Fungi mount efficient responses to altered extracellular pH. Characterization of the underlying mechanisms is fundamentally important in terms of understanding the molecular basis of pH homeostasis ...in higher eukaryotic cells, and for optimizing industrial processes which utilize fungi such as the production of pharmaceutical agents and food-use enzymes. Fungal pH adaptation is also a key requisite for establishment of multiple plant, insect, animal, and human diseases. Due to the differential reliance, respectively, of human and fungal cells upon electroneutral Na(+)-H(+) antiporters and outwardly directed electrogenic proton pumps, fundamental differences in the circuitry of pH homeostasis and adaptation exist, and these might be exploitable from a therapeutic perspective. At the molecular level, fungal pH tolerance is mediated by distinct but complementary homeostatic responses and highly conserved intracellular signaling pathways. Although traditionally studied as independent regulatory entities, the advent of systems biology has fuelled a new awareness of the interconnectivity between these very different modes of regulation. This review focuses upon the most recent advances in molecular understanding of three specific aspects of fungal pH adaptation, namely, sensing, signaling, and homeostasis.
Aspergillosis is a disease determined by various factors that influence fungal growth and fitness. A conserved signal transduction cascade linking environmental stress to amino acid homeostasis is ...the Cross-Pathway Control (CPC) system that acts via phosphorylation of the translation initiation factor eIF2 by a sensor kinase to elevate expression of a transcription factor. Ingestion of Aspergillus fumigatus conidia by macrophages does not trigger this stress response, suggesting that their phagosomal microenvironment is not deficient in amino acids. The cpcC gene encodes the CPC eIF2α kinase, and deletion mutants show increased sensitivity towards amino acid starvation. CpcC is specifically required for the CPC response but has limited influence on the amount of phosphorylated eIF2α. Strains deleted for the cpcC locus are not impaired in virulence in a murine model of pulmonary aspergillosis. Accordingly, basal expression of the Cross-Pathway Control transcriptional activator appears sufficient to support aspergillosis in this disease model.
The pathogenicity of six mutants of Aspergillus fumigatus that had been previously characterized in mice was assessed in Toll-deficient Drosophila melanogaster flies. Four out of six mutants of A. ...fumigatus, which displayed attenuated virulence in mice due to defects in siderophore biosynthesis ( sidA, sidD), PABA metabolism (H515), and starvation stress response ( cpcA), also had attenuated virulence in the fly model. In addition, similarly to previous findings in the mouse model, sidG mutant that is defective in extracellular siderophore biosynthesis retained full virulence in Toll-deficient flies. Overall, our studies reveal a high level of concordance between fly and murine models of invasive aspergillosis.
Integral membrane proteins found in the plasma membrane of fungi have great potential for the development of novel antifungal agents.In-depth studies on fungal signaling pathways define proteins that ...when deleted result in decreased virulence or viability, highlighting their potential as drug targets.New tools and methodologies have been developed to determine the structure of the yeast pheromone-sensing G protein-coupled receptor (GPCR) Ste2, highlighting the tractability of fungal GPCRs for structure determination.Single-particle electron cryo-microscopy was used to determine five structures of Ste2 that show the molecular details of ligand-induced receptor activation and highlight possible receptor regions that are amenable for drug development.
Up to 1.5 million people die yearly from fungal disease, but the repertoire of antifungal drug classes is minimal and the incidence of drug resistance is rising rapidly. This dilemma was recently declared by the World Health Organization as a global health emergency, but the discovery of new antifungal drug classes remains excruciatingly slow. This process could be accelerated by focusing on novel targets, such as G protein-coupled receptor (GPCR)-like proteins, that have a high likelihood of being druggable and have well-defined biology and roles in disease. We discuss recent successes in understanding the biology of virulence and in structure determination of yeast GPCRs, and highlight new approaches that might pay significant dividends in the urgent search for novel antifungal drugs.
