Mobilization of Intracellular Copper Stores by the Ctr2 Vacuolar Copper Transporter

Rat copper transport protein 2 (CTR2) is involved in fertilization through interaction with IZUMO1 and JUNO

In mammalian reproduction, testis-specific protein IZUMO1 and its receptor JUNO on the oocyte surface are essential for sperm-oocyte recognition, binding, and membrane fusion. However, these factors alone are insufficient to accomplish cytoplasmic membrane fusion. It is believed that other gametic proteins interact with them to facilitate sperm-oocyte interaction on the head and mid-tail of rat spermatozoa as well as on the surface of oocytes. In this study, Copper Transport Protein 2 (CTR2) has been identified on the head and mid-tail of rat spermatozoa as well as on the surface of oocytes. CTR2 directly interacts with both IZUMO1 and JUNO, colocalizing with IZUMO1 on the sperm head and with JUNO on the oocyte membrane. Treatment of the capacitated sperm and zona pellucida-free oocytes with anti-CTR2 antibody resulted in a significant decrease in fertilization rates in IVF experiments. These findings suggest that CTR2 plays an important role in mammalian fertilization by interacting with IZUMO1 and JUNO, providing new insights into the molecular mechanisms of mammalian sperm-oocyte adhesion and fusion.

Advances of the mechanism for copper tolerance in plants

Copper (Cu) is a vital trace element necessary for plants growth and development. It acts as a co-factor for enzymes and plays a crucial role in various physiological processes, including photosynthesis, respiration, antioxidant systems, and hormone signaling transduction. However, excessive amounts of Cu can disrupt normal physiological metabolism, thus hindering plant growth, development, and reducing yield. In recent years, the widespread abuse of Cu-containing fungicides and industrial Cu pollution has resulted in significant soil contamination. Therefore, it is of utmost importance to uncover the adverse effects of excessive Cu on plant growth and delve into the molecular mechanisms employed by plants to counteract the stress caused by excessive Cu. Recent studies have confirmed the inhibitory effects of excess Cu on mineral nutrition, chlorophyll biosynthesis, and antioxidant enzyme activity. This review systematically outlines the ways in which plants tolerate excessive Cu stress and summarizes them into eight Cu-tolerance strategies. Furthermore, it highlights the necessity for further research to comprehend the molecular regulatory mechanisms underlying the responses to excessive Cu stress.

Characterization of a High-Affinity Copper Transporter CTR1a in the White-Nose Syndrome Causing Fungal Pathogen Pseudogymnoascus destructans

Copper is an essential micronutrient and the ability to scavenge tightly bound or trace levels of copper ions at the host-pathogen interface is vital for fungal proliferation in animal hosts. Recent studies suggest that trace metal ion acquisition is critical for the establishment and propagation of Pseudogymnoascus destructans, the fungal pathogen responsible for white-nose syndrome (WNS), on their bat host. However, little is known about these metal acquisition pathways in P. destructans. In this study, we report the characterization of the P. destructans high-affinity copper transporter VC83_00191 (PdCTR1a), which is implicated as a virulence factor associated with the WNS disease state. Using Saccharomyces cerevisiae as a recombinant expression host, we find that PdCTR1a can efficiently traffic Cu ions into the yeast cytoplasm. Complementary studies in the native P. destructans fungus provide evidence that PdCTR1a transcripts and protein levels are dictated by Cu-bioavailability in the growth media. Our study demonstrates that PdCTR1a is a functional high-affinity copper transporter and is relevant to Cu homeostasis pathways in P. destructans.

Impact of liver diseases and pharmacological interactions on the transportome involved in hepatic drug disposition

The liver plays a pivotal role in drug disposition owing to the expression of transporters accounting for the uptake at the sinusoidal membrane and the efflux across the basolateral and canalicular membranes of hepatocytes of many different compounds. Moreover, intracellular mechanisms of phases I and II biotransformation generate, in general, inactive compounds that are more polar and easier to eliminate into bile or refluxed back toward the blood for their elimination by the kidneys, which becomes crucial when the biliary route is hampered. The set of transporters expressed at a given time, i.e., the so-called transportome, is encoded by genes belonging to two gene superfamilies named Solute Carriers (SLC) and ATP-Binding Cassette (ABC), which account mainly, but not exclusively, for the uptake and efflux of endogenous substances and xenobiotics, which include many different drugs. Besides the existence of genetic variants, which determines a marked interindividual heterogeneity regarding liver drug disposition among patients, prevalent diseases, such as cirrhosis, non-alcoholic steatohepatitis, primary sclerosing cholangitis, primary biliary cirrhosis, viral hepatitis, hepatocellular carcinoma, cholangiocarcinoma, and several cholestatic liver diseases, can alter the transportome and hence affect the pharmacokinetics of drugs used to treat these patients. Moreover, hepatic drug transporters are involved in many drug-drug interactions (DDI) that challenge the safety of using a combination of agents handled by these proteins. Updated information on these questions has been organized in this article by superfamilies and families of members of the transportome involved in hepatic drug disposition.

Molecular aspects of copper homeostasis in fungi

Copper homeostasis in fungi is a tightly regulated process crucial for cellular functions. Fungi acquire copper from their environment, with transporters facilitating its uptake into the cell. Once inside, copper is utilized in various metabolic pathways, including respiration and antioxidant defense. However, excessive copper can be toxic by promoting cell damage mainly due to oxidative stress and metal displacements. Fungi employ intricate regulatory mechanisms to maintain optimal copper levels. These involve transcription factors that control the expression of genes involved in copper transport, storage, and detoxification. Additionally, chaperone proteins assist in copper trafficking within the cell, ensuring its delivery to specific targets. Furthermore, efflux pumps help remove excess copper from the cell. Altogether, these mechanisms enable fungi to balance copper levels, ensuring proper cellular function while preventing toxicity. Understanding copper homeostasis in fungi is not only essential for fungal biology but also holds implications for various applications, including biotechnology and antifungal drug development.

Characterization of a High-Affinity Copper Transporter in the White-Nose Syndrome Causing Fungal Pathogen Pseudogymnoascus destructans

Copper is an essential micronutrient and the ability to scavenge tightly bound or trace levels of copper ions at the host-pathogen interface is vital for fungal proliferation in animal hosts. Recent studies suggest that trace metal ion acquisition is critical for the establishment and propagation of Pseudogymnoascus destructans, the fungal pathogen responsible for white-nose syndrome (WNS), on their bat host. However, little is known about these metal acquisition pathways in P. destructans. In this study, we report the characterization of the P. destructans high-affinity copper transporter VC83_00191 (PdCTR1a), which is implicated as a virulence factor associated with the WNS disease state. Using Saccharomyces cerevisiae as a recombinant expression host, we find that PdCTR1a localizes to the cell surface plasma membrane and can efficiently traffic Cu-ions into the yeast cytoplasm. Complementary studies in the native P. destructans fungus provide evidence that PdCTR1a transcripts and protein levels are dictated by Cu-bioavailability in the growth media. Our study demonstrates that PdCTR1a is a functional high-affinity copper transporter and is relevant to Cu-homeostasis pathways in P. destructans.

Targeting cuproplasia and cuproptosis in cancer

Copper, an essential trace element that exists in oxidized and reduced forms, has pivotal roles in a variety of biological processes, including redox chemistry, enzymatic reactions, mitochondrial respiration, iron metabolism, autophagy and immune modulation; maintaining copper homeostasis is crucial as both its deficiency and its excess are deleterious. Dysregulated copper metabolism has a dual role in tumorigenesis and cancer therapy. Specifically, cuproplasia describes copper-dependent cell growth and proliferation, including hyperplasia, metaplasia and neoplasia, whereas cuproptosis refers to a mitochondrial pathway of cell death triggered by excessive copper exposure and subsequent proteotoxic stress (although complex interactions between cuproptosis and other cell death mechanisms, such as ferroptosis, are likely and remain enigmatic). In this Review, we summarize advances in our understanding of copper metabolism, the molecular machineries underlying cuproplasia and cuproptosis, and their potential targeting for cancer therapy. These new findings advance the rapidly expanding field of translational cancer research focused on metal compounds.

