Isolectins of Phaseolus vulgaris. Physicochemical studies

A Useful Guide to Lectin Binding: Machine-Learning Directed Annotation of 57 Unique Lectin Specificities

Glycans are critical to every facet of biology and medicine, from viral infections to embryogenesis. Tools to study glycans are rapidly evolving; however, the majority of our knowledge is deeply dependent on binding by glycan binding proteins (e.g., lectins). The specificities of lectins, which are often naturally isolated proteins, have not been well-defined, making it difficult to leverage their full potential for glycan analysis. Herein, we use a combination of machine learning algorithms and expert annotation to define lectin specificity for this important probe set. Our analysis uses comprehensive glycan microarray analysis of commercially available lectins we obtained using version 5.0 of the Consortium for Functional Glycomics glycan microarray (CFGv5). This data set was made public in 2011. We report the creation of this data set and its use in large-scale evaluation of lectin-glycan binding behaviors. Our motif analysis was performed by integrating 68 manually defined glycan features with systematic probing of computational rules for significant binding motifs using mono- and disaccharides and linkages. Combining machine learning with manual annotation, we create a detailed interpretation of glycan-binding specificity for 57 unique lectins, categorized by their major binding motifs: mannose, complex-type N-glycan, O-glycan, fucose, sialic acid and sulfate, GlcNAc and chitin, Gal and LacNAc, and GalNAc. Our work provides fresh insights into the complex binding features of commercially available lectins in current use, providing a critical guide to these important reagents.

The effects of Phaseolus vulgaris erythro- and leucoagglutinating isolectins (PHA-E and PHA-L) delivered via artificial diet and transgenic plants on the growth and development of tomato moth (Lacanobia oleracea) larvae; lectin binding to gut glycoproteins in vitro and in vivo

Red kidney bean, Phaseolus vulgaris, contains a lectin phytohemagglutinin (PHA) with toxicity towards higher animals. PHA exists in the isoforms PHA-E and PHA-L, which agglutinate erythrocytes and lymphocytes, respectively. Lacanobia oleracea larvae were reared from hatch on artificial diets containing PHA-E or PHA-L at 2% (w/w) dietary protein, and on transgenic Arabidopsis plants expressing either lectin at 0.4-0.6% of total soluble proteins. In artificial diet bioassays neither lectin affected larval survival, development, growth nor consumption. In transgenic plant bioassays both PHA-E and PHA-L promoted larval growth and development. This effect was greatest for PHA-E. Mean larval biomass of insects fed on plants expressing PHA-E was significantly greater (up to two-fold) than controls during the final two instars and the insects developed at a significantly greater rate so that after 26 days 83% of PHA-E exposed insects were in the final instar compared to 44% for control insects. PHA-E and PHA-L were detected by Western blotting in haemolymph, sampled from insects fed diets or plant material containing the lectins. However, despite the demonstrated potential for both isolectins to bind to gut glycopolypeptides in vitro neither was found to accumulate in vivo in the guts of exposed insects. Since lectin binding to gut polypeptides is thought to be necessary for insecticidal activity the failure of PHA-E and PHA-L to bind in vivo may account for their lack of toxicity to L. oleracea.

The degradation of lectins, phaseolin and trypsin inhibitors during germination of white kidney beans, Phaseolus vulgaris L

White kidney beans (Phaseolus vulgaris), cv Processor, contain a relatively high content of phaseolin (storage protein), lectins and a special group of glycoproteins as well as a considerable amount of protein-type trypsin inhibitors. Protein digestion of raw 'Processor' beans in monogastrics, for example pigs, is disturbed by poorly digested, phaseolin lectins, which can bind to carbohydrates in brush border membranes of the small intestinal epithelium, and trypsin inhibitors. The effect of the germination of white kidney beans on lectins, phaseolin and trypsin inhibitors was studied in order to achieve a degradation of lectins, phaseolin and trypsin inhibitors and an increase of in vitro enzymatic hydrolysis of the protein of bean flour. Therefore, whole bean extracts were examined throughout a germination period of up to seven days for their lectin and phaseolin pattern, lectin content, binding capacities of functional lectins towards brush border membranes and trypsin inhibitor content. In addition the in vitro enzymatic hydrolysis by pepsin and pancreatin of the protein from flours of (un)germinated white kidney beans was studied. SDS-PAGE demonstrated a degradation of E-lectins and a disappearance of L-lectins and phaseolin during germination. Results indicated a decrease of the lectin content by 85%, a loss of binding capacities of functional lectins towards brush border membranes by 91%, and a decrease of trypsin inhibitors by 76%, in bean flour after germination for seven days. A maximum in in vitro enzymatic hydrolysis of protein from bean flour was already established after germination for half a day.

