Affinity gradients drive copper to cellular destinations

Structural aspects of iron‑sulfur protein biogenesis: An NMR view

Over the last decade, structural aspects involving iron‑sulfur (Fe/S) protein biogenesis have played an increasingly important role in understanding the high mechanistic complexity of mitochondrial and cytosolic machineries maturing Fe/S proteins. In this respect, solution NMR has had a significant impact because of its ability to monitor transient protein-protein interactions, which are abundant in the networks of pathways leading to Fe/S cluster biosynthesis and transfer, as well as thanks to the developments of paramagnetic NMR in both terms of new methodologies and accurate data interpretation. Here, we review the use of solution NMR in characterizing the structural aspects of human Fe/S proteins and their interactions in the framework of Fe/S protein biogenesis. We will first present a summary of the recent advances that have been achieved by paramagnetic NMR and then we will focus our attention on the role of solution NMR in the field of human Fe/S protein biogenesis.

Deadly excess copper

Higher eukaryotes' life is impossible without copper redox activity and, literally, every breath we take biochemically demonstrates this. However, this dependence comes at a considerable price to ensure target-oriented copper action. Thereto its uptake, distribution but also excretion are executed by specialized proteins with high affinity for the transition metal. Consequently, malfunction of copper enzymes/transporters, as is the case in hereditary Wilson disease that affects the intracellular copper transporter ATP7B, comes with serious cellular damage. One hallmark of this disease is the progressive copper accumulation, primarily in liver but also brain that becomes deadly if left untreated. Such excess copper toxicity may also result from accidental ingestion or attempted suicide. Recent research has shed new light into the cell-toxic mechanisms and primarily affected intracellular targets and processes of such excess copper that may even be exploited with respect to cancer therapy. Moreover, new therapies are currently under development to fight against deadly toxic copper.

Copper Toxicity in Acidic Phytoplankton: Impacts of Labile Cu Trafficking and Causes of Mitochondria Dysfunction

Most studies on Cu toxicity relied on indirect physicochemical parameters to predict Cu toxicity resulting from adverse impacts. This study presents a systematic and intuitive picture of Cu toxicity induced by exogenous acidification in phytoplankton Chlamydomonas reinhardtii. We first showed that acidification reduced the algal resistance to environmental Cu stress with a decreased growth rate and increased Cu bioaccumulation. To further investigate this phenomenon, we employed specific fluorescent probes to visualize the intracellular labile Cu pools in different algal cells. Our findings indicated that acidification disrupted the intracellular labile Cu trafficking, leading to a significant increase in labile Cu(I) pools. At the molecular level, Cu toxicity resulted in the inhibition of the Cu(I) import system and activation of the Cu(I) export system in acidic algal cells, likely a response to the imbalance in intracellular labile Cu trafficking. Subcellular analysis revealed that Cu toxicity induced extensive mitochondrial dysfunction and impacted the biogenesis and assembly of the respiratory chain complex in acidic algal cells. Concurrently, we proposed that the activation of polyP synthesis could potentially regulate disrupted intracellular labile Cu trafficking. Our study offers an intuitive, multilevel perspective on the origins and impacts of Cu toxicity in living organisms, providing valuable insights on metal toxicity.

Mitochondrial copper overload promotes renal fibrosis via inhibiting pyruvate dehydrogenase activity

Copper is a trace element essential for numerous biological activities, whereas the mitochondria serve as both major sites of intracellular copper utilization and copper reservoir. Here, we investigated the impact of mitochondrial copper overload on the tricarboxylic acid cycle, renal senescence and fibrosis. We found that copper ion levels are significantly elevated in the mitochondria in fibrotic kidney tissues, which are accompanied by reduced pyruvate dehydrogenase (PDH) activity, mitochondrial dysfunction, cellular senescence and renal fibrosis. Conversely, lowering mitochondrial copper levels effectively restore PDH enzyme activity, improve mitochondrial function, mitigate cellular senescence and renal fibrosis. Mechanically, we found that mitochondrial copper could bind directly to lipoylated dihydrolipoamide acetyltransferase (DLAT), the E2 component of the PDH complex, thereby changing the interaction between the subunits of lipoylated DLAT, inducing lipoylated DLAT protein dimerization, and ultimately inhibiting PDH enzyme activity. Collectively, our study indicates that mitochondrial copper overload could inhibit PDH activity, subsequently leading to mitochondrial dysfunction, cellular senescence and renal fibrosis. Reducing mitochondrial copper overload might therefore serve as a strategy to rescue renal fibrosis.

Metabolic Derangement of Essential Transition Metals and Potential Antioxidant Therapies

Essential transition metals have key roles in oxygen transport, neurotransmitter synthesis, nucleic acid repair, cellular structure maintenance and stability, oxidative phosphorylation, and metabolism. The balance between metal deficiency and excess is typically ensured by several extracellular and intracellular mechanisms involved in uptake, distribution, and excretion. However, provoked by either intrinsic or extrinsic factors, excess iron, zinc, copper, or manganese can lead to cellular damage upon chronic or acute exposure, frequently attributed to oxidative stress. Intracellularly, mitochondria are the organelles that require the tightest control concerning reactive oxygen species production, which inevitably leaves them to be one of the most vulnerable targets of metal toxicity. Current therapies to counteract metal overload are focused on chelators, which often cause secondary effects decreasing patients' quality of life. New therapeutic options based on synthetic or natural antioxidants have proven positive effects against metal intoxication. In this review, we briefly address the cellular metabolism of transition metals, consequences of their overload, and current therapies, followed by their potential role in inducing oxidative stress and remedies thereof.

Dysregulated Wnt/β-catenin signaling confers resistance to cuproptosis in cancer cells

Cuproptosis is characterized by the aggregation of lipoylated enzymes of the tricarboxylic acid cycle and subsequent loss of iron-sulfur cluster proteins as a unique copper-dependent form of regulated cell death. As dysregulation of copper homeostasis can induce cuproptosis, there is emerging interest in exploiting cuproptosis for cancer therapy. However, the molecular drivers of cancer cell evasion of cuproptosis were previously undefined. Here, we found that cuproptosis activates the Wnt/β-catenin pathway. Mechanistically, copper binds PDK1 and promotes its interaction with AKT, resulting in activation of the Wnt/β-catenin pathway and cancer stem cell (CSC) properties. Notably, aberrant activation of Wnt/β-catenin signaling conferred resistance of CSCs to cuproptosis. Further studies showed the β-catenin/TCF4 transcriptional complex directly binds the ATP7B promoter, inducing its expression. ATP7B effluxes copper ions, reducing intracellular copper and inhibiting cuproptosis. Knockdown of TCF4 or pharmacological Wnt/β-catenin blockade increased the sensitivity of CSCs to elesclomol-Cu-induced cuproptosis. These findings reveal a link between copper homeostasis regulated by the Wnt/β-catenin pathway and cuproptosis sensitivity, and suggest a precision medicine strategy for cancer treatment through selective cuproptosis induction.

The physiological and pathophysiological roles of copper in the nervous system

Copper is a critical trace element in biological systems due the vast number of essential enzymes that require the metal as a cofactor, including cytochrome c oxidase, superoxide dismutase and dopamine-β-hydroxylase. Due its key role in oxidative metabolism, antioxidant defence and neurotransmitter synthesis, copper is particularly important for neuronal development and proper neuronal function. Moreover, increasing evidence suggests that copper also serves important functions in synaptic and network activity, the regulation of circadian rhythms, and arousal. However, it is important to note that because of copper's ability to redox cycle and generate reactive species, cellular levels of the metal must be tightly regulated to meet cellular needs while avoiding copper-induced oxidative stress. Therefore, it is essential that the intricate system of copper transporters, exporters, copper chaperones and copper trafficking proteins function properly and in coordinate fashion. Indeed, disorders of copper metabolism such as Menkes disease and Wilson disease, as well as diseases linked to dysfunction of copper-requiring enzymes, such as SOD1-linked amyotrophic lateral sclerosis, demonstrate the dramatic neurological consequences of altered copper homeostasis. In this review, we explore the physiological importance of copper in the nervous system as well as pathologies related to improper copper handling.

