Activation of Cu,Zn-superoxide dismutase in the absence of oxygen and the copper chaperone CCS

Copper ions: The invisible killer of cardiovascular disease (Review)

Copper, a vital trace element, is indispensable for the maintenance of physiological functioning, particularly in the cardiac system. Unlike other forms of cell death such as iron death and apoptosis, copper‑induced cell death has gained increasing recognition as a significant process influencing the development of cardiovascular diseases. The present review highlights the significance of maintaining copper homeostasis in addressing cardiovascular diseases. This review delves into the crucial roles of copper in physiology, including the metabolic pathways and its absorption, transport and excretion. It provides detailed insights into the mechanisms underlying cardiovascular diseases resulting from both excess and deficient copper levels. Additionally, it summarizes strategies for treating copper imbalances through approaches such as copper chelators and ion carriers while discussing their limitations and future prospects.

Role of TRDMT1/DNMT2 in stress adaptation and its influence on transcriptome and proteome dynamics under osmotic stress in Physcomitrium patens

Early land plants such as the moss Physcomitrium patens lack several morphological traits that offer protection to tracheophytes from environmental stresses. These plants instead have evolved several physiological and biochemical mechanisms that facilitate them to adapt to terrestrial stresses such as drought. We have previously shown that loss-of-function mutants of tRNA (cytosine(38)-C(5))-methyltransferase TRDMT1/DNMT2 in P. patens are highly sensitive to oxidative and osmotic stress. To gain insight into the role of PpTRDMT1/PpDNMT2 in modulating genetic networks under osmotic stress, genome-wide transcriptome and proteome studies were undertaken in wild-type and ppdnmt2 plants. Transcriptome analysis revealed 375 genes to be differentially expressed in the ppdnmt2 under stress compared to the WT. Most of these genes are affiliated with carbohydrate metabolic pathways, photosynthesis, cell wall biogenesis, pathways related to isotropic and polarised cell growth and transcription factors among others. Histochemical staining showed elevated levels of reactive oxygen species in ppdnmt2 while transmission electron microscopy revealed no distinct defects in the ultrastructure of chloroplasts. Immunoprecipitation using PpDNMT2-specific antibody coupled with mass spectrometry revealed core proteins of the glycolytic pathway, antioxidant enzymes, proteins of amino acid biosynthetic pathways and photosynthesis-related proteins among others to co-purify with PpTRDMT1/PpDNMT2 under osmotic stress. Yeast two-hybrid assays, protein deletion and α-galactosidase assays showed the cytosol glycolytic protein glyceraldehyde 3-phosphate dehydrogenase to bind to the catalytic motifs in PpTRDMT1/PpDNMT2. Results presented in this study allow us to better understand genetic networks linking enzymes of energy metabolism, epigenetic processes and RNA pol II-mediated transcription during osmotic stress tolerance in P. patens.

Exploring cuproptosis as a mechanism and potential intervention target in cardiovascular diseases

Copper (Cu) is a vital trace element for maintaining human health. Current evidence suggests that genes responsible for regulating copper influx and detoxification help preserve its homeostasis. Adequate Cu levels sustain normal cardiac and blood vessel activity by maintaining mitochondrial function. Cuproptosis, unlike other forms of cell death, is characterized by alterations in mitochondrial enzymes. Therapeutics targeting cuproptosis in cardiovascular diseases (CVDs) mainly include copper chelators, inhibitors of copper chaperone proteins, and copper ionophores. In this review, we expound on the primary mechanisms, critical proteins, and signaling pathways involved in cuproptosis, along with its impact on CVDs and the role it plays in different types of cells. Additionally, we explored the influence of key regulatory proteins and signaling pathways associated with cuproptosis on CVDs and determined whether intervening in copper metabolism and cuproptosis can enhance the outcomes of CVDs. The insights from this review provide a fresh perspective on the pathogenesis of CVDs and new targets for intervention in these diseases.

H3K27 acetylation activated-CCS regulates autophagy and apoptosis of lung cancer by alleviating oxidative stress

Copper chaperone for superoxide dismutase (CCS) is abnormally expressed in various human malignancies. However, the function and mechanism of CCS in lung cancer progression remain unclear. In the current study, CCS protein and mRNA levels were found to be increased in lung adenocarcinoma (LUAD) tissue and cell lines. Patients with higher CCS levels had a poorer prognosis. Decreasing the enrichment of histone H3 Lys27 acetylation (H3K27ac) by A-485 inhibited CCS expression. CCS depletion upregulated reactive oxygen species (ROS) levels, aggravated oxidative stress, inhibited autophagy, inhibited cell survival, and promoted apoptosis. The treatment of antioxidant N-Acetyl-L-cysteine (NAC) rescued these changes induced by CCS depletion. CCS also was found to be related to the immune infiltration of CD8 + T cells and regulatory T cells in LUAD. These data indicated that overexpression of CCS activated by H3K27 acetylation relieved oxidative stress, promoted autophagy, and inhibited apoptosis. CCS may be regarded as a potential therapeutic target for LUAD.

DJ-1 and SOD1 Act Independently in the Protection against Anoxia in Drosophila melanogaster

Redox homeostasis is a vital process the maintenance of which is assured by the presence of numerous antioxidant small molecules and enzymes and the alteration of which is involved in many pathologies, including several neurodegenerative disorders. Among the different enzymes involved in the antioxidant response, SOD1 and DJ-1 have both been associated with the pathogenesis of amyotrophic lateral sclerosis and Parkinson’s disease, suggesting a possible interplay in their mechanism of action. Copper deficiency in the SOD1-active site has been proposed as a central determinant in SOD1-related neurodegeneration. SOD1 maturation mainly relies on the presence of the protein copper chaperone for SOD1 (CCS), but a CCS-independent alternative pathway also exists and functions under anaerobic conditions. To explore the possible involvement of DJ-1 in such a pathway in vivo, we exposed Drosophila melanogaster to anoxia and evaluated the effect of DJ-1 on fly survival and SOD1 levels, in the presence or absence of CCS. Loss of DJ-1 negatively affects the fly response to the anoxic treatment, but our data indicate that the protective activity of DJ-1 is independent of SOD1 in Drosophila, indicating that the two proteins may act in different pathways.

The Superoxide Dismutase Gene Family in Nicotiana tabacum: Genome-Wide Identification, Characterization, Expression Profiling and Functional Analysis in Response to Heavy Metal Stress

Superoxide dismutases (SODs) play an important role in protecting plants against ROS toxicity induced by biotic and abiotic stress. Recent studies have shown that the SOD gene family is involved in plant growth and development; however, knowledge of the SOD gene family in tobacco is still limited. In the present study, the SOD gene family was systematically characterized in the tobacco genome. Based on the conserved motif and phylogenetic tree, 15 NtSOD genes were identified and classified into three subgroups, including 5 NtCSDs, 7 NtFSDs and 3 NtMSDs. The predicted results of the transport peptide or signal peptide were consistent with their subcellular localization. Most NtSOD genes showed relatively well-maintained exon-intron and motif structures in the same subgroup. An analysis of cis-acting elements in SOD gene promoters showed that NtSOD expression was regulated by plant hormones, defense and stress responses, and light. In addition, multiple transcription factors and miRNAs are predicted to be involved in the regulation of NtSOD gene expression. The qPCR results indicated specific spatial and temporal expression patterns of the NtSOD gene family in different tissues and developmental stages, and this gene family played an important role in protecting against heavy metal stress. The results of functional complementation tests in the yeast mutant suggested that NtCSD1a, NtFSD1e and NtMSD1b scavenge ROS produced by heavy metal stress. This study represents the first genome-wide analysis of the NtSOD gene family, which lays a foundation for a better understanding of the function of the NtSOD gene family and improving the tolerance of plants to heavy metal toxicity.

