1H,13C-NMR and X-ray absorption studies of copper(I) glutathione complexes

Mechanisms of microbial hyper-resistance to heavy metals: Cellular metal accumulation, metabolic reorganization, and GroEL chaperonin in extremophilic bacterium Sulfobacillus thermotolerans in response to zinc

Mine waste disposal in dumps and stockpiles causes environmental pollution, particularly through microbe-assisted acid mine drainage (AMD) generation and groundwater contamination with hazardous heavy metal(loid)s. Metal hyper-resistance in acidophilic microorganisms remains an underexplored intriguing phenomenon. Using a multi-level approach, we provide the first data on extreme zinc resistance mechanisms in Sulfobacillus thermotolerans, recognized as one of the most metal-resistant organisms known. Under high zinc levels, Sb. thermotolerans cells exhibited efficient zinc sorption and low intracellular accumulation. Remarkably, mechanisms involved the upregulation of stress response and metabolic pathway proteins, including different GroEL chaperonin forms. Moreover, overexpression of the Sb. thermotolerans StGroEL chaperonin in Escherichia coli enhanced its growth and zinc resistance under zinc stress. 3D structure modeling and ion binding site prediction in StGroEL revealed 46 amino acid residues potentially involved in zinc docking. Thriving in natural and engineered environments, such as sulfide mines, mine waste disposal sites, and AMD, Sb. thermotolerans is a key member of acidophilic microbial communities used in commercial biotechnologies for sulfidic raw material processing. These findings, beyond their fundamental scientific relevance, have important implications for environmental protection, including AMD management, safe hazardous waste disposal, and a broader application of eco-friendly biomining technologies using metal-resistant microbial communities.

Copper-Based Complexes with Adamantane Ring-Conjugated bis(3,5-Dimethyl-pyrazol-1-yl)acetate Ligand as Promising Agents for the Treatment of Glioblastoma

The new ligand L2Ad, obtained by conjugating the bifunctional species bis(3,5-dimethylpyrazol-1-yl)-acetate and the drug amantadine, was used as a chelator for the synthesis of new Cu complexes 1-5. Their structures were investigated by synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and by combining X-ray absorption fine structure (XAFS) spectroscopy techniques and DFT modeling. The structure of complex 3 was determined by single-crystal X-ray diffraction analysis. Tested on U87, T98, and U251 glioma cells, Cu(II) complex 3 and Cu(I) complex 5 decreased cell viability with IC50 values significantly lower than cisplatin, affecting cell growth, proliferation, and death. Their effects were prevented by treatment with the Cu chelator tetrathiomolybdate, suggesting the involvement of copper in their cytotoxic activity. Both complexes were able to increase ROS production, leading to DNA damage and death. Interestingly, nontoxic doses of 3 or 5 enhanced the chemosensitivity to Temozolomide.

Axial assembly of AuNR for tumor theranostics via Zn2+-GSH chelation induced degradation of AuNR@ZIF-8 heterostructures

Tumor microenvironment responsive photothermal ablation is a noninvasive and accurately targeted approach for cancer therapy. Herein, an intracellular directional assembly strategy for enhanced photothermal therapy (PTT) was realized by using ZIF-8 encapsulated Au nanorod (AuNR) heterostructure as the precursor of photothermal convertible material. The ZIF-8 shell selectively degraded in tumor cells upon the chelation between GSH and Zn2+, while the as-formed Zn(SG) connected the released AuNR in end-to-end fashion. The coating of ZIF-8 shell significantly improves the stability and targeting of AuNR, and the released Zn2+ shielded the GSH binding site on the lateral side of AuNR, increased the plasmonic coupling efficiency of AuNR assembly geometer. This design enabled atomic-economical, efficient and low-side effect targeted photothermal therapy through the effective integration of heterostructures.

Interaction between Cu and Thiols of Biological and Environmental Importance: Case Study Using Combined Spectrophotometric/Bathocuproine Sulfonate Disodium Salt Hydrate (BCS) Assay

Considering the biological and ecological importance of Cu-thiol interactions and the discrepancies in previous research, this study focuses on Cu interactions with biologically and ecologically relevant thiols: glutathione (GSH), L-cysteine (L-cys), 3-mercaptopropionic acid (MPA), and thioacetic acid (TAA) in aqueous solution. The addition of Cu(II) to a thiol-containing solution led to a rapid reduction of Cu(II) and the formation of a Cu(I)-thiol complex. The mechanism of Cu(II) reduction and Cu(I) complex formation as well as the kinetics of Cu(I) oxidation strongly depend on the structural properties of the individual thiols investigated. The reducing power of the investigated thiols can be summarized as follows: L-cys ≅ GSH > MPA > TAA. The reaction order, with respect to Cu(I) oxidation, also changes over the time of the reaction course. The deviation of the reaction kinetics from the first order with respect to Cu(I) in the later stages of the reaction course can be attributed to a Fenton-like reaction occurring under low thiol concentration conditions. At high Cu:thiol ratios, in the case of GSH, L-cys, and MPA, the early stage of the reaction course is characterized by high Cu(I) stability, most likely as a result of Cu(I) complexation by the thiols present in excess in the reaction mixture.

