Heterodimeric structure of superoxide dismutase in complex with its metallochaperone

Role of the interaction between troponin T and AMP deaminase by zinc bridge in modulating muscle contraction and ammonia production

The N-terminal region of troponin T (TnT) does not bind any protein of the contractile machinery and the role of its hypervariability remains uncertain. In this review we report the evidence of the interaction between TnT and AMP deaminase (AMPD), a regulated zinc enzyme localized on the myofibril. In periods of intense muscular activity, a decrease in the ATP/ADP ratio, together with a decrease in the tissue pH, is the stimulus for the activation of the enzyme that deaminating AMP to IMP and NH3 displaces the myokinase reaction towards the formation of ATP. In skeletal muscle subjected to strong tetanic contractions, a calpain-like proteolytic activity produces the removal in vivo of a 97-residue N-terminal fragment from the enzyme that becomes desensitized towards the inhibition by ATP, leading to an unrestrained production of NH3. When a 95-residue N-terminal fragment is removed from AMPD by trypsin, simulating in vitro the calpain action, rabbit fast TnT or its phosphorylated 50-residue N-terminal peptide binds AMPD restoring the inhibition by ATP. Taking in consideration that the N-terminus of TnT expressed in human as well as rabbit white muscle contains a zinc-binding motif, we suggest that TnT might mimic the regulatory action of the inhibitory N-terminal domain of AMPD due to the presence of a zinc ion connecting the N-terminal and C-terminal regions of the enzyme, indicating that the two proteins might physiologically associate to modulate muscle contraction and ammonia production in fast-twitching muscle under strenuous conditions.

Molybdenum-Copper Antagonism In Metalloenzymes And Anti-Copper Therapy

The connection between 3d (Cu) and 4d (Mo) via the "Mo-S-Cu" unit is called Mo-Cu antagonism. Biology offers case studies of such interactions in metalloproteins such as Mo/Cu-CO Dehydrogenases (Mo/Cu-CODH), and Mo/Cu Orange Protein (Mo/Cu-ORP). The CODH significantly maintains the CO level in the atmosphere below the toxic level by converting it to non-toxic CO2 for respiring organisms. Several models were synthesized to understand the structure-function relationship of these native enzymes. However, this interaction was first observed in ruminants, and they convert molybdate (MoO4 2- ) into tetrathiomolybdate (MoS4 2- ; TTM), reacting with cellular Cu to yield biological unavailable Mo/S/Cu cluster, then developing Cu-deficiency diseases. These findings inspire the use of TTM as a Cu-sequester drug, especially for treating Cu-dependent human diseases such as Wilson diseases (WD) and cancer. It is well known that a balanced Cu homeostasis is essential for a wide range of biological processes, but negative consequence leads to cell toxicity. Therefore, this review aims to connect the Mo-Cu antagonism in metalloproteins and anti-copper therapy.

Characterization of Copper(II) and Zinc(II) Complexes of Peptides Mimicking the CuZnSOD Enzyme

Antimicrobial peptides are short cationic peptides that are present on biological surfaces susceptible to infection, and they play an important role in innate immunity. These peptides, like other compounds with antimicrobial activity, often have significant superoxide dismutase (SOD) activity. One direction of our research is the characterization of peptides modeling the CuZnSOD enzyme and the determination of their biological activity, and these results may contribute to the development of novel antimicrobial peptides. In the framework of this research, we have synthesized 10, 15, and 16-membered model peptides containing the amino acid sequence corresponding to the Cu(II) and Zn(II) binding sites of the CuZnSOD enzyme, namely the Zn(II)-binding HVGD sequence (80-83. fragments), the Cu(II)-binding sequence HVH (fragments 46-48), and the histidine (His63), which links the two metal ions as an imidazolate bridge: Ac-FHVHEGPHFN-NH2 (L1(10)), Ac-FHVHAGPHFNGGHVG-NH2 (L2(15)), and Ac-FHVHEGPHFNGGHVGD-NH2 (L3(16)). pH-potentiometric, UV-Vis-, and CD-spectroscopy studies of the Cu(II), Zn(II), and Cu(II)-Zn(II) mixed complexes of these peptides were performed, and the SOD activity of the complexes was determined. The binding sites preferred by Cu(II) and Zn(II) were identified by means of CD-spectroscopy. From the results obtained for these systems, it can be concluded that in equimolar solution, the -(NGG)HVGD- sequence of the peptides is the preferred binding site for copper(II) ion. However, in the presence of both metal ions, according to the native enzyme, the -HVGD- sequence offers the main binding site for Zn(II), while the majority of Cu(II) binds to the -FHVH- sequence. Based on the SOD activity assays, complexes of the 15- and 16-membered peptide have a significant SOD activity. Although this activity is smaller than that of the native CuZnSOD enzyme, the complexes showed better performance in the degradation of superoxide anion than other SOD mimics. Thus, the incorporation of specific amino acid sequences mimicking the CuZnSOD enzyme increases the efficiency of model systems in the catalytic decomposition of superoxide anion.

The genome-wide characterization and associated cold-tolerance function of the superoxide dismutase in the cold response of the tick Haemaphysalis longicornis

Accumulating evidence suggests that superoxide dismutase (SOD) is the first line of antioxidant defense in organisms and plays an important role in scavenging reactive oxygen species produced during environmental stress. However, limited information is available regarding the response of SOD genes to cold stress in ticks. Therefore, in the present study, SOD genes were cloned and identified from the genome of Haemaphysalis longicornis, and the function of SOD during the cold response was further explored. Seven SOD genes were characterized: HlCCS1, HlCCS2, HlMSD, HlCSD1, HlCSD2, HlCSD3, and HlCSD4. Bioinformatics analysis showed that HlCCS1 and HlCCS2 are copper chaperones of SODs. HlCSD1-HlCSD4 belong to the Cu/Zn SOD, whereas HlMSD belongs to the Mn SOD gene family. Fluorescence quantitative PCR showed that the expression of HlCCS2, HlMSD, and HlCSD1-3 was upregulated, whereas HlCCS1 and HlCSD4 were downregulated during the cold response of H. longicornis. Western blotting confirmed changes in the relative expression of HlCSD3 and HlMSD in H. longicornis after cold treatment. Mortality of H. longicornis increased significantly after dsRNA injection of HlCCS2, HlMSD, HlCSD1, and HlCSD3. The above results show that SODs have different regulatory functions during the cold response in H. longicornis, and there might be an interaction between treatment temperature and duration. Furthermore, the results lay a foundation for subsequent research on the molecular mechanism of cold tolerance in H. longicornis and shed light on the population distribution and diffusion limit of ticks.