Zn deficiency disrupts Cu and S homeostasis in Chlamydomonas resulting in over accumulation of Cu and Cysteine

Growth of Chlamydomonas reinhardtii in zinc (Zn) limited medium leads to disruption of copper (Cu) homeostasis, resulting in up to 40-fold Cu over-accumulation relative to its typical Cu quota. We show that Chlamydomonas controls its Cu quota by balancing Cu import and export, which is disrupted in a Zn deficient cell, thus establishing a mechanistic connection between Cu and Zn homeostasis. Transcriptomics, proteomics and elemental profiling revealed that Zn-limited Chlamydomonas cells up-regulate a subset of genes encoding "first responder" proteins involved in sulfur (S) assimilation and consequently accumulate more intracellular S, which is incorporated into L-cysteine, γ-glutamylcysteine, and homocysteine. Most prominently, in the absence of Zn, free L-cysteine is increased ∼80-fold, corresponding to ∼2.8 × 109 molecules/cell. Interestingly, classic S-containing metal binding ligands like glutathione and phytochelatins do not increase. X-ray fluorescence microscopy showed foci of S accumulation in Zn-limited cells that co-localize with Cu, phosphorus and calcium, consistent with Cu-thiol complexes in the acidocalcisome, the site of Cu(I) accumulation. Notably, cells that have been previously starved for Cu do not accumulate S or Cys, causally connecting cysteine synthesis with Cu accumulation. We suggest that cysteine is an in vivo Cu(I) ligand, perhaps ancestral, that buffers cytosolic Cu.

Loss of OPT3 function decreases phloem copper levels and impairs crosstalk between copper and iron homeostasis and shoot-to-root signaling in Arabidopsis thaliana

Copper (Cu) and iron (Fe) are essential micronutrients that are toxic when accumulating in excess in cells. Thus, their uptake by roots is tightly regulated. While plants sense and respond to local Cu availability, the systemic regulation of Cu uptake has not been documented in contrast to local and systemic control of Fe uptake. Fe abundance in the phloem has been suggested to act systemically, regulating the expression of Fe uptake genes in roots. Consistently, shoot-to-root Fe signaling is disrupted in Arabidopsis thaliana mutants lacking the phloem companion cell-localized Fe transporter, OLIGOPEPTIDE TRANSPORTER 3 (AtOPT3). We report that AtOPT3 also transports Cu in heterologous systems and contributes to its delivery from sources to sinks in planta. The opt3 mutant contained less Cu in the phloem, was sensitive to Cu deficiency and mounted a transcriptional Cu deficiency response in roots and young leaves. Feeding the opt3 mutant and Cu- or Fe-deficient wild-type seedlings with Cu or Fe via the phloem in leaves downregulated the expression of both Cu- and Fe-deficiency marker genes in roots. These data suggest the existence of shoot-to-root Cu signaling, highlight the complexity of Cu/Fe interactions, and the role of AtOPT3 in fine-tuning root transcriptional responses to the plant Cu and Fe needs.

Cysteine: an ancestral Cu binding ligand in green algae?

Growth of Chlamydomonas reinhardtii in zinc (Zn) limited medium leads to disruption of copper (Cu) homeostasis, resulting in up to 40-fold Cu over-accumulation relative to its typical Cu quota. We show that Chlamydomonas controls its Cu quota by balancing Cu import and export, which is disrupted in a Zn deficient cell, thus establishing a mechanistic connection between Cu and Zn homeostasis. Transcriptomics, proteomics and elemental profiling revealed that Zn-limited Chlamydomonas cells up-regulate a subset of genes encoding "first responder" proteins involved in sulfur (S) assimilation and consequently accumulate more intracellular S, which is incorporated into L-cysteine, γ-glutamylcysteine and homocysteine. Most prominently, in the absence of Zn, free L-cysteine is increased ~80-fold, corresponding to ~ 2.8 × 10 ⁹ molecules/cell. Interestingly, classic S-containing metal binding ligands like glutathione and phytochelatins do not increase. X-ray fluorescence microscopy showed foci of S accumulation in Zn-limited cells that co-localize with Cu, phosphorus and calcium, consistent with Cu-thiol complexes in the acidocalcisome, the site of Cu(I) accumulation. Notably, cells that have been previously starved for Cu do not accumulate S or Cys, causally connecting cysteine synthesis with Cu accumulation. We suggest that cysteine is an in vivo Cu(I) ligand, perhaps ancestral, that buffers cytosolic Cu.

Decreased Expression of the Slc31a1 Gene and Cytoplasmic Relocalization of Membrane CTR1 Protein in Renal Epithelial Cells: A Potent Protective Mechanism against Copper Nephrotoxicity in a Mouse Model of Menkes Disease

Kidneys play an especial role in copper redistribution in the organism. The epithelial cells of proximal tubules perform the functions of both copper uptake from the primary urine and release to the blood. These cells are equipped on their apical and basal membrane with copper transporters CTR1 and ATP7A. Mosaic mutant mice displaying a functional dysfunction of ATP7A are an established model of Menkes disease. These mice exhibit systemic copper deficiency despite renal copper overload, enhanced by copper therapy, which is indispensable for their life span extension. The aim of this study was to analyze the expression of Slc31a1 and Slc31a2 genes (encoding CTR1/CTR2 proteins) and the cellular localization of the CTR1 protein in suckling, young and adult mosaic mutants. Our results indicate that in the kidney of both intact and copper-injected 14-day-old mutants showing high renal copper content, CTR1 mRNA level is not up-regulated compared to wild-type mice given a copper injection. The expression of the Slc31a1 gene in 45-day-old mice is even reduced compared with intact wild-type animals. In suckling and young copper-injected mutants, the CTR1 protein is relocalized from the apical membrane to the cytoplasm of epithelial cells of proximal tubules, the process which prevents copper transport from the primary urine and, thus, protects cells against copper toxicity.

Comparative Copper Resistance Strategies of Rhodonia placenta and Phanerochaete chrysosporium in a Copper/Azole-Treated Wood Microcosm

Copper-based formulations of wood preservatives are widely used in industry to protect wood materials from degradation caused by fungi. Wood treated with preservatives generate toxic waste that currently cannot be properly recycled. Despite copper being very efficient as an antifungal agent against most fungi, some species are able to cope with these high metal concentrations. This is the case for the brown-rot fungus Rhodonia placenta and the white-rot fungus Phanerochaete chrysosporium, which are able to grow efficiently in pine wood treated with Tanalith E3474. Here, we aimed to test the abilities of the two fungi to cope with copper in this toxic environment and to decontaminate Tanalith E-treated wood. A microcosm allowing the growth of the fungi on industrially treated pine wood was designed, and the distribution of copper between mycelium and wood was analysed within the embedded hyphae and wood particles using coupled X-ray fluorescence spectroscopy and Scanning Electron Microscopy (SEM)/Electron Dispersive Spectroscopy (EDS). The results demonstrate the copper biosorption capacities of P. chrysosporium and the production of copper-oxalate crystals by R. placenta. These data coupled to genomic analysis suggest the involvement of additional mechanisms for copper tolerance in these rot fungi that are likely related to copper transport (import, export, or vacuolar sequestration).

