Hemant Preet Kaur

Mushroom lectins: Current status and future perspectives

Lectins are nonimmune proteins or glycoproteins that bind specifically to cell surface carbohydrates, culminating in cell agglutination. These are known to play key roles in host defense system and also in metastasis. Many new sources have been explored for the occurrence of lectins during the last few years. Numerous novel lectins with unique specificities and exploitable properties have been discovered. Mushrooms have attracted a number of researchers in food and pharmaceuticals. Many species have long been used in traditional Chinese medicines or functional foods in Japan and other Asian countries. A number of bioactive constituents have been isolated from mushrooms including polysaccharides, polysaccharopeptides, polysaccharide–protein complexes, proteases, ribonucleases, ribosome inactivating proteins, antifungal proteins, immunomodulatory proteins, enzymes, lectins, etc. Mushroom lectins are endowed with mitogenic, antiproliferative, antitumor, antiviral, and immunestimulating potential. In this review, an attempt has been made to collate the information on mushroom lectins, their blood group and sugar specificities, with an emphasis on their biomedical potential and future perspectives.

Current trends of lectins from microfungi

Lectins are widespread in nature and have been isolated from plants, animals, microorganisms, and viruses. Although several lectins have been reported from microfungi, many more genera still remain unexplored and their physiological role is also uncertain. Microfungal lectins show wide disparity regarding their specificity to erythrocytes. Only a few lectins display specificity to particular human blood types. In addition, they also show agglutination to various animal erythrocytes. Many lectins from microfungi exhibit stringent specificity to animal glycoproteins, while a few have much more simplified sugar binding properties. The role of few microfungal lectins in host-parasite interactions, as storage proteins, and in growth and morphogenesis has been proposed. The current review focuses on an overview of lectins from microfungi, their specificity towards erythrocytes and carbohydrates, physicochemical characteristics, and their possible role and applications.

Purification and Characterization of a Mucin Specific Mycelial Lectin from Aspergillus gorakhpurensis: Application for Mitogenic and Antimicrobial Activity

Background Lectins are carbohydrate binding proteins or glycoproteins that bind reversibly to specific carbohydrates present on the apposing cells, which are responsible for their ability to agglutinate red blood cells, lymphocytes, fibroblasts, etc. Interest in lectins has been intensified due to their carbohydrate specificity as they can be valuable reagents for the investigation of cell surface sugars, purification and characterization of glycoproteins. The present study reports the purification, characterization and evaluation of mitogenic and antimicrobial potential of a mycelial lectin from Aspergillus gorakhpurensis. Methods Affinity chromatography on mucin-sepharose column was carried out for purification of Aspergillus gorakhpurensis lectin. The lectin was characterized for physico-chemical parameters. Mitogenic potential of the lectin was evaluated against splenocytes of Swiss albino mice by MTT assay. Antimicrobial activity of the purified lectin has also been evaluated by disc diffusion assay. Results Single-step affinity purification resulted in 18.6-fold purification of the mycelial lectin. The molecular mass of the lectin was found to be 70 kDa and it was composed of two subunits of 34.8 kDa as determined by gel filtration chromatography, SDS-PAGE and MALDI-TOF analysis. pH optima of the lectin was found to be 6.5–9.5, while optimum temperature for lectin activity was 20–30°C. Lectin was stable within a pH range of 7.0–10.5 and showed fair thermostability. EDTA did not affect lectin activity whereas it was found susceptible to the denaturants tested. MTT assay revealed strong mitogenic potential of A. gorakhpurensis lectin at a concentration upto 150 µg/mL. Antimicrobial activity assay showed its potent antibacterial activity against Bacillus cereus, Staphylococcous aureus and Escherichia coli and marginal antifungal activity against Saccharomyces cerevisiae. Conclusion This is the first report on the mitogenic and antimicrobial potential of Aspergillus gorakhpurensis lectin. The results will provide useful guidelines for further research in clinical applications of this lectin.

Characteristics of yeast lectins and their role in cell–cell interactions

Lectins are ubiquitous proteins with the ability to induce cell agglutination and, mediate cellular and molecular recognition processes in a variety of biological interactions. Fungi display exquisite specificity for target tissues and attach to host glycoconjugates via these sugar-binding proteins. Although only few reports are available on lectin activity of yeasts, these sugar binding proteins have been embraced for their role in cell flocculation, a commercially beneficial property, that simplifies downstream recovery operations in yeast fermentations. The lectins bind to cell wall mannans of the neighboring cells via hydrogen bonds leading to the formation of cell aggregates which get interrupted in the presence of specific sugars. Attachment of pathogenic yeasts to host cell surface is also a consequence of lectin-mediated recognition process. This review provides a brief overview of yeast lectins, with an insight to lectin-mediated cellular recognition phenomenon in yeasts.

Mushroom Lectins as Promising Anticancer Substances

Lectins are proteins/glycoproteins of non-immune origin, which are widely distributed in nature. They have at least one non-catalytic domain, which binds reversibly to specific monosaccharides or oligosaccharides. Lectins recognizing sugar moieties in cell walls or cell membranes alter the membrane physiology and trigger biochemical changes in the cell. Thus, various applications of lectins have been described, for example as tools to identify aberrant glycans expressed by neoplastic cells and as antitumor agents by inducing apoptosis by various mechanisms. In order to widen applications of anti-tumor lectins, a detailed investigation of their action mechanism is required. Mushrooms are a valuable source of novel lectins with unique specificities and potentials for biotechnological and biomedical applications. This article reviews information on anti-proliferative activity of mushroom lectins obtained in-vitro and in-vivo. The possible role of lectins as cancer therapeutics is discussed together with the mechanisms underlying the anti-proliferative activity, which may help to exploit these biomolecules as potential novel antitumor drugs in near future.

