Proteomic profile of tepary bean seed storage proteins in germination with low water potential

BACKGROUND

Tepary bean (Phaseolus acutifolius A. Gray) is one of the five species domesticated from the genus Phaseolus with genetic resistance to biotic and abiotic stress. To understand the mechanisms underlying drought responses in seed storage proteins germinated on water and polyethylene glycol (PEG-6000) at -0.49 MPa, we used a proteomics approach to identify potential molecular target proteins associated with the low water potential stress response.

METHODS

Storage proteins from cotyledons of Tepary bean seeds germinated at 24, 48 and 72 h on water and PEG-6000 at -0.49 MPa were analyzed by one-dimensional electrophoresis (DE) with 2-DE analysis and shotgun mass spectrometry. Using computational database searching and bioinformatics analyses, we performed Gene Ontology (GO) and protein interactome (functional protein association network) String analyses.

RESULTS

Comparative analysis showed that the effect of PEG-6000 on root growth was parallel to that on germination. Based on the SDS‒PAGE protein banding patterns and 2-DE analysis, ten differentially abundant seed storage proteins showed changes in storage proteins, principally in the phaseolin and lectin fractions. We found many proteins that are recognized as drought stress-responsive proteins, and several of them are predicted to be intrinsically related to abiotic stress. The shotgun analysis searched against UniProt's legume database, and Gene Ontology (GO) analysis indicated that most of the seed proteins were cytosolic, with catalytic activity and associated with carbohydrate metabolism. The protein‒protein interaction networks from functional enrichment analysis showed that phytohemagglutinin interacts with proteins associated with the degradation of storage proteins in the cotyledons of common bean during germination.

CONCLUSION

These findings suggest that Tepary bean seed proteins provide valuable information with the potential to be used in genetic improvement and are part of the drought stress response, making our approach a potentially useful strategy for discovering novel drought-responsive proteins in other plant models.

Comparative study, homology modelling and molecular docking with cancer associated glycans of two non-fetuin-binding Tepary bean lectins

We present the purification and characterization of the two most abundant isoforms of lectins isolated from Tepary bean (Phaseolus acutifolius) seeds, which have been shown to differentially affect the survival of different cancer cells. They were separated by concanavalin A-affinity chromatography. After purification, to release the N-glycans, they were digested with the endoglycosidases PNGase and Glycanase A. Fractions resulted from the hydrolysis products were analyzed to determine their carbohydrate composition. Mass spectrometry data indicated that both isoforms contained high mannose glycans being mannose 6 the most abundant form. Furthermore, based on sequence Ans-X-Ser/Thr, where X is any amino acid except proline, a glycosylation site was determined on asparagine 36. When their metal requirement to preserve their biological activity was determined, the lectins showed differences. While lectin A (LA) agglutination activity was best in the presence of magnesium, lectin B (LB) was best with calcium. Additionally, only LA exhibited affinity to human type-A erythrocytes. Although both lectins showed small differences in their properties, an identical structure-model for both lectins was generated by the homology modelling process. Also, the analysis of ligand binding sites and in silico glycosylation were achieved. Molecular docking with colon adenocarcinoma associated-N-glycans revealed some highly possible interactions and, on the other hand, that N-glycan interaction zones of Tepary bean lectins is not restricted to the carbohydrate binding domain but to an extended part of their surface, which could lead new strategies to explain their biological activity.

Recombinant Lectin from Tepary Bean (Phaseolus acutifolius) with Specific Recognition for Cancer-Associated Glycans: Production, Structural Characterization, and Target Identification

