Metal Acquisition and Homeostasis in Fungi

miRNAs regulate the metabolic adaptation of Paracoccidioides brasiliensis during copper deprivation

Copper is an essential metal for cellular processes such as detoxification of reactive oxygen species, oxidative phosphorylation, and iron uptake. However, during infection, the host restricts the bioavailability of this micronutrient to the pathogen as a strategy to combat infection. Recently, we have shown the involvement of miRNAs as an adaptive strategy of P. brasiliensis upon metal deprivation such as iron and zinc. However, their role in copper limitation still needs to be elucidated. Our objective was to characterize the expression profile of miRNAs regulated during copper deprivation in P. brasiliensis and the putative altered processes. Through RNAseq analysis and bioinformatics, we identified 14 differentially expressed miRNAs, two of which putatively regulated oxidative stress response, beta-oxidation, glyoxylate cycle, and cell wall remodeling. Our results suggest that metabolic adaptations carried out by P. brasiliensis in copper deprivation are regulated by miRNAs.

The influence of a copper efflux pump in Histoplasma capsulatum virulence

During the infectious process, pathogenic microorganisms must obtain nutrients from the host in order to survive and proliferate. These nutritional sources include the metallic nutrient copper. Despite its essentiality, copper in large amounts is toxic. Host defense mechanisms use high copper poisoning as a fungicidal strategy to control infection. Transcriptional analyses showed that yeast cultured in the presence of copper or inside macrophages (24 h) had elevated expression of CRP1, a copper efflux pump, suggesting that Histoplasma capsulatum could be exposed to a high copper environment in macrophages during the innate immune stage of infection. Accordingly, macrophages cultured in high copper are more efficient in controlling H. capsulatum growth. Also, silencing of ATP7a, a copper pump that promotes the copper influx in phagosomes, increases fungal survival in macrophages. The rich copper environment faced by the fungus is not dependent on IFN-γ, since fungal CRP1 expression is induced in untreated macrophages. Appropriately, CRP1 knockdown fungal strains are more susceptible to macrophage control than wild-type yeasts. Additionally, CRP1 silencing decreases fungal burden in mice during the phase of innate immune response (4-day postinfection) and CRP1 is required for full virulence in a macrophage cell lines (J774 A.1 and RAW 264.7), as well as primary cells (BMDM). Thus, induction of fungal copper detoxifying genes during innate immunity and the attenuated virulence of CRP1-knockdown yeasts suggest that H. capsulatum is exposed to a copper-rich environment at early infection, but circumvents this condition to establish infection.

Global Molecular Response of Paracoccidioides brasiliensis to Zinc Deprivation: Analyses at Transcript, Protein and MicroRNA Levels

Zinc is one of the main micronutrients for all organisms. One of the defense mechanisms used by the host includes the sequestration of metals used in fungal metabolism, such as iron and zinc. There are several mechanisms that maintain the balance in the intracellular zinc supply. MicroRNAs are effector molecules of responses between the pathogen and host, favoring or preventing infection in many microorganisms. Fungi of the Paracoccidioides genus are thermodimorphic and the etiological agents of paracoccidioidomycosis (PCM). In the current pandemic scenario world mycosis studies continue to be highly important since a significant number of patients with COVID-19 developed systemic mycoses, co-infections that complicated their clinical condition. The objective was to identify transcriptomic and proteomic adaptations in Paracoccidioides brasiliensis during zinc deprivation. Nineteen microRNAs were identified, three of which were differentially regulated. Target genes regulated by those microRNAs are elements of zinc homeostasis such as ZRT1, ZRT3 and COT1 transporters. Transcription factors that have zinc in their structure are also targets of those miRNAs. Transcriptional and proteomic data suggest that P. brasiliensis undergoes metabolic remodeling to survive zinc deprivation and that miRNAs may be part of the regulatory process.