New lectins from aspergilli and their carbohydrate specificity

Lectin activity was assessed in sixteen Aspergillius species using human A, B, O, AB, rabbit, goat, pig and sheep erythrocytes. Neuraminidase and protease treated blood group O erythrocytes were also used to evaluate lectin activity from all the cultures unable to agglutinate native red blood cells. Lectin activity was revealed from Aspergillus acristatus, A. gorakhpurensis, A. panamensis and A. carbonarius extracts, while undiluted extract of A. fischeri showed weak haemagglutination. Lectin activity was expressed after 5 days of growth by A. acristatus, A. gorakhpurensis, A. panamensis and A. carbonarius and after 8 days of cultivation a sharp decline in lectin activity was observed. Higher titres were observed from these species with enzymatically modified blood type O erythrocytes. A variety of carbohydrates were used to study their minimum inhibitory concentration capable of inhibiting haemagglutination. Porcine stomach mucin was found to be the most potent inhibitor of all the lectins. A. gorakhpurensis lectin showed high specificity for chondroitin-6-sulphate and N-acetyl-D-galactosamine. Significant specificity for L-fucose, D-arabinose and 2-deoxy-D-ribose was identified with A. panamensis lectin. Low concentrations of 0.625 mM of D-galactosamine HCl and 0.12 mg/mL of chondroitin-6-sulphate were found optimal to prevent haemagglutination of A. carbonarius extract. A. carbonarius lectin was partially purified 2.75-fold using ammonium sulphate precipitation, dialysis and ultrafiltration. It was found to be stable upto 40°C and within the pH range of 7.0–8.0. Lectin activity was not affected by guanidine-HCl, while it was reduced to half after incubation with urea and thiourea after 24 h.

Immunomodulatory and therapeutic potential of a mucin-specific mycelial lectin from Aspergillus panamensis

The present study reports the evaluation of immunomodulatory and therapeutic potential of a purified Aspergillus panamensis lectin. The immunomodulatory potential of the purified lectin was determined in swiss albino mice by studying its effect on anaphylaxis reaction, arthus reaction, respiratory burst activity, nitric oxide production and quantification of cytokine levels. The therapeutic potential of the lectin was evaluated in male wistar rat models by studying its curative effect on ulcerative colitis. The purified lectin inhibited systemic anaphylaxis and arthus reaction. It enhanced the functional ability of macrophages which was evident from increase in reduction of nitroblue tetrazolium dye and nitric oxide production. It also stimulated the production of Th-1 cytokine IFN-γ and Th-2 cytokine IL-6. Maximum immunomodulatory effect was seen at lectin concentration of 1.5mg/kg body weight. The lectin also showed curative effect against trinitrobenzene sulphonic acid induced ulcerative colitis. The results of this study adequately reflect the role of purified A. panamensis lectin in improving the immune status of mice models. They also show the effect of lectin in reducing the severity of incidence and decrease in clinical symptoms of ulcerative colitis.

Purification and characterization of a thermostable mycelial lectin from basidiomycete Lentinus squarrosulus

Lectins are non-immune carbohydrate-binding proteins or glycoproteins with specific binding sites for certain glycoconjugates. Fungal lectins have been documented for their antitumour, antiproliferative, immunomodulatory, hypotensive and insecticidal effects. In the present study, a mycelial lectin having molecular mass 55 kDa has been purified and characterized from Lentinus squarrosulus. Biological action spectrum of the lectin revealed agglutination of all human blood types (A, B, O, AB), goat, sheep, rabbit and pig erythrocytes. Neuraminidase treatment of blood type O erythrocytes considerably augmented hemagglutination titre. Carbohydrate inhibition studies showed its high affinity to mucin and asialofetuin. Lectin was purified by a combination of ammonium sulphate precipitation, dialysis, ion exchange chromatography and gel filtration chromatography. Optimum pH for lectin activity was observed to be 6.5–8.0 and optimum temperature was 25–30°C. Lectin showed poor pH stability and was stable within pH 7.0–7.5. It was highly thermostable and could withstand temperature upto 70°C. Lectin activity was sensitive to ethylenediaminetetraacetic acid and denaturants.

Modulation of immunocyte functions by a mucin-specific lectin from Aspergillus gorakhpurensis

Lectins are non-immune proteins or glycoproteins with the ability to induce cell agglutination and mediate cellular and molecular recognition processes in a variety of biological interactions. Recently, several mushroom lectins have been reported to show immunomodulatory activities. The immunomodulatory potential of purified A. gorakhpurensis lectin was determined by evaluating its effect on systemic anaphylaxis reaction, arthus reaction, respiratory burst activity, nitric oxide production and levels of cytokines IFN-γ and IL-6. Administration of different doses of purified lectin was found to stimulate immunological activity. Lectin prevented BSA induced Arthus reaction and systemic anaphylaxis. The enhanced functional ability of macrophages was evident from respiratory burst activity and nitric oxide production in splenocyte cultures. Interferon-γ and interleukin-6 levels were significantly up-regulated in lectin treated groups. Maximum modulatory effect was observed at the lectin dose of 3.0mg/kg body weight. The results of the experiments conducted adequately reflect the immunostimulatory effect of purified A. gorakhpurensis lectin.