Copper chaperones

Sensitive detection and intracellular imaging of free copper ions based on DNA-templated silver nanoclusters aggregation-inducing fluorescence enhancement effect

Free copper ions (Cu⁺ and Cu²⁺) have critical toxicity to cells, although copper is an essential element for human body. Hence, sensitive monitoring is crucial to avoid over intake of Cu⁺/Cu²⁺. We herein designed a ssDNA sequence (A₃₁) for synthetizing A₃₁-templated silver nanoclusters (AgNCs), and demonstrated that Cu⁺/Cu²⁺ can induce the aggregation of A₃₁-templated AgNCs and thus greatly enhanced the fluorescence emission of A₃₁-templated AgNCs. Based on Cu⁺/Cu²⁺-induced fluorescence enhancement effect of A₃₁-templated AgNCs, a label-free and signal-on fluorescent sensing platform was developed for the specific and sensitive detection of Cu⁺/Cu²⁺ in biological samples and intracellular imaging of Cu⁺/Cu²⁺ in cells. The signal-on fluorescent sensing platform could be used to rapidly detect Cu⁺ and Cu²⁺ with a detection limit of 0.1 µM within 30 min., and to perform the intracellular imaging of Cu⁺ and Cu²⁺ in cells with good cell permeability and biocompatibility. By using the signal-on fluorescent sensing platform, we have successfully detected Cu⁺ and Cu²⁺ in cells fluids and human serum with a recovery of 90-104% and a RSD (n = 5) < 5%, and performed the imaging of Cu⁺/Cu²⁺ in Hela cells. The developed fluorescent sensing platform has obvious analytical and imaging advantages such as signal-on, simple operation, short analysis time, both Cu⁺ and Cu²⁺ detection, similar or higher sensitivity, good cell permeability and biocompatibility, which promising a reliable approach for the rapid and on-site detection or imaging of free copper ions in biological samples in clinical diagnosis.

Evaluation of Fetal Exposures to Metals and Metalloids through Meconium Analyses: A Review

This paper surveys the existing scientific literature on metals concentrations in meconium. We examine some 32 papers that analyzed meconium for aluminum, arsenic, barium, calcium, chromium, copper, iron, lithium, magnesium, manganese, zinc, lead, mercury, manganese, molybdenum, nickel, phosphorus, lead, antimony, selenium, tin, vanadium, and zinc. Because of the lack of detail in the statistics it is not possible to do a rigorous meta-analysis. What stands out is that almost every study had subjects with seemingly large amounts of at least one of the metals. The significance of metals in meconium is not clear beyond an indication of exposure although some studies have correlated metals in meconium to a number of adverse outcomes. A number of outstanding questions have been identified that, if resolved, would greatly increase the utility of meconium analysis for assessment of long-term gestational metals exposures. Among these are questions of the developmental and long-term significance of metals detected in meconium, the kinetics and interactions among metals in maternal and fetal compartments and questions on best methods for meconium analyses.

Ubiquitin binds the amyloid β peptide and interferes with its clearance pathways

Several lines of evidence point to a compromised proteostasis associated with a reduction of the Ubiquitin Proteasome System (UPS) activity in patients affected by Alzheimer's Disease (AD) and suggest that the amyloid β peptide (Aβ) is an important player in the game. Inspired also by many reports, underlining the presence of ubiquitin (Ub) in the amyloid plaques of AD brains, here we set out to test whether Ub may bind the Aβ peptide and have any effect on its clearance pathways. By using an integrated array of MALDI-TOF/UPLC-HRMS, fluorescence, NMR, SPR, Microscale Thermophoresis (MST) and molecular dynamics studies, we consistently demonstrated that Aβ40 binds Ub with a 1 : 1 stoichiometry and K d in the high micromolar range. In particular, we show that the N-terminal domain of the Aβ peptide (through residues D1, E3 and R5) interacts with the C-terminal tail of Ub (involving residues K63 and E64), inducing the central region of Aβ (14HQKLVFFAEDVGSNK28) to adopt a mixed α-helix/β-turn structure. ELISA assays, carried out in neuroblastoma cell lysates, suggest that Aβ competitively binds Ub also in the presence of the entire pool of cytosolic Ub binding proteins. Ub-bound Aβ has a lower tendency to aggregate into amyloid-like fibrils and is more slowly degraded by the Insulin Degrading Enzyme (IDE). Finally, we observe that the water soluble fragment Aβ1-16 significantly inhibits Ub chain growth reactions. These results evidence how the non-covalent interaction between Aβ peptides and Ub may have relevant effects on the regulation of the upstream events of the UPS and pave the way to future in vivo studies addressing the role played by Aβ peptide in the malfunction of proteome maintenance occurring in AD.