Sod1 integrates oxygen availability to redox regulate NADPH production and the thiol redoxome

Cu/Zn superoxide dismutase (Sod1) is a key antioxidant enzyme, and its importance is underscored by the fact that its ablation in cell and animal models results in oxidative stress; metabolic defects; and reductions in cell proliferation, viability, and lifespan. Curiously, Sod1 detoxifies superoxide radicals (O₂^•−) in a manner that produces an oxidant as byproduct, hydrogen peroxide (H₂O₂). While much is known about the necessity of scavenging O₂^•−, it is less clear what the physiological roles of Sod1-derived H₂O₂ are. We discovered that Sod1-derived H₂O₂ plays an important role in antioxidant defense by stimulating the production of NADPH, a vital cellular reductant required for reactive oxygen species scavenging enzymes, as well as redox regulating a large network of enzymes.

Cu/Zn superoxide dismutase (Sod1) is a highly conserved and abundant antioxidant enzyme that detoxifies superoxide (O₂^•−) by catalyzing its conversion to dioxygen (O₂) and hydrogen peroxide (H₂O₂). Using Saccharomyces cerevisiae and mammalian cells, we discovered that a major aspect of the antioxidant function of Sod1 is to integrate O₂ availability to promote NADPH production. The mechanism involves Sod1-derived H₂O₂ oxidatively inactivating the glycolytic enzyme, GAPDH, which in turn reroutes carbohydrate flux to the oxidative phase of the pentose phosphate pathway (oxPPP) to generate NADPH. The aerobic oxidation of GAPDH is dependent on and rate-limited by Sod1. Thus, Sod1 senses O₂ via O₂^•− to balance glycolytic and oxPPP flux, through control of GAPDH activity, for adaptation to life in air. Importantly, this mechanism for Sod1 antioxidant activity requires the bulk of cellular Sod1, unlike for its role in protection against O₂^•− toxicity, which only requires <1% of total Sod1. Using mass spectrometry, we identified proteome-wide targets of Sod1-dependent redox signaling, including numerous metabolic enzymes. Altogether, Sod1-derived H₂O₂ is important for antioxidant defense and a master regulator of metabolism and the thiol redoxome.

A dual role of cysteine residues in the maturation of prokaryotic Cu/Zn-superoxide dismutase

Bacterial Cu/Zn-superoxide dismutase (SodC) is an enzyme catalyzing the disproportionation of superoxide radicals, to which the binding of copper and zinc ions and the formation of an intramolecular disulfide bond are essential. We previously showed that Escherichia coli SodC (SodC) was prone to spontaneous degradation in vivo in an immature form prior to the introduction of the disulfide bond. The post-translational maintenance involving the metal binding and the disulfide formation would thus control the stability as well as the enzymatic function of SodC; however, a mechanism of the SodC maturation remains obscure. Here, we show that the disulfide-reduced SodC can secure a copper ion as well as a zinc ion through the thiolate groups. Furthermore, the disulfide-reduced SodC was found to bind cuprous and cupric ions more tightly than SodC with the disulfide bond. The thiolate groups ligating the copper ion were then autooxidized to form the intramolecular disulfide bond, leading to the production of enzymatically active SodC. Based upon the experiments in vitro, therefore, we propose a mechanism for the activation of SodC, in which the conserved Cys residues play a dual role: the acquisition of a copper ion for the enzymatic activity and the formation of the disulfide bond for the structural stabilization.

The Copper Chaperone CcsA, Coupled with Superoxide Dismutase SodA, Mediates the Oxidative Stress Response in Aspergillus fumigatus

Superoxide dismutases (SODs) are important metalloenzymes that protect fungal pathogens against the toxic effects of reactive oxygen species (ROS) generated by host defense mechanisms during the infection process. The activation of Cu/Zn-SOD1 is found to be dependent on copper chaperone for SOD1 (Ccs1). However, the role of the Ccs1 ortholog in the human pathogen Aspergillus fumigatus and how these SODs coordinate to mediate oxidative stress response remain elusive. Here, we demonstrated that A. fumigatus CcsA, a Saccharomyces cerevisiae Ccs1 ortholog, is required for cells in response to oxidative response and the activation of Sod1. Deletion of ccsA resulted in increased ROS accumulation and enhanced sensitivity to oxidative stress due to the loss of SodA activity. Molecular characterization of CcsA revealed that the conserved CXC motif is required not only for the physical interaction with SodA but also for the oxidative stress adaption. Notably, addition of Mn²⁺ or overexpression of cytoplasmic Mn-SodC could rescue the defects of the ccsA or sodA deletion mutant, indicating the important role of Mn²⁺ and Mn-SodC in ROS detoxification; however, deletion of the CcsA-SodA complex could not affect A. fumigatus virulence. Collectively, our findings demonstrate that CcsA functions as a Cu/Zn-Sod1 chaperone that participates in the adaptation to oxidative stress in A. fumigatus and provide a better understanding of the CcsA-SodA complex-mediated oxidative stress response in filamentous fungi. IMPORTANCE Reactive oxygen species (ROS) produced by phagocytes have been reported to participate in the killing of fungal pathogens. Superoxide dismutases (SODs) are considered to be the first line of defense against superoxide anions. Characterizing the regulatory mechanisms of SOD activation is important for understanding how fungi adapt to oxidative stress in hosts. Our findings demonstrated that CcsA functions as a SodA chaperone in A. fumigatus and that the conserved CXC motif within CcsA is required for its interaction with SodA and the CcsA-SodA-mediated oxidative response. These data may provide new insights into how fungal pathogens adapt to oxidative stress via the CcsA-SodA complex.

Superoxide Dismutase 1 in Health and Disease: How a Frontline Antioxidant Becomes Neurotoxic

Cu/Zn superoxide dismutase (SOD1) is a frontline antioxidant enzyme catalysing superoxide breakdown and is important for most forms of eukaryotic life. The evolution of aerobic respiration by mitochondria increased cellular production of superoxide, resulting in an increased reliance upon SOD1. Consistent with the importance of SOD1 for cellular health, many human diseases of the central nervous system involve perturbations in SOD1 biology. But far from providing a simple demonstration of how disease arises from SOD1 loss-of-function, attempts to elucidate pathways by which atypical SOD1 biology leads to neurodegeneration have revealed unexpectedly complex molecular characteristics delineating healthy, functional SOD1 protein from that which likely contributes to central nervous system disease. This review summarises current understanding of SOD1 biology from SOD1 genetics through to protein function and stability.

