Plant Antifungal Lectins: Mechanism of Action and Targets on Human Pathogenic Fungi

Purification and antiproliferative effects of lectin from Japanese adzuki beans (Vigna angularis) against cancer cells

Adzuki beans have been historically utilized for both culinary and medicinal purposes in Japan. Lectin derived from Japanese red adzuki beans (JABs, Vigna angularis) exhibits several biological effects; however, to our knowledge, no detailed reports have been published on this topic. We purified lectin from adzuki beans to evaluate its impact on the proliferative activity of cancer cells and establish its biological profile. The Japanese red adzuki bean lectin (JABL) was purified using thyroglobulin-Sepharose 4B and evaluated for blood and sugar specificity and its effect on B16, LM8, Ehrlich ascites, HepG2, HeLa, and Colo679 cell proliferation compared with those of concanavalin A (ConA, Canavalia ensiformis) lectin. The molecular weight of JABL was 60 kDa. JABL showed specificity to thyroglobulin, fetuin, and rabbit erythrocytes, but not to sheep and horse erythrocytes. Additionally, JABL showed no resistance to chymotrypsin but exhibited weak resistance at temperatures >60°C. JABL exerted significantly stronger antiproliferative effects than that of the control on human and mouse cancer cells in a concentration-dependent manner. JABL demonstrated 30%-40% superior antiproliferative activity against Colo679 and B16 cells compared to that against other cells. JABL activity was weaker than ConA activity (approximately 80%-90%) but equivalent to red kidney bean (Phaseolus vulgaris) lectin activity. No inhibitory effect of JABL on TNF-α was observed, which is typically observed with bean lectins. Our results show that JABL might exert antiproliferative effects on mouse and human cancer cells, making it a potential chemopreventive agent for cancer. PRACTICAL APPLICATION: Japanese red adzuki beans are popular in Asia, especially Japan. In Japan, the adzuki bean is a staple food and used in Japanese confectionery for celebrations. Adzuki bean lectin was purified using thyroglobulin-Sepharose 4B. The purified lectin showed specificity for rabbit erythrocytes and anticancer activity in mouse and human cells. The lectin retained its biological activity even when subjected to temperatures exceeding 60°C. Thus, adzuki bean lectin has the potential to be used as a bioactive and anticancer agent in medical research.

Antifungal Action of Arabidopsis thaliana TCP21 via Induction of Oxidative Stress and Apoptosis

The realm of antimicrobial proteins in plants is extensive but remains relatively uncharted. Understanding the mechanisms underlying the action of plant antifungal proteins (AFPs) holds promise for antifungal strategies. This study aimed to bridge this knowledge gap by comprehensively screening Arabidopsis thaliana species to identify novel AFPs. Using MALDI-TOF analysis, we identified a member of the TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR1 (TCP) family of transcription factors as a novel AFP, A. thaliana TCP21 (AtTCP21; accession number NP_196450). Bacterially purified recombinant AtTCP21 inhibited the growth of various pathogenic fungal cells. AtTCP21 was more potent than melittin, a well-known AFP, in combating Colletotrichum gloeosporioides. Growth inhibition assays against various fungal pathogens and yeasts confirmed the pH-dependent antimicrobial activity of AtTCP21. Without inducing any membrane alterations, AtTCP21 penetrates the fungal cell wall and membrane, where it instigates a repressive milieu for fungal cell growth by generating intracellular reactive oxygen species and mitochondrial superoxides; resulting in morphological changes and apoptosis. Our findings demonstrate the redox-regulating effects of AtTCP21 and point to its potential as an antimicrobial agent.

Plant lectins: A new antimicrobial frontier

Pathogenic bacteria, viruses, fungi, parasites, and other microbes constantly change to ensure survival. Several pathogens have adopted strict and intricate strategies to fight medical treatments. Many drugs, frequently prescribed to treat these pathogens, are becoming obsolete and ineffective. Because pathogens have gained the capacity to tolerate or resist medications targeted at them, hence the term antimicrobial resistance (AMR), in that regard, many natural compounds have been routinely used as new antimicrobial agents to treat infections. Thus, plant lectins, the carbohydrate-binding proteins, have been targeted as promising drug candidates. This article reviewed more than 150 published papers on plant lectins with promising antibacterial and antifungal properties. We have also demonstrated how some plant lectins could express a synergistic action as adjuvants to boost the efficacy of obsolete or abandoned antimicrobial drugs. Emphasis has also been given to their plausible mechanism of action. The study further reports on the immunomodulatory effect of plant lectins and how they boost the immune system to curb or prevent infection.

A plant mannose-binding lectin and fluconazole: key targets combination against Candida albicans

AIMS

This study aimed to evaluate the combined effect of a mannose-binding lectin Helja with fluconazole (FLC) on Candida albicans and to get insights about the joint action mechanism.

METHODS AND RESULTS

The fungal growth was assessed following the optical density at 630 nm. Fungal cell morphology and nucleus integrity were analyzed by flow cytometry and confocal laser scanning microscopy using Calcofluor White (CFW) and 4',6-diamidino-2-phenylindole (DAPI) staining, respectively. The basis of Helja+FLC action on cell wall and plasma membrane was analyzed using perturbing agents. The Helja+FLC combination exhibited an inhibitory effect of fungal growth about three times greater than the sum of both compounds separately and inhibited fungal morphological plasticity, an important virulence attribute associated with drug resistance. Cells treated with Helja+FLC showed morphological changes, nucleus disintegration and formation of multimera structures, leading to cell collapse.

CONCLUSIONS

Our findings indicate that the Helja+FLC combination exhibited a potent antifungal activity based on their simultaneous action on different microbial cell targets.

SIGNIFICANCE AND IMPACT OF STUDY

The combination of a natural protein with conventional drugs might be helpful for the design of effective therapeutic strategies against Candida, contributing to minimize the development of drug resistance and host cell toxicity.

Wheat germ agglutinin is involved in the protective action of 24-epibrassinolide on the roots of wheat seedlings under drought conditions

The involvement of wheat germ agglutinin (WGA) in the protective action of 24-epibrassinolide (EBR) against drought stress was studied in the seedling roots of two wheat cultivars differing in drought tolerance. Under dehydration conditions, the contents of ABA and WGA were shown to change significantly in the roots of either drought-tolerant cultivar Omskaya 35 or drought-sensitive cultivar Salavat Yulaev. Meanwhile, accumulation of either ABA or WGA started earlier and was two times greater in plants of drought-tolerant cultivar. Since WGA is an excreted protein, it is not surprising that the level of lectin in the roots gradually decreased by the 7th day of treatment due to its exudation into root environment. Pre-sowing treatment with EBR contributed to additional accumulation of lectin as compared to the control variants of either cultivar, while the hormone treatment did not change ABA content. Meanwhile, under conditions of drought, EBR-pretreated seedlings were characterized by lower level of accumulation of ABA and WGA in the roots. EBR application was found to prevent drought-induced inhibition of cell division in the root apical meristem, while WGA excreted into the root environment may contribute significantly to the effect.