Comparison of Phaseolus vulgaris cultivars on the basis of isolectin differences

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.

Purification, biochemical characterization, and bioactive properties of a lectin purified from the seeds of white tepary bean (phaseolus acutifolius variety latifolius)

The present work shows the characterization of Phaseolus acutifolius variety latifolius, on which little research has been published, and provides detailed information on the corresponding lectin. This protein was purified from a semi-domesticated line of white tepary beans from Sonora, Mexico, by precipitation of the aqueous extract with ammonium sulfate, followed by affinity chromatography on an immobilized fetuin matrix. MALDI TOF analysis of Phaseolus acutifolius agglutinin (PAA) showed that this lectin is composed of monomers with molecular weights ranging between 28 and 31 kDa. At high salt concentrations, PAA forms a dimer of 63 kDa, but at low salt concentrations, the subunits form a tetramer. Analysis of PAA on 2D-PAGE showed that there are mainly three types of subunits with isoelectric points of 4.2, 4.4, and 4.5. The partial sequence obtained by LC/MS/MS of tryptic fragments from the PAA subunits showed 90-100% identity with subunits from genus Phaseolus lectins in previous reports. The tepary bean lectin showed lower hemagglutination activity than Phaseolus vulgaris hemagglutinin (PHA-E) toward trypsinized human A and O type erythrocytes. The hemagglutination activity was inhibited by N-glycans from glycoproteins. Affinity chromatography with the immobilized PAA showed a high affinity to glycopeptides from thyroglobulin, which also has N-glycans with a high content of N-acetylglucosamine. PAA showed less mitogenic activity toward human lymphocytes than PHA-L and Con A. The cytotoxicity of PAA was determined by employing three clones of the 3T3 cell line, demonstrating variability among the clones as follows: T4 (DI₅₀ 51.5 µg/mL); J20 (DI₅₀ 275 µg/mL), and N5 (DI₅₀ 72.5 µg/mL).

Lectin from Phaseolus acutifolius var. escumite: chemical characterization, sugar specificity, and effect on human T-lymphocytes

Purification of the lectin from Phaseolus acutifolius var. escumite was achieved by affinity chromatography on a column containing glutaraldehyzed membranes from blood group O erythrocytes. The lectin is a tetrameric glycoprotein of 121 kDa with 10% of sugar by weight composed by four subunits of 30 kDa as determined by SDS-PAGE. The lectin is composed of four isolectins as determined by ion-exchange chromatography on a mono-S column. The lectin and its isolectins showed identical NH2 terminal residues (ANDLSFNFQR FNETN) with homology to the PHA leucoagglutinin-precursor. Peptide mass fingerprint from each lectin isoform determined from tryptic peptides by MALDI-TOF (matrix assisted laser desorption ionization-time-of-flight) showed differences among subunits, thus suggesting microheterogeneity in their amino acid sequences or different glycosylation patterns. The lectin and its four isolectins agglutinated erythrocytes without serological specificity and showed mitogenic activity on human leukocytes; moreover, the main effect was rather toward CD8+ than to CD4+ human peripheral lymphocytes. The lectin from escumite was not inhibitable by simple sugars; however, the specificity of the lectin and its isoforms was mainly addressed toward galactose residues present in bi- or triantennary N-acetyllactosamine-type glycans.

The in vivo synthesis and accumulation of lectin in developing seeds of black gram (Vigna mungo L. Hepper)

Black gram (Vigna mungo L. Hepper) seed contains two D-galactose-specific lectin species, BGL-I and BGL-II, identified on the basis of elution from ion exchange column and immunochemical cross-reactivity. BGL-I consisted of two monomeric lectins, BGL-I-1 and BGL-1-2, of relative molecular weights 94 and 89 kDa, respectively. BGL-II is another monomeric lectin with a molecular weight of 83 kDa. The in vivo synthesis studies using pulse-chase experiment showed that BGL-II lectin was synthesized as early as 14 days after flowering (DAF). The 94-kDa BGL-I-1 lectin was synthesized around 17 DAF. There was no cotranslational or posttranslational modification of the lectin proteins. The amount of lectin in developing seeds was determined by radial immunodiffusion assay technique. The maximum amount of lectin per seed was found at 28 DAF.

Purification and characterization of novel lectins from Great Northern bean, Phaseolus vulgaris L

Two lectins, GNL-1 and 2, were isolated from extracts of Great Northern bean powder through fractionation with ammonium sulfate, ion-exchange chromatographies on CM- and DEAE-celluloses, and gel filtration chromatography on Sephacryl S-200 HR. These lectins were shown to be homogenous by gel electrophoresis, gel filtration, and isoelectric focusing. The lectins (GNL-1 and 2) have molecular masses of 175 and 145 kDa on gel filtration, respectively. They yield three bands having the respective same molecular masses on SDS-PAGE (GNL-1; alpha-subunit of 34.5 kDa, beta of 37.0, and gamma of 39.0: GNL-2; alpha' of 34.5 kDa, beta' of 37.0, and gamma' of 39.0). Two lectins are shown to be glycoproteins and the carbohydrate contents of GNL-1 and 2 are 5.1 and 4.5%, respectively. The isoelectric points are 5.5 and 5.1 and the extinction coefficients (A 1cm 1%) at 280 nm are 11.37 and 11.45, respectively. These lectins are nonspecific in agglutination for rabbit and any types of human erythrocytes. Inhibition study shows no specificity against mono and disaccharides. On the other hand, binding assay of horseradish peroxidase-glycoproteins to the bands electroblotted onto PVDF membrane reveals that all of the subunits can bind to sugar moieties in fetuin, asialofetuin, and porcine thyroglobulin specifically. Moreover, assay of mitogenic activity shows that GNL-1 is a strong mitogen, but GNL-2 is lack of the activity.