Copper Acts Synergistically With Fluconazole in Candida glabrata by Compromising Drug Efflux, Sterol Metabolism, and Zinc Homeostasis

The synergistic combinations of drugs are promising strategies to boost the effectiveness of current antifungals and thus prevent the emergence of resistance. In this work, we show that copper and the antifungal fluconazole act synergistically against Candida glabrata, an opportunistic pathogenic yeast intrinsically tolerant to fluconazole. Analyses of the transcriptomic profile of C. glabrata after the combination of copper and fluconazole showed that the expression of the multidrug transporter gene CDR1 was decreased, suggesting that fluconazole efflux could be affected. In agreement, we observed that copper inhibits the transactivation of Pdr1, the transcription regulator of multidrug transporters and leads to the intracellular accumulation of fluconazole. Copper also decreases the transcriptional induction of ergosterol biosynthesis (ERG) genes by fluconazole, which culminates in the accumulation of toxic sterols. Co-treatment of cells with copper and fluconazole should affect the function of proteins located in the plasma membrane, as several ultrastructural alterations, including irregular cell wall and plasma membrane and loss of cell wall integrity, were observed. Finally, we show that the combination of copper and fluconazole downregulates the expression of the gene encoding the zinc-responsive transcription regulator Zap1, which possibly, together with the membrane transporters malfunction, generates zinc depletion. Supplementation with zinc reverts the toxic effect of combining copper with fluconazole, underscoring the importance of this metal in the observed synergistic effect. Overall, this work, while unveiling the molecular basis that supports the use of copper to enhance the effectiveness of fluconazole, paves the way for the development of new metal-based antifungal strategies.

Copper Metabolism in Naegleria gruberi and Its Deadly Relative Naegleria fowleri

Although copper is an essential nutrient crucial for many biological processes, an excessive concentration can be toxic and lead to cell death. The metabolism of this two-faced metal must be strictly regulated at the cell level. In this study, we investigated copper homeostasis in two related unicellular organisms: nonpathogenic Naegleria gruberi and the “brain-eating amoeba” Naegleria fowleri. We identified and confirmed the function of their specific copper transporters securing the main pathway of copper acquisition. Adjusting to different environments with varying copper levels during the life cycle of these organisms requires various metabolic adaptations. Using comparative proteomic analyses, measuring oxygen consumption, and enzymatic determination of NADH dehydrogenase, we showed that both amoebas respond to copper deprivation by upregulating the components of the branched electron transport chain: the alternative oxidase and alternative NADH dehydrogenase. Interestingly, analysis of iron acquisition indicated that this system is copper-dependent in N. gruberi but not in its pathogenic relative. Importantly, we identified a potential key protein of copper metabolism of N. gruberi, the homolog of human DJ-1 protein, which is known to be linked to Parkinson’s disease. Altogether, our study reveals the mechanisms underlying copper metabolism in the model amoeba N. gruberi and the fatal pathogen N. fowleri and highlights the differences between the two amoebas.

Nonsense-mediated mRNA decay and metal ion homeostasis and detoxification in Saccharomyces cerevisiae

The highly conserved Nonsense-mediated mRNA decay (NMD) pathway is a translation dependent mRNA degradation pathway. Although NMD is best known for its role in degrading mRNAs with premature termination codons (PTCs) generated during transcription, splicing, or damage to the mRNAs, NMD is now also recognized as a pathway with additional important functions. Notably, NMD precisely regulates protein coding natural mRNAs, hence controlling gene expression within several physiologically significant pathways. Such pathways affected by NMD include nutritional bio-metal homeostasis and metal ion detoxification, as well as crosstalk between these pathways. Here, we focus on the relationships between NMD and various metal homeostasis and detoxification pathways. We review the described role that the NMD pathway plays in magnesium, zinc, iron, and copper homeostasis, as well as cadmium detoxification.

A differential subcellular localization of two copper transporters from the COPT family suggests distinct roles in copper homeostasis in Physcomitrium patens

The moss Physcomitrium (Physcomitrella) patens is a bryophyte that provides genetic information about the adaptation to the life on land by early Embryophytes and is a reference organism for comparative evolutionary studies in plants. Copper is an essential micronutrient for every living organism, its transport across the plasma membrane is achieved by the copper transport protein family COPT/CTR. Two genes related to the COPT family were identified in Physcomitrella patens, PpaCOPT1 and PpaCOPT2. Homology modelling of both proteins showed the presence of three putative transmembrane domains (TMD) and the Mx₃M motif, constituting a potential Cu ⁺ selectivity filter present in other members of this family. Functional characterization of PpaCOPT1 and PpaCOPT2 in the yeast mutant ctr1Δctr3Δ restored its growth on medium with non-fermentable carbon sources at micromolar Cu concentrations, providing support that these two moss proteins function as high affinity Cu ⁺ transporters. Localization of PpaCOPT1 and PpaCOPT2 in yeast cells was observed at the tonoplast and plasma membrane, respectively. The heterologous expression of PpaCOPT2 in tobacco epidermal cells co-localized with the plasma membrane marker. Finally, only PpaCOPT1 was expressed in seven-day old protonema and was influenced by extracellular copper levels. This evidence suggests different roles of PpaCOPT1 and PpaCOPT2 in copper homeostasis in Physcomitrella patens.

Vph1 is associated with the copper homeostasis of Cryptococcus neoformans serotype D

We clarified the roles of VPH1 in Cryptococcus neoformans serotype D by examining the detailed phenotypes of VPH1-deficient cells (Δvph1) in terms of their capability to grow in acidic and alkaline pH, at a high temperature, and under high osmotic conditions, in addition to the involvement of VPH1 in copper (Cu) homeostasis and the expression of some C. neoformans virulence factors. Δvph1 could grow well on minimal medium (YNB) but exhibited hypersensitivity to 20 μM Cu due to the failure to induce Cu-detoxifying metallothionein genes (CMT1 and CMT2). In contrast, Δvph1 exhibited defective growth on rich medium (YPD), and the induction of Cu transporter genes (CTR1 and CTR4) did not occur in this medium, implying that this strain was incapable of the uptake of Cu ions for growth. However, the addition of excess Cu promoted CTR gene expression and supported Δvph1 growth. These results suggested that the lack of the VPH1 gene disturbed Cu homeostasis in C. neoformans. Moreover, the loss of Vph1 function influenced the urease activity of C. neoformans.

Molecular characterization of the COPT/Ctr-type copper transporter family under heavy metal stress in alfalfa

In nature, heavy metals significantly affect crop growth and quality. Among various heavy metals, copper (Cu) is both essential and toxic to plants depending on the concentration and complex homeostatic networks. The Cu transporter family (COPT) plays important roles in Cu homeostasis, including absorption, transportation, and growth in plants; however, this gene family is still poorly understood in alfalfa (Medicago sativa L.). In this study, a total of 12 MsCOPTs were identified and characterized. Based on the conserved motif and phylogenetic analysis, MsCOPTs could be divided into four subgroups (A1, A2, A3, and B). Gene structure, chromosomal location, and synteny analyses of MsCOPTs showed that segmental and tandem duplications likely contributed to their evolution. Tissue-specific expression analysis of MsCOPT genes indicated diverse spatiotemporal expression patterns. Most MsCOPT genes had high transcription levels in roots and nodules, indicating that these genes may play vital roles in the absorption and transport of Cu through root. The complementary heterologous expression function of yeast once again indicates that root-specific COPT can supplement the growth of defective yeast strains on YPEG medium, suggesting that these genes are Cu transporters. In summary, for the first time, our research identified COPT family genes at the whole-genome level to provide guidance for effectively improving the problem of Cu deficiency in the grass-livestock chain and provide theoretical support for the subsequent development of grass and animal husbandry.

A genome-wide copper-sensitized screen identifies novel regulators of mitochondrial cytochrome c oxidase activity

Copper is essential for the activity and stability of cytochrome c oxidase (CcO), the terminal enzyme of the mitochondrial respiratory chain. Loss-of-function mutations in genes required for copper transport to CcO result in fatal human disorders. Despite the fundamental importance of copper in mitochondrial and organismal physiology, systematic identification of genes that regulate mitochondrial copper homeostasis is lacking. To discover these genes, we performed a genome-wide screen using a library of DNA-barcoded yeast deletion mutants grown in copper-supplemented media. Our screen recovered a number of genes known to be involved in cellular copper homeostasis as well as genes previously not linked to mitochondrial copper biology. These newly identified genes include the subunits of the adaptor protein 3 complex (AP-3) and components of the cellular pH-sensing pathway Rim20 and Rim21, both of which are known to affect vacuolar function. We find that AP-3 and Rim mutants exhibit decreased vacuolar acidity, which in turn perturbs mitochondrial copper homeostasis and CcO function. CcO activity of these mutants could be rescued by either restoring vacuolar pH or supplementing growth media with additional copper. Consistent with these genetic data, pharmacological inhibition of the vacuolar proton pump leads to decreased mitochondrial copper content and a concomitant decrease in CcO abundance and activity. Taken together, our study uncovered novel genetic regulators of mitochondrial copper homeostasis and provided a mechanism by which vacuolar pH impacts mitochondrial respiration through copper homeostasis.