Protein-Labeling Reagents Selectively Activated by Copper(I)

Copper is an essential trace element that participates in many biological processes through its unique redox cycling between cuprous (Cu+) and cupric (Cu2+) oxidation states. To elucidate the biological functions of copper, chemical biology tools that enable selective visualization and detection of copper ions and proteins in copper-rich environments are required. Herein, we describe the design of Cu+-responsive reagents based on a conditional protein labeling strategy. Upon binding Cu+, the probes generated quinone methide via oxidative bond cleavage, which allowed covalent labeling of surrounding proteins with high Cu+ selectivity. Using gel- and imaging-based analyses, the best-performing probe successfully detected changes in the concentration of labile Cu+ in living cells. Moreover, conditional proteomics analysis suggested intramitochondrial Cu+ accumulation in cells undergoing cuproptosis. Our results highlight the power of Cu+-responsive protein labeling in providing insights into the molecular mechanisms of Cu+ metabolism and homeostasis.

Interlayer manipulation of bio-inspired Ti3C2Tx nanocontainer through intercalation of amino acid molecules to dramatically boosting uranyl hijacking capability from seawater

More than 4.5 billion tons of unconventional uranium resources [UO2(CO3)3]4- are uniformly dissolved in seawater, providing a sustainable and abundant fuel source for the development of nuclear energy. Herein, we presented a rational design and development of Ti3C2Tx nanocontainer inspired by the exceptional selectivity and affinity exhibited by superb-uranyl proteins through amino acid intercalation. The amino acid intercalation of Ti3C2Tx demonstrated exceptional UO22+ capture capacity (Arg-Ti3C2Tx, His-Ti3C2Tx, and Lys-Ti3C2Tx with qmax values of 594.46, 846.04, and 1030.17 mg/g). Furthermore, these intercalated materials exhibited remarkable sequestration efficiency and selectivity (Uinitial = ∼45.2 ∼7636 μg/L; ∼84.45% ∼98.08%; and ∼2.72 ×104 ∼1.28 ×105 KdU value), despite the presence of an overwhelming surplus of Na+, Ca2+, Mg2+, and Co2+ ions. Significantly, even in the 0.3 M NaHCO3 solution and surpassing 103-fold of the Na3VO4 system, the adsorption efficiency of Lys-Ti3C2Tx still achieved a remarkable 63.73% and 65.05%. Moreover, the Lys-Ti3C2Tx can extract ∼30.23 ∼8664.03 μg/g uranium after 24 h contact in ∼13.3 ∼5000 μg/L concentration from uranium-spiked natural seawater. The mechanism analysis revealed that the high binding capability can be attributed to the chelation of carboxyl and amino groups with uranyl ions. This innovative state-of-the-art approach in regulating uranium harvesting capability through intercalation of amino acid molecules provides novel insights for extracting uranium from seawater.

A Unique Approach: Biomimetic Graphdiyne-Based Nanoplatform to Treat Prostate Cancer by Combining Cuproptosis and Enhanced Chemodynamic Therapy

Purpose

Current treatment approaches for Prostate cancer (PCa) often come with debilitating side effects and limited therapeutic outcomes. There is urgent need for an alternative effective and safe treatment for PCa.

Methods

We developed a nanoplatform to target prostate cancer cells based on graphdiyne (GDY) and a copper-based metal-organic framework (GDY-CuMOF), that carries the chemotherapy drug doxorubicin (DOX) for cancer treatment. Moreover, to provide GDY-CuMOF@DOX with homotypic targeting capability, we coated the PCa cell membrane (DU145 cell membrane, DCM) onto the surface of GDY-CuMOF@DOX, thus obtaining a biomimetic nanoplatform (DCM@GDY-CuMOF@DOX). The nanoplatform was characterized by using transmission electron microscope, atomic force microscope, X-ray diffraction, etc. Drug release behavior, antitumor effects in vivo and in vitro, and biosafety of the nanoplatform were evaluated.

Results

We found that GDY-CuMOF exhibited a remarkable capability to load DOX mainly through π-conjugation and pore adsorption, and it responsively released DOX and generated Cu+ in the presence of glutathione (GSH). In vivo experiments demonstrated that this nanoplatform exhibits remarkable cell-killing efficiency by generating lethal reactive oxygen species (ROS) and mediating cuproptosis. In addition, DCM@GDY-CuMOF@DOX effectively suppresses tumor growth in vivo without causing any apparent side effects.

Conclusion

The constructed DCM@GDY-CuMOF@DOX nanoplatform integrates tumor targeting, drug-responsive release and combination with cuproptosis and chemodynamic therapy, offering insights for further biomedical research on efficient PCa treatment.

Tracking mitochondrial Cu(I) fluctuations through a ratiometric fluorescent probe in AD model cells: Towards understanding how AβOs induce mitochondrial Cu(I) dyshomeostasis

Mitochondrial copper signaling pathway plays a role in Alzheimer's disease (AD), especially in relevant Amyloid-β oligomers (AβOs) neurotoxicity and mitochondrial dysfunction. Clarifying the relationship between mitochondrial copper homeostasis and both of mitochondrial dysfunction and AβOs neurotoxicity is important for understanding AD pathogenesis. Herein, we designed and synthesized a ratiometric fluorescent probe CHC-NS4 for Cu(I). CHC-NS4 possesses excellent ratiometric response, high selectivity to Cu(I) and specific ability to target mitochondria. Under mitochondrial dysfunction induced by oligomycin, mitochondrial Cu(I) levels gradually increased, which may be related to inhibition of ATP7A-mediated Cu(I) exportation and/or high expression of COX. On this basis, CHC-NS4 was further utilized to visualize the fluctuations of mitochondrial Cu(I) levels during progression of AD model cells induced by AβOs. It was found that mitochondrial Cu(I) levels were gradually elevated during the AD progression, which depended on not only AβOs concentration but also incubation time. Moreover, endocytosis maybe served as a prime pathway mode for mitochondrial Cu(I) dyshomeostasis induced by AβOs during AD progression. These results have provided a novel inspiration into mitochondrial copper biology in AD pathogenesis.

MEMO1 binds iron and modulates iron homeostasis in cancer cells

Mediator of ERBB2-driven cell motility 1 (MEMO1) is an evolutionary conserved protein implicated in many biological processes; however, its primary molecular function remains unknown. Importantly, MEMO1 is overexpressed in many types of cancer and was shown to modulate breast cancer metastasis through altered cell motility. To better understand the function of MEMO1 in cancer cells, we analyzed genetic interactions of MEMO1 using gene essentiality data from 1028 cancer cell lines and found multiple iron-related genes exhibiting genetic relationships with MEMO1. We experimentally confirmed several interactions between MEMO1 and iron-related proteins in living cells, most notably, transferrin receptor 2 (TFR2), mitoferrin-2 (SLC25A28), and the global iron response regulator IRP1 (ACO1). These interactions indicate that cells with high-MEMO1 expression levels are hypersensitive to the disruptions in iron distribution. Our data also indicate that MEMO1 is involved in ferroptosis and is linked to iron supply to mitochondria. We have found that purified MEMO1 binds iron with high affinity under redox conditions mimicking intracellular environment and solved MEMO1 structures in complex with iron and copper. Our work reveals that the iron coordination mode in MEMO1 is very similar to that of iron-containing extradiol dioxygenases, which also display a similar structural fold. We conclude that MEMO1 is an iron-binding protein that modulates iron homeostasis in cancer cells.

Coupling of zinc and GTP binding drives G-domain folding in Acinetobacter baumannii ZigA

COG0523 proteins, also known as nucleotide-dependent metallochaperones, are a poorly understood class of small P-loop G3E GTPases. Multiple family members play critical roles in bacterial pathogen survival during an infection as part of the adaptive response to host-mediated "nutritional immunity." Our understanding of the structure, dynamics, and molecular-level function of COG0523 proteins, apart from the eukaryotic homolog, Zng1, remains in its infancy. Here, we use X-ray absorption spectroscopy to establish that Acinetobacter baumannii (Ab) ZigA coordinates ZnII using all three cysteines derived from the invariant CXCC motif to form an S3(N/O) coordination complex, a feature inconsistent with the ZnII-bound crystal structure of a distantly related COG0523 protein of unknown function from Escherichia coli, EcYjiA. The binding of ZnII and guanine nucleotides is thermodynamically linked in AbZigA, and this linkage is more favorable for the substrate GTP relative to the product GDP. Part of this coupling originates with nucleotide-induced stabilization of the G-domain tertiary structure as revealed by global thermodynamics measurements and hydrogen-deuterium exchange mass spectrometry (HDX-MS). HDX-MS also reveals that the HDX behavior of the G2 (switch 1) loop is highly sensitive to nucleotide status and becomes more exchange labile in the GDP (product)-bound state. Significant long-range perturbation of local stability in both the G-domain and the C-terminal domain define a candidate binding pocket for a client protein that appears sensitive to nucleotide status (GDP versus GTP). We place these new insights into the structure, dynamics, and energetics of intermolecular metal transfer into the context of a model for AbZigA metallochaperone function.

