Effect of pH on the binding of Vicia graminea lectin to erythrocytes. Dependence on the chemical character of red-cell receptors

Insights into the Structural Features, Conformational Stability and Functional Activity of the Olneya tesota PF2 Lectin

BACKGROUND

The O. tesota lectin PF2 is a tetrameric protein with subunits of 33 kDa that recognizes only complex carbohydrates, resistant to proteolytic enzymes and has insecticidal activity against Phaseolus beans pest.

OBJECTIVE

To explore PF2 lectin features at different protein structural levels and to evaluate the effect of temperature and pH on its functionality and conformational stability.

METHODS

PF2 lectin was purified by affinity chromatography. Its primary structure was resolved by mass spectrometry and analyzed by bioinformatic tools, including its tertiary structure homology modeling. The effect of temperature and pH on its conformational traits and stability was addressed by dynamic light scattering, circular dichroism, and intrinsic fluorescence. The hemagglutinating activity was evaluated using a suspension of peripheral blood erythrocytes.

RESULTS

The proposed PF2 folding comprises a high content of beta sheets. At pH 7 and 25°C, the hydrodynamic diameter (Dh) was found to be 12.3 nm which corresponds to the oligomeric native state of PF2 lectin. Dh increased under the other evaluated pH and temperature conditions, suggesting protein aggregation. At basic pH, PF2 exhibited low conformational stability. The native PF2 (pH 7) retained its full hemagglutinating activity up to 45°C and exhibited one transition state with a melting temperature of 76.8°C.

CONCLUSION

PF2 showed distinctive characteristics found in legume lectins. The pH influences the functionality and conformational stability of the protein. PF2 lectin displayed a relatively narrow thermostability to the loss of secondary structure and hemagglutinating activity.

Lectin-mediated protocell crosslinking to mimic cell-cell junctions and adhesion

Cell adhesion is a crucial feature of all multicellular organisms, as it allows cells to organise themselves into tissues to carry out specific functions. Here, we present a mimetic approach that uses multivalent lectins with opposing binding sites to crosslink glycan-functionalised giant unilamellar vesicles. The crosslinking process drives the progression from contact puncta into elongated protocellular junctions, which form the vesicles into polygonal clusters resembling tissues. Due to their carbohydrate specificity, different lectins can be engaged in parallel with both natural and synthetic glycoconjugates to generate complex interfaces with distinct lectin domains. In addition, the formation of protocellular junctions can be combined with adhesion to a functionalised support by other ligand-receptor interactions to render increased stability against fluid flow. Furthermore, we consider that adhesion is a complex process of attraction and repulsion by doping the vesicles with a PEG-modified lipid, and demonstrate a dose-dependent decrease of lectin binding and formation of protocellular junctions. We suggest that the engineering of prototissues through lectin-glycan interactions is an important step towards synthetic minimal tissues and in designing artificial systems to reconstruct the fundamental functions of biology.

Purification and characterization of a new dimeric mannose/glucose-binding isolectin from Vicia tetrasperma (L.) Schreber

A new mannose/glucose specific isolectin VTL-II has been purified to electrophoretic homogeneity from the seeds of Vicia tetrasperma (L.) Schreber through successive steps of (i) lectin extraction, (ii) ammonium sulfate fractionation (30-50%), and (iii) affinity chromatography on a column of Sephadex G-50 covalently coupled with D-mannose. The isolectin was found to be a dimeric protein of molecular weight 62 kDa made up of apparently chemically identical subunits unlike the tetrameric isolectins reported earlier from the same plant source. It was found to exhibit (i) 8-16 times higher specificity for rabbit RBC than human RBC, though it showed unspecificity with respect to the different human blood groups, (ii) non-dependence on divalent metal ion for its hemagglutinating activity, (iii) relatively broad pH optimum ranging from pH 7.0 to 8.0, and (iv) thermal inactivation behavior characterized by t(1/2) of 50 degrees C.

Purification of a N-acetyl-D-galactosamine specific lectin from the orchid Laelia autumnalis

From the pseudobulbs of the orchid L. autumnalis a lectin was purified on immobilized porcine mucin with A + H blood group substance. This lectin is a dimeric glycoprotein of M(r) 12,000 with an Sw,20 of 2.2, showing haemagglutinating activity directed mainly to human A1 desialylated erythrocytes. The lectin possesses sugar specificity for N-acetyl-D-galactosamine and also shows high specificity for glycoproteins containing the T (galactose beta 1,3GA1NAc alpha 1,0 Ser/Thr) or the Tn antigen (GalNAc alpha 1,0 Ser/Thr).

Specificity of the isolectins from the plant cactus Machaerocereus eruca for oligosaccharides from porcine stomach mucin

Sugar specificity of the Machaerocereus eruca isolectins, MeAI and MeAII, has been determined by comparing the capacity of glycans with well defined structures to inhibit their haemagglutinating activity. Both are galactose-specific isolectins with high affinity for O-glycans. However, the two M. eruca isolectins recognize different oligosaccharidic sequences belonging to O-glycosidically linked glycans from porcine stomach mucin. The minimal structure recognized by MeAI on the porcine mucin glycans is the O-glycan core Gal beta 1,3GalNAc-ol, whereas MeAII has a more extended site and interacts with a biantennary O-glycan possessing the terminal trisaccharide Fuc alpha 1,2 (GalNAc alpha 1,3) Gal beta 1,4.

Specificity of Amaranthus leucocarpus lectin

We have demonstrated that Amaranthus leucocarpus lectin hemagglutinating activity was powerfully inhibited by the T-antigen, containing Gal(beta 1-3)GalNAc(alpha 1-3)Ser/Thr, and the Tn-antigen, which contains GalNAc(alpha 1-3)Ser/Thr. This suggests that the acetamido group at C-2 and the axial -OH at C-4 of the N-acetyl-D-galactopyranosylamine ring are important for lectin binding. The hemagglutination assays also established that desialylated and Pronase-treated human type O erythrocytes with an M phenotype were better recognized than erythrocytes from all other blood groups. The recognition was dependent on pH and ionic strength.