A novel assessment system of toxicity and stability of CuO nanoparticles via copper super sensitive Saccharomyces cerevisiae mutants

CuO nanoparticles (CuO-NPs) toxicity in organisms is contributed mainly through the copper uptake by both the ionic and nanoparticle form. However, the relative uptake ratio and bioavailability of the two different forms is not well known due to a lack of sensitive and effective assessment systems. We developed a series of both copper resistant and hyper sensitive Saccharomyces cerevisiae mutants to investigate and compare the effects of CuO-NPs and dissolved copper (CuCl₂), on the eukaryote with the purpose of quantitating the relative contributions of nanoparticles and dissolved species for Cu uptake. We observed the toxicity of 10 mM CuO-NPs for copper sensitive strains is equal to that of 0.5 mM CuCl₂ and the main toxic effect is most likely generated from oxidative stress through reactive oxygen species (ROS) production. About 95% CuO-NPs exist in nanoparticle form under neutral environmental conditions. Assessing the cellular metal content of wild type and copper transporter 1(CTR1) knock out cells showed that endocytosis is the major absorption style for CuO-NPs. This study also found a similar toxicity of Ag for both 10 mM Ag-NPs and 0.2 mM AgNO₃ in the copper super sensitive strains. Our study revealed the absorption mechanism of soluble metal based nanomaterials CuO-NPs and Ag-NPs as well as provided a sensitive and delicate system to precisely evaluate the toxicity and stability of nanoparticles.

Copper metabolism in Saccharomyces cerevisiae: an update

Copper is an essential element in all forms of life. It acts as a cofactor of some enzymes and is involved in forming proper protein conformations. However, excess copper ions in cells are detrimental as they can generate free radicals or disrupt protein structures. Therefore, all life forms have evolved conserved and exquisite copper metabolic systems to maintain copper homeostasis. The yeast Saccharomyces cerevisiae has been widely used to investigate copper metabolism as it is convenient for this purpose. In this review, we summarize the mechanism of copper metabolism in Saccharomyces cerevisiae according to the latest literature. In brief, bioavailable copper ions are incorporated into yeast cells mainly via the high-affinity transporters Ctr1 and Ctr3. Then, intracellular Cu⁺ ions are delivered to different organelles or cuproproteins by different chaperones, including Ccs1, Atx1, and Cox17. Excess copper ions bind to glutathione (GSH), metallothioneins, and copper complexes are sequestered into vacuoles to avoid toxicity. Copper-sensing transcription factors Ace1 and Mac1 regulate the expression of genes involved in copper detoxification and uptake/mobilization in response to changes in intracellular copper levels. Though numerous recent breakthroughs in understanding yeast's copper metabolism have been achieved, some issues remain unresolved. Completely elucidating the mechanism of copper metabolism in yeast helps decode the corresponding system in humans and understand how copper-related diseases develop.

Sclerotinia sclerotiorum utilizes host-derived copper for ROS detoxification and infection

Necrotrophic plant pathogen induces host reactive oxygen species (ROS) production, which leads to necrosis in the host, allowing the pathogen to absorb nutrients from the dead tissues. Sclerotinia sclerotiorum is a typical necrotrophic pathogen that causes Sclerotinia stem rot in more than 400 species, resulting in serious economic losses. Here, we found that three S. sclerotiorum genes involved in copper ion import/transport, SsCTR1, SsCCS and SsATX1, were significantly up-regulated during infection of Brassica oleracea. Function analysis revealed that these genes involved in fungal ROS detoxification and virulence. On the host side, four genes putatively involved in copper ion homeostasis, BolCCS, BolCCH, BolMT2A and BolDRT112, were significantly down-regulated in susceptible B. oleracea, but stably expressed in resistant B. oleracea during infection. Their homologs were found to promote resistance to S. sclerotiorum and increase antioxidant activity in Arabidopsis thaliana. Furthermore, copper concentration analysis indicated that copper flow from healthy area into the necrotic area during infection. A model was proposed that S. sclerotiorum utilizes host copper to detoxify ROS in its cells, whereas the resistant hosts may restrict the supply of essential copper nutrients to S. sclerotiorum by maintaining copper ion homeostasis during infection.

From economy to luxury: Copper homeostasis in Chlamydomonas and other algae

Plastocyanin and cytochrome c₆, abundant proteins in photosynthesis, are readouts for cellular copper status in Chlamydomonas and other algae. Their accumulation is controlled by a transcription factor copper response regulator (CRR1). The replacement of copper-containing plastocyanin with heme-containing cytochrome c₆ spares copper and permits preferential copper (re)-allocation to cytochrome oxidase. Under copper-replete situations, the quota depends on abundance of various cuproproteins and is tightly regulated, except under zinc-deficiency where acidocalcisomes over-accumulate Cu(I). CRR1 has a transcriptional activation domain, a Zn-dependent DNA binding SBP-domain with a nuclear localization signal, and a C-terminal Cys-rich region that represses the zinc regulon. CRR1 activates >60 genes in Chlamydomonas through GTAC-containing CuREs; transcriptome differences are recapitulated in the proteome. The differentially-expressed genes encode assimilatory copper transporters of the CTR/SLC31 family including a novel soluble molecule, redox enzymes in the tetrapyrrole pathway that promote chlorophyll biosynthesis and photosystem 1 accumulation, and other oxygen-dependent enzymes, which may influence thylakoid membrane lipids, specifically polyunsaturated galactolipids and γ-tocopherol. CRR1 also down-regulates 2 proteins in Chlamydomonas: for plastocyanin, by activation of proteolysis, while for the di‑iron subunit of the cyclase in chlorophyll biosynthesis, through activation of an upstream promoter that generates a poorly-translated 5' extended transcript containing multiple short ORFs that inhibit translation. The functions of many CRR1-target genes are unknown, and the copper protein inventory in Chlamydomonas includes several whose functions are unexplored. The comprehensive picture of cuproproteins and copper homeostasis in this system is well-suited for reverse genetic analyses of these under-investigated components in copper biology.

Molecular machinery providing copper bioavailability for spermatozoa along the epididymial tubule in mouse

Progressive functional maturation of spermatozoa is completed during the transit of these cells through the epididymis, a tubule structure connecting a testicle to a vas deferens. Epididymal epithelial cells by means of their secretory and absorptive functions determine a highly specialized luminal microenvironment containing multiple organic and inorganic components. The latter include copper ions, which due to their redox properties are indispensable for critical homeostatic processes occurring in spermatozoa floating in different part of epididymis but can be potentially toxic. Main purpose of our study was to determine epididymal region-dependent expression and localization of copper transporters ensuring a tight control of copper concentration in epididymal fluid. We also aimed at identifying proteins responsible for copper uptake by spermatozoa and verifying whether this process is coordinated with copper supply to superoxide dismutase 1 (SOD1), a copper-dependent antioxidant enzyme. Our study identifies two ATPases-ATP7A, ATP7B and Slc31a1, major copper importers/exporters depending on their differential expression on epididymal polarized epithelial cells of the caput, corpus, and cauda. Next, ceruloplasmin seems to be a chief protein transporting copper in the epididymal fluid and providing this biometal to spermatozoa. The entry of copper to germ cells is mediated by Slc31a1 and is correlated with both expressions of copper chaperone for superoxide dismutase (CCS), copper chaperone directly providing copper ions to SOD1 and with the expression and activity of the latter. Our results outline a network of cooperating copper binding proteins expressed in epididymal epithelium and in spermatozoa that orchestrate bioavailability of this microelement for gametes and protect them against copper toxicity.