Dynamic Regulation of Intracellular Labile Cu(I)/Cu(II) Cycle in Microalgae Chlamydomonas reinhardtii: Disrupting the Balance by Cu Stress

The labile metal pool involved in intracellular trafficking and homeostasis is the portion susceptible to environmental stress. Herein, we visualized the different intracellular distributions of labile Cu(I) and Cu(II) pools in the alga Chlamydomonas reinhardtii. We first demonstrated that labile Cu(I) predominantly accumulated in the granules within the cytoplasmic matrix, whereas the labile Cu(II) pool primarily localized in the pyrenoid and chloroplast. The cell cycle played an integral role in balancing the labile Cu(I)/Cu(II) pools. Specifically, the labile Cu(II) pool primarily accumulated during the SM phase following cell division, while the labile Cu(I) pool dynamically changed during the G phase as cell size increased. Notably, the labile Cu(II) pool in algae at the SM stage exhibited heightened sensitivity to environmental Cu stress. Exogenous Cu stress disrupted the intracellular labile Cu(I)/Cu(II) cycle and balance, causing a shift toward the labile Cu(II) pool. Our proteomic analysis further identified a putative cupric reductase, potentially capable of reducing Cu(II) to Cu(I), and four putative multicopper oxidases, potentially capable of oxidizing Cu(I) to Cu(II), which may be involved in the conversion between the labile Cu(I) pool and labile Cu(II) pool. Our study elucidated a dynamic cycle of the intracellular labile Cu(I)/Cu(II) pools, which were accessible and responsive to environmental changes.

Role of Explicit Solvation in Computational Modeling of Chemical Reactions: Mechanism of Cu(I) Transfer Between Thiolate-Based Chelators in Water

Solvation plays important roles in controlling the thermodynamic and kinetic aspects of chemical reactions. The conventional approaches to treat solvation via electronic structure methods are likely to become inadequate, when the reacting solutes have strong electrostatic and hydrogen bonding interactions with the solvent and undergo significant structural changes during the course of the reaction. In this article, we present evidence of such solvent and structural effects in the computational study of the Cu(I) transfer reaction between thiolate-based chelators dithiobutylamine (DTBA) and dithiotheritol (DTT) in water, inspired from biological copper trafficking phenomena. We propose a general solution to the problem by combining classical molecular dynamics (MD) simulations of the bulk system and static quantum chemistry calculations. The fluctuating solvation shell was estimated from MD, and energetics was assessed by averaging QM energies of a series of molecular clusters constructed from the MD snapshots. Applying this approach, we propose a reaction pathway with estimates of relative intermediate stabilities and barriers, which suggest the overall reaction to be reversible in nature and likely to go through both two and three coordinated intermediates, confirming previous studies of similar protein analogues. An interesting fact that emerged from our study was the strong indication that the rate-determining step is the deprotonation of initial thiol bound Cu(I) complex, without involving any Cu(I)-S bonds. The proposed method will lead to a better treatment of solvations, and these mechanistic insights will aid our understanding of biological copper(I) trafficking.

Evidence for disrupted copper availability in human spinal cord supports CuII(atsm) as a treatment option for sporadic cases of ALS

The copper compound CuII(atsm) has progressed to phase 2/3 testing for treatment of the neurodegenerative disease amyotrophic lateral sclerosis (ALS). CuII(atsm) is neuroprotective in mutant SOD1 mouse models of ALS where its activity is ascribed in part to improving availability of essential copper. However, SOD1 mutations cause only ~ 2% of ALS cases and therapeutic relevance of copper availability in sporadic ALS is unresolved. Herein we assessed spinal cord tissue from human cases of sporadic ALS for copper-related changes. We found that when compared to control cases the natural distribution of spinal cord copper was disrupted in sporadic ALS. A standout feature was decreased copper levels in the ventral grey matter, the primary anatomical site of neuronal loss in ALS. Altered expression of genes involved in copper handling indicated disrupted copper availability, and this was evident in decreased copper-dependent ferroxidase activity despite increased abundance of the ferroxidases ceruloplasmin and hephaestin. Mice expressing mutant SOD1 recapitulate salient features of ALS and the unsatiated requirement for copper in these mice is a biochemical target for CuII(atsm). Our results from human spinal cord indicate a therapeutic mechanism of action for CuII(atsm) involving copper availability may also be pertinent to sporadic cases of ALS.

Metabolic energy decline coupled dysregulation of catecholamine metabolism in physiologically highly active neurons: implications for selective neuronal death in Parkinson's disease

Parkinson's disease (PD) is an age-related irreversible neurodegenerative disease which is characterized as a progressively worsening involuntary movement disorder caused by the loss of dopaminergic (DA) neurons in substantia nigra pars compacta (SNpc). Two main pathophysiological features of PD are the accumulation of inclusion bodies in the affected neurons and the predominant loss of neuromelanin-containing DA neurons in substantia nigra pars compacta (SNpc) and noradrenergic (NE) neurons in locus coeruleus (LC). The inclusion bodies contain misfolded and aggregated α-synuclein (α-Syn) fibrils known as Lewy bodies. The etiology and pathogenic mechanisms of PD are complex, multi-dimensional and associated with a combination of environmental, genetic, and other age-related factors. Although individual factors associated with the pathogenic mechanisms of PD have been widely investigated, an integration of the findings to a unified causative mechanism has not been envisioned. Here we propose an integrated mechanism for the degeneration of DA neurons in SNpc and NE neurons in LC in PD, based on their unique high metabolic activity coupled elevated energy demand, using currently available experimental data. The proposed hypothetical mechanism is primarily based on the unique high metabolic activity coupled elevated energy demand of these neurons. We reason that the high vulnerability of a selective group of DA neurons in SNpc and NE neurons in LC in PD could be due to the cellular energy modulations. Such cellular energy modulations could induce dysregulation of DA and NE metabolism and perturbation of the redox active metal homeostasis (especially copper and iron) in these neurons.

Dysfunction in atox-1 and ceruloplasmin alters labile Cu levels and consequently Cu homeostasis in C. elegans

Copper (Cu) is an essential trace element, however an excess is toxic due to its redox properties. Cu homeostasis therefore needs to be tightly regulated via cellular transporters, storage proteins and exporters. An imbalance in Cu homeostasis has been associated with neurodegenerative disorders such as Wilson's disease, but also Alzheimer's or Parkinson's disease. In our current study, we explored the utility of using Caenorhabditis elegans (C. elegans) as a model of Cu dyshomeostasis. The application of excess Cu dosing and the use of mutants lacking the intracellular Cu chaperone atox-1 and major Cu storage protein ceruloplasmin facilitated the assessment of Cu status, functional markers including total Cu levels, labile Cu levels, Cu distribution and the gene expression of homeostasis-related genes. Our data revealed a decrease in total Cu uptake but an increase in labile Cu levels due to genetic dysfunction, as well as altered gene expression levels of Cu homeostasis-associated genes. In addition, the data uncovered the role ceruloplasmin and atox-1 play in the worm's Cu homeostasis. This study provides insights into suitable functional Cu markers and Cu homeostasis in C. elegans, with a focus on labile Cu levels, a promising marker of Cu dysregulation during disease progression.

Structural motifs in the early metallation steps of Zn(II) and Cd(II) binding to apo-metallothionein 1a

Many proteins require a metal cofactor to function and these metals are often involved in the protein folding process. The protein metallothionein (MT) has a dynamic structure capable of binding to a variety of metals with different stoichiometries. The most well-understood structure is the seven-metal, two domain structure formed upon metallation using Zn(II) or Cd(II). However, the partially metallated states and the pathways to form these clusters are less well-understood, although it is known that the pathways are pH dependent. Using stopped flow methods, it is shown that the metallation rates of the less cooperative Zn(II) binding pathway is much more impacted by low pH conditions that that of the more cooperative Cd(II) binding pathway. Electrospray ionization mass spectrometry (ESI-MS) methods reveal specific mixtures of bridging and terminally bound MxSy structures form in the first few metallation steps. Using a combination of methods, the data show that the result of unfolding this intrinsically disordered apo-MT structure using guanidinium chloride is that the formation of preliminary bridging structures that form in the first few metallation steps is impeded. The data show that more terminally bound structures form. Our conclusion is that the compact conformation of the native apo-MT at physiological pH allows for rapid formation of complex metal-thiolate structures with high affinity that provides protection from oxidation, a function that is suppressed upon unfolding. Overall, these results highlight both the importance of the apo-MT structure in the metallation pathway, but also the differences in Zn(II) and Cd(II) binding under different conditions.

