treatment with HGA 10 mg/kg presented diminished myeloperoxidase activity activity (81.6% inhibition) and raised the circulating levels of NO by 50.4% when compared with the carrageenan group. HGA has demonstrated the ability to modulate the inflammatory response in models of inflammation in vivo. HGA is the first marine invertebrate lectin that showed an anti-inflammatory effect. This finding opens a new perspective on the potential of lectins from the marine environment.