Iron Deprivation Modulates the Exoproteome in Paracoccidioides brasiliensis

Fungi of the Paracoccidioides genus are the etiological agents of the systemic mycosis paracoccidioidomycosis and, when in the host, they find a challenging environment that is scarce in nutrients and micronutrients, such as Fe, which is indispensable for the survival of the pathogen. Previous studies have shown that fungi of this genus, in response to Fe deprivation, are able to synthesize and capture siderophores (Fe³⁺ chelators), use Fe-containing host proteins as a source of the metal, and use a non-canonical reductive pathway for Fe³⁺ assimilation. Despite all of these findings, there are still gaps that need to be filled in the pathogen response to metal deprivation. To contribute to the knowledge related to this subject, we obtained the exoproteome of Paracoccidioides brasiliensis (Pb18) undergoing Fe deprivation and by nanoUPLC-MS^E. One hundred forty-one proteins were identified, and out of these, 64 proteins were predicted to be secreted. We also identified the regulation of several virulence factors. Among the results, we highlight Cyb5 as a secreted molecule of Paracoccidioides in the exoproteome obtained during Fe deprivation. Cyb5 is described as necessary for the Fe deprivation response of Saccharomyces cerevisiae and Aspergillus fumigatus. Experimental data and molecular modeling indicated that Cyb5 can bind to Fe ions in vitro, suggesting that it can be relevant in the arsenal of molecules related to iron homeostasis in P. brasiliensis.

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

Histatin 5 Metallopeptides and Their Potential against Candida albicans Pathogenicity and Drug Resistance

Usually caused by Candida albicans, buccal candidiasis begins with the morphological transition between yeast and hyphal cells. Over time and without the correct treatment, it can be disseminated through the bloodstream becoming a systemic infection with high mortality rates. C. albicans already shows resistance against antifungals commonly used in treatments. Therefore, the search for new drugs capable of overcoming antifungal resistance is essential. Histatin 5 (Hst5) is an antimicrobial peptide of the Histatin family, that can be found naturally in human saliva. This peptide presents high antifungal activity against C. albicans. However, Hst5 action can be decreased for interaction with enzymes and metal ions present in the oral cavity. The current work aims to bring a brief review of relevant aspects of the pathogenesis and resistance mechanisms already reported for C. albicans. In addition, are also reported here the main immune responses of the human body and the most common antifungal drugs. Finally, the most important aspects regarding Histatin 5 and the benefits of its interaction with metals are highlighted. The intention of this review is to show the promising use of Hst5 metallopeptides in the development of effective drugs.

Interacting with Hemoglobin: Paracoccidioides spp. Recruits hsp30 on Its Cell Surface for Enhanced Ability to Use This Iron Source

Paracoccidioides spp. are thermally dimorphic fungi that cause paracoccidioidomycosis and can affect both immunocompetent and immunocompromised individuals. The infection can lead to moderate or severe illness and death. Paracoccidioides spp. undergo micronutrients deprivation within the host, including iron. To overcome such cellular stress, this genus of fungi responds in multiple ways, such as the utilization of hemoglobin. A glycosylphosphatidylinositol (GPI)-anchored fungal receptor, Rbt5, has the primary role of acquiring the essential nutrient iron from hemoglobin. Conversely, it is not clear if additional proteins participate in the process of using hemoglobin by the fungus. Therefore, in order to investigate changes in the proteomic level of P. lutzii cell wall, we deprived the fungus of iron and then treated those cells with hemoglobin. Deprived iron cells were used as control. Next, we performed cell wall fractionation and the obtained proteins were submitted to nanoUPLC-MS^E. Protein expression levels of the cell wall F1 fraction of cells exposed to hemoglobin were compared with the protein expression of the cell wall F1 fraction of iron-deprived cells. Our results showed that P. lutzii exposure to hemoglobin increased the level of adhesins expression by the fungus, according to the proteomic data. We confirmed that the exposure of the fungus to hemoglobin increased its ability to adhere to macrophages by flow cytometry. In addition, we found that HSP30 of P. lutzii is a novel hemoglobin-binding protein and a possible heme oxygenase. In order to investigate the importance of HSP30 in the Paracoccidioides genus, we developed a Paracoccidioides brasiliensis knockdown strain of HSP30 via Agrobacterium tumefaciens-mediated transformation and demonstrated that silencing this gene decreases the ability of P. brasiliensis to use hemoglobin as a nutrient source. Additional studies are needed to establish HSP30 as a virulence factor, which can support the development of new therapeutic and/or diagnostic approaches.