Zinc-mediated interaction of copper chaperones through their heavy-metal associated domains

BACKGROUND

A copper chaperone CCS is a multi-domain protein that supplies a copper ion to Cu/Zn-superoxide dismutase (SOD1). Among the domains of CCS, the N-terminal domain (CCS^dI) belongs to a heavy metal-associated (HMA) domain, in which a Cys-x-x-Cys (CxxC) motif binds a heavy metal ion. It has hence been expected that the HMA domain in CCS has a role in the metal trafficking; however, the CxxC motif in the domain is dispensable for supplying a copper ion to SOD1, leaving an open question on roles of CCS^dI in CCS.

METHODS

To evaluate protein-protein interactions of CCS through CCS^dI, yeast two-hybrid assay, a pull-down assay using recombinant proteins, and the analysis with fluorescence resonance energy transfer were performed.

RESULTS

We found that CCS specifically interacted with another copper chaperone HAH1, a HMA domain protein, through CCS^dI. The interaction between CCS^dI and HAH1 was not involved in the copper supply from CCS to SOD1 but was mediated by a zinc ion ligated with Cys residues of the CxxC motifs in CCS^dI and HAH1.

CONCLUSION

While physiological significance of the interaction between copper chaperones awaits further investigation, we propose that CCS^dI would have a role in the metal-mediated interaction with other proteins including heterologous copper chaperones.

Protein metalation in a nutshell

Metalation, the acquisition of metals by proteins, must avoid mis-metalation with tighter binding metals. This is illustrated by four selected proteins that require different metals: all show similar ranked orders of affinity for bioavailable metals, as described in a universal affinity series (the Irving-Williams series). Crucially, cellular protein metalation occurs in competition with other metal binding sites. The strength of this competition defines the intracellular availability of each metal: its magnitude has been estimated by calibrating a cells' set of DNA-binding, metal-sensing, transcriptional regulators. This has established that metal availabilities (as free energies for forming metal complexes) are maintained to the inverse of the universal series. The tightest binding metals are least available. With these availabilities, correct metalation is achieved.

Protein-protein interactions in plant antioxidant defense

The regulation of reactive oxygen species (ROS) levels in plants is ensured by mechanisms preventing their over accumulation, and by diverse antioxidants, including enzymes and nonenzymatic compounds. These are affected by redox conditions, posttranslational modifications, transcriptional and posttranscriptional modifications, Ca²⁺, nitric oxide (NO) and mitogen-activated protein kinase signaling pathways. Recent knowledge about protein-protein interactions (PPIs) of antioxidant enzymes advanced during last decade. The best-known examples are interactions mediated by redox buffering proteins such as thioredoxins and glutaredoxins. This review summarizes interactions of major antioxidant enzymes with regulatory and signaling proteins and their diverse functions. Such interactions are important for stability, degradation and activation of interacting partners. Moreover, PPIs of antioxidant enzymes may connect diverse metabolic processes with ROS scavenging. Proteins like receptor for activated C kinase 1 may ensure coordination of antioxidant enzymes to ensure efficient ROS regulation. Nevertheless, PPIs in antioxidant defense are understudied, and intensive research is required to define their role in complex regulation of ROS scavenging.

Copper delivery to an endospore coat protein of Bacillus subtilis

A family of cytosolic copper (Cu) storage proteins (the Csps) bind large quantities of Cu(I) via their Cys-lined four-helix bundles, and the majority are cytosolic (Csp3s). The presence of Csp3s in many bacteria appears inconsistent with the current dogma that bacteria, unlike eukaryotes, have evolved not to maintain intracellular pools of Cu due to its potential toxicity. Sporulation in Bacillus subtilis has been used to investigate if a Csp3 binds Cu(I) in the cytosol for a target enzyme. The activity of the Cu-requiring endospore multi-Cu oxidase BsCotA (a laccase) increases under Cu-replete conditions in wild type B. subtilis. In the strain lacking BsCsp3 lower BsCotA activity is observed and is unaffected by Cu levels. BsCsp3 loaded with Cu(I) readily activates apo-BsCotA in vitro. Experiments with a high affinity Cu(I) chelator demonstrate that Cu(I) transfer from Cu(I)-BsCsp3 must occur via an associative mechanism. BsCsp3 and BsCotA are both upregulated during late sporulation. We hypothesise that BsCsp3 acquires cuprous ions in the cytosol of B. subtilis for BsCotA.

Genome-wide identification and characterization of superoxide dismutases in four oyster species reveals functional differentiation in response to biotic and abiotic stress

Background

Oysters inhabit in the intertidal zone and may be suffered from environmental stresses, which can increase the production of reactive oxygen species (ROS), resulting in mass mortality. Superoxide dismutases (SODs) protect oysters from ROS damage through different mechanisms compared with vertebrates. However, the molecular and functional differentiation in oyster SODs were rarely analyzed.

Result

In this study, a total of 13, 13, 10, and 8 candidate SODs were identified in the genome of Crassostrea gigas, Crassostrea virginica, Crassostrea hongkongensis, and Saccostrea glomerata respectively. The domain composition, gene structure, subcellular locations, conserved ligands, and cis-elements elucidated the SODs into five groups (Mn-SODs, Cu-only-SODs, Cu/Zn ion ligand Cu/Zn-SOD with enzyme activity, Zn-only-SODs, and no ligand metal ions Cu/Zn-SODs). For single domain Cu/Zn-SODs, only one cytosolic Cu/Zn-SOD (cg_XM_034479061.1) may conserve enzymatic activity while most extracellular Cu/Zn-SOD proteins appeared to lose SOD enzyme activity according to conserved ligand amino acid analysis and expression pattern under biotic and abiotic stress in C. gigas. Further, multi-domain-SODs were identified and some of them were expressed in response to biotic and abiotic stressors in C. gigas. Moreover, the expression patterns of these genes varied in response to different stressors, which may be due to the cis-elements in the gene promoter.

Conclusion

These findings revealed the most extracellular Cu/Zn-SOD proteins appeared to lose SOD enzyme activity in oysters. Further, our study revealed that only one cytosolic Cu/Zn-SOD (cg_XM_034479061.1) may conserve enzymatic activity of SOD. Moreover, the expression patterns of these genes varied in response to different stressors, which may be due to the cis-elements in the promoter. This study provides important insights into the mechanisms through which oysters adapt to harsh intertidal conditions, as well as potential biomarkers of stress response in related species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08610-9.

Radio Signals from Live Cells: The Coming of Age of In-Cell Solution NMR

A detailed knowledge of the complex processes that make cells and organisms alive is fundamental in order to understand diseases and to develop novel drugs and therapeutic treatments. To this aim, biological macromolecules should ideally be characterized at atomic resolution directly within the cellular environment. Among the existing structural techniques, solution NMR stands out as the only one able to investigate at high resolution the structure and dynamic behavior of macromolecules directly in living cells. With the advent of more sensitive NMR hardware and new biotechnological tools, modern in-cell NMR approaches have been established since the early 2000s. At the coming of age of in-cell NMR, we provide a detailed overview of its developments and applications in the 20 years that followed its inception. We review the existing approaches for cell sample preparation and isotopic labeling, the application of in-cell NMR to important biological questions, and the development of NMR bioreactor devices, which greatly increase the lifetime of the cells allowing real-time monitoring of intracellular metabolites and proteins. Finally, we share our thoughts on the future perspectives of the in-cell NMR methodology.