Bean lectins : 5. Quantitative genetic variation in seed lectins of Phaseolus vulgaris L. and its relationship to qualitative lectin variation

Seeds of forty bean cultivars having different lectin types based on two-dimensional isoelectric focusing-sodium dodecyl sulfate polyacrylamide gel electrophoresis (IEF-SDS/PAGE) were analyzed for quantities of lectin, phaseolin and total protein. Significant differences were found among groups of cultivars with different lectin types for the quantity of lectin and phaseolin. Cultivars with more complex lectin types based on IEF-SDS/PAGE tended to have higher quantities of lectin and lower quantities of phaseolin than cultivars with simple lectin types. An association between lectin type and the quantity of lectin and phaseolin was found also in the seeds of F2 plants that segregated in a Mendelian fashion for two lectin types. Seeds from plants with the complex lectin type had more lectin and less phaseolin than seeds from plants with the simple lectin type. Therefore, the genes controlling qualitative lectin variation also may influence the quantitative variation of lectin and phaseolin. The results of this study are related to other studies on the quantitative variation for seed proteins and to the possible molecular basis for variation in the quantity of lectins in beans.

Bean lectins IV: genetic variation in the non-denatured structure of lectins from different Phaseolus vulgaris L. cultivars

Variation in the native conformation of bean lectins was examined using electrophoresis of non-denatured total protein extracts and purified albumin and globulin lectin. The observed variation was related to the genetic variation reported previously for lectin polypeptide composition as revealed by two-dimensional isoelectricfocusing-sodium dodecyl sulfate polyacrylamide gel electrophoresis (IEF-SDS/PAGE). When eleven cultivars with different IEF-SDS/PAGE lectin polypeptide compositions were compared, eight had unique non-denatured lectin patterns and three had identical patterns. For some cultivars differences in non-denatured lectin patterns were observed between the purified albumin and globulin lectin preparations.

Bean lectins : Part 2: Relationship between qualitative lectin variation in Phaseolus vulgaris L. and previous observations on purified bean lectins

The relationship between the polypeptide composition and the agglutination behaviour of the lectin-containing G2/albumin protein groups has allowed the identification of the active lectin polypeptides in different cultivars of Phaseolus vulgaris (Brown et al. accompanying paper). These results were used to ascertain the particular G2/albumin group contained in the various lectin sources used previously for the purification of lectin proteins. Many studies were found to have included lectin sources which contained the same G2/albumin pattern (TG2) and this common denominator has permitted the direct comparison of the properties reported for these purified lectins. Thus, much of the extensive literature on bean lectins is concurred.

Bean lectins : Part 1: Relationships between agglutinating activity and electrophoretic variation in the lectin-containing G2/albumin seed proteins of french bean (Phaseolus vulgaris L.)

Single seeds of over 100 bean cultivars were analyzed by two-dimensional electrophoresis. The cultivars could be classified into eight groups by virtue of their G2/albumin electrophoretic patterns: TG2, SG2, VG2, PrG2, BG2, MG2, PG2, and PiG2, The polypeptide compositions of these types were largely inter-related having particular polypeptides in common. It was possible to correlate the G2/albumin patterns with agglutinating activity of cow and rabbit blood cells as measured by the agglutination ratio (minimum concentration of extract required to agglutinate cow blood cells: minimum concentration of extract required to agglutinate rabbit blood cells). The active lectin polypeptides were identified by extracting lectins from agglutinated erythrocytes and by comparing the qualitative similarities and differences of the G2/albumin patterns and their agglutination activities. A reference catalogue of over 100 bean cultivars giving their phaseolin and G2/albumin electrophoretic patterns, and agglutination ratios is presented.

Immunocytochemical localisation of lectins in cells of Phaseolus vulgaris L. seeds

Antibodies against pure E4- and L4-lectins from the seeds of Phaseolus vulgaris L. raised in rabbits were made monospecific by immunoaffinity chromatography on E4- or L4-lectin Sepharose 4B columns. Localisation of lectins in bean seeds was investigated by indirect immunofluorescence and by electron microscopy on sections stained with colloidal gold particles coated with monospecific anti-E4- and anti-L4-IgG. In parenchyma cells from the cotyledons both E- and L-type lectins were found inside the protein bodies. Apparently the matrix of all protein bodies contained both types of lectins. On the other hand in vascular and in axis cells the two types of lectins were localised in the cytoplasm, outside the protein bodies. Thus these findings suggest different roles for the lectins: in cotyledons this may be a specific form of N storage, while in vascular and axis cells lectins may have a more direct metabolic part to play.