Isolated Saccharomyces cerevisiae vacuoles contain low-molecular-mass transition-metal polyphosphate complexes

Vacuoles play major roles in the trafficking, storage, and homeostasis of metal ions in fungi and plants. In this study, 29 batches of vacuoles were isolated from Saccharomyces cerevisiae. Flow-through solutions (FTS) obtained by passing vacuolar extracts through a 10 kDa cut-off membrane were characterized for metal content using an anaerobic liquid chromatography system interfaced to an online ICP-MS. Nearly all iron, zinc, and manganese ions in these solutions were present as low-molecular-mass (LMM) complexes. Metal-detected peaks with masses between 500-1700 Da dominated; phosphorus-detected peaks generally comigrated. The distribution of metal:polyphosphate complexes was dominated by particular chain-lengths rather than a broad binomial distribution. Similarly treated synthetic FeIII polyphosphate complexes showed similar peaks. Treatment with a phosphatase disrupted the LMM metal-bound species in vacuolar FTSs. These results indicated metal:polyphosphate complexes 6-20 phosphate units in length and coordinated by 1-3 metals on average per chain. The speciation of iron in FTSs from iron-deficient cells was qualitatively similar, but intensities were lower. Under healthy conditions, nearly all copper ions in vacuolar FTSs were present as 1-2 species with masses between 4800-7800 Da. The absence of these high-mass peaks in vacuolar FTS from cup1Δ cells suggests that they were due to metallothionein, Cup1. Disrupting copper homeostasis increased the amount of LMM copper:polyphosphate complexes in vacuoles (masses between 1500-1700 Da). Potentially dangerous LMM copper species in the cytosol of metallothionein-deficient cells may traffic into vacuoles for sequestration and detoxification.

The Yeast Atlas of Appalachia: Species and Phenotypic Diversity of Herbicide Resistance in Wild Yeast

Glyphosate and copper-based herbicides/fungicides affect non-target organisms, and these incidental exposures can impact microbial populations. In this study, glyphosate resistance was found in the historical collection of S. cerevisiae, which was collected over the last century, but only in yeast isolated after the introduction of glyphosate. Although herbicide application was not recorded, the highest glyphosate-resistant S. cerevisiae were isolated from agricultural sites. In an effort to assess glyphosate resistance and impact on non-target microorganisms, different yeast species were harvested from 15 areas with known herbicidal histories, including an organic farm, conventional farm, remediated coal mine, suburban locations, state park, and a national forest. Yeast representing 23 genera were isolated from 237 samples of plant, soil, spontaneous fermentation, nut, flower, fruit, feces, and tree material samples. Saccharomyces, Candida, Metschnikowia, Kluyveromyces, Hanseniaspora, and Pichia were other genera commonly found across our sampled environments. Managed areas had less species diversity, and at the brewery only Saccharomyces and Pichia were isolated. A conventional farm growing RoundUp Ready™ corn had the lowest phylogenetic diversity and the highest glyphosate resistance. The mine was sprayed with multiple herbicides including a commercial formulation of glyphosate; however, the S. cerevisiae did not have elevated glyphosate resistance. In contrast to the conventional farm, the mine was exposed to glyphosate only one year prior to sample isolation. Glyphosate resistance is an example of the anthropogenic selection of nontarget organisms.

Systematic analysis of concentrations of 52 elements in tumor and counterpart normal tissues of patients with non-small cell lung cancer

BACKGROUND

Many studies have documented the abnormal concentrations of major/trace elements in serum or malignant tissues of patients, but very few works systematically tested the concentrations of elements in tumor tissues in comparison with paired adjacent normal tissues from the same patients.

METHODS

Tumor and adjacent normal lung tissues were obtained from 93 patients with previously untreated NSCLC, and 43 patients whose tumor and paired normal lung tissues reached 200 mg or more were selected for measurement of the elements' concentrations using an inductively coupled plasma-atomic emission spectrometer.

RESULTS

We found that the concentrations of the 52 elements varied from 0.4 ng/g tissue (Lu, Pd, and Tm) to 1 658 000 ng/g (Na), 1 951 000 ng/g (P), and 2 495 000 ng/g (K). Thirty eight of the 52 (73.1%) elements showed approximately equal concentrations in tumor and adjacent normal lung tissues of the patients. The concentrations of nine elements (K, P, Mg, Zn, Rb, Cu, Se, Cs, and Tl) in tumor samples were significantly higher than their paired normal lung tissues, and five elements (Na, Fe, Cr, Cd, and Ge) exhibited decreased concentrations in cancer samples compared to counterpart normal lung tissues. Low Fe in tumor samples was associated with smoking history, whereas low Cr was associated with histology (squamous cell carcinoma) of the patients.

CONCLUSIONS

Our results demonstrate that measurement of elements' concentrations in both cancer and paired normal tissues is important to get insights into the roles of these elements in carcinogenesis, and therapeutic approaches to normalize the elements are warranted to treat NSCLCs.

Copper blocks V-ATPase activity and SNARE complex formation to inhibit yeast vacuole fusion

The accumulation of copper in organisms can lead to altered functions of various pathways and become cytotoxic through the generation of reactive oxygen species. In yeast, cytotoxic metals such as Hg⁺ , Cd²⁺ and Cu²⁺ are transported into the lumen of the vacuole through various pumps. Copper ions are initially transported into the cell by the copper transporter Ctr1 at the plasma membrane and sequestered by chaperones and other factors to prevent cellular damage by free cations. Excess copper ions can subsequently be transported into the vacuole lumen by an unknown mechanism. Transport across membranes requires the reduction of Cu²⁺ to Cu⁺ . Labile copper ions can interact with membranes to alter fluidity, lateral phase separation and fusion. Here we found that CuCl₂ potently inhibited vacuole fusion by blocking SNARE pairing. This was accompanied by the inhibition of V-ATPase H⁺ pumping. Deletion of the vacuolar reductase Fre6 had no effect on the inhibition of fusion by copper. This suggests that Cu²⁺ is responsible for the inhibition of vacuole fusion and V-ATPase function. This notion is supported by the differential effects of chelators. The Cu²⁺ -specific chelator triethylenetetramine rescued fusion, whereas the Cu⁺ -specific chelator bathocuproine disulfonate had no effect on the inhibited fusion.

The Rhizophagus irregularis Genome Encodes Two CTR Copper Transporters That Mediate Cu Import Into the Cytosol and a CTR-Like Protein Likely Involved in Copper Tolerance

Arbuscular mycorrhizal fungi increase fitness of their host plants under Cu deficient and toxic conditions. In this study, we have characterized two Cu transporters of the CTR family (RiCTR1 and RiCTR2) and a CTR-like protein (RiCTR3A) of Rhizophagus irregularis. Functional analyses in yeast revealed that RiCTR1 encodes a plasma membrane Cu transporter, RiCTR2 a vacuolar Cu transporter and RiCTR3A a plasma membrane protein involved in Cu tolerance. RiCTR1 was more highly expressed in the extraradical mycelia (ERM) and RiCTR2 in the intraradical mycelia (IRM). In the ERM, RiCTR1 expression was up-regulated by Cu deficiency and down-regulated by Cu toxicity. RiCTR2 expression increased only in the ERM grown under severe Cu-deficient conditions. These data suggest that RiCTR1 is involved in Cu uptake by the ERM and RiCTR2 in mobilization of vacuolar Cu stores. Cu deficiency decreased mycorrhizal colonization and arbuscule frequency, but increased RiCTR1 and RiCTR2 expression in the IRM, which suggest that the IRM has a high Cu demand. The two alternatively spliced products of RiCTR3, RiCTR3A and RiCTR3B, were more highly expressed in the ERM. Up-regulation of RiCTR3A by Cu toxicity and the yeast complementation assays suggest that RiCTR3A might function as a Cu receptor involved in Cu tolerance.