Characterization of a fluorescent 1,8-naphthalimide-functionalized PAMAM dendrimer and its Cu(ii) complexes as cytotoxic drugs: EPR and biological studies in myeloid tumor cells

The activity and interacting ability of a polyamidoamine (PAMAM) dendrimer modified with 4-N-methylpiperazine-1,8-naphthalimide units (termed D) and complexed by Cu(ii) ions, towards healthy and cancer cells were studied. Comparative electron paramagnetic resonance (EPR) studies of the Cu(ii)-D complex are presented: coordination mode, chemical structure, flexibility and stability of these complexes, in the absence and presence of myeloid cancer cells and peripheral blood mononuclear cells (PBMC). The interactions of Cu(ii) ions in the biological media at different equilibrium times were studied, highlighting different stability and interacting conditions with the cells. Furthermore, flow cytometry and confocal analysis, trace the peculiar properties of the dendrimers in PBMC and U937 cells. Indeed, a new probe (Fly) was used as a potential fluorescent tool for biological imaging of Cu(ii). The study highlights that dendrimer and, mainly, the Cu(ii) metallodendrimer are cytotoxic agents for the cells, specifically for U937 tumor cells, inducing mitochondrial dysfunction, ROS increase and lysosome involvement. The metallodendrimer shows antitumor selectivity, fewer affecting healthy PBMC, inducing a massive apoptotic cell death on U937 cells, in line with the high stability of this complex, as verified by EPR studies. The results underline the potentiality of this metallodendrimer to be used as anticancer drug.

The molecular and cellular basis of copper dysregulation and its relationship with human pathologies

Copper (Cu) is an essential micronutrient required for the activity of redox-active enzymes involved in critical metabolic reactions, signaling pathways, and biological functions. Transporters and chaperones control Cu ion levels and bioavailability to ensure proper subcellular and systemic Cu distribution. Intensive research has focused on understanding how mammalian cells maintain Cu homeostasis, and how molecular signals coordinate Cu acquisition and storage within organs. In humans, mutations of genes that regulate Cu homeostasis or facilitate interactions with Cu ions lead to numerous pathologic conditions. Malfunctions of the Cu⁺ -transporting ATPases ATP7A and ATP7B cause Menkes disease and Wilson disease, respectively. Additionally, defects in the mitochondrial and cellular distributions and homeostasis of Cu lead to severe neurodegenerative conditions, mitochondrial myopathies, and metabolic diseases. Cu has a dual nature in carcinogenesis as a promotor of tumor growth and an inducer of redox stress in cancer cells. Cu also plays role in cancer treatment as a component of drugs and a regulator of drug sensitivity and uptake. In this review, we provide an overview of the current knowledge of Cu metabolism and transport and its relation to various human pathologies.

A pH Switch Controls Zinc Binding in Tomato Copper-Zinc Superoxide Dismutase

Copper-zinc superoxide dismutase (SOD1) is a major antioxidant metalloenzyme that protects cells from oxidative damage by superoxide anions (O₂^-). Structural, biophysical, and other characteristics have in the past been compiled for mammalian SOD1s and for the highly homologous fungal and bovine SOD1s. Here, we characterize the biophysical properties of a plant SOD1 from tomato chloroplasts and present several of its crystal structures. The most unusual of these structures is a structure at low pH in which tSOD1 harbors zinc in the copper-binding site but contains no metal in the zinc-binding site. The side chain of D83, normally a zinc ligand, adopts an alternate rotameric conformation to form an unusual bidentate hydrogen bond with the side chain of D124, precluding metal binding in the zinc-binding site. This alternate conformation of D83 appears to be responsible for the previously observed pH-dependent loss of zinc from the zinc-binding site of SOD1. Titrations of cobalt into apo tSOD1 at a similar pH support the lack of an intact zinc-binding site. Further characterization of tSOD1 reveals that it is a weaker dimer relative to human SOD1 and that it can be activated in vivo through a copper chaperone for the SOD1-independent mechanism.

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.

Copper metabolism as a unique vulnerability in cancer

The last 25 years have witnessed tremendous progress in identifying and characterizing proteins that regulate the uptake, intracellular trafficking and export of copper. Although dietary copper is required in trace amounts, sufficient quantities of this metal are needed to sustain growth and development in humans and other mammals. However, copper is also a rate-limiting nutrient for the growth and proliferation of cancer cells. Oral copper chelators taken with food have been shown to confer anti-neoplastic and anti-metastatic benefits in animals and humans. Recent studies have begun to identify specific roles for copper in pathways of oncogenic signaling and resistance to anti-neoplastic drugs. Here, we review the general mechanisms of cellular copper homeostasis and discuss roles of copper in cancer progression, highlighting metabolic vulnerabilities that may be targetable in the development of anticancer therapies.

Viral pseudoenzymes in infection and immunity

Pseudoenzymes are proteins that are evolutionarily related to active enzymes, but lack relevant catalytic activity. As obligate intracellular pathogens, viruses complete their life cycle fully dependent on the cellular supplies of macromolecule and energy. Traditionally, studies of viral proteins sharing high homology with host counterparts reveal insightful mechanisms by which host signaling pathways are delicately regulated. Recent investigations into the action of cellular pseudoenzymes elucidate diverse molecular means how enzymes are differentially controlled under various physiological conditions, hinting to the potential that pathogens may exploit these regulatory modalities. To date, there have been three types of viral pseudoenzymes reported and our understanding concerning their mechanism of regulation is rudimentary at best. However, it is clear that viral pseudoenzymes are emerging with surprising functions in infection and immunity, and we are only at the beginning to understand this new group of enzyme regulators. In this review, we will summarize current knowledge in viral pseudoenzymes and provide a perspective for future research.

Exploring the Extended Biological Functions of the Human Copper Chaperone of Superoxide Dismutase 1

The human copper chaperone of SOD1 (designated as CCS) was discovered more than two decades ago. It is an important copper binding protein and a homolog of Saccharomyces cerevisiae LYS7. To date, no studies have systematically or specifically elaborated on the functional development of CCS. This review summarizes the essential information about CCS, such as its localization, 3D structure, and copper binding ability. An emphasis is placed on its interacting protein partners and its biological functions in vivo and in vitro. Three-dimensional structural analysis revealed that CCS is composed of three domains. Its primary molecular function is the delivery of copper to SOD1 and activation of SOD1. It has also been reported to bind to XIAP, Mia40, and X11α, and other proteins. Through these protein partners, CCS is implicated in several vital biological processes in vivo, such as copper homeostasis, apoptosis, angiogenesis and oxidative stress. This review is anticipated to assist scientists in systematically understanding the latest research developments of CCS for facilitating the development of new therapeutics targeting CCS in the future.