The "Little Iron Waltz": The Ternary Response of Paracoccidioides spp. to Iron Deprivation

Paracoccidioides is a genus of thermodimorphic fungi that causes paracoccidioidomycosis. When in the host, the fungus undergoes several challenges, including iron deprivation imposed by nutritional immunity. In response to the iron deprivation triggered by the host, the fungus responds in a ternary manner using mechanisms of high affinity and specificity for the uptake of Fe, namely non-classical reductive iron uptake pathway, uptake of host iron proteins, and biosynthesis and uptake of siderophores. This triple response resembles the rhythmic structure of a waltz, which features three beats per compass. Using this connotation, we have constructed this review summarizing relevant findings in this area of study and pointing out new discoveries and perspectives that may contribute to the expansion of this "little iron waltz".

Molecular characterization of siderophore biosynthesis in Paracoccidioides brasiliensis

Iron is an essential nutrient for all organisms. For pathogenic fungi, iron is essential for the success of infection. Thus, these organisms have developed high affinity iron uptake mechanisms to deal with metal deprivation imposed by the host. Siderophore production is one of the mechanisms that fungal pathogens employ for iron acquisition. Paracoccidioides spp. present orthologous genes encoding the enzymes necessary for the biosynthesis of hydroxamates, and plasma membrane proteins related to the transport of these molecules. All these genes are induced in iron deprivation. In addition, it has been observed that Paracoccidioides spp. are able to use siderophores to scavenge iron. Here we observed that addition of the xenosiderophore ferrioxamine B FOB) to P. brasiliensis culture medium results in repression (at RNA and protein levels) of the SidA, the first enzyme of the siderophore biosynthesis pathway. Furthermore, SidA activity was reduced in the presence of FOB, suggesting that P. brasiliensis blocks siderophores biosynthesis and can explore siderophores in the environment to scavenge iron. In order to support the importance of siderophores on Paracoccidioides sp. life and infection cycle, silenced mutants for the sidA gene were obtained by antisense RNA technology. The obtained AsSidA strains displayed decreased siderophore biosynthesis in iron deprivation conditions and reduced virulence to an invertebrate model.

Nitrogen Catabolite Repression in members of Paracoccidioides complex

Paracoccidioides complex is a genus that comprises pathogenic fungi which are responsible by systemic disease Paracoccidioidomycosis. In host tissues, pathogenic fungi need to acquire nutrients in order to survive, making the uptake of nitrogen essential for their establishment and dissemination. Nitrogen utilization is employed by the alleviation of Nitrogen Catabolite Repression (NCR) which ensures the use of non-preferential or alternative nitrogen sources when preferential sources are not available. NCR is controlled by GATA transcription factors which act through GATA binding sites on promoter regions in NCR-sensitive genes. This process is responsible for encoding proteins involved with the scavenge, uptake and catabolism of a wide variety of non-preferential nitrogen sources. In this work, we predict the existence of AreA GATA transcription factor and feature the zinc finger domain by three-dimensional structure in Paracoccidioides. Furthermore, we demonstrate the putative genes involved with NCR response by means of in silico analysis. The gene expression profile under NCR conditions was evaluated. Demonstrating that P. lutzii supported transcriptional regulation and alleviated NCR in non-preferential nitrogen-dependent medium. The elucidation of NCR in members of Paracoccidioides complex will provide new knowledge about survival, dissemination and virulence for these pathogens with regard to nitrogen-scavenging strategies in the interactions of host-pathogens.