Mycological studies of yeasts are entering a new phase, with the sequencing of multiple fungal genomes informing our understanding of their ability to cause disease and interact with the host. At the ...same time, the ongoing use of traditional methods in many clinical mycology laboratories continues to provide information for the diagnosis and treatment of patients. This volume reviews various aspects of pathogenic yeasts and what is known about their molecular and cellular biology and virulence, in addition to looking at clinical and laboratory findings. As each chapter is written by a leading expert in the field, this book summarizes in one volume much of the latest research on several pathogenic yeasts, including Candida, Cryptococcus, Malassezia and yeasts of emerging importance. The importance of laboratory diagnosis, antifungal susceptibility testing, antifungal resistance and yeast diseases in animals are reviewed.
•First description of a LINE element of the Tad clade in Aspergillus fumigatus.•We detected highly active transcription in Af293 but none in CEA10.•Distribution of elements varies greatly between ...isolates of different origins.•Evidence that stress conditions and virus infection might facilitate transposition.•Results raise numerous questions about how these elements are regulated.
Functional genomic analysis of the mould pathogen Aspergillus fumigatus has identified multiple secondary metabolism genes upregulated in the host niche. Intriguingly, transcriptomic analyses of infectious germlings, germinating spores and mutants lacking the LaeA methyltransferase reveal differential expression of transposable elements (TEs), which often flank secondary metabolite gene clusters. In this study we investigate, in clinical and environmental isolates, the structure and distribution of a specific class of A. fumigatus long interspersed nuclear element (LINE)-like retrotransposons occupying subtelomeric loci in the A. fumigatus genome, and probe their stability in response to laboratory- and host-imposed stresses. In silico analyses revealed that this class belongs to the Tad clade of LINE-like elements. Southern blotting with a LINE-specific probe in clinical and environmental isolates revealed a high variability in the insertion pattern between strains and active transcription of LINE-like element(s) was discernable, in the type strain Af293, by RT-PCR. One out of 14 tested clinical isolates did not contain any LINEs at all, arguing against an absolute requirement for LINE-mediated activities in human infections. Finally, we found preliminary evidence of an association between mycovirus-infection and the expansion of Tad-element populations in discrete A. fumigatus genomes.
Secondary metabolite arsenal of an opportunistic pathogenic fungus Bignell, Elaine; Cairns, Timothy C.; Throckmorton, Kurt ...
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
12/2016, Letnik:
371, Številka:
1709
Journal Article
Recenzirano
Odprti dostop
Aspergillus fumigatus is a versatile fungus able to successfully exploit diverse environments from mammalian lungs to agricultural waste products. Among its many fitness attributes are dozens of ...genetic loci containing biosynthetic gene clusters (BGCs) producing bioactive small molecules (often referred to as secondary metabolites or natural products) that provide growth advantages to the fungus dependent on environment. Here we summarize the current knowledge of these BGCs—18 of which can be named to product—their expression profiles in vivo, and which BGCs may enhance virulence of this opportunistic human pathogen. Furthermore, we find extensive evidence for the presence of many of these BGCs, or similar BGCs, in distantly related genera including the emerging pathogen Pseudogymnoascus destructans, the causative agent of white-nose syndrome in bats, and suggest such BGCs may be predictive of pathogenic potential in other fungi.
This article is part of the themed issue ‘Tackling emerging fungal threats to animal health, food security and ecosystem resilience’.
Many fungi grow over a wide pH range and their gene expression is tailored to the environmental pH. In Aspergillus nidulans , the transcription factor PacC, an activator of genes expressed in ...alkaline conditions and a repressor of those expressed in acidic conditions, undergoes two processing proteolyses, the first being pH-signal dependent and the second proteasomal. Signal transduction involves a ‘go-between’ connecting two complexes, one of which comprises two plasma membrane proteins and an arrestin and the other comprises PacC, a cysteine protease, a scaffold and endosomal components. The Saccharomyces cerevisiae PacC orthologue, Rim101p, differs in that it does not undergo the second round of proteolysis and it functions directly as a repressor only. PacC/Rim101-mediated pH regulation is crucial to fungal pathogenicity.
PDF