Herein, we report the production of a recombinant Tepary bean lectin (rTBL-1), its three-dimensional (3D) structure, and its differential recognition for cancer-type glycoconjugates. rTBL-1 was expressed in Pichia pastoris, yielding 316 mg per liter of culture, and was purified by nickel affinity chromatography. Characterization of the protein showed that rTBL-1 is a stable 120 kDa homo-tetramer folded as a canonical leguminous lectin with two divalent cations (Ca2+ and Mn2+) attached to each subunit, confirmed in its 3D structure solved by X-ray diffraction at 1.9 Å resolution. Monomers also presented a ~2.5 kDa N-linked glycan located on the opposite face of the binding pocket. It does not participate in carbohydrate recognition but contributes to the stabilization of the interfaces between protomers. Screening for potential rTBL-1 targets by glycan array identified 14 positive binders, all of which correspond to β1-6 branched N-glycans' characteristics of cancer cells. The presence of α1-6 core fucose, also tumor-associated, improved carbohydrate recognition. rTBL-1 affinity for a broad spectrum of mono- and disaccharides was evaluated by isothermal titration calorimetry (ITC); however, no interaction was detected, corroborating that carbohydrate recognition is highly specific and requires larger ligands for binding. This would explain the differential recognition between healthy and cancer cells by Tepary bean lectins.

Quantum Dot Labelling of Tepary Bean (Phaseolus acutifolius) Lectins by Microfluidics

Lectins are bioactive proteins with the ability to recognize cell membrane carbohydrates in a specific way. Diverse plant lectins have shown diagnostic and therapeutic potential against cancer, and their cytotoxicity against transformed cells is mediated through the induction of apoptosis. Previous works have determined the cytotoxic activity of a Tepary bean (Phaseolus acutifolius) lectin fraction (TBLF) and its anti-tumorigenic effect on colon cancer. In this work, lectins from the TBLF were additionally purified by ionic-exchange chromatography. Two peaks with agglutination activity were obtained: one of them was named TBL-IE2 and showed a single protein band in two-dimensional electrophoresis; this one was thus selected for coupling to quantum dot (QD) nanoparticles by microfluidics (TBL-IE2-QD). The microfluidic method led to low sample usage, and resulted in homogeneous complexes, whose visualization was achieved using multiphoton and transmission electron microscopy. The average particle size (380 nm) and the average zeta potential (-18.51 mV) were determined. The cytotoxicity of the TBL-IE2 and TBL-IE2-QD was assayed on HT-29 colon cancer cells, showing no differences between them (p ≤ 0.05), where the LC50 values were 1.0 × 10-3 and 1.7 × 10-3 mg/mL, respectively. The microfluidic technique allowed control of the coupling between the QD and the protein, substantially improving the labelling process, providing a rapid and efficient method that enabled the traceability of lectins. Future studies will focus on the potential use of the QD-labelled lectin to recognize tumor tissues.

Rhizosecretion of a cisgenic lectin by genetic manipulation of Tepary bean plants (Phaseolus acutifolius)

Tepary bean (Phaseolus acutifolius) lectin fraction (TBLF) has been shown to specifically bind and induce cell death of different types of cancer cells and also has exhibited an effect on early colon tumorigenesis. However, the development of a pharmaceutical formula is not possible yet because the production process is expensive and slow and provides low yields. Therefore, the purpose of the present work was to develop a strategy to produce one bioactive lectin by rhizosecretion through root exudates on genetically modified plants. Amplification of Tepary bean transcripts was performed using degenerate primers, and the products obtained were sequenced. Multiple alignments of sequences led to elucidating one of the lectins present in TBLF. Its coding sequence was flanked by an N-terminal secretion signal peptide and a 6xHis-tail. This construction was introduced into P. acutifolius plants using Agrobacterium tumefaciens to subsequently carry out the in vitro growth of the plants. When roots grew, plants were transferred to hydroponic conditions and root exudates were analyzed. Results showed the presence of a glycosylated cisgenic lectin with biological activity, confirming that the strategy followed provides an alternative for the synthetic production and purification of this lectin.