A lytic polysaccharide monooxygenase-like protein functions in fungal copper import and meningitis

Infection by the fungal pathogen Cryptococcus neoformans causes lethal meningitis, primarily in immune-compromised individuals. Colonization of the brain by C. neoformans is dependent on copper (Cu) acquisition from the host, which drives critical virulence mechanisms. While C. neoformans Cu+ import and virulence are dependent on the Ctr1 and Ctr4 proteins, little is known concerning extracellular Cu ligands that participate in this process. We identified a C. neoformans gene, BIM1, that is strongly induced during Cu limitation and which encodes a protein related to lytic polysaccharide monooxygenases (LPMOs). Surprisingly, bim1 mutants are Cu deficient, and Bim1 function in Cu accumulation depends on Cu2+ coordination and cell-surface association via a glycophosphatidyl inositol anchor. Bim1 participates in Cu uptake in concert with Ctr1 and expression of this pathway drives brain colonization in mouse infection models. These studies demonstrate a role for LPMO-like proteins as a critical factor for Cu acquisition in fungal meningitis.

A discrete Cu2(Pd-bpy)2L2 heterometallic compound with superoxide dismutase enzyme like activity

An aqueous soluble discrete heterometallic compound consisting of Cu(ii) and Pd(ii) units with SOD mimicking activity has been demonstrated.

Copper and Neurotoxicity in Autism Spectrum Disorder

Free radicals (FR) act on living organisms and present unpaired electrons in the molecular orbitals of oxygen or nitrogen species. They are classified as redox reactions and account for a wide range of processes in biological systems. Genetic and environmental factors may alter the levels of FR in the cell, leading to deleterious consequences such as membrane lipid peroxidation, protein nitration, enzyme, carbohydrate and DNA damage, ultimately resulting in premature aging and a pro-inflammatory microenvironment as observed in Alzheimer's disease (AD) and autism spectrum disorder (ASD). O2 radical ability to act as a Lewis base and to form a complex with metal transition such as iron and copper (Lewis acids) leads to biomolecules oxidation at physiological pH, thus increasing the possibility of injury and oxidative damage in biological tissues. In this review, we discuss the role of metals, like copper, and the amyloid precursor protein (APP) derivative (s-APP-alpha) as an antioxidant and a possible adjuvant in the treatment of some autistic spectrum disorder symptoms (ASD).

Targeting of copper-trafficking chaperones causes gene-specific systemic pathology in Drosophila melanogaster: prospective expansion of mutational landscapes that regulate tumor resistance to cisplatin

Copper, a transition metal, is an essential component for normal growth and development. It acts as a critical co-factor of many enzymes that play key roles in diverse cellular processes. The present study attempts to investigate the regulatory functions decisively controlling copper trafficking during development and aging of the Drosophila model system. Hence, through engagement of the GAL4/UAS genetic platform and RNAi technology, we herein examined the in vivo significance of Atox1 and CCS genes, products of which pivotally govern cellular copper trafficking in fly tissue pathophysiology. Specifically, we analyzed the systemic effects of their targeted downregulation on the eye, wing, neuronal cell populations and whole-body tissues of the fly. Our results reveal that, in contrast to the eye, suppression of their expression in the wing leads to a notable increase in the percentage of malformed organs observed. Furthermore, we show that Atox1 or CCS gene silencing in either neuronal or whole-body tissues can critically affect the viability and climbing capacity of transgenic flies, while their double-genetic targeting suggests a rather synergistic mode of action of the cognate protein products. Interestingly, pharmacological intervention with the anti-cancer drug cisplatin indicates the major contribution of CCS copper chaperone to cisplatin's cellular trafficking, and presumably to tumor resistance often acquired during chemotherapy. Altogether, it seems that Atox1 and CCS proteins serve as tissue/organ-specific principal regulators of physiological Drosophila development and aging, while their tissue-dependent downregulation can provide important insights for Atox1 and CCS potential exploitation as predictive gene biomarkers of cancer-cell chemotherapy responses.

Summary: We demonstrate the essential roles of Atox1 and CCS copper-trafficking chaperones in Drosophila development and aging. We also provide insights for their therapeutic exploitation as cisplatin regulators during cancer chemotherapy.

Folding of copper proteins: role of the metal?

Copper is a redox-active transition metal ion required for the function of many essential human proteins. For biosynthesis of proteins coordinating copper, the metal may bind before, during or after folding of the polypeptide. If the metal binds to unfolded or partially folded structures of the protein, such coordination may modulate the folding reaction. The molecular understanding of how copper is incorporated into proteins requires descriptions of chemical, thermodynamic, kinetic and structural parameters involved in the formation of protein-metal complexes. Because free copper ions are toxic, living systems have elaborate copper-transport systems that include particular proteins that facilitate efficient and specific delivery of copper ions to target proteins. Therefore, these pathways become an integral part of copper protein folding in vivo. This review summarizes biophysical-molecular in vitro work assessing the role of copper in folding and stability of copper-binding proteins as well as protein-protein copper exchange reactions between human copper transport proteins. We also describe some recent findings about the participation of copper ions and copper proteins in protein misfolding and aggregation reactions in vitro.

Copper-zinc superoxide dismutase (Sod1) activation terminates interaction between its copper chaperone (Ccs) and the cytosolic metal-binding domain of the copper importer Ctr1

Copper-zinc superoxide dismutase (Sod1) is a critical antioxidant enzyme that rids the cell of reactive oxygen through the redox cycling of a catalytic copper ion provided by its copper chaperone (Ccs). Ccs must first acquire this copper ion, directly or indirectly, from the influx copper transporter, Ctr1. The three proteins of this transport pathway ensure careful trafficking of copper ions from cell entry to target delivery, but the intricacies remain undefined. Biochemical examination of each step in the pathway determined that the activation of the target (Sod1) regulates the Ccs·Ctr1 interaction. Ccs stably interacts with the cytosolic C-terminal tail of Ctr1 (Ctr1c) in a copper-dependent manner. This interaction becomes tripartite upon the addition of an engineered immature form of Sod1 creating a stable Cu(I)-Ctr1c·Ccs·Sod1 heterotrimer in solution. This heterotrimer can also be made by the addition of a preformed Sod1·Ccs heterodimer to Cu(I)-Ctr1c, suggestive of multiple routes to the same destination. Only complete Sod1 activation (i.e. active site copper delivery and intra-subunit disulfide bond formation) breaks the Sod1·Ccs·Ctr1c complex. The results provide a new and extended view of the Sod1 activation pathway(s) originating at cellular copper import.

