Candida albicans is a leading human fungal pathogen that can cause life-threatening infections in immunocompromised individuals, with mortality rates of ~40%. The ability of this organism to grow in both yeast and filamentous forms is critical for the establishment of systemic infection. ABSTRACT The ability to transition between yeast and filamentous growth states is critical for virulence of the leading human fungal pathogen Candida albicans. Large-scale genetic screens have identified hundreds of genes required for this morphological switch, but the mechanisms by which many of these genes orchestrate this developmental transition remain largely elusive. In this study, we characterized the role of Ent2 in governing morphogenesis in C. albicans. We showed that Ent2 is required for filamentous growth under a wide range of inducing conditions and is also required for virulence in a mouse model of systemic candidiasis. We found that the epsin N-terminal homology (ENTH) domain of Ent2 enables morphogenesis and virulence and does so via a physical interaction with the Cdc42 GTPase-activating protein (GAP) Rga2 and regulation of its localization. Further analyses revealed that overexpression of the Cdc42 effector protein Cla4 can overcome the requirement for the ENTH-Rga2 physical interaction, indicating that Ent2 functions, at least in part, to enable proper activation of the Cdc42-Cla4 signaling pathway in the presence of a filament-inducing cue. Overall, this work characterizes the mechanism by which Ent2 regulates hyphal morphogenesis in C. albicans, unveils the importance of this factor in enabling virulence in an in vivo model of systemic candidiasis and adds to the growing understanding of the genetic control of a key virulence trait. IMPORTANCE Candida albicans is a leading human fungal pathogen that can cause life-threatening infections in immunocompromised individuals, with mortality rates of ~40%. The ability of this organism to grow in both yeast and filamentous forms is critical for the establishment of systemic infection. Genomic screens have identified many genes required for this morphological transition, yet our understanding of the mechanisms that regulate this key virulence trait remains incomplete. In this study, we characterized Ent2 as a core regulator of C. albicans morphogenesis. We show that Ent2 regulates hyphal morphogenesis through an interaction between its ENTH domain and the Cdc42 GAP, Rga2, which signals through the Cdc42-Cla4 signaling pathway. Finally, we show that the Ent2 protein, and specifically its ENTH domain, is required for virulence in a mouse model of systemic candidiasis. Overall, this work identifies Ent2 as a key regulator of filamentation and virulence in C. albicans.

Ent2 Governs Morphogenesis and Virulence in Part through Regulation of the Cdc42 Signaling Cascade in the Fungal Pathogen Candida albicans

ABSTRACT The fungus Candida albicans is a frequent colonizer of humans but also an opportunistic pathogen causing superficial to severe infections, especially in vulnerable individuals. Its broad metabolic flexibility is key for the fungal adaptation to host environments, evasion from immune attack, and virulence. Amino acid metabolism and homeostasis, in particular, are critical for fungal fitness—illustrated by a rapid metabolic shift in response to amino acid starvation to restore intracellular metabolic balance. To investigate the cellular mechanisms underlying such compensatory metabolic processes, we performed data-driven genome-scale metabolic modeling based on transcriptional metabolic profiles of amino acid-starved cells to identify condition-specific fungal metabolic fluxes and pathway activities specific to cellular response to amino acid starvation. Most prominently, we predicted altered activity of the shikimate pathway upon amino acid limitation and identified a simultaneous induction of aromatic amino acid (AAA) biosynthesis and a metabolic gene cluster required for the catabolism of hydroxybenzenes. Further phenotypic and transcriptional analyses not only verified the transcription factor Zcf25 as the central regulator of the catechol-branch of this pathway, but also condition-specific co-regulation of AAA and hydroxybenzene metabolism mediated by Zcf25 and the transcriptional regulator of amino acid metabolism Stp2. These findings propose a so far unknown metabolic link between amino acid and hydroxybenzene metabolism in C. albicans , therewith adding another layer to its metabolic plasticity. IMPORTANCE The opportunistic human fungal pathogen Candida albicans possesses a remarkable metabolic plasticity, which is essential for both fungal commensalism and virulence and influences its physiology and behavior in multiple ways. The investigation of such processes particularly benefits from the emergence of multi-omics and in silico approaches. In this study, we combined a multi-omics approach with genome-scale metabolic modeling to investigate the fungal metabolic adaptation to amino acid utilization and starvation. Most strikingly, we found an altered activity of the shikimate pathway upon amino acid starvation, accompanied by a simultaneous induction of two metabolic gene clusters required for the metabolism of hydroxybenzenes. Further analyses revealed so far unknown potential functional and regulatory links between both metabolic pathways, which provide starting points for future research leading to a better understanding of the fungal adaptation to dynamic host conditions. 

A multi-omics analysis unveils functional and regulatory links between hydroxybenzene and aromatic amino acid metabolism in Candida albicans

Structural characterization of shikimate pathway multi-enzyme Aro1 from opportunistic fungal pathogen Candida albicans provides the first molecular image of all five domains. Only four of these domains are active and individually essential for C. albicans viability. In the human fungal pathogen Candida albicans, ARO1 encodes an essential multi-enzyme that catalyses consecutive steps in the shikimate pathway for biosynthesis of chorismate, a precursor to folate and the aromatic amino acids. We obtained the first molecular image of C. albicans Aro1 that reveals the architecture of all five enzymatic domains and their arrangement in the context of the full-length protein. Aro1 forms a flexible dimer allowing relative autonomy of enzymatic function of the individual domains. Our activity and in cellulo data suggest that only four of Aro1’s enzymatic domains are functional and essential for viability of C. albicans, whereas the 3-dehydroquinate dehydratase (DHQase) domain is inactive because of active site substitutions. We further demonstrate that in C. albicans, the type II DHQase Dqd1 can compensate for the inactive DHQase domain of Aro1, suggesting an unrecognized essential role for this enzyme in shikimate biosynthesis. In contrast, in Candida glabrata and Candida parapsilosis, which do not encode a Dqd1 homolog, Aro1 DHQase domains are enzymatically active, highlighting diversity across Candida species.

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Molecular analysis and essentiality of Aro1 shikimate biosynthesis multi-enzyme in Candida albicans

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Molecular analysis and essentiality of Aro1 shikimate biosynthesis multi-enzyme in Candida albicans