Superoxide dismutase 1 (SOD1) and cadmium: A three models approach to the comprehension of its neurotoxic effects

Cadmium (Cd) is a widespread toxic environmental contaminant, released by anthropogenic activities. It interferes with essential metal ions homeostasis and affects protein structures and functions by substituting zinc, copper and iron. In this study, the effect of cadmium on SOD1, a CuZn metalloenzyme catalyzing superoxide conversion into hydrogen peroxide, has been investigated in three different biological models. We first evaluated the effects of cadmium combined with copper and/or zinc on the recombinant GST-SOD1, expressed in E. coli BL21. The enzyme activity and expression were investigated in the presence of fixed copper and/or zinc doses with different cadmium concentrations, in the cellular medium. Cadmium caused a dose-dependent reduction in SOD1 activity, while the expression remains constant. Similar results were obtained in the cellular model represented by the human SH-SY5Y neuronal cell line. After cadmium treatment for 24 and 48 h, SOD1 enzymatic activity decreased in a dose- and time-dependent way, while the protein expression remained constant. Finally, a 16 h cadmium treatment caused a 25 % reduction of CuZn-SOD activity without affecting the protein expression in the Caenorhabditis elegans model. Taken together our results show an inhibitory effect of cadmium on SOD1 enzymatic activity, without affecting the protein expression, in all the biological models used, suggesting that cadmium can displace zinc from the enzyme catalytic site.

Antioxidative effect of DJ-1 is enhanced in NG108-15 cells by DPMQ-induced copper influx

Disruption of copper homeostasis is closely involved in neurodegenerative disorders. This study examined whether a hybrid copper-binding compound, (E)-2-(4-(dimethylamino)phenylimino)methyl)quinolin-8-ol (DPMQ), is able to protect NG108-15 cells against oxidative stress. We found that treatment of cells with rotenone or hydrogen peroxide increased cellular oxidative stress and resulted in mitochondrial dysfunction and apoptosis. The cellular levels of Nrf2 and the Cu²⁺ chaperone DJ-1 were also decreased. These oxidative detrimental effects were all inhibited when cells were cotreated with DPMQ. DPMQ increased cellular Cu²⁺ content, DJ-1 protein level, superoxide dismutase (SOD) activity, and Nrf2 nuclear translocation under basal state. The activity of SOD decreased under redox imbalance and this decrease was blocked by DPMQ treatment, while the protein level of SOD1 remained unaltered regardless of the oxidative stress and DPMQ treatment. Using endogenous proteins, coimmunoprecipitation showed that DJ-1 bound with SOD1 and Nrf2 individually. The amount of Nrf2, bound to DJ-1, consistently reflected its cellular level, while the amount of SOD1, bound to DJ-1, was potentiated by DPMQ, being greater in the basal state than under redox imbalance. Simultaneous inclusion of nonpermeable Cu²⁺ chelator tetrathiomolybdate or triethylenetetramine during DPMQ treatment blocked all aforementioned effects of DPMQ, showing that the dependency of the effect of DPMQ on extracellular Cu²⁺. In addition, silencing of DJ-1 blocked the protection of DPMQ against oxidative stress. Taken all together, our results suggest that DPMQ stabilizes DJ-1 in a Cu²⁺-dependent manner, which then brings about SOD1 activation and Nrf2 nuclear translocation; these together alleviate cellular oxidative stress.

The histone H3-H4 tetramer is a copper reductase enzyme

Eukaryotic histone H3-H4 tetramers contain a putative copper (Cu2+) binding site at the H3-H3' dimerization interface with unknown function. The coincident emergence of eukaryotes with global oxygenation, which challenged cellular copper utilization, raised the possibility that histones may function in cellular copper homeostasis. We report that the recombinant Xenopus laevis H3-H4 tetramer is an oxidoreductase enzyme that binds Cu2+ and catalyzes its reduction to Cu1+ in vitro. Loss- and gain-of-function mutations of the putative active site residues correspondingly altered copper binding and the enzymatic activity, as well as intracellular Cu1+ abundance and copper-dependent mitochondrial respiration and Sod1 function in the yeast Saccharomyces cerevisiae The histone H3-H4 tetramer, therefore, has a role other than chromatin compaction or epigenetic regulation and generates biousable Cu1+ ions in eukaryotes.

Copper Sources for Sod1 Activation

Copper ions (i.e., copper) are a critical part of several cellular processes, but tight regulation of copper levels and trafficking are required to keep the cell protected from this highly reactive transition metal. Cu, Zn superoxide dismutase (Sod1) protects the cell from the accumulation of radical oxygen species by way of the redox cycling activity of copper in its catalytic center. Multiple posttranslational modification events, including copper incorporation, are reliant on the copper chaperone for Sod1 (Ccs). The high-affinity copper uptake protein (Ctr1) is the main entry point of copper into eukaryotic cells and can directly supply copper to Ccs along with other known intracellular chaperones and trafficking molecules. This review explores the routes of copper delivery that are utilized to activate Sod1 and the usefulness and necessity of each.

Nucleation and kinetics of SOD1 aggregation in human cells for ALS1

Aberrant structural formations of Cu/Zn superoxide dismutase enzyme (SOD1) are the probable mechanism by which circumscribed mutations in the SOD1 gene cause familial amyotrophic lateral sclerosis (ALS1). SOD1 forms aberrant structures which can proceed by nucleation to insoluble aggregates. Here, the SOD1 aggregation reaction was investigated predominantly by time-course studies on ALS1 variants G85R, G37R, D101G, and D101N in human embryonic kidney cells (HEK293FT), with analysis by detergent ultracentrifugation extractions and high-resolution PAGE methodologies. Nucleation was found to be pseudo-zeroth order and dependent on time and concentration at constant 37.0 °C and pH 7.4. The predominant subsets of the total SOD1 expression set which comprised the nucleation phase were both soluble and insoluble inactive monomers, trimers, and hexamers with reduced intra-disulfide bonds. Superoxide exposure via paraquat initiated the formation of SOD1 trimers in untransfected SH-SY5Y cells and increased the aggregation propensity of G85R in HEK293FT. These data show the kinetic formation of aberrant SOD1 subsets implicated in ALS1 and indicate that superoxide substrate may initiate its radical polymerization. In an instance of the utility of methodological reductionism in molecular theory: though many ALS1 variants retain their global enzymatic activity, the SOD1 subsets most implicated in causing ALS1 do not retain their specific activity.

Copper Chaperone for Superoxide Dismutase Promotes Breast Cancer Cell Proliferation and Migration via ROS-Mediated MAPK/ERK Signaling

Copper chaperone for superoxide dismutase (CCS) is a critical component of oxidation–reduction system and functions as a potential tumor promoter in several cancers. However, the function and clinical significance of CCS in breast cancer remain unclear. Here, we found CCS was highly expressed in breast cancer, where it promoted breast cancer cell proliferation and migration. Suppression of CCS expression was sufficient to attenuate the phosphorylation level of ERK1/2 and increase the accumulation of reactive oxygen species (ROS). Mechanistically, we found that knockdown of CCS decreases the activity of ERK1/2 mediated by the accumulation of ROS, which leads to the inhibition of cell proliferation and migration. In summary, these results indicated that CCS promotes the growth and migration of breast cancer cells via regulating the ERK1/2 activity mediated by ROS.

