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Updated: Mar 15, 2026
Biolistic Transformation of a Fluorescent Tagged Gene into the Opportunistic Fungal Pathogen Cryptococcus neoformans
Published on: March 19, 2015
A Small Protein Associated with Fungal Energy Metabolism Affects the Virulence of Cryptococcus neoformans in Mammals
Erin E McClelland1, Udupi A Ramagopal2, Johanna Rivera3
1Department of Biology, Middle Tennessee State University, Murfreesboro, Tennessee, United States of America.
Abstract:
The pathogenic yeast Cryptococcus neoformans causes cryptococcosis, a life-threatening fungal disease. C. neoformans has multiple virulence mechanisms that are non-host specific, induce damage and interfere with immune clearance. Microarray analysis of C. neoformans strains serially passaged in mice associated a small gene (CNAG_02591) with virulence. This gene, hereafter identified as HVA1 (hypervirulence-associated protein 1), encodes a protein that has homologs of unknown function in plant and animal fungi, consistent with a conserved mechanism. Expression of HVA1 was negatively correlated with virulence and was reduced in vitro and in vivo in both mouse- and Galleria-passaged strains of C. neoformans. Phenotypic analysis in hva1Δ and hva1Δ+HVA1 strains revealed no significant differences in established virulence factors. Mice infected intravenously with the hva1Δ strain had higher fungal burden in the spleen and brain, but lower fungal burden in the lungs, and died faster than mice infected with H99W or the hva1Δ+HVA1 strain. Metabolomics analysis demonstrated a general increase in all amino acids measured in the disrupted strain and a block in the TCA cycle at isocitrate dehydrogenase, possibly due to alterations in the nicotinamide cofactor pool. Macrophage fungal burden experiments recapitulated the mouse hypervirulent phenotype of the hva1Δ strain only in the presence of exogenous NADPH. The crystal structure of the Hva1 protein was solved, and a comparison of structurally similar proteins correlated with the metabolomics data and potential interactions with NADPH. We report a new gene that modulates virulence through a mechanism associated with changes in fungal metabolism.
Insights
A newly identified gene, HVA1 (hypervirulence-associated protein 1), in Cryptococcus neoformans is linked to fungal metabolism and virulence. Its absence increases fungal burden in organs and accelerates mortality in mice, suggesting a role in controlling fungal pathogenesis.
Area of Science:
- Mycology
- Pathogen Biology
- Molecular Genetics
Background:
- Cryptococcus neoformans is a pathogenic yeast causing life-threatening cryptococcosis.
- Virulence mechanisms of C. neoformans are non-host specific and interfere with immune clearance.
- Microarray analysis identified a small gene, CNAG_02591, associated with virulence.
Purpose of the Study:
- To investigate the role of the C. neoformans gene CNAG_02591, identified as HVA1 (hypervirulence-associated protein 1), in fungal virulence.
- To elucidate the mechanism by which HVA1 influences fungal pathogenesis and host-pathogen interactions.
Main Methods:
- Gene deletion (hva1Δ) and complementation (hva1Δ+HVA1) in C. neoformans strains.
- In vivo virulence studies in mouse models and Galleria mellonella.
- Metabolomics analysis to assess metabolic changes in HVA1-deficient strains.
- Macrophage-based fungal burden experiments.
- Crystal structure determination of the Hva1 protein.
Main Results:
- HVA1 expression was negatively correlated with virulence and reduced in passaged strains.
- Mice infected with hva1Δ strain showed increased spleen and brain fungal burden, faster mortality, and altered lung burden.
- Metabolomics revealed increased amino acids and a TCA cycle block at isocitrate dehydrogenase in the hva1Δ strain.
- Exogenous NADPH partially rescued the hypervirulent phenotype of the hva1Δ strain in macrophages.
- Structural analysis suggested Hva1 interacts with NADPH.
Conclusions:
- HVA1 is a novel gene that modulates Cryptococcus neoformans virulence.
- The mechanism involves alterations in fungal metabolism, particularly the TCA cycle and cofactor availability (NADPH).
- HVA1 plays a conserved role in fungal pathogenesis, potentially through metabolic regulation.
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