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.

Switchable catalysis and CO2 sensing by reduction resistant, luminescent copper-thiolate complexes

Metal-thiolate complexes have been the focus of research for several years because of their unique photophysical properties and their use as a precursor for synthesizing various well-defined metal nanoclusters. A rational understanding of their structure-property relationship is necessary to realize their full potential in practical applications. Herein, we demonstrate the synthesis of a unique copper-thiolate complex with reversibly switchable catalytic and photoluminescence (PL) properties. The as-synthesized complex at basic pH (Complex B) showed cyan PL with a strong peak at ∼488 nm (cyan) and a small shoulder peak at ∼528 nm (green). When the pH of the complex was changed to acidic (Complex A), the PL was switched to light green. Such pH-responsive PL properties were demonstrated to be useful for pH and CO₂ sensing. The switchable properties originate from their two distinct structural states at two different pHs. We found that Complex A was resistant to high concentrations of a strong reducing agent, and had an intermediate oxidation state of copper (Cu⁺) with good thermodynamic stability. Furthermore, the switchable catalytic property was investigated with a 4-nitrophenol reduction and 3,3',5,5'-tetramethylbenzidine (TMB) oxidation reaction. The reduction kinetics followed pseudo-first-order, where the catalytic activity was enhanced by more than 10³ times when Complex B was switched to Complex A. A similar trend was also observed for TMB oxidation. Our design strategy demonstrates that redox switchable metal-thiolate complexes could be a powerful candidate for a plethora of applications.

An Enzyme-Engineered Nonporous Copper(I) Coordination Polymer Nanoplatform for Cuproptosis-Based Synergistic Cancer Therapy

Cuproptosis, a newly identified form of regulated cell death that is copper-dependent, offers great opportunities for exploring the use of copper-based nanomaterials inducing cuproptosis for cancer treatment. Here, a glucose oxidase (GOx)-engineered nonporous copper(I) 1,2,4-triazolate ([Cu(tz)]) coordination polymer (CP) nanoplatform, denoted as GOx@[Cu(tz)], for starvation-augmented cuproptosis and photodynamic synergistic therapy is developed. Importantly, the catalytic activity of GOx is shielded in the nonporous scaffold but can be "turned on" for efficient glucose depletion only upon glutathione (GSH) stimulation in cancer cells, thereby proceeding cancer starvation therapy. The depletion of glucose and GSH sensitizes cancer cells to the GOx@[Cu(tz)]-mediated cuproptosis, producing aggregation of lipoylated mitochondrial proteins, the target of copper-induced toxicity. The increased intracellular hydrogen peroxide (H₂ O₂ ) levels, due to the oxidation of glucose, activates the type I photodynamic therapy (PDT) efficacy of GOx@[Cu(tz)]. The in vivo experimental results indicate that GOx@[Cu(tz)] produces negligible systemic toxicity and inhibits tumor growth by 92.4% in athymic mice bearing 5637 bladder tumors. This is thought to be the first report of a cupreous nanomaterial capable of inducing cuproptosis and cuproptosis-based synergistic therapy in bladder cancer, which should invigorate studies pursuing rational design of efficacious cancer therapy strategies based on cuproptosis.

Unveiling the interplay between homogeneous and heterogeneous catalytic mechanisms in copper-iron nanoparticles working under chemically relevant tumour conditions

The present work sheds light on a generally overlooked issue in the emerging field of bio-orthogonal catalysis within tumour microenvironments (TMEs): the interplay between homogeneous and heterogeneous catalytic processes. In most cases, previous works dealing with nanoparticle-based catalysis in the TME focus on the effects obtained (e.g. tumour cell death) and attribute the results to heterogeneous processes alone. The specific mechanisms are rarely substantiated and, furthermore, the possibility of a significant contribution of homogeneous processes by leached species - and the complexes that they may form with biomolecules - is neither contemplated nor pursued. Herein, we have designed a bimetallic catalyst nanoparticle containing Cu and Fe species and we have been able to describe the whole picture in a more complex scenario where both homogeneous and heterogeneous processes are coupled and fostered under TME relevant chemical conditions. We investigate the preferential leaching of Cu ions in the presence of a TME overexpressed biomolecule such as glutathione (GSH). We demonstrate that these homogeneous processes initiated by the released by Cu-GSH interactions are in fact responsible for the greater part of the cell death effects found (GSH, a scavenger of reactive oxygen species, is depleted and highly active superoxide anions are generated in the same catalytic cycle). The remaining solid CuFe nanoparticle becomes an active catalyst to supply oxygen from oxygen reduced species, such as superoxide anions (by-product from GSH oxidation) and hydrogen peroxide, another species that is enriched in the TME. This activity is essential to sustain the homogeneous catalytic cycle in the oxygen-deprived tumour microenvironment. The combined heterogeneous-homogeneous mechanisms revealed themselves as highly efficient in selectively killing cancer cells, due to their higher GSH levels compared to healthy cell lines.