Copper regulates the host innate immune response against bacterial infection via activation of ALPK1 kinase

Copper is an essential trace element for the human body, and its requirement for optimistic immune functions has been recognized for decades. How copper is involved in the innate immune pathway, however, remains to be clarified. Here, we report that copper serves as a signal molecule to regulate the kinase activity of alpha-kinase 1 (ALPK1), a cytosolic pattern-recognition receptor (PRR), and therefore promotes host cell defense against bacterial infection. We show that in response to infection, host cells actively accumulate copper in the cytosol, and the accumulated cytosolic copper enhances host cell defense against evading pathogens, including intracellular and, unexpectedly, extracellular bacteria. Subsequently, we demonstrate that copper activates the innate immune pathway of host cells in an ALPK1-dependent manner. Further mechanistic studies reveal that copper binds to ALPK1 directly and is essential for the kinase activity of this cytosolic PRR. Moreover, the binding of copper to ALPK1 enhances the sensitivity of ALPK1 to the bacterial metabolite ADP-heptose and eventually prompts host cells to elicit an enhanced immune response during bacterial infection. Finally, using a zebrafish in vivo model, we show that a copper-treated host shows an increased production of proinflammatory cytokines, enhanced recruitment of phagosome cells, and promoted bacterial clearance. Our findings uncover a previously unrecognized role of copper in the modulation of host innate immune response against bacterial pathogens and advance our knowledge on the cross talk between cytosolic copper homeostasis and immune system.

Discovery of an unusual copper homeostatic mechanism in yeast cells respiring on minimal medium and an unexpectedly diverse labile copper pool

Copper is essential for all eukaryotic cells but many details of how it is trafficked within the cell and how it is homeostatically regulated remain uncertain. Here, we characterized the copper content of cytosol and mitochondria using liquid chromatography with ICP-MS detection. Chromatograms of cytosol exhibited over two dozen peaks due to copper proteins and coordination complexes. Yeast cells respiring on minimal media did not regulate copper import as media copper concentration increased; rather, they imported copper at increasing rates while simultaneously increasing the expression of metallothionein CUP1 which then sequestered most of the excessive imported copper. Peak intensities due to superoxide dismutase SOD1, other copper proteins, and numerous coordination complexes also increased, but not as drastically. The labile copper pool was unexpectedly diverse and divided into two groups. One group approximately comigrated with copper-glutathione, -cysteine, and -histidine standards; the other developed only at high media copper concentrations and at greater elution volumes. Most cytosolic copper arose from copper-bound proteins, especially CUP1. Cytosol contained an unexpectedly high percentage of apo-copper proteins and apo-coordination complexes. Copper-bound forms of non-CUP1 proteins and complexes coexisted with apo-CUP1 and with the chelator BCS. Both experiments suggest unexpectedly stable-binding copper proteins and coordination complexes in cytosol. COX17Δ cytosol chromatograms were like those of WT cells. Chromatograms of soluble mitochondrial extracts were obtained, and mitoplasting helped distinguish copper species in the intermembrane space versus in the matrix/inner membrane. Issues involving the yeast copperome, copper homeostasis, labile copper pool, and copper trafficking are discussed.

Investigation of NO Role in Neural Tissue in Brain and Spinal Cord Injury

Nitric oxide (NO) production in injured and intact brain regions was compared by EPR spectroscopy in a model of brain and spinal cord injury in Wistar rats. The precentral gyrus of the brain was injured, followed by the spinal cord at the level of the first lumbar vertebra. Seven days after brain injury, a reduction in NO content of 84% in injured brain regions and 66% in intact brain regions was found. The difference in NO production in injured and uninjured brain regions persisted 7 days after injury. The copper content in the brain remained unchanged one week after modeling of brain and spinal cord injury. The data obtained in the experiments help to explain the problems in the therapy of patients with combined brain injury.

Copper trafficking systems in cells: insights into coordination chemistry and toxicity

Transition metal ions, such as copper, are indispensable components in the biological system. Copper ions which primarily exist in two major oxidation states Cu(I) and Cu(II) play crucial roles in various cellular processes including antioxidant defense, biosynthesis of neurotransmitters, and energy metabolism, owing to their inherent redox activity. The disturbance in copper homeostasis can contribute to the development of copper metabolism disorders, cancer, and neurodegenerative diseases, highlighting the significance of understanding the copper trafficking system in cellular environments. This review aims to offer a comprehensive overview of copper homeostatic machinery, with an emphasis on the coordination chemistry of copper transporters and trafficking proteins. While copper chaperones and the corresponding metalloenzymes are thoroughly discussed, we also explore the potential existence of low-molecular-mass metal complexes within cellular systems. Furthermore, we summarize the toxicity mechanisms originating from copper deficiency or accumulation, which include the dysregulation of oxidative stress, signaling pathways, signal transduction, and amyloidosis. This perspective review delves into the current knowledge regarding the intricate aspects of the copper trafficking system, providing valuable insights into potential treatment strategies from the standpoint of bioinorganic chemistry.

Cuproptosis: Harnessing Transition Metal for Cancer Therapy

Transition metal elements, such as copper, play diverse and pivotal roles in oncology. They act as constituents of metalloenzymes involved in cellular metabolism, function as signaling molecules to regulate the proliferation and metastasis of tumors, and are integral components of metal-based anticancer drugs. Notably, recent research reveals that excessive copper can also modulate the occurrence of programmed cell death (PCD), known as cuprotosis, in cancer cells. This modulation occurs through the disruption of tumor cell metabolism and the induction of proteotoxic stress. This discovery uncovers a mode of interaction between transition metals and proteins, emphasizing the intricate link between copper homeostasis and tumor metabolism. Moreover, they provide innovative therapeutic strategies for the precise diagnosis and treatment of malignant tumors. At the crossroads of chemistry and oncology, we undertake a comprehensive review of copper homeostasis in tumors, elucidating the molecular mechanisms underpinning cuproptosis. Additionally, we summarize current nanotherapeutic approaches that target cuproptosis and provide an overview of the available laboratory and clinical methods for monitoring this process. In the context of emerging concepts, challenges, and opportunities, we emphasize the significant potential of nanotechnology in the advancement of this field.

α-lipoic acid ameliorates consequences of copper overload by up-regulating selenoproteins and decreasing redox misbalance

α-lipoic acid (LA) is an essential cofactor for mitochondrial dehydrogenases and is required for cell growth, metabolic fuel production, and antioxidant defense. In vitro, LA binds copper (Cu) with high affinity and as an endogenous membrane permeable metabolite could be advantageous in mitigating the consequences of Cu overload in human diseases. We tested this hypothesis in 3T3-L1 preadipocytes with inactivated Cu transporter Atp7a; these cells accumulate Cu and show morphologic changes and mitochondria impairment. Treatment with LA corrected the morphology of Atp7a-/- cells similar to the Cu chelator bathocuproinedisulfonate (BCS) and improved mitochondria function; however, the mechanisms of LA and BCS action were different. Unlike BCS, LA did not decrease intracellular Cu but instead increased selenium levels that were low in Atp7a-/- cells. Proteome analysis confirmed distinct cell responses to these compounds and identified upregulation of selenoproteins as the major effect of LA on preadipocytes. Upregulation of selenoproteins was associated with an improved GSH:GSSG ratio in cellular compartments, which was lowered by elevated Cu, and reversal of protein oxidation. Thus, LA diminishes toxic effects of elevated Cu by improving cellular redox environment. We also show that selenium levels are decreased in tissues of a Wilson disease animal model, especially in the liver, making LA an attractive candidate for supplemental treatment of this disease.

Moving metals: How microbes deliver metal cofactors to metalloproteins

First row d-block metal ions serve as vital cofactors for numerous essential enzymes and are therefore required nutrients for all forms of life. Despite this requirement, excess free transition metals are toxic. Free metal ions participate in the production of noxious reactive oxygen species and mis-metalate metalloproteins, rendering enzymes catalytically inactive. Thus, bacteria require systems to ensure metalloproteins are properly loaded with cognate metal ions to maintain protein function, while avoiding metal-mediated cellular toxicity. In this perspective we summarize the current mechanistic understanding of bacterial metallocenter maturation with specific emphasis on metallochaperones; a group of specialized proteins that both shield metal ions from inadvertent reactions and distribute them to cognate target metalloproteins. We highlight several recent advances in the field that have implicated new classes of proteins in the distribution of metal ions within bacterial proteins, while speculating on the future of the field of bacterial metallobiology.

