Biology subjects

Thorn, H. I.

Publications and source records attributed to Thorn, H. I..

3 recordsLinked to original sources

bioRxiv2026

Triazole Stress Induces Accelerated Degradation of Aspergillus fumigatus Hmg1

Triazole antifungals inhibit the lanosterol C14-demethylase Cyp51A/B and are the first-line treatment for invasive aspergillosis caused by Aspergillus fumigatus. We previously proposed that triazoles impose a secondary constraint on ergosterol biosynthesis through negative feedback regulation of HMG-CoA reductase (Hmg1) through its sterol sensing domain (SSD), and SSD mutations compromise this regulation to produce resistance. The molecular mechanism underpinning this feedback remained unknown. In this study, we show that voriconazole drives accelerated protein degradation of Hmg1 and that SSD mutation abolishes this regulated degradation. Triazole-induced Hmg1 degradation is proteasome-dependent and partially requires the ERAD E3 ubiquitin ligase, HrdA, and INSIG ortholog, InsA, both conserved regulators of HMG-CoA Reductase abundance. We provide genetic evidence that the initiating negative feedback signal is not triazole acting directly on Hmg1 but lanosterol accumulation resulting from Cyp51A/B inhibition. To test whether depleting Hmg1 protein could re-sensitize resistant strains, we utilized a GFP-targeted degradation system designed to target Hmg1 for degradation without engaging its SSD. Combining this system with voriconazole treatment reduced the MIC at least four-fold in both conidia and established hyphae in susceptible and resistant strains. Together, our findings support a model wherein triazole-induced lanosterol accumulation drives HrdA/InsA-dependent accelerated degradation of Hmg1 and establish that pharmacologically inducing this secondary mechanism can enhance triazole activity in both susceptible and resistant isolates.

microbiology↗

bioRxiv2026

Biotinylation-dependent near-neighbor analysis for identification of septation regulators in Aspergillus fumigatus

Recent work has established septation as a critical process for virulence in A. fumigatus, as strains lacking septa are avirulent. While our work has focused on the well-studied Septation Initiation Network (SIN), understanding of septation machinery upstream and downstream of SIN remains limited in filamentous fungi. Proximity labeling techniques are powerful tools to study pathway interactions, especially those that are transient. Recent advances have seen TurboID used to study pathways and processes important for fungal pathogenesis. In this study, we adapt TurboID for use in Aspergillus fumigatus and use overlapping datasets of two SIN components, the terminal NDR kinase SidB and its binding partner MobA, to identify putative septation effectors. Many known septation effectors, including septins and cell wall synthesis proteins, were enriched in our datasets, validating the approach. Phenotypic characterization of hits identified by LC-MS/MS revealed several previously uncharacterized gene products involved in septum formation and cell wall stress tolerance. These included the PP2A regulatory subunit PabA and IQGAP SepG, which have been shown to regulate septation in Aspergillus nidulans. Thus, TurboID is a useful tool to study fungal signaling and physiology in A. fumigatus and may be used to improve understanding of pathogenic processes.

microbiology↗

bioRxiv2023

The Aspergillus fumigatus maiA gene contributes to cell wall homeostasis and fungal virulence.

In this study, two distinct in vitro infection models of Aspergillus fumigatus, using murine macrophages (RAW264.7) and human lung epithelial cells (A549), were employed to identify the genes important for fungal adaptation during infection. Transcriptomic analyses of co-incubated Aspergillus uncovered 140 fungal genes up-regulated in common between both models that, when compared with a previously published in vivo transcriptomic study, allowed the identification of 13 genes consistently up-regulated in all three infection conditions. Among them, the maiA gene, responsible for a critical step in the L-phenylalanine degradation pathway, was identified. Disruption of maiA resulted in a mutant strain unable to complete the Phe degradation pathway, leading to an excessive production of pyomelanin when this amino acid served as the sole carbon source. Moreover, the disruption mutant exhibited noticeable cell wall abnormalities, with reduced levels of {beta}-glucans within the cell wall. the maiA-1 mutant strain induced reduced inflammation in primary macrophages and displayed significantly lower virulence in a neutropenic mouse model of infection. This is the first study linking the A. fumigatus maiA gene to fungal cell wall homeostasis and virulence.

microbiology↗