1,3-β-d-Glucan synthase of Paracoccidioides brasiliensis: recombinant protein, expression and cytolocalization in the yeast and mycelium phases

A review on polysaccharide biosynthesis in Cordyceps militaris

Cordyceps militaris (C. militaris) is an edible parasitic fungus with medicinal properties. Its bioactive polysaccharides are structurally diverse and exhibit various metabolic and biological activities, including antitumor, hypoglycemic, antioxidant, hypolipidemic, anti-inflammatory, immunostimulatory, and anti-atherosclerotic effects. These properties make C. militaris-derived polysaccharides a promising candidate for future development. Recent advancements in microbial fermentation technology have enabled successful laboratory cultivation and extraction of these polysaccharides. These polysaccharides are structurally diverse and exhibit various biological activities, such as immunostimulatory, antioxidant, antitumor, hypolipidemic, and anti-atherosclerotic effects. This review aims to summarize the structure and production mechanisms of polysaccharides from C. militaris, covering extraction methods, key genes and pathways involved in biosynthesis, and fermentation factors that influence yield and activity. Furthermore, the future potential and challenges of utilizing polysaccharides in the development of health foods and pharmaceuticals are addressed. This review serves as a valuable reference in the fields of food and medicine, and provides a theoretical foundation for the study of polysaccharides.

Biochemical and structural characterization of a glucan synthase GFGLS2 from edible fungus Grifola frondosa to synthesize β-1, 3-glucan

BACKGROUND

Grifola frondosa is a Basidiomycete fungus belonging to the family of Grifolaceae and the order of Polyporales. β-Glucans are the main polymers in G. frondosa, playing a crucial role in the physiology and representing the healthy benefits for humans. The membrane-integrated β-1, 3-glucan synthase (GLS) is responsible for glucan synthesis, cell wall assembly, differentiation and growth of the edible fungi. However, the structural/catalytic characteristics and mechanisms of β-1, 3-glucan synthases in G. frondosa are still unknown due to their extremely complex structures with multi-transmembranes and large molecular masses.

RESULTS

Herein, a β-1, 3-glucan synthase (GFGLS2) was purified and identified from the cultured mycelia with a specific activity of 60.01 pmol min-1 μg-1 for the first time. The GFGLS2 showed a strict specificity to UDP-glucose with a Vmax value of 1.29 ± 0.04 µM min-1 at pH 7.0 and synthesized β-1, 3-glucan with a maximum degree of polymerization (DP) of 62. Sequence Similarity Network (SSN) analysis revealed that GFGLS2 has a close relationship with others in Ganoderma sinense, Trametes coccinea, Polyporus brumalis, and Trametes pubescens. With the assistance of 3D structure modelling by AlphaFold 2, molecular docking and molecular dynamics simulations, the central hydrophilic domain (Class III) in GFGLS2 was the main active sites through binding the substrate UDP-glucose to 11 amino acid residues via hydrogen bonds, π-stacking and salt bridges.

CONCLUSIONS

The biochemical, 3D structural characterization and potential catalytic mechanism of a membrane-bound β-1, 3-glucan synthase GFGLS2 from cultured mycelia of G. frondosa were well investigated and would provide a reasonable full picture of β-1, 3-glucan synthesis in fungi.

UDP-Glycosyltransferases in Edible Fungi: Function, Structure, and Catalytic Mechanism

UDP-glycosyltransferases (UGTs) are the most studied glycosyltransferases, and belong to large GT1 family performing the key roles in antibiotic synthesis, the development of bacterial glycosyltransferase inhibitors, and in animal inflammation. They transfer the glycosyl groups from nucleotide UDP-sugars (UDP-glucose, UDP-galactose, UDP-xylose, and UDP-rhamnose) to the acceptors including saccharides, proteins, lipids, and secondary metabolites. The present review summarized the recent of UDP-glycosyltransferases, including their structures, functions, and catalytic mechanism, especially in edible fungi. The future perspectives and new challenges were also summarized to understand of their structure–function relationships in the future. The outputs in this field could provide a reference to recognize function, structure, and catalytic mechanism of UDP-glycosyltransferases for understanding the biosynthesis pathways of secondary metabolites, such as hydrocarbons, monoterpenes, sesquiterpene, and polysaccharides in edible fungi.