Copper induces neuron-sparing, ferredoxin 1-independent astrocyte toxicity mediated by oxidative stress

Copper is an essential enzyme cofactor in oxidative metabolism, anti-oxidant defenses, and neurotransmitter synthesis. However, intracellular copper, when improperly buffered, can also lead to cell death. Given the growing interest in the use of copper in the presence of the ionophore elesclomol (CuES) for the treatment of gliomas, we investigated the effect of this compound on the surround parenchyma-namely neurons and astrocytes in vitro. Here, we show that astrocytes were highly sensitive to CuES toxicity while neurons were surprisingly resistant, a vulnerability profile that is opposite of what has been described for zinc and other toxins. Bolstering these findings, a human astrocytic cell line was similarly sensitive to CuES. Modifications of cellular metabolic pathways implicated in cuproptosis, a form of copper-regulated cell death, such as inhibition of mitochondrial respiration or knock-down of ferredoxin 1 (FDX1), did not block CuES toxicity to astrocytes. CuES toxicity was also unaffected by inhibitors of apoptosis, necrosis or ferroptosis. However, we did detect the presence of lipid peroxidation products in CuES-treated astrocytes, indicating that oxidative stress is a mediator of CuES-induced glial toxicity. Indeed, treatment with anti-oxidants mitigated CuES-induced cell death in astrocytes indicating that oxidative stress is a mediator of CuES-induced glial toxicity. Lastly, prior induction of metallothioneins 1 and 2 in astrocytes with zinc plus pyrithione was strikingly protective against CuES toxicity. As neurons express high levels of metallothioneins basally, these results may partially account for their resistance to CuES toxicity. These results demonstrate a unique toxic response to copper in glial cells which contrasts with the cell selectivity profile of zinc, another biologically relevant metal.

Biochemical and Molecular Pathways in Neurodegenerative Diseases: An Integrated View

Neurodegenerative diseases (NDDs) like Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) are defined by a myriad of complex aetiologies. Understanding the common biochemical molecular pathologies among NDDs gives an opportunity to decipher the overlapping and numerous cross-talk mechanisms of neurodegeneration. Numerous interrelated pathways lead to the progression of neurodegeneration. We present evidence from the past pieces of literature for the most usual global convergent hallmarks like ageing, oxidative stress, excitotoxicity-induced calcium butterfly effect, defective proteostasis including chaperones, autophagy, mitophagy, and proteosome networks, and neuroinflammation. Herein, we applied a holistic approach to identify and represent the shared mechanism across NDDs. Further, we believe that this approach could be helpful in identifying key modulators across NDDs, with a particular focus on AD, PD, and ALS. Moreover, these concepts could be applied to the development and diagnosis of novel strategies for diverse NDDs.

Cu(I) binds to Zn7-MT2 via two parallel pathways

Metallothionein proteins are essential for Cu(I) and Zn(II) homeostasis as well as heavy metal detoxification. The metallation properties of MT2 are of great interest due to their wide patterns of expression and correlation with multiple diseases including cancers, neurological disorders, and respiratory diseases. Use of isotopically pure 63Cu(I) and 68Zn(II) eliminates the complexity of the Cu, Zn-MT2 mass spectral peaks due to significant overlap of naturally abundant isotopes. This allows for the resolution of the precise Cu(I) and Zn(II) stoichiometries when both Cu(I) and Zn(II) are bound to MT2 at physiological pH as expected in vivo. Exact Cu: Zn ratios were determined from mass spectral simulations carried out for every point in the titration. We report that Cu(I) metallation of Zn7-MT2 can only be understood in terms of two pathways occurring in parallel with pathway ① resulting in Cu5Zn5-MT2 and Cu9Zn3-MT2. Pathway ② results in Cu6Zn4-MT2 and Cu10Zn2-MT2, which are the major products of the reaction. From the electrospray ionization (ESI)-mass spectral data we report a series of formation constants (KF) for species starting from Zn7-MT2 up to Cu11Zn2-MT2. Room temperature phosphorescence and circular dichroism (CD) spectra were measured in parallel with the ESI-mass spectrometry data allowing for the assignment of specific species to specific spectral bands. Through analysis of the CD spectral bands, we propose that Cu(I) binds to the β domain first to form a Cu5Zn1 cluster or Cu6 cluster with emission at 670 and 750 nm, respectively, leaving the Zn4 cluster in the α domain.

Metallothionein-3: 63 Cu(I) binds to human 68 Zn7 -βα MT3 with no preference for Cu4 -β cluster formation

Human metallothioneins (MTs) are involved in binding the essential elements, Cu(I) and Zn(II), and the toxic element, Cd(II), in metal-thiolate clusters using 20 reduced cysteines. The brain-specific MT3 binds a mixture of Cu(I) and Zn(II) in vivo. Its metallation properties are critically important because of potential connections between Cu, Zn and neurodegenerative diseases. We report that the use of isotopically pure 63 Cu(I) and 68 Zn(II) greatly enhances the element resolution in the ESI-mass spectral data revealing species with differing Cu:Zn ratios but the same total number of metals. Room temperature phosphorescence and circular dichroism spectral data measured in parallel with ESI-mass spectral data identified the presence of specific Cu(I)-thiolate clusters in the presence of Zn(II). A series of Cu(I)-thiolate clusters form following Cu(I) addition to apo MT3: the two main clusters that form are a Cu6 cluster in the β domain followed by a Cu4 cluster in the α domain. 63 Cu(I) addition to 68 Zn7 -MT3 results in multiple species, including clustered Cu5 Zn5 -MT3 and Cu9 Zn3 -MT3. We assign the domain location of the metals for Cu5 Zn5 -MT3 as a Cu5 Zn1 -β cluster and a Zn4 -α cluster and for Cu9 Zn3 -MT3 as a Cu6 -β cluster and a Cu3 Zn3 -α cluster. While many reports of the average MT3 metal content exist, determining the exact Cu,Zn stoichiometry has proven very difficult even with native ESI-MS. The work in this paper solves the ambiguity introduced by the overlap of the naturally abundant Cu(I) and Zn(II) isotopes. Contrary to other reports, there is no indication of a major fraction of Cu4 -β-Znn -α-MT3 forming.

Self-Assembled Copper-Based Nanoparticles for Glutathione Activated and Enzymatic Cascade-Enhanced Ferroptosis and Immunotherapy in Cancer Treatment

As an emerging cancer treatment strategy, ferroptosis is greatly restricted by excessive glutathione (GSH) in tumor microenvironment (TME) and low reactive oxygen species (ROS) generation efficiency. Here, this work designs self-assembled copper-alanine nanoparticles (CACG) loaded with glucose oxidase (GOx) and cinnamaldehyde (Cin) for in situ glutathione activated and enzymatic cascade-enhanced ferroptosis and immunotherapy. In response to GSH-rich and acidic TME, CACG allows to effectively co-deliver Cu2+ , Cin, and GOx into tumors. Released Cin consumes GSH through Michael addition, accompanying with the reduction of Cu2+ into Cu+ for further GSH depletion. With the cascade of Cu+ -catalyzed Fenton reactions and enzyme-catalyzed reactions by GOx, CACG could get rid of the restriction of insufficient hydrogen peroxide in TME, leading to a robust and constant generation of ROS. With the high efficiency of GSH depletion and ROS production, ferroptosis is significantly enhanced by CACG in vivo. Moreover, elevated oxidative stress triggers robust immune responses by promoting dendritic cells maturation and T cell infiltration. The in vivo results prove that CACG could efficiently inhibit tumor growth in 4T1 tumor-bearing mouse model without causing obvious systemic toxicity, suggesting the great potential of CACG in enhancing ferroptosis and immunotherapy for effective cancer treatment.

ARBM101 (Methanobactin SB2) Drains Excess Liver Copper via Biliary Excretion in Wilson's Disease Rats

BACKGROUND & AIMS

Excess copper causes hepatocyte death in hereditary Wilson's disease (WD). Current WD treatments by copper-binding chelators may gradually reduce copper overload; they fail, however, to bring hepatic copper close to normal physiological levels. Consequently, lifelong daily dose regimens are required to hinder disease progression. This may result in severe issues due to nonadherence or unwanted adverse drug reactions and also due to drug switching and ultimate treatment failures. This study comparatively tested bacteria-derived copper binding agents-methanobactins (MBs)-for efficient liver copper depletion in WD rats as well as their safety and effect duration.

