Target validation and ligand development for a pathogenic fungal profilin, using a knock-down strain of pathogenic yeast Candida glabrata and structure-based ligand design

Multi-Omics Profiling of Candida albicans Grown on Solid Versus Liquid Media

Candida albicans is a common pathogenic fungus that presents a challenge to healthcare facilities. It can switch between a yeast cell form that diffuses through the bloodstream to colonize internal organs and a filamentous form that penetrates host mucosa. Understanding the pathogen's strategies for environmental adaptation and, ultimately, survival, is crucial. As a complementary study, herein, a multi-omics analysis was performed using high-resolution timsTOF MS to compare the proteomes and metabolomes of Wild Type (WT) Candida albicans (strain DK318) grown on agar plates versus liquid media. Proteomic analysis revealed a total of 1793 proteins and 15,013 peptides. Out of the 1403 identified proteins, 313 proteins were significantly differentially abundant with a p-value < 0.05. Of these, 156 and 157 proteins were significantly increased in liquid and solid media, respectively. Metabolomics analysis identified 192 metabolites in total. The majority (42/48) of the significantly altered metabolites (p-value 0.05 FDR, FC 1.5), mainly amino acids, were significantly higher in solid media, while only 2 metabolites were significantly higher in liquid media. The combined multi-omics analysis provides insight into adaptative morphological changes supporting Candida albicans' life cycle and identifies crucial virulence factors during biofilm formation and bloodstream infection.

A novel Candida glabrata doxycycline-inducible system for in vitro/in vivo use

Candida glabrata is an important pathogen causing superficial to invasive disease in human. Conditional expression systems are helpful in addressing the function of genes and especially when they can be applied to in vivo studies. Tetracycline-dependent regulation systems have been used in diverse fungi to turn-on (Tet-on) or turn-off (Tet-off) gene expression either in vitro but also in vivo in animal models. Up to now, only a Tet-off expression has been constructed for gene expression in C. glabrata. Here, we report a Tet-on gene expression system which can be used in vitro and in vivo in any C. glabrata genetic background. This system was used in a mice model of systemic infection to demonstrate that the general amino acid permease Gap1 is important for C. glabrata virulence.

Erg25 Controls Host-Cholesterol Uptake Mediated by Aus1p-Associated Sterol-Rich Membrane Domains in Candida glabrata

The uptake of cholesterol from the host is closely linked to the proliferation of pathogenic fungi and protozoa during infection. For some pathogenic fungi, cholesterol uptake is an important strategy for decreasing susceptibility to antifungals that inhibit ergosterol biosynthesis. In this study, we show that Candida glabrata ERG25, which encodes an enzyme that demethylates 4,4-dimethylzymosterol, is required for cholesterol uptake from host serum. Based on the screening of C. glabrata conditional knockdown mutants for each gene involved in ergosterol biosynthesis, ERG25 knockdown was found to decrease lethality of infected mice. ERG25 knockdown impairs the plasma membrane localization of the sterol importer Aus1p, suggesting that the accumulated 4,4-dimethylzymosterol destabilizes the lipid domain with which Aus1p functionally associates. ERG25 knockdown further influences the structure of the membrane compartment of Can1p (MCC)/eisosomes (ergosterol-rich lipid domains), but not the localization of the membrane proteins Pma1p and Hxt1p, which localize to sterol-poor domains. In the sterol-rich lipid domain, Aus1p-contining domain was mostly independent of MCC/eisosomes, and the nature of these domains was also different: Ausp1-contining domain was a dynamic network-like domain, whereas the MCC/eisosomes was a static dot-like domain. However, deletion of MCC/eisosomes was observed to influence the localization of Aus1p after Aus1p was transported from the endoplasmic reticulum (ER) through the Golgi apparatus to the plasma membrane. These findings suggest that ERG25 plays a key role in stabilizing sterol-rich lipid domains, constituting a promising candidate target for antifungal therapy.

Differential cell wall remodeling of two chitin synthase deletants Δchs3A and Δchs3B in the pathogenic yeast Candida glabrata

It is known that cell wall remodeling and the salvaging pathway act to compensate for an impaired or a damaged cell wall. Lately, it has been indicated that this mechanism is partly required for resistance to the glucan synthesis inhibitor echinocandin. While cell wall remodeling has been described in mutants of glucan or mannan synthesis, it has not yet been reported in a chitin synthesis mutant. Here, we describe a novel cell wall remodeling and salvaging pathway in chitin synthesis mutants, Δchs3A and Δchs3B, of the pathogenic yeast Candida glabrata. Electron microscopic analysis revealed a thickened mannoprotein layer in Δchs3A cells and a thickened chitin-glucan layer of Δchs3B cells, and it indicated the hypothesis that mannan synthase and chitin-glucan synthase indemnify Δchs3A and Δchs3B cells, respectively. The double-mutant CHS3A and MNN10, encoding α-1,6-mannosyltransferase, showed synergistic stress sensitization, and the Δchs3B strain showed supersensitivity to echinocandins. Hence, these findings support the above hypothesis of remodeling. Furthermore, unlike Δchs3A cells, Δchs3B cells showed supersensitivity to calcineurin inhibitor FK506 and Tor1p kinase inhibitor rapamycin, indicating that the Δchs3B strain uses the calcineurin pathway and a Tor1p kinase for cell wall remodeling.