Reaction of N-Acetylcysteine with Cu2+: Appearance of Intermediates with High Free Radical Scavenging Activity: Implications for Anti-/Pro-Oxidant Properties of Thiols

We studied the kinetics of the reaction of N-acetyl-l-cysteine (NAC or RSH) with cupric ions at an equimolar ratio of the reactants in aqueous acid solution (pH 1.4−2) using UV/Vis absorption and circular dichroism (CD) spectroscopies. Cu2+ showed a strong catalytic effect on the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radical (ABTSr) consumption and autoxidation of NAC. Difference spectra revealed the formation of intermediates with absorption maxima at 233 and 302 nm (ε302/Cu > 8 × 103 M−1 cm−1) and two positive Cotton effects centered at 284 and 302 nm. These intermediates accumulate during the first, O2-independent, phase of the NAC autoxidation. The autocatalytic production of another chiral intermediate, characterized by two positive Cotton effects at 280 and 333 nm and an intense negative one at 305 nm, was observed in the second reaction phase. The intermediates are rapidly oxidized by added ABTSr; otherwise, they are stable for hours in the reaction solution, undergoing a slow pH- and O2-dependent photosensitive decay. The kinetic and spectral data are consistent with proposed structures of the intermediates as disulfide-bridged dicopper(I) complexes of types cis-/trans-CuI2(RS)2(RSSR) and CuI2(RSSR)2. The electronic transitions observed in the UV/Vis and CD spectra are tentatively attributed to Cu(I) → disulfide charge transfer with an interaction of the transition dipole moments (exciton coupling). The catalytic activity of the intermediates as potential O2 activators via Cu(II) peroxo-complexes is discussed. A mechanism for autocatalytic oxidation of Cu(I)−thiolates promoted by a growing electronically coupled −[CuI2(RSSR)]n− polymer is suggested. The obtained results are in line with other reported observations regarding copper-catalyzed autoxidation of thiols and provide new insight into these complicated, not yet fully understood systems. The proposed hypotheses point to the importance of the Cu(I)−disulfide interaction, which may have a profound impact on biological systems.

Do glutathione and copper interact to modify Alzheimer's disease pathogenesis?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder first described in 1906 that is currently estimated to impact ∼40 million people worldwide. Extensive research activities have led to a wealth of information on the pathogenesis, hallmarks, and risk factors of AD; however, therapeutic options remain extremely limited. The large number of pathogenic factors that have been reported to potentially contribute to AD include copper dyshomeostasis as well as increased oxidative stress, which is related to alterations to molecular antioxidants like glutathione (GSH). While the individual roles of GSH and copper in AD have been studied by many research groups, their interactions have received relatively little attention, although they appear to interact and affect each other's regulation. Existing knowledge on how GSH-copper interactions may affect AD is sparse and lacks focus. This review first highlights the most relevant individual roles that GSH and copper play in physiology and AD, and then collects and assesses research concerning their interactions, in an effort to provide a more accessible and understandable picture of the role of GSH, copper, and their interactions in AD.

Intermediate Cu(II)-Thiolate Species in the Reduction of Cu(II)GHK by Glutathione: A Handy Chelate for Biological Cu(II) Reduction

Gly-His-Lys (GHK) is a tripeptide present in the human bloodstream that exhibits a number of biological functions. Its activity is attributed to the copper-complexed form, Cu(II)GHK. Little is known, however, about the molecular aspects of the mechanism of its action. Here, we examined the reaction of Cu(II)GHK with reduced glutathione (GSH), which is the strongest reductant naturally occurring in human plasma. Spectroscopic techniques (UV–vis, CD, EPR, and NMR) and cyclic voltammetry helped unravel the reaction mechanism. The impact of temperature, GSH concentration, oxygen access, and the presence of ternary ligands on the reaction were explored. The transient GSH-Cu(II)GHK complex was found to be an important reaction intermediate. The kinetic and redox properties of this complex, including tuning of the reduction rate by ternary ligands, suggest that it may provide a missing link in copper trafficking as a precursor of Cu(I) ions, for example, for their acquisition by the CTR1 cellular copper transporter.

Gly-His-Lys (GHK) is a human bioactive tripeptide thought to be activated by Cu(II) binding, but little is known about the molecular aspects of its action. UV−vis, circular dichroism (CD), EPR, and NMR spectroscopies, and cyclic voltammetry were used to examine the reduction of Cu(II)GHK with glutathione (GSH), the most abundant biological thiol. A semistable GSH-Cu(II)GHK reaction intermediate was discovered, with properties suitable for delivering Cu(I) to biological transport proteins.