METHODS

Copper chelators were tested in vitro and in vivo in WD rats. Metabolic cage housing allowed the accurate assessment of animal copper balances and long-term experiments related to the determination of minimal treatment phases.

RESULTS

We found that copper-binding ARBM101 (previously known as MB-SB2) depletes WD rat liver copper dose dependently via fecal excretion down to normal physiological levels within 8 days, superseding the need for continuous treatment. Consequently, we developed a new treatment consisting of repetitive cycles, each of ∼1 week of ARBM101 applications, followed by months of in-between treatment pauses to ensure a healthy long-term survival in WD rats.

CONCLUSIONS

ARBM101 safely and efficiently depletes excess liver copper from WD rats, thus allowing for short treatment periods as well as prolonged in-between rest periods.

Two Distinct Thermodynamic Gradients for Cellular Metalation of Vitamin B12

The acquisition of Co^II by the corrin component of vitamin B₁₂ follows one of two distinct pathways, referred to as early or late Co^II insertion. The late insertion pathway exploits a Co^II metallochaperone (CobW) from the COG0523 family of G3E GTPases, while the early insertion pathway does not. This provides an opportunity to contrast the thermodynamics of metalation in a metallochaperone-requiring and a metallochaperone-independent pathway. In the metallochaperone-independent route, sirohydrochlorin (SHC) associates with the CbiK chelatase to form Co^II-SHC. Co^II-buffered enzymatic assays indicate that SHC binding enhances the thermodynamic gradient for Co^II transfer from the cytosol to CbiK. In the metallochaperone-dependent pathway, hydrogenobyrinic acid a,c-diamide (HBAD) associates with the CobNST chelatase to form Co^II-HBAD. Here, Co^II-buffered enzymatic assays indicate that Co^II transfer from the cytosol to HBAD-CobNST must somehow traverse a highly unfavorable thermodynamic gradient for Co^II binding. Notably, there is a favorable gradient for Co^II transfer from the cytosol to the Mg^IIGTP-CobW metallochaperone, but further transfer of Co^II from the GTP-bound metallochaperone to the HBAD-CobNST chelatase complex is thermodynamically unfavorable. However, after nucleotide hydrolysis, Co^II transfer from the chaperone to the chelatase complex is calculated to become favorable. These data reveal that the CobW metallochaperone can overcome an unfavorable thermodynamic gradient for Co^II transfer from the cytosol to the chelatase by coupling this process to GTP hydrolysis.

Full Copper Resistance in Cupriavidus metallidurans Requires the Interplay of Many Resistance Systems

The metal-resistant bacterium Cupriavidus metallidurans uses its copper resistance components to survive the synergistic toxicity of copper ions and gold complexes in auriferous soils. The cup, cop, cus, and gig determinants encode as central component the Cu(I)-exporting P_IB1-type ATPase CupA, the periplasmic Cu(I)-oxidase CopA, the transenvelope efflux system CusCBA, and the Gig system with unknown function, respectively. The interplay of these systems with each other and with glutathione (GSH) was analyzed. Copper resistance in single and multiple mutants up to the quintuple mutant was characterized in dose-response curves, Live/Dead-staining, and atomic copper and glutathione content of the cells. The regulation of the cus and gig determinants was studied using reporter gene fusions and in case of gig also RT-PCR studies, which verified the operon structure of gigPABT. All five systems contributed to copper resistance in the order of importance: Cup, Cop, Cus, GSH, and Gig. Only Cup was able to increase copper resistance of the Δcop Δcup Δcus Δgig ΔgshA quintuple mutant but the other systems were required to increase copper resistance of the Δcop Δcus Δgig ΔgshA quadruple mutant to the parent level. Removal of the Cop system resulted in a clear decrease of copper resistance in most strain backgrounds. Cus cooperated with and partially substituted Cop. Gig and GSH cooperated with Cop, Cus, and Cup. Copper resistance is thus the result of an interplay of many systems. IMPORTANCE The ability of bacteria to maintain homeostasis of the essential-but-toxic "Janus"-faced element copper is important for their survival in many natural environments but also in case of pathogenic bacteria in their respective host. The most important contributors to copper homeostasis have been identified in the last decades and comprise P_IB1-type ATPases, periplasmic copper- and oxygen-dependent copper oxidases, transenvelope efflux systems, and glutathione; however, it is not known how all these players interact. This publication investigates this interplay and describes copper homeostasis as a trait emerging from a network of interacting resistance systems.

Important Structural Features of Thiolate-Rich Four-Helix Bundles for Cu(I) Uptake and Removal

A family of bacterial copper storage proteins (the Csps) possess thiolate-lined four-helix bundles whose cores can be filled with Cu(I) ions. The majority of Csps are cytosolic (Csp3s), and in vitro studies carried out to date indicate that the Csp3s from Methylosinus trichosporium OB3b (MtCsp3), Bacillus subtilis (BsCsp3), and Streptomyces lividans (SlCsp3) are alike. Bioinformatics have highlighted homologues with potentially different Cu(I)-binding properties from these characterized "classical" Csp3s. Determination herein of the crystal structure of the protein (RkCsp3) from the methanotroph Methylocystis sp. strain Rockwell with Cu(I) bound identifies this as the first studied example of a new subgroup of Csp3s. The most significant structural difference from classical Csp3s is the presence of only two Cu(I) sites at the mouth of the bundle via which Cu(I) ions enter and leave. This is due to the absence of three Cys residues and a His-containing motif, which allow classical Csp3s to bind five to six Cu(I) ions in this region. Regardless, RkCsp3 exhibits rapid Cu(I) binding and the fastest measured Cu(I) removal rate for a Csp3 when using high-affinity ligands as surrogate partners. New experiments on classical Csp3s demonstrate that their His-containing motif is not essential for fast Cu(I) uptake and removal. Other structural features that could be important for these functionally relevant in vitro properties are discussed.

Ceria Nanoparticles as Copper Chaperones that Activate SOD1 for Synergistic Antioxidant Therapy to Treat Ischemic Vascular Diseases

All exogenous nanomaterials undergo rapid biotransformation once injected into the body and fall short of executing the intended purpose. Here, it is reported that copper-deposited ceria nanoparticles (CuCe NPs) exhibit enhanced antioxidant effects over pristine ceria nanoparticles, as the released copper buffers the depletion of glutathione while providing the bioavailable copper as a cofactor for the antioxidant enzyme, superoxide dismutase 1. The upregulated intracellular antioxidants along with the ceria nanoparticles synergistically scavenge reactive oxygen species and promote anti-inflammation and M2 polarization of macrophages by modulating signal transducer and activator of transcription 1 and 6 (STAT1 and STAT6). The therapeutic effect of CuCe NPs is demonstrated in ischemic vascular diseases (i.e., murine models of hindlimb ischemia and myocardial infarction) in which the copper-deposition affords increased perfusion and alleviation in tissue damage. The results provide rationale that metal oxide nanomaterials can be designed in a way to induce the upregulation of specific biological factors for optimal therapeutic performance.

Cope with copper: From copper linked mechanisms to copper-based clinical cancer therapies

Recent studies have established a strong link between copper and cancer biology, as copper is necessary for cancer growth and metastasis. Beyond the conventional concept of copper serving as a catalytic cofactor of metalloenzymes, emerging evidence demonstrates copper as a regulator for signaling transduction and gene expression, which are vital for tumorigenesis and cancer progression. Interestingly, strong redox-active properties make copper both beneficial and detrimental to cancer cells. Cuproplasia is copper-dependent cell growth and proliferation, whereas cuproptosis is copper-dependent cell death. Both mechanisms act in cancer cells, suggesting that copper depletion and copper supplementation may be viable approaches for developing novel anticancer therapies. In this review, we summarized the current understanding of copper's biological role and related molecular mechanisms in cancer proliferation, angiogenesis, metastasis, autophagy, immunosuppressive microenvironment development, and copper-mediated cancer cell death. We also highlighted copper-based strategies for cancer treatment. The current challenges of copper in cancer biology and therapy and their potential solutions were also discussed. Further investigation in this field will yield a more comprehensive molecular explanation for the causal relationship between copper and cancers. It will reveal a series of key regulators governing copper-dependent signaling pathways, thereby providing potential targets for developing copper-related anticancer drugs.