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.

Copper-zinc superoxide dismutase is activated through a sulfenic acid intermediate at a copper ion entry site

Metallochaperones are a diverse family of trafficking molecules that provide metal ions to protein targets for use as cofactors. The copper chaperone for superoxide dismutase (Ccs1) activates immature copper-zinc superoxide dismutase (Sod1) by delivering copper and facilitating the oxidation of the Sod1 intramolecular disulfide bond. Here, we present structural, spectroscopic, and cell-based data supporting a novel copper-induced mechanism for Sod1 activation. Ccs1 binding exposes an electropositive cavity and proposed "entry site" for copper ion delivery on immature Sod1. Copper-mediated sulfenylation leads to a sulfenic acid intermediate that eventually resolves to form the Sod1 disulfide bond with concomitant release of copper into the Sod1 active site. Sod1 is the predominant disulfide bond-requiring enzyme in the cytoplasm, and this copper-induced mechanism of disulfide bond formation obviates the need for a thiol/disulfide oxidoreductase in that compartment.

Oxygen-dependent activation of Cu,Zn-superoxide dismutase-1

Copper zinc superoxide dismutase (Sod1) is a critical enzyme in limiting reactive oxygen species in both the cytosol and the mitochondrial intermembrane space.

The Disulfide Bond, but Not Zinc or Dimerization, Controls Initiation and Seeded Growth in Amyotrophic Lateral Sclerosis-linked Cu,Zn Superoxide Dismutase (SOD1) Fibrillation

Aggregation of copper-zinc superoxide dismutase (SOD1) is a defining feature of familial ALS caused by inherited mutations in the sod1 gene, and misfolded and aggregated forms of wild-type SOD1 are found in both sporadic and familial ALS cases. Mature SOD1 owes its exceptional stability to a number of post-translational modifications as follows: formation of the intramolecular disulfide bond, binding of copper and zinc, and dimerization. Loss of stability due to the failure to acquire one or more of these modifications is proposed to lead to aggregation in vivo. Previously, we showed that the presence of apo-, disulfide-reduced SOD1, the most immature form of SOD1, results in initiation of fibrillation of more mature forms that have an intact Cys-57-Cys-146 disulfide bond and are partially metallated. In this study, we examine the ability of each of the above post-translational modifications to modulate fibril initiation and seeded growth. Cobalt or zinc binding, despite conferring great structural stability, neither inhibits the initiation propensity of disulfide-reduced SOD1 nor consistently protects disulfide-oxidized SOD1 from being recruited into growing fibrils across wild-type and a number of ALS mutants. In contrast, reduction of the disulfide bond, known to be necessary for fibril initiation, also allows for faster recruitment during seeded amyloid growth. These results identify separate factors that differently influence seeded growth and initiation and indicate a lack of correlation between the overall thermodynamic stability of partially mature SOD1 states and their ability to initiate fibrillation or be recruited by a growing fibril.

ErbB2 overexpression upregulates antioxidant enzymes, reduces basal levels of reactive oxygen species, and protects against doxorubicin cardiotoxicity

Levels of the HER2/ErbB2 protein in the heart are upregulated in some women during breast cancer therapy, and these women are at high risk for developing heart dysfunction after sequential treatment with anti-ErbB2/trastuzumab or doxorubicin. Doxorubicin is known to increase oxidative stress in the heart, and thus we considered the possibility that ErbB2 protein influences the status of cardiac antioxidant defenses in cardiomyocytes. In this study, we measured reactive oxygen species (ROS) in cardiac mitochondria and whole hearts from mice with cardiac-specific overexpression of ErbB2 (ErbB2(tg)) and found that, compared with control mice, high levels of ErbB2 in myocardium result in lower levels of ROS in mitochondria (P = 0.0075) and whole hearts (P = 0.0381). Neonatal cardiomyocytes isolated from ErbB2(tg) hearts have lower ROS levels and less cellular death (P < 0.0001) following doxorubicin treatment. Analyzing antioxidant enzyme levels and activities, we found that ErbB2(tg) hearts have increased levels of glutathione peroxidase 1 (GPx1) protein (P < 0.0001) and GPx activity (P = 0.0031) in addition to increased levels of two known GPx activators, c-Abl (P = 0.0284) and Arg (P < 0.0001). Interestingly, although mitochondrial ROS emission is reduced in the ErbB2(tg) hearts, oxygen consumption rates and complex I activity are similar to control littermates. Compared with these in vivo studies, H9c2 cells transfected with ErbB2 showed less cellular toxicity and produced less ROS (P < 0.0001) after doxorubicin treatment but upregulated GR activity (P = 0.0237) instead of GPx. Our study shows that ErbB2-dependent signaling contributes to antioxidant defenses and suggests a novel mechanism by which anticancer therapies involving ErbB2 antagonists can harm myocardial structure and function.

Oxygen regulates molecular mechanisms of cancer progression and metastasis

Oxygen is the basic molecule which supports life and it truly is "god's gift to life." Despite its immense importance, research on "oxygen biology" has never received the light of the day and has been limited to physiological and biochemical studies. It seems that in modern day biology, oxygen research is summarized in one word "hypoxia." Scientists have focused on hypoxia-induced transcriptomics and molecular-cellular alterations exclusively in disease models. Interestingly, the potential of oxygen to control the basic principles of biology like homeostatic maintenance, transcription, replication, and protein folding among many others, at the molecular level, has been completely ignored. Here, we present a perspective on the crucial role played by oxygen in regulation of basic biological phenomena. Our conclusion highlights the importance of establishing novel research areas like oxygen biology, as there is great potential in this field for basic science discoveries and clinical benefits to the society.

Cysteine residues in Cu,Zn-superoxide dismutase are essential to toxicity in Caenorhabditis elegans model of amyotrophic lateral sclerosis

Dominant mutations in Cu,Zn-superoxide dismutase (SOD1) cause a familial form of amyotrophic lateral sclerosis (ALS). A pathological hallmark of the familial ALS is the formation of mutant SOD1 aggregates, leading to the proposal that SOD1 gains toxicities through protein misfolding triggered by mutations. Nevertheless, molecular requirements for mutant SOD1 to acquire pathogenicity still remain obscure. Here, we show that Cys residues in SOD1 are essential to exerting toxicities of SOD1 in a Caenorhabditis elegans model. Exogenous expression of wild-type as well as pathogenic mutant SOD1 fused with a fluorescent protein in C. elegans resulted in the accumulation of disulfide-reduced SOD1 and retarded the worm's motility. In contrast, little effects of exogenously expressed SOD1 on the motility were observed when all four Cys residues in SOD1 were replaced with Ser. Taken together, we propose that deregulation of Cys chemistry in SOD1 proteins is involved in the pathogenesis of SOD1-related ALS.