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."

Ubiquitin Associates with the N-Terminal Domain of Nerve Growth Factor: The Role of Copper(II) Ions

Many biochemical pathways involving nerve growth factor (NGF), a neurotrophin with copper(II) binding abilities, are regulated by the ubiquitin (Ub) proteasome system. However, whether NGF binds Ub and the role played by copper(II) ions in modulating their interactions have not yet been investigated. Herein NMR spectroscopy, circular dichroism, ESI-MS, and titration calorimetry are employed to characterize the interactions of NGF with Ub. NGF_1-14 , which is a short model peptide encompassing the first 14 N-terminal residues of NGF, binds the copper-binding regions of Ub (K_D =8.6 10^-5  m). Moreover, the peptide undergoes a random coil-polyproline type II helix structural conversion upon binding to Ub. Notably, copper(II) ions inhibit NGF_1-14 /Ub interactions. Further experiments performed with the full-length NGF confirmed the existence of a copper(II)-dependent association between Ub and NGF and indicated that the N-terminal domain of NGF was a valuable paradigm that recapitulated many traits of the full-length protein.

The Yin and Yang of copper during infection

Copper is an essential micronutrient for both pathogens and the animal hosts they infect. However, copper can also be toxic in cells due to its redox properties and ability to disrupt active sites of metalloproteins, such as Fe-S enzymes. Through these toxic properties, copper is an effective antimicrobial agent and an emerging concept in innate immunity is that the animal host intentionally exploits copper toxicity in antimicrobial weaponry. In particular, macrophages can attack invading microbes with high copper and this metal is also elevated at sites of lung infection. In addition, copper levels in serum rise during infection with a wide array of pathogens. To defend against this toxic copper, the microbial intruder is equipped with a battery of copper detoxification defenses that promote survival in the host, including copper exporting ATPases and copper binding metallothioneins. However, it is important to remember that copper is also an essential nutrient for microbial pathogens and serves as important cofactor for enzymes such as cytochrome c oxidase for respiration, superoxide dismutase for anti-oxidant defense and multi-copper oxidases that act on metals and organic substrates. We therefore posit that the animal host can also thwart pathogen growth by limiting their copper nutrients, similar to the well-documented nutritional immunity effects for starving microbes of essential zinc, manganese and iron micronutrients. This review provides both sides of the copper story and evaluates how the host can exploit either copper-the-toxin or copper-the-nutrient in antimicrobial tactics at the host-pathogen battleground.

Phosphatidylserine-functionalized Fe3O4@SiO2 nanoparticles combined with enzyme-encapsulated liposomes for the visual detection of Cu2+

We reported on novel phosphatidylserine-functionalized Fe₃O₄@SiO₂ NPs and enzyme-encapsulated liposomes for the visual detection of Cu²⁺ by employing phosphatidylserine for Cu²⁺ recognition and the enzymatic catalysis/oxidation of TMB as a signal generator.

Coupling a novel spiro-rhodamine B lactam derivative to Fe3O4 nanoparticles for visual detection of free copper ions with high sensitivity and specificity

A novel spiro-rhodamine B lactam derivative, which can be coupled to Fe₃O₄ NPs and act as a Cu²⁺-selective visual sensor is reported. It can be used to directly detect as little as 50 nM of Cu²⁺ in river or tap water by only naked-eye observation.

A novel phosphatidylserine-functionalized AuNP for the visual detection of free copper ions with high sensitivity and specificity

In this paper, we have reported on novel phosphatidylserine-functionalized AuNPs (gold nanoparticles) for the visual detection of Cu²⁺ by employing phosphatidylserine for Cu²⁺ recognition and AuNPs for signal generation. The phosphatidylserine (1,2-dioleoyl-sn-glycero-3-phospho-l-serine, DOPS) was covalently assembled on the AuNP surface to obtain DOPS-functionalized AuNPs. It was demonstrated that DOPS-functionalized AuNPs could specifically bind Cu²⁺ and lead to the aggregation of AuNPs, which gave rise to a colour change from wine-red to blue and a new absorption band around 650 nm. This provides a sensing platform for the simple, rapid and field portable colorimetric detection of Cu²⁺. By using the sensing platform, a selective and sensitive visual biosensor for the detection of Cu²⁺ was developed. The proposed biosensor has outstanding analytical advantages such as good stability, relatively high sensitivity, low cost and short analysis time. It can be used to detect concentrations of Cu²⁺ as low as 30 μM in river water by observation with the naked eye and of 1.55 μM Cu²⁺ in river water by UV-visible spectrophotometry, within 10 min and with a recovery of 98-103% and a relative standard deviation (RSD) < 4% (n = 6). The proposed biosensor is promising for on-site detection of trace Cu²⁺ in clinical diagnosis or environmental monitoring.