The Molecular Basis for Zinc Bioavailability

Zinc is an essential micronutrient, and its deficiency is perhaps the most prevalent and least understood worldwide. Recent advances have expanded the understanding of zinc’s unique chemistry and molecular roles in a vast array of critical functions. However, beyond the concept of zinc absorption, few studies have explored the molecular basis of zinc bioavailability that determines the proportion of dietary zinc utilized in zinc-dependent processes in the body. The purpose of this review is to merge the concepts of zinc molecular biology and bioavailability with a focus on the molecular determinants of zinc luminal availability, absorption, transport, and utilization.

A novel dehydroabietic acid-based multifunctional fluorescent probe for the detection and bioimaging of Cu2+/Zn2+/ClO. Analyst 2023;148:1867-1876. [PMID: 36942689 DOI: 10.1039/d3an00001j]

A multifunctional dehydroabietic acid-based fluorescent probe (CPS) was designed and synthesized by introducing the 2,6-bis(1H-benzo[d]imidazol-2-yl)phenol fluorophore. The probe CPS could selectively recognize Cu²⁺, Zn²⁺ and ClO^- ions from other analytes, and it showed fluorescence quenching behavior toward Cu²⁺ and a ratiometric response to Zn²⁺ and ClO^- by changing from green fluorescence to blue and cyan, respectively. The detection limits toward Cu²⁺, Zn²⁺ and ClO^- ions were 3.8 nM, 0.253 μM and 0.452 μM, respectively. In addition, CPS presented many fascinating merits, such as high selectivity, a short response time (15-20 s), a wide pH range (3-10) and high photostability. The sensing mechanisms of CPS were verified by ¹H-NMR, ESI-MS, FT-IR and Job's plot methods. Meanwhile, CPS exhibited satisfactory detection performance in water samples. More importantly, the probe could be applied as a promising tool for visual bioimaging of three ions in living cells and zebrafishes.

Metalloallostery and Transition Metal Signaling: Bioinorganic Copper Chemistry Beyond Active Sites

Transition metal chemistry is essential to life, where metal binding to DNA, RNA, and proteins underpins all facets of the central dogma of biology. In this context, metals in proteins are typically studied as static active site cofactors. However, the emergence of transition metal signaling, where mobile metal pools can transiently bind to biological targets beyond active sites, is expanding this conventional view of bioinorganic chemistry. This Minireview focuses on the concept of metalloallostery, using copper as a canonical example of how metals can regulate protein function by binding to remote allosteric sites (e.g., exosites). We summarize advances in and prospects for the field, including imaging dynamic transition metal signaling pools, allosteric inhibition or activation of protein targets by metal binding, and metal-dependent signaling pathways that underlie nutrient vulnerabilities in diseases spanning obesity, fatty liver disease, cancer, and neurodegeneration.

Cu(ii)-BODIPY photosensitizer for CAIX overexpressed cancer stem cell therapy

Chemoresistance originating from cancer stem cells (CSCs) is a major cause of cancer treatment failure and highlights the need to develop CSC-targeting therapies. Although enormous progress in both photodynamic therapy (PDT) and chemodynamic therapy (CDT) has been made in recent decades, the efficacy of these modalities against CSC remains limited. Here, we report a new generation photosensitizer, CA9-BPS-Cu(ii), a system that combines three subunits within a single molecule, namely a copper catalyst for CDT, a boron dipyrromethene photosensitizer for PDT, and acetazolamide for CSC targeting via carbonic anhydrase-9 (CA9) binding. A therapeutic effect in MDA-MB-231 cells was observed that is ascribed to elevated oxidative stress mediated by a combined CDT/PDT effect, as well as through copper-catalysed glutathione oxidation. The CSC targeting ability of CA9-BPS-Cu(ii) was evident from the enhanced affinity of CA9-BPS-Cu(ii) towards CD133-positive MDA-MB-231 cells where CA9 is overexpressed vs. CD133-negative cells. Moreover, the efficacy of CA9-BPS-Cu(ii) was successfully demonstrated in a xenograft mouse tumour model.

pCO2-driven seawater acidification affects aqueous-phase copper toxicity in juvenile flounder Paralichthys olivaceus: Metal accumulation, antioxidant defenses and detoxification in livers

Ocean acidification potentially influences the biotoxicity of metals and the antioxidant defense systems of marine organisms. This study investigated how pCO₂-driven seawater acidification (SA) affected aqueous-phase copper (Cu) toxicity in the juvenile flounder Paralichthys olivaceus from the perspective of hepatic oxidative stress and damage to better understand the mechanisms underlying the biological effects produced by the two stressors. Fish were exposed to aqueous-phase Cu at relevant ambient and polluted concentrations (0, 5, 10, 50, 100 and 200 μg L^-1) at different pH levels (no SA: pH 8.10; moderate SA: pH 7.70, pCO₂ ∼1353.89 μatm; extreme SA: pH 7.30, pCO₂ ∼3471.27 μatm) for 28 days. A battery of biomarkers in the livers was examined to investigate their roles in antioxidant defense and detoxification in response to coexposure. Hepatic Cu accumulation (30.22-184.90 mg kg^-1) was positively correlated with Cu concentrations. The biomarkers responded adaptively to different redox states following SA and Cu exposure. In unacidified seawater, increases in Cu concentrations significantly induced hepatic lipid peroxidation (LPO, by up to 27.03 %), although compensatory responses in antioxidant defenses and detoxification were activated. Moderate SA helped maintain hepatic redox homeostasis and alleviated LPO through different defense strategies, depending on Cu concentrations. Under extreme SA, antioxidant-based defenses were activated to cope with oxidative stress at ambient-low Cu concentrations but failed to defend against Cu toxicity at polluted Cu levels, and LPO (by up to 63.90 %) was significantly induced. Additionally, thiols (GSH and MT) responded actively to cope with Cu toxicity under SA. SOD, CAT, EROD, and GST were also sensitively involved in defending against hepatic oxidative stress during coexposure. These findings highlight the notable interactive effects of SA and Cu and provide a basis for understanding antioxidant-based defenses in marine fish confronting environmental challenges.

63Cu(I) binding to human kidney 68Zn7-βα MT1A: determination of Cu(I)-thiolate cluster domain specificity from ESI-MS and room temperature phosphorescence spectroscopy

Mammalian metallothioneins (MTs) are important proteins in Zn(II) and Cu(I) homeostasis with the Zn(II) and Cu(I) binding to the 20 cysteines in metal-thiolate clusters. Previous electrospray ionization (ESI) mass spectrometric (MS) analyses of Cu(I) binding to Zn7-MT were complicated by significant overlap of the natural abundance isotopic patterns for Zn(II) and Cu(I) leading to impossibly ambiguous stoichiometries. In this paper, isotopically pure 63Cu(I) and 68Zn(II) allowed determination of the specific stoichiometries in the 68 Zn,63Cu-βα MT1A species formed following the stepwise addition of 63Cu(I) to 68Zn7-βα MT1A. These species were characterized by ESI-MS and room temperature emission spectroscopy. The key species that form and their emission band centres are Zn5Cu5-βα MT1A (λ = 684 nm), Zn4Cu6-βα MT1A (λ = 750 nm), Zn3Cu9-βα MT1A (λ = 750 nm), Zn2Cu10-βα MT1A (λ = 750 nm), and Zn1Cu14-βα MT1A (λ = 634 nm). The specific domain stoichiometry of each species was determined by assessing the species forming following 63Cu(I) addition to the 68Zn3-β MT1A and 68Zn4-α MT1A domain fragments. The domain fragment emission suggests that Zn5Cu5-βα MT1A contains a Zn1Cu5-β cluster and the Zn4Cu6-βα MT1A, Zn3Cu9-βα MT1A, and Zn2Cu10-βα MT1A each contain a Cu6-β cluster. The species forming with >10 mol. eq. of 63Cu(I) in βα-MT1A exhibit emission from the Cu6-β cluster and an α domain cluster. This high emission intensity is seen at the end of the titrations of 68Zn7-βα MT1A and the 68Zn4-α MT1A domain fragment suggesting that the initial presence of the Zn(II) results in clustered Cu(I) binding in the α domain.