Soluble and membrane-bound protein carrier mediate direct copper transport to the ethylene receptor family

The plant hormone ethylene is a key regulator of plant growth, development and stress adaption. Ethylene perception and response are mediated by a family of integral membrane receptors (ETRs) localized at the ER-Golgi network. The biological function of these receptors relies on a protein-bound copper cofactor. Nonetheless, molecular processes and structures controlling assembly and integration of the metal into the functional plant hormone receptor are still unknown. Here, we have explored the molecular pathways of copper transfer from the plant cytosol to the ethylene receptor family by analyzing protein-protein interactions of receptors with soluble and membrane-bound plant copper carriers. Our results suggest that receptors primarily acquire their metal cofactor from copper transporter RESPONSIVE-TO-ANTAGONIST-1 (RAN1) which has been loaded with the transition metal beforehand by soluble copper carriers of the ATX1-family. In addition, we found evidence for a direct interaction of ETRs with soluble chaperones ANTIOXIDANT-1 (ATX1) and COPPER TRANSPORT PROTEIN (CCH) raising the possibility of a direct copper exchange between soluble chaperones and receptors.

Silver Ions as a Tool for Understanding Different Aspects of Copper Metabolism

In humans, copper is an important micronutrient because it is a cofactor of ubiquitous and brain-specific cuproenzymes, as well as a secondary messenger. Failure of the mechanisms supporting copper balance leads to the development of neurodegenerative, oncological, and other severe disorders, whose treatment requires a detailed understanding of copper metabolism. In the body, bioavailable copper exists in two stable oxidation states, Cu(I) and Cu(II), both of which are highly toxic. The toxicity of copper ions is usually overcome by coordinating them with a wide range of ligands. These include the active cuproenzyme centers, copper-binding protein motifs to ensure the safe delivery of copper to its physiological location, and participants in the Cu(I) ↔ Cu(II) redox cycle, in which cellular copper is stored. The use of modern experimental approaches has allowed the overall picture of copper turnover in the cells and the organism to be clarified. However, many aspects of this process remain poorly understood. Some of them can be found out using abiogenic silver ions (Ag(I)), which are isoelectronic to Cu(I). This review covers the physicochemical principles of the ability of Ag(I) to substitute for copper ions in transport proteins and cuproenzyme active sites, the effectiveness of using Ag(I) to study copper routes in the cells and the body, and the limitations associated with Ag(I) remaining stable in only one oxidation state. The use of Ag(I) to restrict copper transport to tumors and the consequences of large-scale use of silver nanoparticles for human health are also discussed.

An NMR View of Protein Dynamics in Health and Disease

Biological molecules are often highly dynamic, and this flexibility can be critical for function. The large range of sampled timescales and the fact that many of the conformers that are continually explored are only transiently formed and sparsely populated challenge current biophysical approaches. Solution nuclear magnetic resonance (NMR) spectroscopy has emerged as a powerful method for characterizing biomolecular dynamics in detail, even in cases where excursions involve short-lived states. Here, we briefly review a number of NMR experiments for studies of biomolecular dynamics on the microsecond-to-second timescale and focus on applications to protein and nucleic acid systems that clearly illustrate the functional relevance of motion in both health and disease.

Cloning, Expression, and Bioinformatics Analysis of Heavy Metal Resistance Gene afe_1862 from Acidithiobacillus ferrooxidans L1 in Escherichia coli

Molecular studies of copper and cadmium resistances in acidophilic bacteria are significant in biomining. In this study, afe_1862, which encodes a heavy metal-binding protein in Acidithiobacillus ferrooxidans L1, was amplified using PCR, cloned into the pET32a plasmid, and sequenced. Following SDS-PAGE analysis, optimization of the expression conditions and heterologous overexpression of afe_1862 in Escherichia coli BL21 in the presence of Cu²⁺ and Cd²⁺ were studied as well. The results indicated that AFE_1862 has higher resistance to Cu²⁺ than Cd²⁺. Bioinformatics analysis illustrated that AFE_1862 has a conserved HMA domain containing heavy metal-binding sites, which may play a role in transporting or detoxifying heavy metals.

Redox Mechanisms in Neurodegeneration: From Disease Outcomes to Therapeutic Opportunities

SIGNIFICANCE

Once considered to be mere by-products of metabolism, reactive oxygen, nitrogen and sulfur species are now recognized to play important roles in diverse cellular processes such as response to pathogens and regulation of cellular differentiation. It is becoming increasingly evident that redox imbalance can impact several signaling pathways. For instance, disturbances of redox regulation in the brain mediate neurodegeneration and alter normal cytoprotective responses to stress. Very often small disturbances in redox signaling processes, which are reversible, precede damage in neurodegeneration. Recent Advances: The identification of redox-regulated processes, such as regulation of biochemical pathways involved in the maintenance of redox homeostasis in the brain has provided deeper insights into mechanisms of neuroprotection and neurodegeneration. Recent studies have also identified several post-translational modifications involving reactive cysteine residues, such as nitrosylation and sulfhydration, which fine-tune redox regulation. Thus, the study of mechanisms via which cell death occurs in several neurodegenerative disorders, reveal several similarities and dissimilarities. Here, we review redox regulated events that are disrupted in neurodegenerative disorders and whose modulation affords therapeutic opportunities.

CRITICAL ISSUES

Although accumulating evidence suggests that redox imbalance plays a significant role in progression of several neurodegenerative diseases, precise understanding of redox regulated events is lacking. Probes and methodologies that can precisely detect and quantify in vivo levels of reactive oxygen, nitrogen and sulfur species are not available.

FUTURE DIRECTIONS

Due to the importance of redox control in physiologic processes, organisms have evolved multiple pathways to counteract redox imbalance and maintain homeostasis. Cells and tissues address stress by harnessing an array of both endogenous and exogenous redox active substances. Targeting these pathways can help mitigate symptoms associated with neurodegeneration and may provide avenues for novel therapeutics. Antioxid. Redox Signal. 30, 1450-1499.

Molecular recognition and maturation of SOD1 by its evolutionarily destabilised cognate chaperone hCCS

Superoxide dismutase-1 (SOD1) maturation comprises a string of posttranslational modifications which transform the nascent peptide into a stable and active enzyme. The successive folding, metal ion binding, and disulphide acquisition steps in this pathway can be catalysed through a direct interaction with the copper chaperone for SOD1 (CCS). This process confers enzymatic activity and reduces access to noncanonical, aggregation-prone states. Here, we present the functional mechanisms of human copper chaperone for SOD1 (hCCS)-catalysed SOD1 activation based on crystal structures of reaction precursors, intermediates, and products. Molecular recognition of immature SOD1 by hCCS is driven by several interface interactions, which provide an extended surface upon which SOD1 folds. Induced-fit complexation is reliant on the structural plasticity of the immature SOD1 disulphide sub-loop, a characteristic which contributes to misfolding and aggregation in neurodegenerative disease. Complexation specifically stabilises the SOD1 disulphide sub-loop, priming it and the active site for copper transfer, while delaying disulphide formation and complex dissociation. Critically, a single destabilising amino acid substitution within the hCCS interface reduces hCCS homodimer affinity, creating a pool of hCCS available to interact with immature SOD1. hCCS substrate specificity, segregation between solvent and biological membranes, and interaction transience are direct results of this substitution. In this way, hCCS-catalysed SOD1 maturation is finessed to minimise copper wastage and reduce production of potentially toxic SOD1 species.