Phosphatidylserine reversibly binds Cu2+ with extremely high affinity

Phosphatidylserine (PS) embedded within supported lipid bilayers was found to bind Cu(2+) from solution with extraordinarily high affinity. In fact, the equilibrium dissociation constant was in the femtomolar range. The resulting complex formed in a 1:2 Cu(2+)-to-PS ratio and quenches a broad spectrum of lipid-bound fluorophores in a reversible and pH-dependent fashion. At acidic pH values, the fluorophores were almost completely unquenched, while at basic pH values significant quenching (85-90%) was observed. The pH at which the transition occurred was dependent on the PS concentration and ranged from approximately pH 5 to 8. The quenching kinetics was slow at low Cu(2+) concentrations and basic pH values (up to several hours), while the unquenching reaction was orders of magnitude more rapid upon lowering the pH. This was consistent with diffusion-limited complex formation at basic pH but rapid dissociation under acidic conditions. The tight binding of Cu(2+) to PS may have physiological consequences under certain circumstances.

Methionine motifs of copper transport proteins provide general and flexible thioether-only binding sites for Cu(I) and Ag(I)

Cellular acquisition of copper in eukaryotic organisms is primarily accomplished through high-affinity copper transport proteins (Ctr). The extracellular N-terminal regions of both human and yeast Ctr1 contain multiple methionine residues organized in copper-binding Mets motifs. These motifs comprise combinations of methionine residues arranged in clusters of MXM and MXXM, where X can be one of several amino acids. Model peptides corresponding to 15 different Mets motifs were synthesized and determined to selectively bind Cu(I) and Ag(I), with no discernible affinity for divalent metal ions. These are rare examples of biological thioether-only metal binding sites. Effective dissociation constant (KD) values for the model Mets peptides and Cu(I) were determined by an ascorbic acid oxidation assay and validated through electrospray ionization mass spectrometry and range between 2 and 11 microM. Affinity appears to be independent of pH, the arrangement of the motif, and the composition of intervening amino acids, all of which reveal the generality and flexibility of the MX1-2MX1-2M domain. Circular dichroism spectroscopy, 1H-NMR spectroscopy, and X-ray absorption spectroscopy were also used to characterize the binding event. These results are intended to aid the development of the still unknown mechanism of copper transport across the cell membrane.

Copper redistribution in Atox1-deficient mouse fibroblast cells

Quantitative synchrotron X-ray fluorescence (SXRF) imaging of adherent mouse fibroblast cells deficient in antioxidant-1 (Atox1), a metallochaperone protein responsible for delivering Cu to cuproenzymes in the trans-Golgi network, revealed striking differences in the subcellular Cu distribution compared with wild-type cells. Whereas the latter showed a pronounced perinuclear localization of Cu, the Atox1-deficient cells displayed a mostly unstructured and diffuse distribution throughout the entire cell body. Comparison of the SXRF elemental maps for Zn and Fe of the same samples showed no marked differences between the two cell lines. The data underscore the importance of Atox1, not only as a metallochaperone for delivering Cu to cuproenzymes, but also as a key player in maintaining the proper distribution and organization of Cu at the cellular level.

Post-translational modifications of superoxide dismutase

Post-translational modifications of proteins control many biological processes through the activation, inactivation, or gain-of-function of the proteins. Recent developments in mass spectrometry have enabled detailed structural analyses of covalent modifications of proteins and also have shed light on the post-translational modification of superoxide dismutase. In this review, we introduce some covalent modifications of superoxide dismutase, nitration, phosphorylation, glutathionylaion, and glycation. Nitration has been the most extensively analyzed modification both in vitro and in vivo. Reaction of human Cu,Zn superoxide dismutase (SOD) with reactive nitrogen species resulted in nitration of a single tryptophan residue to 6-nitrotryptophan, which could be a new biomarker of a formation of reactive nitrogen species. On the other hand, tyrosine 34 of human MnSOD was exclusively nitrated to 3-nitrotyrosine and almost completely inactivated by the reaction with peroxynitrite. The nitrated MnSOD has been found in many diseases caused by ischemia/reperfusion, inflammation, and others and may have a pivotal role in the pathology of the diseases. Most of the post-translational modifications have given rise to a reduced activity of SOD. Since phosphorylation and nitration of SOD have been shown to have a possible reversible process, these modifications may be related to a redox signaling process in cells. Finally we briefly introduce a metal insertion system of SOD, focusing particularly on the iron misincorporation of nSOD, as a part of post-translational modifications.