Functional Characterization and Structural Basis of the β-1,3-Glucan Synthase CMGLS from Mushroom Cordyceps militaris

β-1,3-Glucan synthases play key roles in glucan synthesis, cell wall assembly, and growth of fungi. However, their multi-transmembrane domains (over 14 TMHs) and large molecular masses (over 100 kDa) significantly hamper understanding of their catalytic characteristics and mechanisms. In the present study, the 5841-bp gene CMGLS encoding the 221.7 kDa membrane-bound β-1,3-glucan synthase CMGLS in Cordyceps militaris was cloned, identified, and structurally analyzed. CMGLS was partially purified with a specific activity of 87.72 pmol/min/μg, a purification fold of 121, and a yield of 10.16% using a product-entrapment purification method. CMGLS showed a strict specificity to UDP-glucose with a K_m value of 84.28 μM at pH 7.0 and synthesized β-1,3-glucan with a maximum degree of polymerization (DP) of 70. With the assistance of AlphaFold and molecular docking, the 3D structure of CMGLS and its binding features with substrate UDP-glucose were proposed for the first time to our knowledge. UDP-glucose potentially bound to at least 11 residues via hydrogen bonds, π-stacking ,and salt bridges, and Arg 1436 was predicted as a key residue directly interacting with the moieties of glucose, phosphate, and the ribose ring on UDP-glucose. These findings would open an avenue to recognize and understand the glucan synthesis process and catalytic mechanism of β-1,3-glucan synthases in mushrooms.

Updates in Paracoccidioides Biology and Genetic Advances in Fungus Manipulation

The dimorphic fungi of the Paracoccidioides genus are the causative agents of paracoccidioidomycosis (PCM). This disease is endemic in Latin America and primarily affects workers in rural areas. PCM is considered a neglected disease, despite being a disabling disease that has a notable impact on the public health system. Paracoccidioides spp. are thermally dimorphic fungi that present infective mycelia at 25 °C and differentiate into pathogenic yeast forms at 37 °C. This transition involves a series of morphological, structural, and metabolic changes which are essential for their survival inside hosts. As a pathogen, the fungus is subjected to several varieties of stress conditions, including the host immune response, which involves the production of reactive nitrogen and oxygen species, thermal stress due to temperature changes during the transition, pH alterations within phagolysosomes, and hypoxia inside granulomas. Over the years, studies focusing on understanding the establishment and development of PCM have been conducted with several limitations due to the low effectiveness of strategies for the genetic manipulation of Paracoccidioides spp. This review describes the most relevant biological features of Paracoccidioides spp., including aspects of the phylogeny, ecology, stress response, infection, and evasion mechanisms of the fungus. We also discuss the genetic aspects and difficulties of fungal manipulation, and, finally, describe the advances in molecular biology that may be employed in molecular research on this fungus in the future.

Identification of a new antifungal compound against isocitrate lyase of Paracoccidioides brasiliensis

Aim: To perform virtual screening of compounds based on natural products targeting isocitrate lyase of Paracoccidioides brasiliensis. Materials & methods: Homology modeling and molecular dynamics simulations were applied in order to obtain conformational models for virtual screening. The selected hits were tested in vitro against enzymatic activity of ICL of the dimorphic fungus P. brasiliensis and growth of the Paracoccidioides spp. The cytotoxicity and selectivity index of the compounds were defined. Results & conclusion: Carboxamide, lactone and β-carboline moieties were identified as interesting chemical groups for the design of new antifungal compounds. The compounds inhibited ICL of the dimorphic fungus P. brasiliensis activity. The compound 4559339 presented minimum inhibitory concentration of 7.3 μg/ml in P. brasiliensis with fungicidal effect at this concentration. Thus, a new potential antifungal against P. brasiliensis is proposed.

Extracellular Vesicle-Associated Transitory Cell Wall Components and Their Impact on the Interaction of Fungi with Host Cells

Classic cell wall components of fungi comprise the polysaccharides glucans and chitin, in association with glycoproteins and pigments. During the last decade, however, system biology approaches clearly demonstrated that the composition of fungal cell walls include atypical molecules historically associated with intracellular or membrane locations. Elucidation of mechanisms by which many fungal molecules are exported to the extracellular space suggested that these atypical components are transitorily located to the cell wall. The presence of extracellular vesicles (EVs) at the fungal cell wall and in culture supernatants of distinct pathogenic species suggested a highly functional mechanism of molecular export in these organisms. Thus, the passage of EVs through fungal cell walls suggests remarkable molecular diversity and, consequently, a potentially variable influence on the host antifungal response. On the basis of information derived from the proteomic characterization of fungal EVs from the yeasts Cryptoccocus neoformans and Candida albicans and the dimorphic fungi Histoplasma capsulatum and Paracoccidioides brasiliensis, our manuscript is focused on the clear view that the fungal cell wall is much more complex than previously thought.