The yeast copper chaperone for copper-zinc superoxide dismutase (CCS1) is a multifunctional chaperone promoting all levels of SOD1 maturation

Copper (Cu) is essential for the survival of aerobic organisms through its interaction with molecular oxygen (O₂). However, Cu's chemical properties also make it toxic, requiring specific cellular mechanisms for Cu uptake and handling, mediated by Cu chaperones. CCS1, the budding yeast (S. cerevisiae) Cu chaperone for Cu-zinc (Zn) superoxide dismutase (SOD1) activates by directly promoting both Cu delivery and disulfide formation in SOD1. The complete mechanistic details of this transaction along with recently proposed molecular chaperone-like functions for CCS1 remain undefined. Here, we present combined structural, spectroscopic, kinetic, and thermodynamic data that suggest a multifunctional chaperoning role(s) for CCS1 during SOD1 activation. We observed that CCS1 preferentially binds a completely immature form of SOD1 and that the SOD1·CCS1 interaction promotes high-affinity Zn(II) binding in SOD1. Conserved aromatic residues within the CCS1 C-terminal domain are integral in these processes. Previously, we have shown that CCS1 delivers Cu(I) to an entry site at the SOD1·CCS1 interface upon binding. We show here that Cu(I) is transferred from CCS1 to the entry site and then to the SOD1 active site by a thermodynamically driven affinity gradient. We also noted that efficient transfer from the entry site to the active site is entirely dependent upon the oxidation of the conserved intrasubunit disulfide bond in SOD1. Our results herein provide a solid foundation for proposing a complete molecular mechanism for CCS1 activity and reclassification as a first-of-its-kind "dual chaperone."

Prediction of Misfolding-Specific Epitopes in SOD1 Using Collective Coordinates

We introduce a global, collective coordinate bias into molecular dynamics simulations that partially unfolds a protein, in order to predict misfolding-specific epitopes based on the regions that locally unfold. Several metrics are used to measure local disorder, including solvent exposed surface area (SASA), native contacts ( Q), and root mean squared fluctuations (RMSF). The method is applied to Cu, Zn superoxide dismutase (SOD1). For this protein, the processes of monomerization, metal loss, and conformational unfolding due to microenvironmental stresses are all separately taken into account. Several misfolding-specific epitopes are predicted, and consensus epitopes are calculated. These predicted epitopes are consistent with the "lower-resolution" peptide sequences used to raise disease-specific antibodies, but the epitopes derived from collective coordinates contain shorter, more refined sequences for the key residues constituting the epitope.

Copper signalling: causes and consequences

Copper-containing enzymes perform fundamental functions by activating dioxygen (O2) and therefore allowing chemical energy-transfer for aerobic metabolism. The copper-dependence of O2 transport, metabolism and production of signalling molecules are supported by molecular systems that regulate and preserve tightly-bound static and weakly-bound dynamic cellular copper pools. Disruption of the reducing intracellular environment, characterized by glutathione shortage and ambient Cu(II) abundance drives oxidative stress and interferes with the bidirectional, copper-dependent communication between neurons and astrocytes, eventually leading to various brain disease forms. A deeper understanding of of the regulatory effects of copper on neuro-glia coupling via polyamine metabolism may reveal novel copper signalling functions and new directions for therapeutic intervention in brain disorders associated with aberrant copper metabolism.

Redox Interconversion between Cobalt(III) Thiolate and Cobalt(II) Disulfide Compounds

The redox interconversion between Co(III) thiolate and Co(II) disulfide compounds has been investigated experimentally and computationally. Reactions of cobalt(II) salts with disulfide ligand L¹SSL¹ (L¹SSL¹ = di-2-(bis(2-pyridylmethyl)amino)-ethyl disulfide) result in the formation of either the high-spin cobalt(II) disulfide compound [Co^II₂(L¹SSL¹)Cl₄] or a low-spin, octahedral cobalt(III) thiolate compound, such as [Co^III(L¹S)(MeCN)₂](BF₄)₂. Addition of thiocyanate anions to a solution containing the latter compound yielded crystals of [Co^III(L¹S)(NCS)₂]. The addition of chloride ions to a solution of [Co^III(L¹S)(MeCN)₂](BF₄)₂ in acetonitrile results in conversion of the cobalt(III) thiolate compound to the cobalt(II) disulfide compound [Co^II₂(L¹SSL¹)Cl₄], as monitored with UV–vis spectroscopy; subsequent addition of AgBF₄ regenerates the Co(III) compound. Computational studies show that exchange by a chloride anion of the coordinated acetonitrile molecule or thiocyanate anion in compounds [Co^III(L¹S)(MeCN)₂]²⁺ and [Co^III(L¹S)(NCS)₂] induces a change in the character of the highest occupied molecular orbitals, showing a decrease of the contribution of the p orbital on sulfur and an increase of the d orbital on cobalt. As a comparison, the synthesis of iron compounds was undertaken. X-ray crystallography revealed that structure of the dinuclear iron(II) disulfide compound [Fe^II₂(L¹SSL¹)Cl₄] is different from that of cobalt(II) compound [Co^II₂(L¹SSL¹)Cl₄]. In contrast to cobalt, reaction of ligand L¹SSL¹ with [Fe(MeCN)₆](BF₄)₂ did not yield the expected Fe(III) thiolate compound. This work is an unprecedented example of redox interconversion between a high-spin Co(II) disulfide compound and a low-spin Co(III) thiolate compound triggered by the nature of the anion.

Low-spin Co^III−thiolate compounds and high-spin Co^II and Fe^II disulfide compound have been synthesized from reactions of a disulfide ligand with Co^II and Fe^II salts. The redox interconversion between the cobalt compounds has been investigated. It is shown that addition of chloride ions to a solution of the Co^III−thiolate compound results in the formation of the Co^II-disulfide compound, whereas removal of chloride anions from the Co^II disulfide compound regenerates the Co^III−thiolate complex.