Effects of the loss of Atox1 on the cellular pharmacology of cisplatin

Previous work has demonstrated that the copper (Cu) transporters Ctr1, Atp7a and Atp7b regulate the cellular pharmacology of cisplatin (CDDP) by mediating its uptake and efflux. It was also shown that, in the process of uptake by Ctr1, CDDP triggers the rapid proteasomal degradation of its own transporter. The current study examined the role of the metallochaperone Atox1 in the regulation of uptake, efflux and subcellular distribution of CDDP by using a pair of fibroblast cell lines established from Atox1(+/+) and Atox1(-/-) mice. Atox1 is a metallochaperone that is known to play a central role in distributing Cu within the cells and was recently shown to act as a Cu-dependent transcription factor. Loss of Atox1 increased Cu accumulation and reduced efflux. In contrast, loss of Atox1 reduced the influx of CDDP and subsequent accumulation in vesicular compartments and in DNA. Loss of Atox1 was found to block the CDDP-induced down regulation of Ctr1. Ctr1 was found to be polyubiquitinated in an Atox1-dependent manner during CDDP exposure. In conclusion, Atox1 is required for the polyubiquitination of Ctr1 and the Ctr1-mediated uptake of CDDP.

Activation of superoxide dismutases: putting the metal to the pedal

Superoxide dismutases (SOD) are important anti-oxidant enzymes that guard against superoxide toxicity. Various SOD enzymes have been characterized that employ either a copper, manganese, iron or nickel co-factor to carry out the disproportionation of superoxide. This review focuses on the copper and manganese forms, with particular emphasis on how the metal is inserted in vivo into the active site of SOD. Copper and manganese SODs diverge greatly in sequence and also in the metal insertion process. The intracellular copper SODs of eukaryotes (SOD1) can obtain copper post-translationally, by way of interactions with the CCS copper chaperone. CCS also oxidizes an intrasubunit disulfide in SOD1. Adventitious oxidation of the disulfide can lead to gross misfolding of immature forms of SOD1, particularly with SOD1 mutants linked to amyotrophic lateral sclerosis. In the case of mitochondrial MnSOD of eukaryotes (SOD2), metal insertion cannot occur post-translationally, but requires new synthesis and mitochondrial import of the SOD2 polypeptide. SOD2 can also bind iron in vivo, but is inactive with iron. Such metal ion mis-incorporation with SOD2 can become prevalent upon disruption of mitochondrial metal homeostasis. Accurate and regulated metallation of copper and manganese SOD molecules is vital to cell survival in an oxygenated environment.

Mitochondrial involvement in genetically determined transition metal toxicity II. Copper toxicity

Copper, like iron, is an essential transition metal ion in which its redox reactivity, whilst essential for the activity of mitochondrial enzymes, can also be a source of harmful reactive oxygen species if not chelated to biomolecules. Therefore, both metals are sequestered by protein chaperones and moved across membranes by protein transporters with the excess held in storage proteins for future use. In the case of copper, the storage proteins in the mitochondria are a distinct ceruloplasmin and metallothionein (MT). If the cell accumulates too much copper or copper is needed by other cells, then copper can be chaperoned to the trans-Golgi secretory compartment where it is transported into the Golgi by ATP-dependent pumps ATP7A/B. In liver, the copper is then incorporated into ceruloplasmin in vesicles that travel to the plasma membrane and release ceruloplasmin into the plasma. This paper reviews the genetic basis for diseases associated with copper deficit or excess, particularly those attributed to defective ATP7A/B transporters, with special emphasis on pathologies related to a loss of mitochondrial function.