Effects of intragastrically-administered Tepary bean lectins on digestive and immune organs: Preclinical evaluation

Previous work showed that Tepary bean (Phaseolus acutifolius) lectins exhibit differential cytotoxic effects on cancer cell lines by apoptosis induction. In vivo studies using a Tepary bean lectin fraction (TBLF, 50 mg/kg of body weight) after colon cancer induction in rats showed that TBLF inhibited early precancerous lesions without systemic toxicity however, loss of body weight gain and activation of immune cells were observed. In order to know more about the possible adverse effects, we evaluated the administration of TBLF on digestive and immune organs. Sprague Dawley rats were administered TBLF for six weeks and allowed to recover for two weeks. Immune activation was observed through an increased lymphocyte-granulocyte ratio, an increased number of lymphoid follicles in intestinal Peyer's patches and a slight expansion of the splenic white pulp. Atrophy was observed in small intestine villi and crypt foci of the colon without normalization after the recovery period. Pancreas histopathology showed hypertrophy after the six-week administration period, particularly vacuolation and trabecular widening; but after the two-week recovery period atrophy was observed, suggesting a partial compensatory type process. Our results show that TBLF activates the immune system and affects digestive organs through direct interaction with intestinal epithelium, and indirectly by producing pancreatic hyperfunction. Further work will focus in longer recuperation periods after TBLF treatment.

Phaseolus acutifolius Lectin Fractions Exhibit Apoptotic Effects on Colon Cancer: Preclinical Studies Using Dimethilhydrazine or Azoxi-Methane as Cancer Induction Agents

Phaseolus acutifolius (Tepary bean) lectins have been studied as cytotoxic molecules on colon cancer cells. The toxicological profile of a Tepary bean lectin fraction (TBLF) has shown low toxicity in experimental animals; exhibiting anti-nutritional effects such as a reduction in body weight gain and a decrease in food intake when using a dose of 50 mg/kg on alternate days for six weeks. Taking this information into account, the focus of this work was to evaluate the effect of the TBLF on colon cancer using 1,2-dimethylhydrazine (DMH) or azoxy-methane/dextran sodium sulfate (AOM/DSS) as colon cancer inductors. Rats were treated with DMH or AOM/DSS and then administered with TBFL (50 mg/kg) for six weeks. TBLF significantly decreased early tumorigenesis triggered by DMH by 70%, but without any evidence of an apoptotic effect. In an independent experiment, AOM/DSS was used to generate aberrant cryptic foci, which decreased by 50% after TBLF treatment. TBLF exhibited antiproliferative and proapoptotic effects related to a decrease of the signal transduction pathway protein Akt in its activated form and an increase of caspase 3 activity, but not to p53 activation. Further studies will deepen our knowledge of specific apoptosis pathways and cellular stress processes such as oxidative damage.

Tolerability assessment of a lectin fraction from Tepary bean seeds (Phaseolus acutifolius) orally administered to rats

•

We examine the toxicological profile of Tepary Bean lectins by oral route.

•

Tepary bean lectins showed digestion resistance up to 72 h.

•

Tepary bean lectins induce granulocyte increase after 24 h treatment.

•

A reduction in body weight gain was observed after 6 weeks treatment.

•

No toxicity was observed for Tepary bean lectins after 6 weeks.

Our previous studies have shown that a lectin rich fraction (TBLF) extracted from Tepary bean seeds differentially inhibits cancer cells proliferation in vitro. Before testing the in vivo anticancer effect, the acute and subchronic toxicological assays in rats were conducted, where an oral dose of 50 mg/body weight kg was determined as the NOAEL. This study evaluated the resistance to digestion and complete blood count (CBC) after 24 h of the orally administered 50 mg/kg TBLF. The digestion resistance test showed lectins activity retention after 72 h and the CBC study showed a high level of eosinophils, suggesting an allergic-like response. Tolerability was assayed after 6 weeks of treatment by dosing with an intragastric cannula every third day per week. It was observed a transient reduction in food intake and body weight in the first weeks, resulting in body weight gain reduction of 10% respect to the control group at the end of the study. Additionally, organs weight, histopathological analysis and blood markers for nutritional status and for liver, pancreas and renal function were not affected. Our results suggest that 50 mg/kg TBLF administered by oral route, exhibit no toxicity in rats and it was well tolerated. Further studies will focus on long-term studies.