Unusual Reduction Mechanism of Copper in Cysteine-Rich Environment

Copper-cysteine interactions play an important role in Biology and herein we used the copper-substituted rubredoxin (Cu-Rd) from Desulfovibrio gigas to gain further insights into the copper-cysteine redox chemistry. EPR spectroscopy results are consistent with Cu-Rd harboring a Cu^II center in a sulfur-rich coordination, in a distorted tetrahedral structure ( g_∥,⊥ = 2.183 and 2.032 and A_∥,⊥ = 76.4 × 10^-4 and 12 × 10^-4 cm^-1). In Cu-Rd, two oxidation states at Cu-center (Cu^II and Cu^I) are associated with Cys oxidation-reduction, alternating in the redox cycle, as pointed by electrochemical studies that suggest internal geometry rearrangements associated with the electron transfer processes. The midpoint potential of [Cu^I(S-Cys)₂(Cys-S-S-Cys)]/[Cu^II(S-Cys)₄] redox couple was found to be -0.15 V vs NHE showing a large separation of cathodic and anodic peaks potential (Δ E_p = 0.575 V). Interestingly, sulfur-rich Cu^II-Rd is highly stable under argon in dark conditions, which is thermodynamically unfavorable to Cu-thiol autoreduction. The reduction of copper and concomitant oxidation of Cys can both undergo two possible pathways: oxidative as well as photochemical. Under O₂, Cu^II plays the role of the electron carrier from one Cys to O₂ followed by internal geometry rearrangement at the Cu site, which facilitates reduction at Cu-center to yield Cu^I(S-Cys)₂(Cys-S-S-Cys). Photoinduced (irradiated at λ_ex = 280 nm) reduction of the Cu^II center is observed by UV-visible photolysis (above 300 nm all bands disappeared) and tryptophan fluorescence (∼335 nm peak enhanced) experiments. In both pathways, geometry reorganization plays an important role in copper reduction yielding an energetically compatible donor-acceptor system. This model system provides unusual stability and redox chemistry rather than the universal Cu-thiol auto redox chemistry in cysteine-rich copper complexes.

In-Cell NMR in Human Cells: Direct Protein Expression Allows Structural Studies of Protein Folding and Maturation

Cellular structural biology methods are needed to characterize biological processes at atomic resolution in the physiological environment of the cell. Toward this goal, solution in-cell NMR is a powerful approach because it provides structural and dynamic data on macromolecules inside living cells. Several approaches have been developed for in-cell NMR in cultured human cells, which are needed to study processes related to human diseases that rely on the delivery of exogenous macromolecules to the cells. Such strategies, however, may not be applicable to proteins that are sensitive to the external environment or prone to aggregate and can introduce artifacts during protein purification or delivery. As a complementary approach, direct protein expression for in-cell NMR in human cells was developed. This strategy is especially useful when studying processes like protein folding, maturation, and post-translational modification, starting right after protein synthesis. Compared with the protein expression techniques in mammalian cells commonly used in cellular biology, the low sensitivity of NMR requires higher protein levels. Among the cell lines used for high-yield protein expression, the HEK293T cell line was chosen, as it can be efficiently transfected with a cost-effective reagent. A vector originally designed for secreted proteins allows high-level cytosolic protein expression. For isotopic labeling, commercially available or homemade labeled media are employed. Uniform or amino acid type-selective labeling strategies are possible. Protein expression can be targeted to specific organelles (e.g., mitochondria), allowing for in organello NMR applications. A variant of the approach was developed that allows the sequential expression of two or more proteins, with only one selectively labeled. Protein expression in HEK293T cells was applied to recapitulate the maturation steps of intracellular superoxide dismutase 1 (SOD1) and to study the effect of mutations linked to familial amyotrophic lateral sclerosis (fALS) by in-cell NMR. Intracellular wild-type SOD1 spontaneously binds zinc, while it needs the copper chaperone for superoxide dismutase (CCS) for copper delivery and disulfide bond formation. Some fALS-linked mutations impair zinc binding and cause SOD1 to irreversibly unfold, likely forming the precursor of cytotoxic aggregates. The SOD-like domain of CCS acts as a molecular chaperone toward mutant SOD1, stabilizing its folding and allowing zinc binding and correct maturation. Changes in protein redox state distributions can also be investigated by in-cell NMR. Mitochondrial proteins require the redox-regulating partners glutaredoxin 1 (Grx1) and thioredoxin (Trx) to remain in the reduced, import-competent state in the cytosol, whereas SOD1 requires CCS for disulfide bond formation. In both cases, the proteins do not equilibrate with the cytosolic redox pool. Cysteine oxidation in response to oxidative stress can also be monitored. In the near future, in-cell NMR in human cells will likely benefit from technological advancements in NMR hardware, the development of bioreactor systems for increased sample lifetime, the application of paramagnetic NMR to obtain structural restraints, and advanced tools for genome engineering and should be increasingly integrated with advanced cellular imaging techniques.

Copper transporters and copper chaperones: roles in cardiovascular physiology and disease

Copper (Cu) is an essential micronutrient but excess Cu is potentially toxic. Its important propensity to cycle between two oxidation states accounts for its frequent presence as a cofactor in many physiological processes through Cu-containing enzymes, including mitochondrial energy production (via cytochrome c-oxidase), protection against oxidative stress (via superoxide dismutase), and extracellular matrix stability (via lysyl oxidase). Since free Cu is potentially toxic, the bioavailability of intracellular Cu is tightly controlled by Cu transporters and Cu chaperones. Recent evidence reveals that these Cu transport systems play an essential role in the physiological responses of cardiovascular cells, including cell growth, migration, angiogenesis and wound repair. In response to growth factors, cytokines, and hypoxia, their expression, subcellular localization, and function are tightly regulated. Cu transport systems and their regulators have also been linked to various cardiovascular pathophysiologies such as hypertension, inflammation, atherosclerosis, diabetes, cardiac hypertrophy, and cardiomyopathy. A greater appreciation of the central importance of Cu transporters and Cu chaperones in cell signaling and gene expression in cardiovascular biology offers the possibility of identifying new therapeutic targets for cardiovascular disease.

Quantifying the Interaction between Copper-Zinc Superoxide Dismutase (Sod1) and its Copper Chaperone (Ccs1)

Immature copper-zinc superoxide dismutase (Sod1) is activated by its copper chaperone (Ccs1). Ccs1 delivers a single copper ion and catalyzes oxidation of an intra-subunit disulfide bond within each Sod1 monomer through a mechanistically ambiguous process. Here, we use residue specific fluorescent labeling of immature Sod1 to quantitate the thermodynamics of the Sod1•Ccs1 interaction while determining a more complete view of Ccs1 function. Ccs1 preferentially binds a completely immature form of Sod1 that is metal deficient and disulfide reduced (E, E-Sod1^SH). However, binding induces structural changes that promote high-affinity zinc binding by the Ccs1-bound Sod1 molecule. This adds further support to the notion that Ccs1 likely plays dual chaperoning roles during the Sod1 maturation process. Further analysis reveals that in addition to the copper-dependent roles during Sod1 activation, the N- and C-terminal domains of Ccs1 also have synergistic roles in securing both Sod1 recognition and its own active conformation. These results provide new and measurable analyses of the molecular determinants guiding Ccs1-mediated Sod1 activation.

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.