Selenium-deficient diet induces inflammatory response in the pig adrenal glands by activating TLR4/NF-κB pathway via miR-30d-R_1

Selenium (Se) is an important trace element to maintain the body's dynamic balance. Lack of Se can cause inflammation. Studies have shown that inflammation often leads to disorders of the hypothalamic-pituitary-adrenal axis, but the mechanism by which Se deficiency causes inflammation of the porcine adrenal glands is still unclear. In order to study the effect of Se deficiency on the adrenal glands of pigs, we obtained Se-deficient pig adrenal glands through a low-Se diet. The results of mass spectrometry showed that the Se content in the Se-deficient group was only one-tenth of the control group. We detected the expression of the toll-like receptor 4 (TLR4) and downstream factors by qRT-PCR and Western blotting, and found that the lack of Se affected the TLR4/NF-κB pathway. It is known that miR-155-3p, miR-30d-R_1, and miR-146b have all been verified for targeting relationship with TLR4. We confirmed by qRT-PCR that miR-30d-R_1 decreased most significantly in the Se-deficient pig model. Then we tested 25 selenoproteins and some indicators of oxidative stress. It is confirmed that Se deficiency reduces the antioxidant capacity and induces oxidative stress in pig adrenal tissue. In short, a diet lacking Se induces oxidative stress in pig adrenal tissues and leads to inflammation through the miR-30d-R_1/TLR4 pathway. This study provides a reference for the prevention of adrenal inflammation in pigs from a nutritional point of view.

Ultrathin 2D Copper(I) 1,2,4-Triazolate Coordination Polymer Nanosheets for Efficient and Selective Gene Silencing and Photodynamic Therapy

Gene silencing holds promise for cancer therapeutics because of its potential to inhibit genes involved in tumor development. However, gene silencing is still restricted by its limited efficacy and safety. Nanoscale coordination polymers (CPs) emerge as promising nanocarriers for gene delivery, but their responsiveness and potential therapeutic properties have rarely been explored simultaneously. Here, multifunctional ultrathin 2D nanosheets of Cu(I) 1,2,4-triazolate CP with a thickness of 4.5 ± 0.8 nm are synthesized using a bottom-up method. These CP nanosheets can act as both an effective DNAzyme nanocarrier for gene therapy and an intrinsic photosensitizer for hypoxia-tolerant type I photodynamic therapy (PDT), which is ascribed to the Fenton-like reaction. Because of the glutathione (GSH)-responsiveness of the CP nanosheets, DNAzyme-loaded CP nanosheets exhibit excellent cancer-cell-targeting gene silencing of the early growth response factor-1 (EGR-1), with messenger RNA inhibited by 84% in MCF-7 (human breast cancer cells) and only 6% in MCF-10A (normal human mammary epithelial cells). After tail intravenous injection into MCF-7-tumor-bearing mice, the CP nanosheets loaded with chlorin-e6-modified DNAzyme under photoirradiation show a high antitumor efficacy (88.0% tumor regression), demonstrating a promising therapeutic platform with efficient and selective gene silencing and PDT of cancer.

Cu Homeostasis in Bacteria: The Ins and Outs

Copper (Cu) is an essential trace element for all living organisms and used as cofactor in key enzymes of important biological processes, such as aerobic respiration or superoxide dismutation. However, due to its toxicity, cells have developed elaborate mechanisms for Cu homeostasis, which balance Cu supply for cuproprotein biogenesis with the need to remove excess Cu. This review summarizes our current knowledge on bacterial Cu homeostasis with a focus on Gram-negative bacteria and describes the multiple strategies that bacteria use for uptake, storage and export of Cu. We furthermore describe general mechanistic principles that aid the bacterial response to toxic Cu concentrations and illustrate dedicated Cu relay systems that facilitate Cu delivery for cuproenzyme biogenesis. Progress in understanding how bacteria avoid Cu poisoning while maintaining a certain Cu quota for cell proliferation is of particular importance for microbial pathogens because Cu is utilized by the host immune system for attenuating pathogen survival in host cells.