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.

Isolation of soybean trypsin inhibitors by affinity chromatography on anhydrotrypsin-Sepharose 4B

By repeated treatments of trypsin with phenylmethylsulfonyl fluoride (PMSF), followed by base elimination of PMS from the PMS-trypsin, a catalytically inactive anhydrotrypsin preparation of low (less than 1%) active trypsin content was obtained. Inactive material was removed by affinity chromatography on trypsin inhibitor-Sepharose 4B and the purified anhydrotrypsin with full binding capacity for trypsin inhibitors was coupled to cyanogen bromide-activated Sepharose 4B. When used below its maximum capacity for trypsin inhibitors the anhydrotrypsin-Sepharose-4B affinity column absorbed both classes of inhibitors present in soybean. When overloaded, the Kunitz type was bound preferentially. Based on this observation, conditions for the partial separation of the two types of inhibitors were worked out.

Structure and stability of Ricinus communis haemagglutinin

The molecular properties of the haemagglutinin of Ricinus communis (RCA I or RCA 120) were evaluated by analytical ultracentrifugation, light-scattering, c.d. and fluorescence. The native molecule had a fairly expanded structure (f/f0 = 1.43) and dissociated into two subunits of equal size in 6 M-guanidinium chloride. This native structure was stable in alkali (up to pH 11) and resistant to thermal denaturation at neutrality. A pH-triggered change in the haemagglutinin conformation was observed and characterized by analytical ultracentrifugation, c.d. and fluorescence between pH 7 and 4.5, the range in which its affinity for galactosides decreased [Yamasaki, Absar & Funatsu (1985) Biochim, Biophys. Acta 828, 155-161]. These results are discussed in relation to those reported in the literature for other lectins and more especially ricin, for which a pH-dependent conformation transition has been observed in the same range of low pH.

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.

Dry beans of Phaseolus. A review. Part 2. Chemical composition: carbohydrates, fiber, minerals, vitamins, and lipids

Beans of Phaseolus are an important food crop both economically and nutritionally, and are cultivated and consumed worldwide. With ever rising costs of meats and fresh fruits and vegetables, dry beans are expected to contribute more to the human nutrition in coming years. Traditionally, they have been referred to as "poor man's meat" and have contributed significantly to the diets of many people of several countries in Asia, Africa, Middle East, and South America. In recent years, a renewed interest in bean research in Western European countries and the U.S. is evident. In this review, certain biochemical, technological, nutritional, and toxicological aspects are discussed and the limitations and problems associated with dry beans of Phaseolus as human food are addressed.

Dry beans of Phaseolus: a review. Part 3

Beans of Phaseolus are important food crops both economically and nutritionally, and are cultivated and consumed world wide. With ever rising costs of meats, fresh fruits, and vegetables, dry beans are expected to contribute more to the human nutrition in coming years. Traditionally, they have been referred to as "poor man's meat" and have contributed significantly to the diets of many people of several countries in Asia, Africa, the Middle East, and South America. In recent years, a renewed interest in bean research in Western European countries and the U.S. is evident. In this review, certain biochemical, technological, nutritional, and toxicological aspects are discussed and the limitations and problems associated with dry beans of Phaseolus as human food are addressed.

