No abstract

Lectin from the seeds of Dioclea sclerocarpa (DSL) was purified in a single step by affinity chromatography on a Sephadex G-50 column. The primary sequence, as determined by tandem mass spectrometry, revealed a protein with 237 amino acids and 81% of identity with ConA. DSL has a molecular mass of 25,606 Da. The β and γ chains weigh 12,873 Da and 12,752 Da, respectively. DSL hemagglutinated rabbit erythrocytes (both native and treated with proteolytic enzymes), showing stability even after one hour of exposure to a specific pH range. The hemagglutinating activity of DSL was optimal between pH 6.0 and 8.0, but was inhibited after incubation with D-galactose and D-glucose. The pure protein possesses a molecular mass of 25 kDa by SDS-PAGE and 25,606 Da by mass spectrometry. The secondary structure content was estimated using the software SELCON3. The results indicate that b-sheet secondary structures are predominant in DSL (approximately 42.3% antiparallel b-sheet and 6.7% parallel b-sheet). In addition to the b-sheet, the predicted secondary structure of DSL features 4.1% a-helices, 15.8% turns and 31.3% other contributions. Upon thermal denaturation, evaluated by measuring changes in ellipticity at 218 nm induced by a temperature increase from 20 °C to 98 °C, DSL displayed cooperative sigmoidal behavior with transition midpoint at 84 °C and permitted the observation of two-state model (native and denatured).

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.

Legume lectins are the most thoroughly studied group of lectins and have been widely linked to many pathological processes. Their use as immunohistochemistry markers for cell profiling and cancer diagnosis have made these molecules important tools for immunological studies and have stimulated the prospection and characterization of new lectins. The crystal structures of a recombinant seed lectin from Vatairea macrocarpa (rVML) and its complexes with GalNAcα1-O-Ser, GalNAc and α-lactose, have been determined at 1.90, 1.97, 2.70 and 1.83Å resolution, respectively. Small angle X-ray scattering and calorimetry assays have confirmed the same pH stable oligomerization pattern and binding profiles proposed for its wild-type counterpart. In silico analyzes have explored the potential of this recombinant lectin as new tool for cancer research through a comparative profile with other legume lectins widely used for cancer diagnosis and prognosis. The results suggest the recognition of specific epitopes exhibited on different cancer cells as a process that relies on the disposition of hydrophobic clusters and charged regions around the lectin carbohydrate-binding site, favouring the anchorage of different groups in the antigen boundaries, highlighting the different potential of each analyzed lectin. In conclusion, the experimental results and comparative analysis show that rVML is as a promising tool for cancer research, able to bind with high affinity specific tumor-associated antigens, highly stable and easily produced.

Lectins are proteins that show a variety of biological activities. However, they share in common at least one domain capable of recognizing specific carbohydrates reversibly without changing its structure. The legume lectins family is the most studied family of plant lectins, in particular the Diocleinae subtribe, which possesses high degree of structural similarity, but variable biological activities. This variability lies in small differences that can be analyzed in studies based on structures. In particular, Dioclea sclerocarpa seed lectin (DSL) presents low ability to relax endothelialized rat aorta in comparison with other Dioclea lectins such as Dioclea violacea (DVL), Dioclea virgata (DvirL) and Dioclea rostrata (DRL). The DSL relaxation mechanism relies on nitric oxide production and carbohydrate recognition domain (CRD). This feature can be explained by structural differences, since DSL has a carbohydrate recognition domain design less favorable. In addition, the presence of a glutamate residue at position 205 proved to be a decisive factor for the low relaxant effect of Dioclea lectins.