Emerging Approaches to Investigate the Influence of Transition Metals in the Proteinopathies

Transition metals have essential roles in brain structure and function, and are associated with pathological processes in neurodegenerative disorders classed as proteinopathies. Synchrotron X-ray techniques, coupled with ultrahigh-resolution mass spectrometry, have been applied to study iron and copper interactions with amyloid β (1–42) or α-synuclein. Ex vivo tissue and in vitro systems were investigated, showing the capability to identify metal oxidation states, probe local chemical environments, and localize metal-peptide binding sites. Synchrotron experiments showed that the chemical reduction of ferric (Fe³⁺) iron and cupric (Cu²⁺) copper can occur in vitro after incubating each metal in the presence of Aβ for one week, and to a lesser extent for ferric iron incubated with α-syn. Nanoscale chemical speciation mapping of Aβ-Fe complexes revealed a spatial heterogeneity in chemical reduction of iron within individual aggregates. Mass spectrometry allowed the determination of the highest-affinity binding region in all four metal-biomolecule complexes. Iron and copper were coordinated by the same N-terminal region of Aβ, likely through histidine residues. Fe³⁺ bound to a C-terminal region of α-syn, rich in aspartic and glutamic acid residues, and Cu²⁺ to the N-terminal region of α-syn. Elucidating the biochemistry of these metal-biomolecule complexes and identifying drivers of chemical reduction processes for which there is evidence ex-vivo, are critical to the advanced understanding of disease aetiology.

Elucidation of the Structure of a Thiol Functionalized Cu-tmpa Complex Anchored to Gold via a Self-Assembled Monolayer

The structure of the copper complex of the 6-((1-butanethiol)oxy)-tris(2-pyridylmethyl)amine ligand (Cu-tmpa-O(CH₂)₄SH) anchored to a gold surface has been investigated. To enable covalent attachment of the complex to the gold surface, a heteromolecular self-assembled monolayer (SAM) of butanethiol and a thiol-substituted tmpa ligand was used. Subsequent formation of the immobilized copper complex by cyclic voltammetry in the presence of Cu(OTf)₂ resulted in the formation of the anchored Cu-tmpa-O(CH₂)₄SH system which, according to scanning electron microscopy and X-ray diffraction, did not contain any accumulated copper nanoparticles or crystalline copper material. Electrochemical investigation of the heterogenized system barely showed any redox activity and lacked the typical Cu^II/I redox couple in contrast to the homogeneous complex in solution. The difference between the heterogenized system and the homogeneous complex was confirmed by X-ray photoelectron spectroscopy; the XPS spectrum did not show any satellite features of a Cu^II species but instead showed the presence of a Cu^I ion in a ∼2:3 ratio to nitrogen and a ∼2:7 ratio to sulfur. The +I oxidation state of the copper species was confirmed by the edge position in the X-ray absorption near-edge structure (XANES) region of the X-ray absorption spectrum. These results show that upon immobilization of Cu-tmpa-O(CH₂)₄SH, the resulting structure is not identical to the homogeneous Cu^II-tmpa complex. Upon anchoring, a novel Cu^I species is formed instead. This illustrates the importance of a thorough characterization of heterogenized molecular systems before drawing any conclusions regarding the structure–function relationships.

Both the oxidation state and the structure of the Cu^II complex of tris(2-pyridylmethyl)amine (Cu-tmpa) change upon anchoring it to a gold surface via a self-assembled monolayer. It was shown by XPS and XANES that a Cu^I species is formed upon anchoring instead in which each tmpa ligand contains roughly two to three copper ions.

Copper Utilization, Regulation, and Acquisition by Aspergillus fumigatus

Copper is an essential micronutrient for the opportunistic human pathogen, Aspergillus fumigatus. Maintaining copper homeostasis is critical for survival and pathogenesis. Copper-responsive transcription factors, AceA and MacA, coordinate a complex network responsible for responding to copper in the environment and determining which response is necessary to maintain homeostasis. For example, A. fumigatus uses copper exporters to mitigate the toxic effects of copper while simultaneously encoding copper importers and small molecules to ensure proper supply of the metal for copper-dependent processes such a nitrogen acquisition and respiration. Small molecules called isocyanides recently found to be produced by A. fumigatus may bind copper and partake in copper homeostasis similarly to isocyanide copper chelators in bacteria. Considering that the host uses copper as a microbial toxin and copper availability fluctuates in various environmental niches, understanding how A. fumigatus maintains copper homeostasis will give insights into mechanisms that facilitate the development of invasive aspergillosis and its survival in nature.

Functions of the C2H2 Transcription Factor Gene thmea1 in Trichoderma harzianum under Copper Stress Based on Transcriptome Analysis