The tcrB gene is part of the tcrYAZB operon conferring copper resistance in Enterococcus faecium and Enterococcus faecalis

The plasmid-localized tcrB (transferable copper-resistance gene B) gene from Enterococcus faecium was identified to be part of an operon called the tcrYAZB operon, which has a genetic organization similar to the copYZAB copper-homeostasis gene cluster from Enterococcus hirae. Putative promoter (P(tcr))- and repressor-binding sites highly similar to the E. hirae cop-promoter region were identified upstream of the tcrYAZB genes. The P(tcr) promoter was cloned in both the absence and the presence of the proximal repressor-encoding tcrY gene into a promoter-probe vector. Induction of the promoter was shown in liquid growth medium containing increasing concentrations of copper sulphate. To determine the growth advantage conferred by the tcrYAZB genes in a copper environment, a tcr-deletion mutant was isolated, and its growth was compared with that of its copper-resistant ancestor (strain A17sv1) in sublethal concentrations of copper sulphate. A competition assay using these two isogenic strains showed that copper sulphate concentrations of 3 mmol l(-1) and above are sufficient to select for copper resistance.

Copper-zinc superoxide dismutase and amyotrophic lateral sclerosis

Copper-zinc superoxide dismutase (CuZnSOD, SOD1 protein) is an abundant copper- and zinc-containing protein that is present in the cytosol, nucleus, peroxisomes, and mitochondrial intermembrane space of human cells. Its primary function is to act as an antioxidant enzyme, lowering the steady-state concentration of superoxide, but when mutated, it can also cause disease. Over 100 different mutations have been identified in the sod1 genes of patients diagnosed with the familial form of amyotrophic lateral sclerosis (fALS). These mutations result in a highly diverse group of mutant proteins, some of them very similar to and others enormously different from wild-type SOD1. Despite their differences in properties, each member of this diverse set of mutant proteins causes the same clinical disease, presenting a challenge in formulating hypotheses as to what causes SOD1-associated fALS. In this review, we draw together and summarize information from many laboratories about the characteristics of the individual mutant SOD1 proteins in vivo and in vitro in the hope that it will aid investigators in their search for the cause(s) of SOD1-associated fALS.

NGF promotes copper accumulation required for optimum neurite outgrowth and protein methylation

The role of copper in biological phenomena that involve signal transduction is poorly understood. A well-defined cellular model of neuronal differentiation has been utilized to examine the requirement for copper during nerve growth factor (NGF) signal transduction that results in neurite outgrowth. Experiments demonstrate that NGF increases cellular copper content within 3 days of treatment. Copper chelators reduce the effects of NGF on neurite outgrowth and copper accumulation. The effects of tetraethylene pentamine (TEPA), a copper-specific chelator, are reversible by removal from the culture medium and/or by addition of equimolar copper chloride. Because previous work demonstrated that NGF increases protein methylation in PC12 cells, we examined whether TEPA also inhibits S-adenosylhomocysteine hydrolase (SAHH), an essential copper enzyme involved in all protein methylation reactions. In addition to direct in vitro inhibition of SAHH, we show that TEPA decreases protein arginine methyltransferase 1(PRMT1)-specific enzyme activity in PC12 cells and sympathetic neurons. These data comprise the first biochemical and cellular evidence to address the mechanism of copper involvement in neuronal differentiation.

Binding of copper(I) by the Wilson disease protein and its copper chaperone

The Wilson disease protein (WND) is a transport ATPase involved in copper delivery to the secretory pathway. Mutations in WND and its homolog, the Menkes protein, lead to genetic disorders of copper metabolism. The WND and Menkes proteins are distinguished from other P-type ATPases by the presence of six soluble N-terminal metal-binding domains containing a conserved CXXC metal-binding motif. The exact roles of these domains are not well established, but possible functions include exchanging copper with the metallochaperone Atox1 and mediating copper-responsive cellular relocalization. Although all six domains can bind copper, genetic and biochemical studies indicate that the domains are not functionally equivalent. One way the domains could be tuned to perform different functions is by having different affinities for Cu(I). We have used isothermal titration calorimetry to measure the association constant (K(a)) and stoichiometry (n) values of Cu(I) binding to the WND metal-binding domains and to their metallochaperone Atox1. The association constants for both the chaperone and target domains are approximately 10(5) to 10(6) m(-1), suggesting that the handling of copper by Atox1 and copper transfer between Atox1 and WND are under kinetic rather than thermodynamic control. Although some differences in both n and K(a) values are observed for variant proteins containing less than the full complement of six metal-binding domains, the data for domains 1-6 were best fitted with a single site model. Thus, the individual functions of the six WND metal-binding domains are not conferred by different Cu(I) affinities but instead by fold and electrostatic surface properties.