New insights into copper homeostasis in filamentous fungi

Copper is a metal ion that is required as a micronutrient for growth and proliferation. However, copper accumulation generates toxicity by multiple mechanisms, potentially leading to cell death. Due to its toxic nature at high concentrations, different chemical variants of copper have been extensively used as antifungal agents in agriculture and medicine. Most studies on copper homeostasis have been carried out in bacteria, yeast, and mammalian organisms. However, knowledge on filamentous fungi is less well documented. This review summarizes the knowledge gathered in the last few years about copper homeostasis in the filamentous fungi Aspergillus fumigatus and Aspergillus nidulans: The mechanism of action of copper, the uptake and detoxification systems, their regulation at the transcriptional level, and the role of copper homeostasis in fungal pathogenicity are presented.

Harnessing Metal Homeostasis Offers Novel and Promising Targets Against Candida albicans

Fungal infections, particularly of Candida species, which are the commensal organisms of human, are one of the major debilitating diseases in immunocompromised patients. The limited number of antifungal drugs available to treat Candida infections, with the concomitant increasing incidence of multidrug-resistant (MDR) strains, further worsens the therapeutic options. Thus, there is an urgent need for the better understanding of MDR mechanisms, and their reversal, by employing new strategies to increase the efficacy and safety profiles of currently used therapies against the most prevalent human fungal pathogen, Candida albicans. Micronutrient availability during C. albicans infection is regarded as a critical factor that influences the progression and magnitude of the disease. Intracellular pathogens colonize a variety of anatomical locations that are likely to be scarce in micronutrients, as a defense strategy adopted by the host, known as nutritional immunity. Indispensable critical micronutrients are required both by the host and by C. albicans, especially as a cofactor in important metabolic functions. Since these micronutrients are not freely available, C. albicans need to exploit host reservoirs to adapt within the host for survival. The ability of pathogenic organisms, including C. albicans, to sense and adapt to limited micronutrients in the hostile environment is essential for survival and confers the basis of its success as a pathogen. This review describes that micronutrients availability to C. albicans is a key attribute that may be exploited when one considers designing strategies aimed at disrupting MDR in this pathogenic fungi. Here, we discuss recent advances that have been made in our understanding of fungal micronutrient acquisition and explore the probable pathways that may be utilized as targets.

Molecular Characteristics of the Conserved Aspergillus nidulans Transcription Factor Mac1 and Its Functions in Response to Copper Starvation

Copper is an essential cofactor of enzymes during a variety of biochemical processes. Therefore, Cu acquisition plays critical roles in cell survival and proliferation, especially during Cu starvation. Knowledge of the key motif(s) by which the low-Cu-responsive transcription factor Mac1 senses Cu is important for understanding how Cu uptake is controlled. Findings in this study demonstrated that the Cu fist motif, but not Cys-rich motifs, is essential for Mac1-mediated Cu uptake in Aspergillus. In addition, Cu transporters CtrA2 and CtrC are both required for Mac1-mediated Cu uptake during Cu starvation in A. nidulans, indicating that species-specific machinery exists for Cu acquisition in Aspergillus.

Copper (Cu) is an essential trace element in all organisms, and Cu acquisition during periods of starvation is important for cell survival and proliferation. Although the Cu starvation-responsive transcription factor Mac1 as well as its targeted Cu transporters have been identified in Aspergillus fumigatus, the molecular mechanisms of Mac1-mediated Cu acquisition have not yet been investigated in Aspergillus. We demonstrated that Mac1 and its regulated Cu transporters are required for growth and conidiophore development during Cu starvation in Aspergillus nidulans. Moreover, A. nidulans Mac1 (AnMac1) showed highly functional conservation with the A. fumigatus homolog but not with homologs in Saccharomyces cerevisiae and Schizosaccharomyces pombe. Molecular characterization of Mac1 in A. nidulans demonstrated that the “Cu fist” motif (i.e., residues 1 through 40) harboring Cys, RGHR, and GRP residues is required for the Mac1-mediated low-Cu response but not the Cys-rich motifs REP-I and REP-II. Notably, overexpression of either the CtrA2 Cu transporter or the CtrC Cu transporter individually was unable to functionally rescue the defects in the AnMac1 deletion strain, implying that Cu uptake might require both CtrA2 and CtrC during Cu starvation, which is different from results seen with A. fumigatus. Findings in this study further suggest that the conserved Mac1-mediated Cu uptake machinery in A. fumigatus and A. nidulans is also species specific.

IMPORTANCE Copper is an essential cofactor of enzymes during a variety of biochemical processes. Therefore, Cu acquisition plays critical roles in cell survival and proliferation, especially during Cu starvation. Knowledge of the key motif(s) by which the low-Cu-responsive transcription factor Mac1 senses Cu is important for understanding how Cu uptake is controlled. Findings in this study demonstrated that the Cu fist motif, but not Cys-rich motifs, is essential for Mac1-mediated Cu uptake in Aspergillus. In addition, Cu transporters CtrA2 and CtrC are both required for Mac1-mediated Cu uptake during Cu starvation in A. nidulans, indicating that species-specific machinery exists for Cu acquisition in Aspergillus.

The Role of Copper Homeostasis at the Host-Pathogen Axis: From Bacteria to Fungi

Copper is an essential trace element participating in many vital biological processes, however it becomes a toxic agent when in excess. Thus, precise and tight regulation of copper homeostasis processes, including transport, delivery, storage, detoxification, and efflux machineries, is important, ensuring that only the amount needed to sustain basic biological functions and simultaneously prevent copper toxicity in the cell is maintained. Numerous exciting studies have revealed that copper plays an indispensable role at the microbial pathogen-host axis for entities ranging from pathogenic bacteria to deadly fungal species. Analyses of copper homeostases in bacteria and fungi extensively demonstrate that copper is utilized by the host immune system as an anti-microbial agent. The expression of copper efflux and detoxification from microbial pathogens is induced to counteract the host's copper bombardment, which in turn disrupts these machineries, resulting in the attenuation of microbial survival in host tissue. We hereby review the latest work in copper homeostases in pathogenic bacteria and fungi and focus on the maintenance of a copper balance at the pathogen-host interaction axis.

The Yellow Stripe-Like (YSL) Gene Functions in Internal Copper Transport in Peanut

Copper (Cu) is involved in fundamental biological processes for plant growth and development. However, Cu excess is harmful to plants. Thus, Cu in plant tissues must be tightly regulated. In this study, we found that the peanut Yellow Stripe-Like family gene AhYSL3.1 is involved in Cu transport. Among five AhYSL genes, AhYSL3.1 and AhYSL3.2 were upregulated by Cu deficiency in peanut roots and expressed mainly in young leaves. A yeast complementation assay suggested that the plasma membrane-localized AhYSL3.1 was a Cu-nicotianamine complex transporter. High expression of AhYSL3.1 in tobacco and rice plants with excess Cu resulted in a low concentration of Cu in young leaves. These transgenic plants were resistant to excess Cu. The above results suggest that AhYSL3.1 is responsible for the internal transport of Cu in peanut.

Reconstitution of a thermophilic Cu+ importer in vitro reveals intrinsic high-affinity slow transport driving accumulation of an essential metal ion

Acquisition of the trace element copper (Cu) is critical to drive essential eukaryotic processes such as oxidative phosphorylation, iron mobilization, peptide hormone biogenesis, and connective tissue maturation. The Ctr1/Ctr3 family of Cu importers, first discovered in fungi and conserved in mammals, are critical for Cu+ movement across the plasma membrane or mobilization from endosomal compartments. Whereas ablation of Ctr1 in mammals is embryonic lethal, and Ctr1 is critical for dietary Cu absorption, cardiac function, and systemic iron distribution, little is known about the intrinsic contribution of Ctr1 for Cu+ permeation through membranes or its mechanism of action. Here, we identify three members of a Cu+ importer family from the thermophilic fungus Chaetomium thermophilum: Ctr3a and Ctr3b, which function on the plasma membrane, and Ctr2, which likely functions in endosomal Cu mobilization. All three proteins drive Cu and isoelectronic silver (Ag) uptake in cells devoid of Cu+ importers. Transport activity depends on signature amino acid motifs that are conserved and essential for all Ctr1/3 transporters. Ctr3a is stable and amenable to purification and was incorporated into liposomes to reconstitute an in vitro Ag+ transport assay characterized by stopped-flow spectroscopy. Ctr3a has intrinsic high-affinity metal ion transport activity that closely reflects values determined in vivo, with slow turnover kinetics. Given structural models for mammalian Ctr1, Ctr3a likely functions as a low-efficiency Cu+ ion channel. The Ctr1/Ctr3 family may be tuned to import essential yet potentially toxic Cu+ ions at a slow rate to meet cellular needs, while minimizing labile intracellular Cu+ pools.