Trichoderma spp. are important biocontrol filamentous fungi and have tremendous potential in soil bioremediation. In our previous studies, a C2H2 type transcription factor coding gene (thmea1) was cloned from a biocontrol agent T. harzianum Th-33; the encoded sequence of thmea1 contained 3 conserved C2H2 domains with Swi5 and Ace2 in Saccharomyces cerevisiae. The thmea1 knockout mutant Δthmea1 showed 12.9% higher copper tolerance than the wild-type Th33. To elucidate the function of thmea1 and its relationship with copper stress response, we conducted transcriptome sequencing and analysis of wild-type Th33 and Δthmea1 under 0.8 mM copper stress. A total of 1061 differentially expressed genes (DEGs) were identified between the two strains, all DEGs were assigned to KEGG pathway database, 383 DEGs were annotated in 191 individual pathways, and the categories of ribosomal protein synthesis and amino acid metabolism were the most highly enriched ones. Analysis of related DEGs showed that the expression levels of intracellular glutathione detoxification enzyme, heat shock proteins, and ribosomal proteins in Δthmea1 were higher than that of the wild-type Th33, and the expression of metallothionein (MT) gene did not change. In addition, the expression levels of genes coding for proteins associated with the Ccc2p-mediated copper chaperone Atx1p transport of copper ions into the Golgi secretory pathway increased, as well as the copper amine oxidase (CuAO). These findings suggest that Thmea1 is a negative regulated factor of copper tolerance ability in T. harzianum. It does not show metallothionein expression activator activities as that of Ace2 in S. cerevisiae. We hypothesize that after T. harzianum has lost its thmea1 gene, the ability of cells to scavenge reactive oxygen species, mainly through the glutathione antioxidant system, is enhanced, whereas protein synthesis and repair and copper secretion increase under copper stress, which increases the ability of the mutant strain to tolerate copper stress.

Copper Acquisition and Utilization in Fungi

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

Glutathione limits aquacopper(I) to sub-femtomolar concentrations through cooperative assembly of a tetranuclear cluster

The tripeptide glutathione (GSH) is a crucial intracellular reductant and radical scavenger, but it may also coordinate the soft Cu(I) cation and thereby yield pro-oxidant species. The GSH-Cu(I) interaction is thus a key consideration for both redox and copper homeostasis in cells. However, even after nearly four decades of investigation, the nature and stability of the GSH-Cu(I) complexes formed under biologically relevant conditions remain controversial. Here, we revealed the unexpected predominance of a tetranuclear [Cu₄(GS)₆] cluster that is sufficiently stable to limit the effective free aquacopper(I) concentration to the sub-femtomolar regime. Combined spectrophotometric-potentiometric titrations at biologically realistic GSH/Cu(I) ratios, enabled by our recently developed Cu(I) affinity standards and corroborated by low-temperature phosphorescence studies, established cooperative assembly of [Cu₄(GS)₆] as the dominant species over a wide pH range, from 5.5 to 7.5. Our robust model for the glutathione-Cu(I) equilibrium system sets a firm upper limit on the thermodynamic availability of intracellular copper that is 3 orders of magnitude lower than previously estimated. Taking into account their ability to catalyze the production of deleterious superoxide, the formation of Cu(I)-glutathione complexes might be avoided under normal physiological conditions. The actual intracellular Cu(I) availability may thus be regulated a further 3 orders of magnitude below the GSH/Cu(I) affinity limit, consistent with the most recent affinity determinations of Cu(I) chaperones.

Binding of Copper and Cisplatin to Atox1 Is Mediated by Glutathione through the Formation of Metal-Sulfur Clusters

Copper is an essential nutrient required for many biological processes involved in primary metabolism, but free copper is toxic due to its ability to catalyze formation of free radicals. To prevent toxic effects, in the cell copper is bound to proteins and low molecular weight compounds, such as glutathione, at all times. The widely used chemotherapy agent cisplatin is known to bind to copper-transporting proteins, including copper chaperone Atox1. Cisplatin interactions with Atox1 and other copper transporters are linked to cancer resistance to platinum-based chemotherapy. Here we analyze the binding of copper and cisplatin to Atox1 in the presence of glutathione under redox conditions that mimic intracellular environment. We show that copper(I) and glutathione form large polymers with a molecular mass of approximately 8 kDa, which can transfer copper to Atox1. Cisplatin also can form polymers with glutathione, albeit at a slower rate. Analysis of simultaneous binding of copper and cisplatin to Atox1 under physiological conditions shows that both metals are bound to the protein through copper-sulfur-platinum bridges.

Copper ATPase CopA from Escherichia coli: Quantitative Correlation between ATPase Activity and Vectorial Copper Transport

Cu-ATPases are membrane copper transporters present in all kingdoms of life. They play a central role in Cu homeostasis by pumping Cu ions across cell membranes with energy derived from ATP hydrolysis. In this work, the Cu-ATPase CopA from Escherichia coli was expressed and purified in fully functional form and demonstrated to bind Cu(I) with subfemtomolar affinity. It was incorporated into the lipid membrane of giant unilamellar vesicles (GUVs) whose dimensions match those of eukaryotic cells. An ¹H NMR approach provided a quantitative ATPase activity assay for the enzyme either dissolved in detergent or embedded in GUV membranes. The activity varied with the Cu(I) availability in an optimized assay solution for either environment, demonstrating a direct correlation between ATPase activity and Cu(I) transport. Quantitative analysis of the Cu content trapped by the GUVs is consistent with a Cu:ATP turnover ratio of 1.