Effects of Argentilactone on the Transcriptional Profile, Cell Wall and Oxidative Stress of Paracoccidioides spp

Paracoccidioides spp., a dimorphic pathogenic fungus, is the etiologic agent of paracoccidioidomycosis (PCM). PCM is an endemic disease that affects at least 10 million people in Latin America, causing severe public health problems. The drugs used against pathogenic fungi have various side effects and limited efficacy; therefore, there is an inevitable and urgent medical need for the development of new antifungal drugs. In the present study, we evaluated the transcriptional profile of Paracoccidioides lutzii exposed to argentilactone, a constituent of the essential oil of Hyptis ovalifolia. A total of 1,058 genes were identified, of which 208 were up-regulated and 850 were down-regulated. Cell rescue, defense and virulence, with a total of 26 genes, was a functional category with a large number of genes induced, including heat shock protein 90 (hsp90), cytochrome c peroxidase (ccp), the hemoglobin ligand RBT5 (rbt5) and superoxide dismutase (sod). Quantitative real-time PCR revealed an increase in the expression level of all of those genes. An enzymatic assay showed a significant increase in SOD activity. The reduced growth of Pbhsp90-aRNA, Pbccp-aRNA, Pbsod-aRNA and Pbrbt5-aRNA isolates in the presence of argentilactone indicates the importance of these genes in the response of Paracoccidioides spp. to argentilactone. The response of the P. lutzii cell wall to argentilactone treatment was also evaluated. The results showed that argentilactone caused a decrease in the levels of polymers in the cell wall. These results suggest that argentilactone is a potential candidate for antifungal therapy.

Paracoccidioidomycosis (PCM) is a neglected human systemic mycosis caused by Paracoccidioides spp. fungus that invades the host’s lungs and can disseminate to many other organs. Treatment usually involves amphotericin B, sulfadiazine, trimethoprim-sulfamethoxazole, itraconazole, ketoconazole or fluconazole for six months to two years. In this way, many adverse effects are associated with treatment, and patients can have many co-morbidities and difficulties in complying with treatment. For those reasons, more effective and less toxic drugs are needed. The discovery of a potentially bioactive molecule and its correlation with a biological target is an important step in the research and development of drugs. One of the ways in which cells adjust to environmental change is by changing the pattern of gene expression. Thus, the transcriptome is potential experimental strategy to elucidate the mode of action of bioactive molecules. Here, Paracoccidoides spp. altered the expression of genes, leading to a further understanding of the action of the compound argentilactone in the fungal cells. Argentilactone seems to be able to modulate cellular targets, to induce oxidative stress and to interfere with the biosynthesis of the P. lutzii cell wall.

Characterization of Paracoccidioides brasiliensis by FT-IR spectroscopy and nanotechnology

Paracoccidioides brasiliensis, the etiological agent of paracoccidioidomycosis, is a dimorphic fungus existing as mycelia in the environment (or at 25°C in vitro) and as yeast cells in the human host (or at 37°C in vitro). Because mycological examination of lesions in patients frequently is unable to show the presence of the fungus and serological tests can misdiagnose the disease with other mycosis, the development of new approach's for molecular identification of P. brasiliensis spurges is needed. This study describes the use of a gold nanoprobe of a known gene sequence of P. brasiliensis as a molecular tool to identify P. brasiliensis by regular polymerase chain reaction (PCR) associated with a colorimetric methods. This approach is suitable for testing in remote areas because it does not require any further step than gene amplification, being safer and cheaper than electrophoresis methods. The proposed test showed a color change of the PCR reaction mixture from red to blue in negative samples, whereas the solution remains red in positive samples. We also performed a Fourier Transform Infrared (FT-IR) Spectroscopy analysis to characterize and compare the chemical composition between yeast and mycelia forms, which revealed biochemical differences between these two forms. The analysis of the spectra showed that differences were distributed in chemical bonds of proteins, lipids and carbohydrates. The most prominent difference between both forms was vibration modes related to 1,3-β-glucan usually found in mycelia and 1,3-α-glucan found in yeasts and also chitin forms. In this work, we introduce FT-IR as a new method suitable to reveal overall differences that biochemically distinguish each form of P. brasiliensis that could be additionally used to discriminate biochemical differences among a single form under distinct environmental conditions.

Paracoccidioides brasiliensis AND Paracoccidioides lutzii, A SECRET LOVE AFFAIR

To commemorate Prof. Carlos da Silva Lacaz's centennial anniversary, the authors have written a brief account of a few, out of hundreds, biological, ecological, molecular and phylogenetic studies that led to the arrival of Paracoccidioides lutzii, hidden for more than a century within Paracoccidioides brasiliensis. Lacaz's permanent interest in this fungus, and particularly his conviction on the benefits that research on paracoccidioidomycosis would bring to patients, were pivotal in the development of the field.