The megavirus chilensis Cu,Zn-superoxide dismutase: the first viral structure of a typical cellular copper chaperone-independent hyperstable dimeric enzyme

Giant viruses able to replicate in Acanthamoeba castellanii penetrate their host through phagocytosis. After capsid opening, a fusion between the internal membranes of the virion and the phagocytic vacuole triggers the transfer in the cytoplasm of the viral DNA together with the DNA repair enzymes and the transcription machinery present in the particles. In addition, the proteome analysis of purified mimivirus virions revealed the presence of many enzymes meant to resist oxidative stress and conserved in the Mimiviridae. Megavirus chilensis encodes a predicted copper, zinc superoxide dismutase (Cu,Zn-SOD), an enzyme known to detoxify reactive oxygen species released in the course of host defense reactions. While it was thought that the metal ions are required for the formation of the active-site lid and dimer stabilization, megavirus chilensis SOD forms a very stable metal-free dimer. We used electron paramagnetic resonance (EPR) analysis and activity measurements to show that the supplementation of the bacterial culture with copper and zinc during the recombinant expression of Mg277 is sufficient to restore a fully active holoenzyme. These results demonstrate that the viral enzyme's activation is independent of a chaperone both for disulfide bridge formation and for copper incorporation and suggest that its assembly may not be as regulated as that of its cellular counterparts. A SOD protein is encoded by a variety of DNA viruses but is absent from mimivirus. As in poxviruses, the enzyme might be dispensable when the virus infects Acanthamoeba cells but may allow megavirus chilensis to infect a broad range of eukaryotic hosts.

IMPORTANCE

Mimiviridae are giant viruses encoding more than 1,000 proteins. The virion particles are loaded with proteins used by the virus to resist the vacuole's oxidative stress. The megavirus chilensis virion contains a predicted copper, zinc superoxide dismutase (Cu,Zn-SOD). The corresponding gene is present in some megavirus chilensis relatives but is absent from mimivirus. This first crystallographic structure of a viral Cu,Zn-SOD highlights the features that it has in common with and its differences from cellular SODs. It corresponds to a very stable dimer of the apo form of the enzyme. We demonstrate that upon supplementation of the growth medium with Cu and Zn, the recombinant protein is fully active, suggesting that the virus's SOD activation is independent of a copper chaperone for SOD generally used by eukaryotic SODs.

YCF1-mediated cadmium resistance in yeast is dependent on copper metabolism and antioxidant enzymes

AIMS

Acquisition and detoxification of metal ions are vital biological processes. Given the requirement of metallochaperones in cellular copper distribution and metallation of cuproproteins, this study investigates whether the metallochaperones also deliver metal ions for transporters functioning in metal detoxification.

RESULTS

Resistance to excess cadmium and copper of the yeast Saccharomyces cerevisiae, which is conferred by PCA1 and CaCRP1 metal efflux P-type ATPases, respectively, does not rely on known metallochaperones, Atx1p, Ccs1p, and Cox17p. Copper deficiency induced by the expression of CaCRP1 encoding a copper exporter occurs in the absence of Atx1p. Intriguingly, CCS1 encoding the copper chaperone for superoxide dismutase 1 (Sod1p) is necessary for cadmium resistance that is mediated by Ycf1p, a vacuolar cadmium sequestration transporter. This is attributed to Ccs1p's role in the maturation of Sod1p rather than its direct interaction with Ycf1p for cadmium transfer. Functional defect in Ycf1p associated with the absence of Sod1p as well as another antioxidant enzyme Glr1p is rescued by anaerobic growth or substitutions of specific cysteine residues of Ycf1p to alanine or serine. This further supports oxidative inactivation of Ycf1p in the absence of Ccs1p, Sod1p, or Glr1p.

INNOVATION

These results provide new insights into the mechanisms of metal metabolism, interaction among metal ions, and the roles for antioxidant systems in metal detoxification.

CONCLUSION

Copper metabolism and antioxidant enzymes maintain the function of Ycf1p for cadmium defense.

A primary role for disulfide formation in the productive folding of prokaryotic Cu,Zn-superoxide dismutase

Enzymatic activation of Cu,Zn-superoxide dismutase (SOD1) requires not only binding of a catalytic copper ion but also formation of an intramolecular disulfide bond. Indeed, the disulfide bond is completely conserved among all species possessing SOD1; however, it remains obscure how disulfide formation controls the enzymatic activity of SOD1. Here, we show that disulfide formation is a primary event in the folding process of prokaryotic SOD1 (SodC) localized to the periplasmic space. Escherichia coli SodC was found to attain β-sheet structure upon formation of the disulfide bond, whereas disulfide-reduced SodC assumed little secondary structure even in the presence of copper and zinc ions. Moreover, reduction of the disulfide bond made SodC highly susceptible to proteolytic degradation. We thus propose that the thiol-disulfide status in SodC controls the intracellular stability of this antioxidant enzyme and that the oxidizing environment of the periplasm is required for the enzymatic activation of SodC.

Mechanisms of mutant SOD1 induced mitochondrial toxicity in amyotrophic lateral sclerosis

In amyotrophic lateral sclerosis (ALS), mitochondrial dysfunction is recognized as one of the key elements contributing to the pathology. Mitochondria are the major source of intracellular reactive oxygen species (ROS). Increased production of ROS as well as oxidative damage of proteins and lipids have been demonstrated in many models of ALS. Moreover, these changes were also observed in tissues of ALS patients indicative of important role for oxidative stress in the disease pathology. However, the origin of oxidative stress in ALS has remained unclear. ALS linked mutant Cu/Zn-superoxide dismutase 1 (SOD1) has been shown to significantly associate with mitochondria, especially in the spinal cord. In animal models, increased recruitment of mutant SOD1 (mutSOD1) to mitochondria appears already before the disease onset, suggestive of causative role for the manifestation of pathology. Recently, substantial in vitro and in vivo evidence has accumulated demonstrating that localization of mutSOD1 to the mitochondrial intermembrane space (IMS) inevitably leads to impairment of mitochondrial functions. However, the exact mechanisms of the selectivity and toxicity have remained obscure. Here we discuss the current knowledge on the role of mutSOD1 in mitochondrial dysfunction in ALS from the novel perspective emphasizing the misregulation of dismutase activity in IMS as a major mechanism for the toxicity.

Candida albicans SOD5 represents the prototype of an unprecedented class of Cu-only superoxide dismutases required for pathogen defense

The human fungal pathogens Candida albicans and Histoplasma capsulatum have been reported to protect against the oxidative burst of host innate immune cells using a family of extracellular proteins with similarity to Cu/Zn superoxide dismutase 1 (SOD1). We report here that these molecules are widespread throughout fungi and deviate from canonical SOD1 at the primary, tertiary, and quaternary levels. The structure of C. albicans SOD5 reveals that although the β-barrel of Cu/Zn SODs is largely preserved, SOD5 is a monomeric copper protein that lacks a zinc-binding site and is missing the electrostatic loop element proposed to promote catalysis through superoxide guidance. Without an electrostatic loop, the copper site of SOD5 is not recessed and is readily accessible to bulk solvent. Despite these structural deviations, SOD5 has the capacity to disproportionate superoxide with kinetics that approach diffusion limits, similar to those of canonical SOD1. In cultures of C. albicans, SOD5 is secreted in a disulfide-oxidized form and apo-pools of secreted SOD5 can readily capture extracellular copper for rapid induction of enzyme activity. We suggest that the unusual attributes of SOD5-like fungal proteins, including the absence of zinc and an open active site that readily captures extracellular copper, make these SODs well suited to meet challenges in zinc and copper availability at the host-pathogen interface.