Thiol-based copper handling by the copper chaperone Atox1

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

The Copper(II)-Catalyzed Oxidation of Glutathione

The kinetics and mechanisms of the copper(II)-catalyzed GSH (glutathione) oxidation are examined in the light of its biological importance and in the use of blood and/or saliva samples for GSH monitoring. The rates of the free thiol consumption were measured spectrophotometrically by reaction with DTNB (5,5'-dithiobis-(2-nitrobenzoic acid)), showing that GSH is not auto-oxidized by oxygen in the absence of a catalyst. In the presence of Cu²⁺ , reactions with two timescales were observed. The first step (short timescale) involves the fast formation of a copper-glutathione complex by the cysteine thiol. The second step (longer timescale) is the overall oxidation of GSH to GSSG (glutathione disulfide) catalyzed by copper(II). When the initial concentrations of GSH are at least threefold in excess of Cu²⁺ , the rate law is deduced to be -d[thiol]/dt=k[copper-glutathione complex][O₂ ]^0.5 [H₂ O₂ ]^-0.5 . The 0.5^th reaction order with respect to O₂ reveals a pre-equilibrium prior to the rate-determining step of the GSSG formation. In contrast to [Cu²⁺ ] and [O₂ ], the rate of the reactions decreases with increasing concentrations of GSH. This inverse relationship is proposed to be a result of the competing formation of an inactive form of the copper-glutathione complex (binding to glutamic and/or glycine moieties).

Reaction Mechanisms of Metals with Hydrogen Sulfide and Thiols in Model Wine. Part 1: Copper-Catalyzed Oxidation

Sulfidic off-odors as a result of hydrogen sulfide (H2S) and low-molecular-weight thiols are commonly encountered in wine production. These odors are usually removed by the process of Cu(II) fining, a process that remains poorly understood. The present study aims to elucidate the underlying mechanisms by which Cu(II) interacts with H2S and thiol compounds (RSH) under wine-like conditions. Copper complex formation was monitored along with H2S, thiol, oxygen, and acetaldehyde concentrations after the addition of Cu(II) (50 or 100 μM) to air-saturated model wine solutions containing H2S, cysteine, 6-sulfanylhexan-1-ol, or 3-sulfanylhexan-1-ol (300 μM each). The presence of H2S and thiols in excess to Cu(II) led to the rapid formation of ∼1.4:1 H2S/Cu and ∼2:1 thiol/Cu complexes, resulting in the oxidation of H2S and thiols and reduction of Cu(II) to Cu(I), which reacted with oxygen. H2S was observed to initially oxidize rather than form insoluble copper sulfide. The proposed reaction mechanisms provide insight into the extent to which H2S can be selectively removed in the presence of thiols in wine.

Development of new peptide-based receptor of fluorescent probe with femtomolar affinity for Cu(+) and detection of Cu(+) in Golgi apparatus

Developing fluorescent probes for monitoring intracellular Cu(+) is important for human health and disease, whereas a few types of their receptors showing a limited range of binding affinities for Cu(+) have been reported. In the present study, we first report a novel peptide receptor of a fluorescent probe for the detection of Cu(+). Dansyl-labeled tripeptide probe (Dns-LLC) formed a 1:1 complex with Cu(+) and showed a turn-on fluorescent response to Cu(+) in aqueous buffered solutions. The dissociation constant of Dns-LLC for Cu(+) was determined to be 12 fM, showing that Dns-LLC had more potent binding affinity for Cu(+) than those of previously reported chemical probes for Cu(+). The binding mode study showed that the thiol group of the peptide receptor plays a critical role in potent binding with Cu(+) and the sulfonamide and amide groups of the probe might cooperate to form a complex with Cu(+). Dns-LLC detected Cu(+) selectively by a turn-on response among various biologically relevant metal ions, including Cu(2+) and Zn(2+). The selectivity of the peptide-based probe for Cu(+) was strongly dependent on the position of the cysteine residue in the peptide receptor part. The fluorescent peptide-based probe penetrated the living RKO cells and successfully detected Cu(+) in the Golgi apparatus in live cells by a turn-on response. Given the growing interest in imaging Cu(+) in live cells, a novel peptide receptor of Cu(+) will offer the potential for developing a variety of fluorescent probes for Cu(+) in the field of copper biochemistry.

Organometallic Half-Sandwich Dichloridoruthenium(II) Complexes with 7-Azaindoles: Synthesis, Characterization and Elucidation of Their Anticancer Inactivity against A2780 Cell Line

A series of organometallic half-sandwich dichloridoruthenium(II) complexes of the general formula [Ru(η6-p-cym)(naza)Cl2] (1-8; p-cym = p-cymene; naza = 7-azaindole or its derivatives) was synthesised and fully characterized by elemental analysis, mass spectrometry, and infrared and multinuclear NMR spectroscopy. A single-crystal X-ray structural analysis of [Ru(η6-p-cym)(2Me4Claza)Cl2] (6) revealed a typical piano-stool geometry with an N7-coordination mode of 2-methyl-4-chloro-7-azaindole (2Me4Claza). The complexes have been found to be inactive against human ovarian cancer cell line A2780 up to the highest applied concentration (IC50 > 50.0 μM). An inactivity of the complexes is caused by their instability in water-containing solvents connected with a release of the naza N-donor ligand, as proved by the detailed 1H NMR, mass spectrometry and fluorescence experiments.