Transcriptome Profile of the Response of Paracoccidioides spp. to a Camphene Thiosemicarbazide Derivative

Paracoccidioidomycosis (PCM) is a systemic granulomatous human mycosis caused by fungi of the genus Paracoccidioides, which is geographically restricted to Latin America. Inhalation of spores, the infectious particles of the fungus, is a common route of infection. The PCM treatment of choice is azoles such as itraconazole, but sulfonamides and amphotericin B are used in some cases despite their toxicity to mammalian cells. The current availability of treatments highlights the need to identify and characterize novel targets for antifungal treatment of PCM as well as the need to search for new antifungal compounds obtained from natural sources or by chemical synthesis. To this end, we evaluated the antifungal activity of a camphene thiosemicarbazide derivative (TSC-C) compound on Paracoccidioides yeast. To determine the response of Paracoccidioides spp. to TSC-C, we analyzed the transcriptional profile of the fungus after 8 h of contact with the compound. The results demonstrate that Paracoccidioides lutzii induced the expression of genes related to metabolism; cell cycle and DNA processing; biogenesis of cellular components; cell transduction/signal; cell rescue, defense and virulence; cellular transport, transport facilities and transport routes; energy; protein synthesis; protein fate; transcription; and other proteins without classification. Additionally, we observed intensely inhibited genes related to protein synthesis. Analysis by fluorescence microscopy and flow cytometry revealed that the compound induced the production of reactive oxygen species. Using an isolate with down-regulated SOD1 gene expression (SOD1-aRNA), we sought to determine the function of this gene in the defense of Paracoccidioides yeast cells against the compound. Mutant cells were more susceptible to TSC-C, demonstrating the importance of this gene in response to the compound. The results presented herein suggest that TSC-C is a promising candidate for PCM treatment.

Human neutrophils produce extracellular traps against Paracoccidioides brasiliensis

Neutrophils play an important role as effector cells and contribute to the resistance of the host against microbial pathogens. Neutrophils are able to produce extracellular traps (NETs) in response to medically important fungi, including Aspergillus spp., Candida albicans and Cryptococcus gattii. However, NET production in response to Paracoccidioides brasiliensis has yet to be studied. We have demonstrated that human neutrophils produce NETs against both conidia and yeasts of P. brasiliensis. Although the NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI) did not alter NET production against conidia, it partially suppressed NET formation against P. brasiliensis yeasts. Cytochalasin D or IFN-γ did not affect the production of NETs against the fungus. Additionally, a mutant strain of P. brasiliensis with reduced expression of an alternative oxidase induced significantly higher levels of NETs in comparison with the WT strain. Finally, c.f.u. quantification of P. brasiliensis showed no significant differences when neutrophils were treated with DPI, DNase I or cytochalasin D as compared with untreated cells. These data establish that NET formation by human neutrophils appears to be either dependent or independent of reactive oxygen species production, correlating with the fungal morphotype used for stimulation. However, this mechanism was ineffective in killing the fungus.

Inhibition of Paracoccidioides lutzii Pb01 isocitrate lyase by the natural compound argentilactone and its semi-synthetic derivatives

The dimorphic fungus Paracoccidioides spp. is responsible for paracoccidioidomycosis, the most prevalent systemic mycosis in Latin America, causing serious public health problems. Adequate treatment of mycotic infections is difficult, since fungi are eukaryotic organisms with a structure and metabolism similar to those of eukaryotic hosts. In this way, specific fungus targets have become important to search of new antifungal compound. The role of the glyoxylate cycle and its enzymes in microbial virulence has been reported in many fungal pathogens, including Paracoccidioides spp. Here, we show the action of argentilactone and its semi-synthetic derivative reduced argentilactone on recombinant and native isocitrate lyase from Paracoccidioides lutzii Pb01 (PbICL) in the presence of different carbon sources, acetate and glucose. Additionally, argentilactone and its semi-synthetic derivative reduced argentilactone exhibited relevant inhibitory activity against P. lutzii Pb01 yeast cells and dose-dependently influenced the transition from the mycelium to yeast phase. The other oxygenated derivatives tested, epoxy argentilactone and diol argentilactone-, did not show inhibitory action on the fungus. The results were supported by in silico experiments.

The paracoccidioides cell wall: past and present layers toward understanding interaction with the host

The cell wall of pathogenic fungi plays import roles in the interaction with the host, so that its composition and structure may determine the course of infection. Here we present an overview of the current and past knowledge on the cell wall constituents of Paracoccidioides brasiliensis and P. lutzii. These are temperature-dependent dimorphic fungi that cause paracoccidioidomycosis, a systemic granulomatous, and debilitating disease. Focus is given on cell wall carbohydrate and protein contents, their immune-stimulatory features, adhesion properties, drug target characteristics, and morphological phase specificity. We offer a journey toward the future understanding of the dynamic nature of the cell wall and of the changes that may occur when the fungus infects the human host.