Proteomic profiling of the monothiol glutaredoxin Grx3 reveals its global role in the regulation of iron dependent processes

Abstract

Iron is an essential nutrient required as a cofactor for many biological processes. As a fungal commensal-pathogen of humans, Candida albicans encounters a range of bioavailable iron levels in the human host and maintains homeostasis with a conserved regulatory circuit. How C. albicans senses and responds to iron availability is unknown. In model yeasts, regulation of the iron homeostasis circuit requires monothiol glutaredoxins (Grxs), but their functions beyond the regulatory circuit are unclear. Here, we show Grx3 is required for virulence and growth on low iron for C. albicans. To explore the global roles of Grx3, we applied a proteomic approach and performed in vivo cross-linked tandem affinity purification coupled with mass spectrometry. We identified a large number of Grx3 interacting proteins that function in diverse biological processes. This included Fra1 and Bol2/Fra2, which function with Grxs in intracellular iron trafficking in other organisms. Grx3 interacts with and regulates the activity of Sfu1 and Hap43, components of the C. albicans iron regulatory circuit. Unlike the regulatory circuit, which determines expression or repression of target genes in response to iron availability, Grx3 amplifies levels of gene expression or repression. Consistent with the proteomic data, the grx3 mutant is sensitive to heat shock, oxidative, nitrosative, and genotoxic stresses, and shows growth dependence on histidine, leucine, and tryptophan. We suggest Grx3 is a conserved global regulator of iron-dependent processes occurring within the cell.

The monothiol glutaredoxin Grx4 influences thermotolerance, cell wall integrity, and Mpk1 signaling in Cryptococcus neoformans

“…Notably, the impaired thermotolerance of a grx4Δ mutant may partially explain the avirulence of the grx4Δ mutant ( Attarian et al 2018 ). Consistent with our observations, the Grx4 ortholog in another human pathogenic fungus, C. albicans , is also required for robust growth at elevated temperature indicating a conserved role in thermotolerance ( Alkafeef et al 2020 ). Other phenotypes of the grx4Δ mutant in C. neoformans may also be important in the context of disease and identification of therapeutic targets.…”

“…Monothiol glutaredoxins such as Grx4 are involved in iron regulation, and the biogenesis and trafficking of iron-sulfur clusters in a variety of fungi, including A. fumigatus , C. albicans , C. neoformans , S. cerevisiae , and S. pombe ( Ojeda et al 2006 ; Labbé et al 2013 ; Encinar del Dedo et al 2015 ; Dlouhy et al 2017 ; Misslinger et al 2019 ; Attarian et al 2018 ; Alkafeef et al 2020 ; Ramos-Alonso et al 2020 ; Gupta and Outten 2020 ). We previously identified phenotypes for grx4Δ mutants related to iron homeostasis, including hypersensitivity to phleomycin, electron transport chain inhibitors, and agents that provoke oxidative stress and DNA damage ( Attarian et al 2018 ).…”

“…The role of monothiol glutaredoxins via interactions with transcription factors appears to be conserved because Grx3 and Grx4 in S. cerevisiae also function in iron homeostasis by regulating the iron-responsive transcription factor Aft1 ( Gupta and Outten 2020 ), and participate in the defense against oxidative stress caused by reactive oxygen species (ROS) ( Pujol-Carrion and Torre-Ruiz 2017 ). Furthermore, Grx4 also plays a role in oxidative stress response in C. albicans ( Alkafeef et al 2020 ). Notably, the iron regulator SreA in Alternaria alternata that is similar to Cir1 also influences sensitivity to oxidative stress and agents that challenge CWI ( Chung et al 2020 ).…”

β-N-Methylamino-L-Alanine (BMAA) Causes Severe Stress in Nostoc sp. PCC 7120 Cells under Diazotrophic Conditions: A Proteomic Study

“…Mammalian glutaredoxin 3 (Grx3) is critical for maintaining redox homeostasis and essential for the defense mechanism against oxidative stress [ 84 ]. A large list of Glutaredoxin-3 associated proteins of Candida albicans was identified by using a proteomic approach [ 85 ]. These proteins were found to have diverse functions, including iron-sulfur trafficking, iron homeostasis, metabolism redox homeostasis, protein translation, DNA maintenance, and repair.…”

“…These proteins were found to have diverse functions, including iron-sulfur trafficking, iron homeostasis, metabolism redox homeostasis, protein translation, DNA maintenance, and repair. The authors concluded that Glutaredoxin-3 is a global regulator of iron homeostasis and of other iron-dependent cellular processes [ 85 ]. Glutaredoxin-3 is significant in transcriptional iron regulation and in intracellular iron distribution.…”