Identification and functional characterization of the ZmCOPT copper transporter family in maize

Copper (Cu) is an essential micronutrient for plant growth and development; Cu homeostasis in plant is maintained by the important functions of Ctr/COPT-type Cu transporters. Although the COPT genes have been identified in Arabidopsis thaliana and rice, little is known about Cu transporters in maize. In this study, three-members of putative maize Cu transporters (ZmCOPT 1, 2 and 3) are identified. ZmCOPT genes have expression in all of the tested tissues, including roots, stems, leaves and flowers (male and female), and their expression levels vary responding to stress due to Cu-deficiency and excess. Functional complementation and overexpression together with Cu uptake measurements in ZmCOPTs-transformed ctr1⊿ctr2⊿mutant strain or the wild type strain of Saccharomyces cerevisiae show that the three ZmCOPT members possess the ability to be Cu transporters. Among these, ZmCOPT1 and ZmCOPT2 have high-affinity while ZmCOPT3 has low-affinity. In addition, ZmCOPT2 tend to specifically transport Cu (I) but no other bivalent metal ions.

Copper Acquisition and Utilization in Fungi

Fungal cells colonize and proliferate in distinct niches, from soil and plants to diverse tissues in human hosts. Consequently, fungi are challenged with the goal of obtaining nutrients while simultaneously elaborating robust regulatory mechanisms to cope with a range of availability of nutrients, from scarcity to excess. Copper is essential for life but also potentially toxic. In this review we describe the sophisticated homeostatic mechanisms by which fungi acquire, utilize, and control this biochemically versatile trace element. Fungal pathogens, which can occupy distinct host tissues that have their own intrinsic requirements for copper homeostasis, have evolved mechanisms to acquire copper to successfully colonize the host, disseminate to other tissues, and combat host copper bombardment mechanisms that would otherwise mitigate virulence.

Metals in fungal virulence

Metals are essential for life, and they play a central role in the struggle between infecting microbes and their hosts. In fact, an important aspect of microbial pathogenesis is the 'nutritional immunity', in which metals are actively restricted (or, in an extended definition of the term, locally enriched) by the host to hinder microbial growth and virulence. Consequently, fungi have evolved often complex regulatory networks, uptake and detoxification systems for essential metals such as iron, zinc, copper, nickel and manganese. These systems often differ fundamentally from their bacterial counterparts, but even within the fungal pathogens we can find common and unique solutions to maintain metal homeostasis. Thus, we here compare the common and species-specific mechanisms used for different metals among different fungal species-focusing on important human pathogens such as Candida albicans, Aspergillus fumigatus or Cryptococcus neoformans, but also looking at model fungi such as Saccharomyces cerevisiae or A. nidulans as well-studied examples for the underlying principles. These direct comparisons of our current knowledge reveal that we have a good understanding how model fungal pathogens take up iron or zinc, but that much is still to learn about other metals and specific adaptations of individual species-not the least to exploit this knowledge for new antifungal strategies.

Magnesium uptake by connecting fluid-phase endocytosis to an intracellular inorganic cation filter

Cells acquire free metals through plasma membrane transporters. But, in natural settings, sequestering agents often render metals inaccessible to transporters, limiting metal bioavailability. Here we identify a pathway for metal acquisition, allowing cells to cope with this situation. Under limited bioavailability of Mg²⁺, yeast cells upregulate fluid-phase endocytosis and transfer solutes from the environment into their vacuole, an acidocalcisome-like compartment loaded with highly concentrated polyphosphate. We propose that this anionic inorganic polymer, which is an avid chelator of Mg²⁺, serves as an immobilized cation filter that accumulates Mg²⁺ inside these organelles. It thus allows the vacuolar exporter Mnr2 to efficiently transfer Mg²⁺ into the cytosol. Leishmania parasites also employ acidocalcisomal polyphosphate to multiply in their Mg²⁺-limited habitat, the phagolysosomes of inflammatory macrophages. This suggests that the pathway for metal uptake via endocytosis, acidocalcisomal polyphosphates and export into the cytosol, which we term EAPEC, is conserved.

Metal bioavailability is frequently limited by sequestering agents which makes them inaccessible to cells. Here the authors show that cells can increase Mg²⁺ uptake via fluid phase endocytosis and accumulate this metal in their vacuole loaded with polyphosphate, and later can be exported to the cytosol.

Cu-sensing transcription factor Mac1 coordinates with the Ctr transporter family to regulate Cu acquisition and virulence in Aspergillus fumigatus

Copper (Cu) is an essential trace element and is regarded as an important virulence factor in fungal pathogens. Previous studies suggest that a putative Cu-sensing transcription factor Mac1 and the Cu transporter Ctr family play important roles during fungal development and virulence. However, how Cu importers of the Ctr family are involved in the Cu acquisition and what is the functional relationship between them have not been fully investigated yet. Here, we demonstrate that the yeast Mac1 homolog in the opportunistic human pathogen Aspergillus fumigatus is required during colony development under low Cu conditions. Transcriptional profiling combined with LacZ reporter analyses indicate that Cu transporters ctrA2 and ctrC are expressed in an Afmac1-dependent manner upon Cu starvation, and over-expression of ctrA2 or ctrC transporters almost completely rescue the Afmac1-deletion defects, suggesting a redundancy of both transporters in Afmac1-mediated Cu uptake. Genetic analysis showed that ctrC may play a dominant role against Cu starvation relative to ctrA2 and elevated expression of ctrA2 can compensate for ctrC deletion under Cu starvation. Interestingly, both ctrA2 and ctrC deletions can suppress ctrB deletion colony defects. Our findings suggest that Ctr family proteins might coordinately regulate their functions to adapt to different Cu environments. Compared to yeast homologs, Cu family proteins in A. fumigatus may have their own working styles. Most importantly, the Afmac1 deletion strain shows a significantly attenuated pathogenicity in the neutropenic immunocompromised (a combination of cyclophosphamide and hydrocortisone) mice model, demonstrating that Afmac1 is required for pathogenesis in vivo.

Cell-surface copper transporters and superoxide dismutase 1 are essential for outgrowth during fungal spore germination

During fungal spore germination, a resting spore returns to a conventional mode of cell division and resumes vegetative growth, but the requirements for spore germination are incompletely understood. Here, we show that copper is essential for spore germination in Schizosaccharomyces pombe Germinating spores develop a single germ tube that emerges from the outer spore wall in a process called outgrowth. Under low-copper conditions, the copper transporters Ctr4 and Ctr5 are maximally expressed at the onset of outgrowth. In the case of Ctr6, its expression is broader, taking place before and during outgrowth. Spores lacking Ctr4, Ctr5, and the copper sensor Cuf1 exhibit complete germination arrest at outgrowth. In contrast, ctr6 deletion only partially interferes with formation of outgrowing spores. At outgrowth, Ctr4-GFP and Ctr5-Cherry first co-localize at the spore contour, followed by re-location to a middle peripheral spore region. Subsequently, they move away from the spore body to occupy the periphery of the nascent cell. After breaking of spore dormancy, Ctr6 localizes to the vacuole membranes that are enriched in the spore body relative to the germ tube. Using a copper-binding tracker, results showed that labile copper is preferentially localized to the spore body. Further analysis showed that Ctr4 and Ctr6 are required for copper-dependent activation of the superoxide dismutase 1 (SOD1) during spore germination. This activation is critical because the loss of SOD1 activity blocked spore germination at outgrowth. Taken together, these results indicate that cell-surface copper transporters and SOD1 are required for completion of the spore germination program.