Human copper chaperone for superoxide dismutase 1 mediates its own oxidation-dependent import into mitochondria

Oxidative stress is counteracted by various cellular systems, including copper-zinc superoxide dismutase 1 (SOD1) and its activating chaperone, that is, the copper chaperone for SOD1 (CCS1). Both enzymes are structurally related, and both localize to the cytosol and the mitochondrial intermembrane space where they specifically counteract mitochondria-derived superoxide. The mechanism by which human CCS1 is transported into mitochondria is largely unclear. Here we show that CCS1 import depends on the presence of mature CCS1 in the mitochondria. During import, a disulphide bond is formed in CCS1 in a CCS1-dependent reaction. We demonstrate that oxidation and import depend on the presence of cysteine residues at positions 227 and 141/144 in CCS1. Notably, CCS1 import parallels SOD1 import that also depends on CCS1. Our observations suggest that CCS1 serves as a specialized import receptor in mitochondria that facilitates the import and folding of SOD1 and CCS1, thereby extending the substrate spectrum of oxidation-dependent protein import in the mitochondrial intermembrane space.

Absence of superoxide dismutase activity causes nuclear DNA fragmentation during the aging process

Superoxide dismutases (SOD) serve as an important antioxidant defense mechanism in aerobic organisms, and deletion of these genes shortens the replicative life span in the budding yeast Saccharomyces cerevisiae. Even though involvement of superoxide dismutase enzymes in ROS scavenging and the aging process has been studied extensively in different organisms, analyses of DNA damages has not been performed for replicatively old superoxide dismutase deficient cells. In this study, we investigated the roles of SOD1, SOD2 and CCS1 genes in preserving genomic integrity in replicatively old yeast cells using the single cell comet assay. We observed that extend of DNA damage was not significantly different among the young cells of wild type, sod1Δ and sod2Δ strains. However, ccs1Δ mutants showed a 60% higher amount of DNA damage in the young stage compared to that of the wild type cells. The aging process increased the DNA damage rates 3-fold in the wild type and more than 5-fold in sod1Δ, sod2Δ, and ccs1Δ mutant cells. Furthermore, ROS levels of these strains showed a similar pattern to their DNA damage contents. Thus, our results confirm that cells accumulate DNA damages during the aging process and reveal that superoxide dismutase enzymes play a substantial role in preserving the genomic integrity in this process.

Cellular distribution of copper to superoxide dismutase involves scaffolding by membranes

Efficient delivery of copper ions to specific intracellular targets requires copper chaperones that acquire metal cargo through unknown mechanisms. Here we demonstrate that the human and yeast copper chaperones (CCS) for superoxide dismutase 1 (SOD1), long thought to exclusively reside in the cytosol and mitochondrial intermembrane space, can engage negatively charged bilayers through a positively charged lipid-binding interface. The significance of this membrane-binding interface is established through SOD1 activity and genetic complementation studies in Saccharomyces cerevisiae, showing that recruitment of CCS to the membrane is required for activation of SOD1. Moreover, we show that a CCS:SOD1 complex binds to bilayers in vitro and that CCS can interact with human high affinity copper transporter 1. Shifting current paradigms, we propose that CCS-dependent copper acquisition and distribution largely occur at membrane interfaces and that this emerging role of the bilayer may reflect a general mechanistic aspect of cellular transition metal ion acquisition.

Redox environment is an intracellular factor to operate distinct pathways for aggregation of Cu,Zn-superoxide dismutase in amyotrophic lateral sclerosis

Dominant mutations in Cu,Zn-superoxide dismutase (SOD1) cause a familial form of amyotrophic lateral sclerosis (fALS). Misfolding and aggregation of mutant SOD1 proteins are a pathological hallmark of SOD1-related fALS cases; however, the molecular mechanism of SOD1 aggregation remains controversial. Here, I have used E. coli as a model organism and shown multiple distinct pathways of SOD1 aggregation that are dependent upon its thiol-disulfide status. Overexpression of fALS-mutant SOD1s in the cytoplasm of E. coli BL21 and SHuffle^TM, where redox environment is reducing and oxidizing, respectively, resulted in the formation of insoluble aggregates with notable differences; a disulfide bond of SOD1 was completely reduced in BL21 or abnormally formed between SOD1 molecules in SHuffle^TM. Depending upon intracellular redox environment, therefore, mutant SOD1 is considered to misfold/aggregate through distinct pathways, which would be relevant in description of the pathological heterogeneity of SOD1-related fALS cases.

Structure of Cu(I)-bound DJ-1 reveals a biscysteinate metal binding site at the homodimer interface: insights into mutational inactivation of DJ-1 in Parkinsonism

The Parkinsonism-associated protein DJ-1 has been suggested to activate the Cu-Zn superoxide dismutase (SOD1) by providing its copper cofactor. The structural and chemical means by which DJ-1 could support this function is unknown. In this study, we characterize the molecular interaction of DJ-1 with Cu(I). Mass spectrometric analysis indicates binding of one Cu(I) ion per DJ-1 homodimer. The crystal structure of DJ-1 bound to Cu(I) confirms metal coordination through a docking accessible biscysteinate site formed by juxtaposed cysteine residues at the homodimer interface. Spectroscopy in crystallo validates the identity and oxidation state of the bound metal. The measured subfemtomolar dissociation constant (Kd = 6.41 × 10(-16) M) of DJ-1 for Cu(I) supports the physiological retention of the metal ion. Our results highlight the requirement of a stable homodimer for copper binding by DJ-1. Parkinsonism-linked mutations that weaken homodimer interactions will compromise this capability.

Yeast copper-zinc superoxide dismutase can be activated in the absence of its copper chaperone

Copper-zinc superoxide dismutase (Sod1) is an abundant intracellular enzyme that catalyzes the disproportionation of superoxide to give hydrogen peroxide and dioxygen. In most organisms, Sod1 acquires copper by a combination of two pathways, one dependent on the copper chaperone for Sod1 (CCS), and the other independent of CCS. Examples have been reported of two exceptions: Saccharomyces cerevisiae, in which Sod1 appeared to be fully dependent on CCS, and Caenorhabditis elegans, in which Sod1 was completely independent of CCS. Here, however, using overexpressed Sod1, we show there is also a significant amount of CCS-independent activation of S. cerevisiae Sod1, even in low-copper medium. In addition, we show CCS-independent oxidation of the disulfide bond in S. cerevisiae Sod1. There appears to be a continuum between CCS-dependent and CCS-independent activation of Sod1, with yeast falling near but not at the CCS-dependent end.