Effects of dietary zinc/copper ratios on the metabolism of zinc and copper in weaned pigs

This study compared the effects of different dietary zinc/copper ratios on zinc (Zn) and copper (Cu) metabolism in weaned pigs. One hundred and sixty piglets (7.81 ± 0.25 kg; 21 d of age) were used in a completely randomized 2 × 2 factorial design composed with high (H) and low (L) levels of added dietary Zn (100 and 3,000 mg/kg) and dietary Cu (6 and 130 mg/kg). Piglets were slaughtered at 21, 28, 35, and 42 d of age for blood and tissues collection. Serum, jejunum mucosa, liver, and kidney concentrations of Zn and Cu were analyzed as well as tissues mRNA abundance of genes related to their metabolism. Serum and liver Zn concentrations increased at days 28, 35, and 42 in HZn groups compared to pre-treatment levels (day 21; P ≤ 0.01) but for LZn animals, values decreased at days 28, 35, and 42 in liver (P ≤ 0.01) but remained stable vs. day 21 levels in serum (P ≥ 0.37). Serum, jejunum mucosa, liver, and kidney Zn concentrations were greater in HZn groups from day 28 (P ≤ 0.01). In jejunum mucosa, the mRNA expression of ZIP4 was lower in HZn piglets at day 28 (P ≤ 0.01) and at day 42 whereas HCu supplementation increased ZIP4 expression in LZn but not in HZn diets (P = 0.05). For ZNT1, MT3, and MT1, values of relative mRNA expression were greater for HZn animals in jejunum mucosa, liver, and kidney (P ≤ 0.01) from day 28. In kidney (P < 0.01) at day 42, HZn supplementation increased MTs expression in both LCu or HCu groups. Serum and liver Cu concentrations decreased at days 35 and 42 in all treatments compared to day 21 (P ≤ 0.04), except LZnHCu in liver that was not different from day 21 (P ≥ 0.17). Serum Cu concentrations were lower in HZn and greater in HCu groups at days 35 and 42 (P ≤ 0.01) whereas hepatic Cu was reduced by HZn diets in both LCu and HCu groups at days 35 and 42 (P ≤ 0.01). Jejunum Cu concentrations were increased by HCu diets in HZn but not in LZn groups at days 28 and 42 (P ≤ 0.04). Renal Cu concentrations were greater in HZn groups at day 28 (P < 0.01) whereas at day 42 HZn diets increased Cu values in both LCu and HCu groups (P ≤ 0.01). The expression of ATP7A in kidney at day 42 was greater for HZn groups (P = 0.02). In conclusion, high dietary Zn levels were not efficiently regulated by homeostatic mechanisms and significantly impaired Cu homeostasis. Low dietary Zn/Cu ratios allow a more efficient regulation of the metabolism of these trace minerals in post-weaning piglets. The current official recommendations for Zn and Cu to post-weaning piglets apparently do not fulfill their requirements.

Mitochondrial copper in human genetic disorders

Copper is an essential micronutrient that serves as a cofactor for enzymes involved in diverse physiological processes, including mitochondrial energy generation. Copper enters cells through a dedicated copper transporter and is distributed to intracellular cuproenzymes by copper chaperones. Mitochondria are critical copper-utilizing organelles that harbor an essential cuproenzyme cytochrome c oxidase, which powers energy production. Mutations in copper transporters and chaperones that perturb mitochondrial copper homeostasis result in fatal genetic disorders. Recent studies have uncovered the therapeutic potential of elesclomol, a copper ionophore, for the treatment of copper deficiency disorders such as Menkes disease. Here we review the role of copper in mitochondrial energy metabolism in the context of human diseases and highlight the recent developments in copper therapeutics.

Metal trafficking in the cell: Combining atomic resolution with cellular dimension

Metals are widely present in biological systems as simple ions or complex cofactors, and are involved in a variety of processes essential for life. Their transport inside cells and insertion into the binding sites of the proteins that need metals to function occur through complex and selective pathways involving dedicated multiprotein machineries specifically and transiently interacting with each other, often sharing the coordination of metal ions and/or cofactors. The understanding of these machineries requires integrated approaches, ranging from bioinformatics to experimental investigations, possibly in the cellular context. In this review, we report two case studies where the use of integrated in vitro and in cellulo approaches is necessary to clarify at atomic resolution essential aspects of metal trafficking in cells.

The Oncopig as an Emerging Model to Investigate Copper Regulation in Cancer

Emerging evidence points to several fundamental contributions that copper (Cu) has to promote the development of human pathologies such as cancer. These recent and increasing identification of the roles of Cu in cancer biology highlights a promising field in the development of novel strategies against cancer. Cu and its network of regulatory proteins are involved in many different contextual aspects of cancer from driving cell signaling, modulating cell cycle progression, establishing the epithelial-mesenchymal transition, and promoting tumor growth and metastasis. Human cancer research in general requires refined models to bridge the gap between basic science research and meaningful clinical trials. Classic studies in cultured cancer cell lines and animal models such as mice and rats often present caveats when extended to humans due to inherent genetic and physiological differences. However, larger animal models such as pigs are emerging as more appropriate tools for translational research as they present more similarities with humans in terms of genetics, anatomical structures, organ sizes, and pathological manifestations of diseases like cancer. These similarities make porcine models well-suited for addressing long standing questions in cancer biology as well as in the arena of novel drug and therapeutic development against human cancers. With the emergent roles of Cu in human health and pathology, the pig presents an emerging and valuable model to further investigate the contributions of this metal to human cancers. The Oncopig Cancer Model is a transgenic swine model that recapitulates human cancer through development of site and cell specific tumors. In this review, we briefly outline the relationship between Cu and cancer, and how the novel Oncopig Cancer Model may be used to provide a better understanding of the mechanisms and causal relationships between Cu and molecular targets involved in cancer.

The mitochondrial Cu+ transporter PiC2 (SLC25A3) is a target of MTF1 and contributes to the development of skeletal muscle in vitro

The loading of copper (Cu) into cytochrome c oxidase (COX) in mitochondria is essential for energy production in cells. Extensive studies have been performed to characterize mitochondrial cuproenzymes that contribute to the metallation of COX, such as Sco1, Sco2, and Cox17. However, limited information is available on the upstream mechanism of Cu transport and delivery to mitochondria, especially through Cu-impermeable membranes, in mammalian cells. The mitochondrial phosphate transporter SLC25A3, also known as PiC2, binds Cu+ and transports the ion through these membranes in eukaryotic cells, ultimately aiding in the metallation of COX. We used the well-established differentiation model of primary myoblasts derived from mouse satellite cells, wherein Cu availability is necessary for growth and maturation, and showed that PiC2 is a target of MTF1, and its expression is both induced during myogenesis and favored by Cu supplementation. PiC2 deletion using CRISPR/Cas9 showed that the transporter is required for proliferation and differentiation of primary myoblasts, as both processes are delayed upon PiC2 knock-out. The effects of PiC2 deletion were rescued by the addition of Cu to the growth medium, implying the deleterious effects of PiC2 knockout in myoblasts may be in part due to a failure to deliver sufficient Cu to the mitochondria, which can be compensated by other mitochondrial cuproproteins. Co-localization and co-immunoprecipitation of PiC2 and COX also suggest that PiC2 may participate upstream in the copper delivery chain into COX, as verified by in vitro Cu+-transfer experiments. These data indicate an important role for PiC2 in both the delivery of Cu to the mitochondria and COX, favoring the differentiation of primary myoblasts.

The carboxy terminal transmembrane domain of SPL7 mediates interaction with RAN1 at the endoplasmic reticulum to regulate ethylene signalling in Arabidopsis

In Arabidopsis, copper (Cu) transport to the ethylene receptor ETR1 mediated using RAN1, a Cu transporter located at the endoplasmic reticulum (ER), and Cu homeostasis mediated using SPL7, the key Cu-responsive transcription factor, are two deeply conserved vital processes. However, whether and how the two processes interact to regulate plant development remain elusive. We found that its C-terminal transmembrane domain (TMD) anchors SPL7 to the ER, resulting in dual compartmentalisation of the transcription factor. Immunoprecipitation coupled mass spectrometry, yeast-two-hybrid assay, luciferase complementation imaging and subcellular co-localisation analyses indicate that SPL7 interacts with RAN1 at the ER via the TMD. Genetic analysis revealed that the ethylene-induced triple response was significantly compromised in the spl7 mutant, a phenotype rescuable by RAN1 overexpression but not by SPL7 without the TMD. The genetic interaction was corroborated by molecular analysis showing that SPL7 modulates RAN1 abundance in a TMD-dependent manner. Moreover, SPL7 is feedback regulated by ethylene signalling via EIN3, which binds the SPL7 promoter and represses its transcription. These results demonstrate that ER-anchored SPL7 constitutes a cellular mechanism to regulate RAN1 in ethylene signalling and lay the foundation for investigating how Cu homeostasis conditions ethylene sensitivity in the developmental context.