Effects of maturation on the conformational free-energy landscape of SOD1

Amyotrophic lateral sclerosis (ALS) is a devastating fatal syndrome characterized by very rapid degeneration of motor neurons. A leading hypothesis is that ALS is caused by toxic protein misfolding and aggregation, as also occurs in many other neurodegenerative disorders, such as prion, Alzheimer's, Parkinson's, and Huntington's diseases. A prominent cause of familial ALS is mutations in the protein superoxide dismutase (SOD1), which promote the formation of misfolded SOD1 conformers that are prone to aberrant interactions both with each other and with other cellular components. We have shown previously that immature SOD1, lacking bound Cu and Zn metal ions and the intrasubunit disulfide bond (apoSOD1^2SH), has a rugged free-energy surface (FES) and exchanges with four other conformations (excited states) that have millisecond lifetimes and sparse populations on the order of a few percent. Here, we examine further states of SOD1 along its maturation pathway, as well as those off-pathway resulting from metal loss that have been observed in proteinaceous inclusions. Metallation and disulfide bond formation lead to structural transformations including local ordering of the electrostatic loop and native dimerization that are observed in rare conformers of apoSOD1^2SH; thus, SOD1 maturation may occur via a population-switch mechanism whereby posttranslational modifications select for preexisting structures on the FES. Metallation and oxidation of SOD1 stabilize the native, mature conformation and decrease the number of detected excited conformational states, suggesting that it is the immature forms of the protein that contribute to misfolded conformations in vivo rather than the highly stable enzymatically active dimer.

A molecular chaperone activity of CCS restores the maturation of SOD1 fALS mutants

Superoxide dismutase 1 (SOD1) is an important metalloprotein for cellular oxidative stress defence, that is mutated in familiar variants of Amyotrophic Lateral Sclerosis (fALS). Some mutations destabilize the apo protein, leading to the formation of misfolded, toxic species. The Copper Chaperone for SOD1 (CCS) transiently interacts with SOD1 and promotes its correct maturation by transferring copper and catalyzing disulfide bond formation. By in vitro and in-cell NMR, we investigated the role of the SOD-like domain of CCS (CCS-D2). We showed that CCS-D2 forms a stable complex with zinc-bound SOD1 in human cells, that has a twofold stabilizing effect: it both prevents the accumulation of unstructured mutant SOD1 and promotes zinc binding. We further showed that CCS-D2 interacts with apo-SOD1 in vitro, suggesting that in cells CCS stabilizes mutant apo-SOD1 prior to zinc binding. Such molecular chaperone function of CCS-D2 is novel and its implications in SOD-linked fALS deserve further investigation.

The Role of Metal Binding in the Amyotrophic Lateral Sclerosis-Related Aggregation of Copper-Zinc Superoxide Dismutase

Protein misfolding and conformational changes are common hallmarks in many neurodegenerative diseases involving formation and deposition of toxic protein aggregates. Although many players are involved in the in vivo protein aggregation, physiological factors such as labile metal ions within the cellular environment are likely to play a key role. In this review, we elucidate the role of metal binding in the aggregation process of copper-zinc superoxide dismutase (SOD1) associated to amyotrophic lateral sclerosis (ALS). SOD1 is an extremely stable Cu-Zn metalloprotein in which metal binding is crucial for folding, enzymatic activity and maintenance of the native conformation. Indeed, demetalation in SOD1 is known to induce misfolding and aggregation in physiological conditions in vitro suggesting that metal binding could play a key role in the pathological aggregation of SOD1. In addition, this study includes recent advances on the role of aberrant metal coordination in promoting SOD1 aggregation, highlighting the influence of metal ion homeostasis in pathologic aggregation processes.

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.

Thiol-based copper handling by the copper chaperone Atox1

Human antioxidant protein 1 (Atox1) plays a crucial role in cellular copper homeostasis. Atox1 captures cytosolic copper for subsequent transfer to copper pumps in trans Golgi network, thereby facilitating copper supply to various copper-dependent oxidereductases matured within the secretory vesicles. Atox1 and other copper chaperones handle cytosolic copper using Cys thiols which are ideal ligands for coordinating Cu(I). Recent studies demonstrated reversible oxidation of these Cys residues in copper chaperones, linking cellular redox state to copper homeostasis. Highlighted in this review are unique redox properties of Atox1 and other copper chaperones. Also, summarized are the redox nodes in the cytosol which potentially play dominant roles in the redox regulation of copper chaperones. © 2016 IUBMB Life, 69(4):246-254, 2017.

S-acylation of SOD1, CCS, and a stable SOD1-CCS heterodimer in human spinal cords from ALS and non-ALS subjects

Previously, we found that human Cu, Zn-superoxide dismutase (SOD1) is S-acylated (palmitoylated) in vitro and in amyotrophic lateral sclerosis (ALS) mouse models, and that S-acylation increased for ALS-causing SOD1 mutants relative to wild type. Here, we use the acyl resin-assisted capture (acyl-RAC) assay to demonstrate S-acylation of SOD1 in human post-mortem spinal cord homogenates from ALS and non-ALS subjects. Acyl-RAC further revealed that endogenous copper chaperone for SOD1 (CCS) is S-acylated in both human and mouse spinal cords, and in vitro in HEK293 cells. SOD1 and CCS formed a highly stable heterodimer in human spinal cord homogenates that was resistant to dissociation by boiling, denaturants, or reducing agents and was not observed in vitro unless both SOD1 and CCS were overexpressed. Cysteine mutations that attenuate SOD1 maturation prevented the SOD1-CCS heterodimer formation. The degree of S-acylation was highest for SOD1-CCS heterodimers, intermediate for CCS monomers, and lowest for SOD1 monomers. Given that S-acylation facilitates anchoring of soluble proteins to cell membranes, our findings suggest that S-acylation and membrane localization may play an important role in CCS-mediated SOD1 maturation. Furthermore, the highly stable S-acylated SOD1-CCS heterodimer may serve as a long-lived maturation intermediate in human spinal cord.

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.

Copper dyshomoeostasis in Parkinson's disease: implications for pathogenesis and indications for novel therapeutics

Copper is a biometal essential for normal brain development and function, thus copper deficiency or excess results in central nervous system disease. Well-characterized disorders of disrupted copper homoeostasis with neuronal degeneration include Menkes disease and Wilson's disease but a large body of evidence also implicates disrupted copper pathways in other neurodegenerative disorders, including Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis, Huntington's disease and prion diseases. In this short review we critically evaluate the data regarding changes in systemic and brain copper levels in Parkinson's disease, where alterations in brain copper are associated with regional neuronal cell death and disease pathology. We review copper regulating mechanisms in the human brain and the effects of dysfunction within these systems. We then examine the evidence for a role for copper in pathogenic processes in Parkinson's disease and consider reports of diverse copper-modulating strategies in in vitro and in vivo models of this disorder. Copper-modulating therapies are currently advancing through clinical trials for Alzheimer's and Huntington's disease and may also hold promise as disease modifying agents in Parkinson's disease.