An expanding range of functions for the copper chaperone/antioxidant protein Atox1

SIGNIFICANCE

Antioxidant protein 1 (Atox1 in human cells) is a copper chaperone for the copper export pathway with an essential role in cellular copper distribution. In vitro, Atox1 binds and transfers copper to the copper-transporting ATPases, stimulating their catalytic activity. Inactivation of Atox1 in cells inhibits maturation of secreted cuproenzymes as well as copper export from cells.

RECENT ADVANCES

Accumulating data suggest that cellular functions of Atox1 are not limited to its copper-trafficking role and may include storage of labile copper, modulation of transcription, and antioxidant defense. The conserved metal binding site of Atox1, CxGC, differs from the metal-binding sites of copper-transporting ATPases and has a physiologically relevant redox potential that equilibrates with the GSH:GSSG pair.

CRITICAL ISSUES

Tight relationship appears to exist between intracellular copper levels and glutathione (GSH) homeostasis. The biochemical properties of Atox1 place it at the intersection of cellular networks that regulate copper distribution and cellular redox balance. Mechanisms through which Atox1 facilitates copper export and contributes to oxidative defense are not fully understood.

FUTURE DIRECTIONS

The current picture of cellular redox homeostasis and copper physiology will be enhanced by further mechanistic studies of functional interactions between the GSH:GSSG pair and copper-trafficking machinery.

Species-specific activation of Cu/Zn SOD by its CCS copper chaperone in the pathogenic yeast Candida albicans

Candida albicans is a pathogenic yeast of important public health relevance. Virulence of C. albicans requires a copper and zinc containing superoxide dismutase (SOD1), but the biology of C. albicans SOD1 is poorly understood. To this end, C. albicans SOD1 activation was examined in baker's yeast (Saccharomyces cerevisiae), a eukaryotic expression system that has proven fruitful for the study of SOD1 enzymes from invertebrates, plants, and mammals. In spite of the 80% similarity between S. cerevisiae and C. albicans SOD1 molecules, C. albicans SOD1 is not active in S. cerevisiae. The SOD1 appears incapable of productive interactions with the copper chaperone for SOD1 (CCS1) of S. cerevisiae. C. albicans SOD1 contains a proline at position 144 predicted to dictate dependence on CCS1. By mutation of this proline, C. albicans SOD1 gained activity in S. cerevisiae, and this activity was independent of CCS1. We identified a putative CCS1 gene in C. albicans and created heterozygous and homozygous gene deletions at this locus. Loss of CCS1 resulted in loss of SOD1 activity, consistent with its role as a copper chaperone. C. albicans CCS1 also restored activity to C. albicans SOD1 expressed in S. cerevisiae. C. albicans CCS1 is well adapted for activating its partner SOD1 from C. albicans, but not SOD1 from S. cerevisiae. In spite of the high degree of homology between the SOD1 and CCS1 molecules in these two fungal species, there exists a species-specific barrier in CCS-SOD interactions which may reflect the vastly different lifestyles of the pathogenic versus the noninfectious yeast.

Mechanistic aspects of hSOD1 maturation from the solution structure of Cu(I) -loaded hCCS domain 1 and analysis of disulfide-free hSOD1 mutants

Superoxide dismutase 1 (SOD1) maturation within the cell is mainly accomplished with the SOD1-specific chaperone, CCS, a dimeric protein with three distinct domains in each monomer. We recently showed that the first domain of human CCS (hCCSD1) is responsible for copper transfer to its protein partner, human SOD1 (hSOD1). The NMR solution structure of the copper(I)-loaded form of hCCSD1 reported here contributes further to characterization of the copper-transfer mechanism to hSOD1. NMR spectroscopy was also used to examine the hSOD1 mutants C57A, C146A, and C57A/C146A, which are unable to form the structurally conserved disulfide bond in SOD1, in order to investigate the role of these cysteines during hSOD1 copper acquisition. Together, the information on both hCCS and hSOD1, along with a sequence analysis of eukaryotic CCSD1, allows us to propose important mechanistic aspects regarding the copper-transfer process from hCCS to hSOD1.

SOD1 integrates signals from oxygen and glucose to repress respiration

Cu/Zn superoxide dismutase (SOD1) is an abundant enzyme that has been best studied as a regulator of antioxidant defense. Using the yeast Saccharomyces cerevisiae, we report that SOD1 transmits signals from oxygen and glucose to repress respiration. The mechanism involves SOD1-mediated stabilization of two casein kinase 1-gamma (CK1γ) homologs, Yck1p and Yck2p, required for respiratory repression. SOD1 binds a C-terminal degron we identified in Yck1p/Yck2p and promotes kinase stability by catalyzing superoxide conversion to peroxide. The effects of SOD1 on CK1γ stability are also observed with mammalian SOD1 and CK1γ and in a human cell line. Therefore, in a single circuit, oxygen, glucose, and reactive oxygen can repress respiration through SOD1/CK1γ signaling. Our data therefore may provide mechanistic insight into how rapidly proliferating cells and many cancers accomplish glucose-mediated repression of respiration in favor of aerobic glycolysis.

Redox properties of the disulfide bond of human Cu,Zn superoxide dismutase and the effects of human glutaredoxin 1

The intramolecular disulfide bond in hSOD1 [human SOD1 (Cu,Zn superoxide dismutase 1)] plays a key role in maintaining the protein's stability and quaternary structure. In mutant forms of SOD1 that cause familial ALS (amyotrophic lateral sclerosis), this disulfide bond is more susceptible to chemical reduction, which may lead to destabilization of the dimer and aggregation. During hSOD1 maturation, disulfide formation is catalysed by CCS1 (copper chaperone for SOD1). Previous studies in yeast demonstrate that the yeast GSH/Grx (glutaredoxin) redox system promotes reduction of the hSOD1 disulfide in the absence of CCS1. In the present study, we probe further the interaction between hSOD1, GSH and Grxs to provide mechanistic insight into the redox kinetics and thermodynamics of the hSOD1 disulfide. We demonstrate that hGrx1 (human Grx1) uses a monothiol mechanism to reduce the hSOD1 disulfide, and the GSH/hGrx1 system reduces ALS mutant SOD1 at a faster rate than WT (wild-type) hSOD1. However, redox potential measurements demonstrate that the thermodynamic stability of the disulfide is not consistently lower in ALS mutants compared with WT hSOD1. Furthermore, the presence of metal cofactors does not influence the disulfide redox potential. Overall, these studies suggest that differences in the GSH/hGrx1 reaction rate with WT compared with ALS mutant hSOD1 and not the inherent thermodynamic stability of the hSOD1 disulfide bond may contribute to the greater pathogenicity of ALS mutant hSOD1.

Human superoxide dismutase 1 (hSOD1) maturation through interaction with human copper chaperone for SOD1 (hCCS)

Copper chaperone for superoxide dismutase 1 (SOD1), CCS, is the physiological partner for the complex mechanism of SOD1 maturation. We report an in vitro model for human CCS-dependent SOD1 maturation based on the study of the interactions of human SOD1 (hSOD1) with full-length WT human CCS (hCCS), as well as with hCCS mutants and various truncated constructs comprising one or two of the protein's three domains. The synergy between electrospray ionization mass spectrometry (ESI-MS) and NMR is fully exploited. This is an in vitro study of this process at the molecular level. Domain 1 of hCCS is necessary to load hSOD1 with Cu(I), requiring the heterodimeric complex formation with hSOD1 fostered by the interaction with domain 2. Domain 3 is responsible for the catalytic formation of the hSOD1 Cys-57-Cys-146 disulfide bond, which involves both hCCS Cys-244 and Cys-246 via disulfide transfer.