Purification of peanut (Arachis hypogaea) agglutinin isolectins by chromatofocusing

This report describes the purification and isolation of the isolectins of peanut agglutinin (PNA). We find the affinity-purified PNA to have an amino acid composition similar to that reported by Lotan et al. (J. Biol. Chem. 250, 8518-8523 (1975)); however, our preparation contains three tryptophan residues per subunit rather than two as reported by Lotan et al. This higher tryptophan content is consistent with the extinction coefficient (E1 mg/ml 280) of 0.96 as previously reported (Fish et al., Arch. Biochem. Biophys. 190, 693-698 (1978)). The PNA, purified by affinity chromatography on lactosyl-Sepharose, contains six major and three minor components capable of agglutinating neuraminidase-treated erythrocytes. Seven of the isolectins were obtained in a highly purified form by chromatofocusing, a column chromatographic technique which separates proteins on the basis of their isoelectric points. Isoelectric focusing of the purified isolectins indicates that they have the following isoelectric points: A, 6.70; B, 6.55; C, 6.35; D, 6.25; E, 6.10; F, 5.90; and G, 5.70. Preliminary studies on the subunit composition of the isolectins are also presented.

Isolation and characterization of a lectin from the seeds of Dioclea grandiflora (Mart.)

By a combination of solubility fractionation, affinity and molecular-sieve chromatography, a lectin preparation containing several closely related lectin components of different isoelectric point was isolated from the seeds of Dioclea grandiflora Mart. The lectins showed a carbohydrate specificty for D-mannose (D-glucose)-binding and had a requirement for the presence of Ca(2+) and Mn(2+). The results of preliminary characterization studies showed that the D. grandiflora lectins had similar properties to those of concanavalin A, the lectin from the seeds of Canavalia ensiformis, a plant also belonging to the tribe Diocleae. Thus the D. grandiflora lectins contained no covalently bound carbohydrate and had an amino-acid composition characterized by a low content of methionine and the virtual absence of cysteine. Above pH 4.8 they had molecular weight of about 100,000, while below pH 3.1 they were dissociated to half-molecules. Between these two pH values there was a fast association-dissociation equilibrium for the two species. In dissociating solvents, three subunits were obtained of the approximate size of 25-26,000, 13-14,000 and 8-9,000. The lectins from C. grandiflora similar to concanavalin A were more distantly related to the lectins obtained from the members of the tribe Vicieae although these were also specific for D-mannose (D-glucose)-binding.

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.

Molecular size, subunit structure and microheterogeneity of glycoprotein II from the seeds of kidney bean (Phaseolus vulgaris L.)

The isolation of Glycoprotein II from the seeds of kidney bean (Phaseolus vulgaris) cv. 'Processor' is described. This glycoprotein was shown by SDS-gel electrophoresis to dissociate into four subunits, 53 000, 50 000, 47 000 and 43 000 (alpha : beta : gamma : delta), in an approximate ratio of 2 : 0.2 : 2 : 1. At neutral and slightly alkaline pH values its molecular weight was about 142 000 (protomer) while at pH 5 it was mainly in the form of a tetramer with a molecular weight value of about 560 000. Samples of Glycoprotein II were shown by isoelectric focusing, molecular sieve chromatography and immunochemical methods to be microheterogenous. A number of fractions were prepared by these methods in which the proportion of the major subunits (alpha : gamma : delta) varied between 1 : 1 : 1 to 3 : 3 : 1. These ratios were also shown to change during development of the seed. On the basis of these results it is suggested that, at and above pH 7, samples of Glycoprotein II consist of microheterogenous population of molecules each containing three subunits per protomer. However, in these protomers the subunits are drawn, in different ratios, from the four subunits available. When the net molecular charge is small, at and around the isoelectric zone of Glycoptotein II, the protomer is converted mainly into the more stable tetramer containing 12 subunits.

Immunocytochemical localization of ingested kidney bean (Phaseolus vulgaris) lectins in rat gut

The binding of ingested kidney bean (Phaseolus vulgaris) lectins to the luminal surface of the rat gut was investigated by an indirect immunofluorescence method in which the primary antiserum was monospecific for kidney bean globulin lectins. The major lectin-positive sites were found to be the non-crypt regions of villi in the proximal region of the small intestine; exactly the same regions displayed extensive disruption of microvilli. Lectins were not localized in the brush border regions of ileal villi and no microvillus abnormalities were detected in this region of the gut. The luminal surface of the caecum was strongly lectin-positive and here also microvillus disruption was evident. Low levels of lectins were detected on the luminal surface of the colon; no microvillus abnormalities were detected in this region.