The pH Signaling Transcription Factor PAC-3 Regulates Metabolic and Developmental Processes in Pathogenic Fungi

The zinc finger transcription factor PAC-3/RIM101/PacC has a defined role in the secretion of enzymes and proteins in response to ambient pH, and also contributes to the virulence of species. Herein we evaluated the role of PAC-3 in the regulation of Neurospora crassa genes, in a model that examined the plant-fungi interactions. N. crassa is a model fungal species capable of exhibiting dynamic responses to its environment by employing endophytic or phytopathogenic behavior according to a given circumstance. Since plant growth and productivity are highly affected by pH and phosphorus (P) acquisition, we sought to verify the impact that induction of a Δpac-3 mutation would have under limited and sufficient Pi availability, while ensuring that the targeted physiological adjustments mimicked ambient pH and nutritional conditions required for efficient fungal growth and development. Our results suggest direct regulatory functions for PAC-3 in cell wall biosynthesis, homeostasis, oxidation-reduction processes, hydrolase activity, transmembrane transport, and modulation of genes associated with fungal virulence. Pi-dependent modulation was observed mainly in genes encoding for transporter proteins or related to cell wall development, thereby advancing the current understanding regarding colonization and adaptation processes in response to challenging environments. We have also provided comprehensive evidence that suggests a role for PAC-3 as a global regulator in plant pathogenic fungi, thus presenting results that have the potential to be applied to various types of microbes, with diverse survival mechanisms.

Identification of membrane proteome of Paracoccidioides lutzii and its regulation by zinc

Aim:

During infection development in the host, Paracoccidioides spp. faces the deprivation of micronutrients, a mechanism called nutritional immunity. This condition induces the remodeling of proteins present in different metabolic pathways. Therefore, we attempted to identify membrane proteins and their regulation by zinc in Paracoccidioides lutzii.

Materials & methods:

Membranes enriched fraction of yeast cells of P. lutzii were isolated, purified and identified by 2D LC–MS/MS detection and database search.

Results & conclusion:

Zinc deprivation suppressed the expression of membrane proteins such as glycoproteins, those involved in cell wall synthesis and those related to oxidative phosphorylation. This is the first study describing membrane proteins and the effect of zinc deficiency in their regulation in one member of the genus Paracoccidioides.

The methodology of protein identification allows the characterization of biological processes performed by those molecules. Therefore, we performed a membrane proteomic analysis of Paracoccidioides lutzii and further evaluated the responses of the fungus to zinc deprivation. The results obtained in the work allowed the characterization of membrane proteins present in organelles that are related to different cellular functions. Zinc deprivation changes processes related to cellular physiology and metabolism. These results help us to understand the process of pathogen–host interaction, since zinc deprivation is a condition present during infection.

Paracoccidioides spp. ferrous and ferric iron assimilation pathways

Iron is an essential micronutrient for almost all organisms, including fungi. Usually, fungi can uptake iron through receptor-mediated internalization of a siderophore or heme, and/or reductive iron assimilation (RIA). Traditionally, the RIA pathway consists of ferric reductases (Fres), ferroxidase (Fet3) and a high-affinity iron permease (Ftr1). Paracoccidioides spp. genomes do not present an Ftr1 homolog. However, this fungus expresses zinc regulated transporter homologs (Zrts), members of the ZIP family of membrane transporters that are able in some organisms to transport zinc and iron. A 2,3,5-triphenyltetrazolium chloride (TTC)-overlay assay indicates that both Pb01 and Pb18 express a ferric reductase activity; however, ⁵⁹Fe uptake assays indicate that only in Pb18 is this activity coupled to a reductase-dependent iron uptake pathway. In addition, Zrts are up-regulated in iron deprivation, as indicated by RNAseq and qRT-PCR using Pb01 transcripts. RNAseq strategy also demonstrated that transcripts related to siderophore uptake and biosynthesis are up-regulated in iron-deprived condition. The data suggest that the fungus could use both a non-classical RIA, comprising ferric reductases and Fe/Zn permeases (Zrts), and siderophore uptake pathways under iron-limited conditions. The study of iron metabolism reveals novel surface molecules that could function as accessible targets for drugs to block iron uptake and, consequently, inhibit pathogen's proliferation.