Functional partnership of the copper export machinery and glutathione balance in human cells

Cells use the redox properties of copper in numerous physiologic processes, including antioxidant defense, neurotransmitter biosynthesis, and angiogenesis. Copper delivery to the secretory pathway is an essential step in copper utilization and homeostatic maintenance. We demonstrate that the glutathione/glutathione disulfide (GSH/GSSG) pair controls the copper transport pathway by regulating the redox state of a copper chaperone Atox1. GSSG oxidizes copper-coordinating cysteines of Atox1 with the formation of an intramolecular disulfide. GSH alone is sufficient to reduce the disulfide, restoring the ability of Atox1 to bind copper; glutaredoxin 1 facilitates this reaction when GSH is low. In cells, high GSH both reduces Atox1 and is required for cell viability in the absence of Atox1. In turn, Atox1, which has a redox potential similar to that of glutaredoxin, becomes essential for cell survival when GSH levels decrease. Atox1(+/+) cells resist short term glutathione depletion, whereas Atox1(-/-) cells under the same conditions are not viable. We conclude that GSH balance and copper homeostasis are functionally linked and jointly maintain conditions for copper secretion and cell proliferation.

Cu(I) affinities of the domain 1 and 3 sites in the human metallochaperone for Cu,Zn-superoxide dismutase

The delivery of copper by the human metallochaperone CCS is a key step in the activation of Cu,Zn-superoxide dismutase (SOD1). CCS is a three-domain protein with Cu(I)-binding CXXC and CXC motifs in domains 1 and 3, respectively. A detailed analysis of the binding of copper to CCS, including variants in which the Cys residues from domains 1 and 3 have been mutated to Ser, and also using separate domain 1 and 3 constructs, demonstrates that CCS is able to bind 1 equiv of Cu(I) in both of these domains. The Cu(I) affinity of domain 1 is approximately 5 × 10(17) M(-1) at pH 7.5, while that of domain 3 is at least 1 order of magnitude weaker. The CXXC site will therefore be preferentially loaded with Cu(I), suggesting that domain 1 plays a role in the acquisition of the metal. The delivery of copper to the target occurs via domain 3 whose structural flexibility and ability to be transiently metalated during copper delivery appear to be more important than the Cu(I) affinity of its CXC motif. The Cu(I) affinity of domain 1 of CCS is comparable to that of HAH1, another cytosolic copper metallochaperone. CCS and HAH1 readily exchange Cu(I), providing a mechanism whereby cross-talk can occur between copper trafficking pathways.

Copper chaperone-dependent and -independent activation of three copper-zinc superoxide dismutase homologs localized in different cellular compartments in Arabidopsis

Superoxide dismutases (SODs) are important antioxidant enzymes that catalyze the disproportionation of superoxide anion to oxygen and hydrogen peroxide to guard cells against superoxide toxicity. The major pathway for activation of copper/zinc SOD (CSD) involves a copper chaperone for SOD (CCS) and an additional minor CCS-independent pathway reported in mammals. We characterized the CCS-dependent and -independent activation pathways for three CSDs localized in different cellular compartments in Arabidopsis (Arabidopsis thaliana). The main activation pathway for CSD1 in the cytoplasm involved a CCS-dependent and -independent pathway, which was similar to that for human CSD. Activation of CSD2 in chloroplasts depended totally on CCS, similar to yeast (Saccharomyces cerevisiae) CSD. Peroxisome-localized CSD3 via a CCS-independent pathway was similar to nematode (Caenorhabditis elegans) CSD in retaining activity in the absence of CCS. In Arabidopsis, glutathione played a role in CCS-independent activation, as was reported in humans, but an additional factor was required. These findings reveal a highly specific and sophisticated regulation of CSD activation pathways in planta relative to other known CCS-independent activation.

Copper chaperone-dependent and -independent activation of three copper-zinc superoxide dismutase homologs localized in different cellular compartments in Arabidopsis

Superoxide dismutases (SODs) are important antioxidant enzymes that catalyze the disproportionation of superoxide anion to oxygen and hydrogen peroxide to guard cells against superoxide toxicity. The major pathway for activation of copper/zinc SOD (CSD) involves a copper chaperone for SOD (CCS) and an additional minor CCS-independent pathway reported in mammals. We characterized the CCS-dependent and -independent activation pathways for three CSDs localized in different cellular compartments in Arabidopsis (Arabidopsis thaliana). The main activation pathway for CSD1 in the cytoplasm involved a CCS-dependent and -independent pathway, which was similar to that for human CSD. Activation of CSD2 in chloroplasts depended totally on CCS, similar to yeast (Saccharomyces cerevisiae) CSD. Peroxisome-localized CSD3 via a CCS-independent pathway was similar to nematode (Caenorhabditis elegans) CSD in retaining activity in the absence of CCS. In Arabidopsis, glutathione played a role in CCS-independent activation, as was reported in humans, but an additional factor was required. These findings reveal a highly specific and sophisticated regulation of CSD activation pathways in planta relative to other known CCS-independent activation.

Post-translational modification of Cu/Zn superoxide dismutase under anaerobic conditions

In eukaryotic organisms, the largely cytosolic copper- and zinc-containing superoxide dismutase (Cu/Zn SOD) enzyme represents a key defense against reactive oxygen toxicity. Although much is known about the biology of this enzyme under aerobic conditions, less is understood regarding the effects of low oxygen levels on Cu/Zn SOD enzymes from diverse organisms. We show here that like bakers' yeast (Saccharomyces cerevisiae), adaptation of the multicellular Caenorhabditis elegans to growth at low oxygen levels involves strong downregulation of its Cu/Zn SOD. Much of this regulation occurs at the post-translational level where CCS-independent activation of Cu/Zn SOD is inhibited. Hypoxia inactivates the endogenous Cu/Zn SOD of C. elegans Cu/Zn SOD as well as a P144 mutant of S. cerevisiae Cu/Zn SOD (herein denoted Sod1p) that is independent of CCS. In our studies of S. cerevisiae Sod1p, we noted a post-translational modification to the inactive enzyme during hypoxia. Analysis of this modification by mass spectrometry revealed phosphorylation at serine 38. Serine 38 represents a putative proline-directed kinase target site located on a solvent-exposed loop that is positioned at one end of the Sod1p β-barrel, a region immediately adjacent to residues previously shown to influence CCS-dependent activation. Although phosphorylation of serine 38 is minimal when the Sod1p is abundantly active (e.g., high oxygen level), up to 50% of Sod1p can be phosphorylated when CCS activation of the enzyme is blocked, e.g., by hypoxia or low-copper conditions. Serine 38 phosphorylation can be a marker for inactive pools of Sod1p.