Gene duplication and neo-functionalization in the evolutionary and functional divergence of the metazoan copper transporters Ctr1 and Ctr2

Copper is an essential element for proper organismal development and is involved in a range of processes, including oxidative phosphorylation, neuropeptide biogenesis, and connective tissue maturation. The copper transporter (Ctr) family of integral membrane proteins is ubiquitously found in eukaryotes and mediates the high-affinity transport of Cu+ across both the plasma membrane and endomembranes. Although mammalian Ctr1 functions as a Cu+ transporter for Cu acquisition and is essential for embryonic development, a homologous protein, Ctr2, has been proposed to function as a low-affinity Cu transporter, a lysosomal Cu exporter, or a regulator of Ctr1 activity, but its functional and evolutionary relationship to Ctr1 is unclear. Here we report a biochemical, genetic, and phylogenetic comparison of metazoan Ctr1 and Ctr2, suggesting that Ctr2 arose over 550 million years ago as a result of a gene duplication event followed by loss of Cu+ transport activity. Using a random mutagenesis and growth selection approach, we identified amino acid substitutions in human and mouse Ctr2 proteins that support copper-dependent growth in yeast and enhance copper accumulation in Ctr1-/- mouse embryonic fibroblasts. These mutations revert Ctr2 to a more ancestral Ctr1-like state while maintaining endogenous functions, such as stimulating Ctr1 cleavage. We suggest key structural aspects of metazoan Ctr1 and Ctr2 that discriminate between their biological roles, providing mechanistic insights into the evolutionary, biochemical, and functional relationships between these two related proteins.

Heme Assimilation in Schizosaccharomyces pombe Requires Cell-surface-anchored Protein Shu1 and Vacuolar Transporter Abc3

The Schizosaccharomyces pombe shu1⁺ gene encodes a cell-surface protein required for assimilation of exogenous heme. In this study, shaving experiments showed that Shu1 is released from membrane preparations when spheroplast lysates are incubated with phosphoinositide-specific phospholipase C (PI-PLC). Shu1 cleavability by PI-PLC and its predicted hydropathy profile strongly suggested that Shu1 is a glycosylphosphatidylinositol-anchored protein. When heme biosynthesis is selectively blocked in hem1Δ mutant cells, the heme analog zinc mesoporphyrin IX (ZnMP) first accumulates into vacuoles and then subsequently, within the cytoplasm in a rapid and Shu1-dependent manner. An HA₄-tagged shu1⁺ allele that retained wild-type function localizes to the cell surface in response to low hemin concentrations, but under high hemin concentrations, Shu1-HA₄ re-localizes to the vacuolar membrane. Inactivation of abc3⁺, encoding a vacuolar membrane transporter, results in hem1Δ abc3Δ mutant cells being unable to grow in the presence of hemin as the sole iron source. In hem1Δ abc3Δ cells, ZnMP accumulates primarily in vacuoles and does not sequentially accumulate in the cytosol. Consistent with a role for Abc3 as vacuolar hemin exporter, results with hemin-agarose pulldown assays showed that Abc3 binds to hemin. In contrast, an Abc3 mutant in which an inverted Cys-Pro motif had been replaced with Ala residues fails to bind hemin with high affinity. Taken together, these results show that Shu1 undergoes rapid hemin-induced internalization from the cell surface to the vacuolar membrane and that the transporter Abc3 participates in the mobilization of stored heme from the vacuole to the cytosol.

How Mammalian Cells Acquire Copper: An Essential but Potentially Toxic Metal

Cu is an essential micronutrient, and its role in an array of critical physiological processes is receiving increasing attention. Among these are wound healing, angiogenesis, protection against reactive oxygen species, neurotransmitter synthesis, modulation of normal cell and tumor growth, and many others. Free Cu is absent inside cells, and a network of proteins has evolved to deliver this essential, but potentially toxic, metal ion to its intracellular target sites following uptake. Although the total body content is low (∼100 mg), dysfunction of proteins involved in Cu homeostasis results in several well-characterized human disease states. The initial step in cellular Cu handling is its transport across the plasma membrane, a subject of study for only about the last 25 years. This review focuses on the initial step in Cu homeostasis, the properties of the major protein, hCTR1, that mediates Cu uptake, and the status of our understanding of this highly specialized transport system. Although a high-resolution structure of the protein is still lacking, an array of biochemical and biophysical studies have provided a picture of how hCTR1 mediates Cu(I) transport and how Cu is delivered to the proteins in the intracellular milieu. Recent studies provide evidence that the transporter also plays a key protective role in the regulation of cellular Cu via regulatory endocytosis, lowering its surface expression, in response to elevated Cu loads.

Effects of waterborne Cu exposure on intestinal copper transport and lipid metabolism of Synechogobius hasta

The present study was conducted to explore the effects of waterborne Cu exposure on intestinal Cu transport and lipid metabolism of Synechogobius hasta. S. hasta were exposed to 0, 0.4721 and 0.9442μM Cu, respectively. Sampling occurred on days 0, 21 and 42, respectively. Growth performance, intestinal lipid deposition, Cu content, and activities and mRNA expression of enzymes and genes involved in Cu transport and lipid metabolism were analyzed. Cu exposure decreased WG and SGR on days 21 and 42. Cu exposure increased intestinal Cu and lipid contents. Increased Cu accumulation was attributable to increased enzymatic activities (Cu-ATPase and Cu, Zn-SOD) and genes' (CTR1, CTR2, DMT1, ATP7a, ATP7b, MT1 and MT2) expression involved in Cu transport. Waterborne Cu exposure also increased activities of lipogenic enzymes (6PGD and ICDH on both days 21 and 42, ME on day 42), up-regulated mRNA levels of lipogenic genes (G6PD, 6PGD, ME, ICDH, FAS and ACCa), lipolytic genes (ACCb, CPT I and HSLa) and genes involved in intestinal fatty acid uptake (IFABP and FATP4) on both days 21 and 42. The up-regulation of lipolysis may result from the increased metabolic expenditure for detoxification and maintenance of the normal body functions in a response to Cu exposure. Meantime, Cu exposure increased lipogenesis and fatty acid uptake, leading to net lipid accumulation in the intestine despite increased lipolysis. To our knowledge, this is the first report involved in intestinal lipid metabolism in combination with intestinal Cu absorption following waterborne Cu exposure, which provides new insights and evidence into Cu toxicity in fish.

Roles of vacuolar H+-ATPase in the oxidative stress response of Candida glabrata

Vacuolar H(+)-ATPase (V-ATPase) is responsible for the acidification of eukaryotic intracellular compartments and plays an important role in oxidative stress response (OSR), but its molecular bases are largely unknown. Here, we investigated how V-ATPase is involved in the OSR by using a strain lacking VPH2, which encodes an assembly factor of V-ATPase, in the pathogenic fungus Candida glabrata The loss of Vph2 resulted in increased H2O2 sensitivity and intracellular reactive oxygen species (ROS) level independently of mitochondrial functions. The Δvph2 mutant also displayed growth defects under alkaline conditions accompanied by the accumulation of intracellular ROS and these phenotypes were recovered in the presence of the ROS scavenger N-acetyl-l-cysteine. Both expression and activity levels of mitochondrial manganese superoxide dismutase (Sod2) and catalase (Cta1) were decreased in the Δvph2 mutant. Phenotypic analyses of strains lacking and overexpressing these genes revealed that Sod2 and Cta1 play a predominant role in endogenous and exogenous OSR, respectively. Furthermore, supplementation of copper and iron restored the expression of SOD2 specifically in the Δvph2 mutant, suggesting that the homeostasis of intracellular cupper and iron levels maintained by V-ATPase was important for the Sod2-mediated OSR. This report demonstrates novel roles of V-ATPase in the OSR in C. glabrata.