DFT Investigation of the Mechanism of Action of Organoiridium(III) Complexes As Anticancer Agents

The potential use of synthetic metal complexes able to catalyze chemical transformations in living organisms is currently attracting a great deal of attention. Recently, organometallic ruthenium and iridium complexes have revealed an unexpected ability to modulate the redox status of cancer cells. In particular, half-sandwich organoiridium(III) cyclopentadienyl complexes of general formula [(η(5)-Cp(x))Ir(III)(X(∧)Y)Z](0/+), where Cp(x) = Cp*, Cp(xph) (tetramethyl-(phenyl)cyclopentadienyl) or Cp(xbiph) (tetramethyl(biphenyl)-cyclopentadienyl), X(∧)Y = bidentate ligand with nitrogen, oxygen, and/or carbon donor atoms, and Z = Cl, H2O, or pyridine (py) have shown promising antiproliferative activity toward cancer cells, higher potency than cisplatin, and a different mechanism of action due to the increase of the oxidative stress in cells. As such, complexes can belong to the class of DNA interacting compounds and attack on DNA can represent a secondary mechanism of action. We have explored here by means of density functional calculations (M06-L) and with the support of experimental observations for both [(η(5)-Cp(xbiph))Ir-(phpy) (Cl)], 1-Cl, and [(η(5)-Cp(xbiph))Ir-(phpy) (py)], 1-py, complexes the mechanistic aspects of the hydrolysis reaction, H2O2 ROS production by assisted hydride transfer from NADH to molecular oxygen, interaction with purine nucleobases adenine and guanine as well as gluthatione, that is highly abundant in cells, alongside the reaction mechanism for the oxidation of the formed sulfur-coordinated thiolate to the corresponding sulfenato complex. The comparison between kinetic and thermodynamic parameters calculated for all the involved processes shows that, according to the hypothesis based on experimental findings, the interaction with the tripeptide glutathione causes deactivation of 1-Cl, whereas 1-py, in both its aquated and nonaquated form, can induce cell apoptosis in a dual manner: DNA damage and H2O2 ROS production to increase oxidative stress.

Recognition- and reactivity-based fluorescent probes for studying transition metal signaling in living systems

Metals are essential for life, playing critical roles in all aspects of the central dogma of biology (e.g., the transcription and translation of nucleic acids and synthesis of proteins). Redox-inactive alkali, alkaline earth, and transition metals such as sodium, potassium, calcium, and zinc are widely recognized as dynamic signals, whereas redox-active transition metals such as copper and iron are traditionally thought of as sequestered by protein ligands, including as static enzyme cofactors, in part because of their potential to trigger oxidative stress and damage via Fenton chemistry. Metals in biology can be broadly categorized into two pools: static and labile. In the former, proteins and other macromolecules tightly bind metals; in the latter, metals are bound relatively weakly to cellular ligands, including proteins and low molecular weight ligands. Fluorescent probes can be useful tools for studying the roles of transition metals in their labile forms. Probes for imaging transition metal dynamics in living systems must meet several stringent criteria. In addition to exhibiting desirable photophysical properties and biocompatibility, they must be selective and show a fluorescence turn-on response to the metal of interest. To meet this challenge, we have pursued two general strategies for metal detection, termed “recognition” and “reactivity”. Our design of transition metal probes makes use of a recognition-based approach for copper and nickel and a reactivity-based approach for cobalt and iron. This Account summarizes progress in our laboratory on both the development and application of fluorescent probes to identify and study the signaling roles of transition metals in biology. In conjunction with complementary methods for direct metal detection and genetic and/or pharmacological manipulations, fluorescent probes for transition metals have helped reveal a number of principles underlying transition metal dynamics. In this Account, we give three recent examples from our laboratory and collaborations in which applications of chemical probes reveal that labile copper contributes to various physiologies. The first example shows that copper is an endogenous regulator of neuronal activity, the second illustrates cellular prioritization of mitochondrial copper homeostasis, and the third identifies the “cuprosome” as a new copper storage compartment in Chlamydomonas reinhardtii green algae. Indeed, recognition- and reactivity-based fluorescent probes have helped to uncover new biological roles for labile transition metals, and the further development of fluorescent probes, including ones with varied K_d values and new reaction triggers and recognition receptors, will continue to reveal exciting and new biological roles for labile transition metals.

Redox-implications associated with the formation of complexes between copper ions and reduced or oxidized glutathione

Binding of copper by reduced glutathione (GSH) is generally seen as a mechanism to lower, if not abolish, the otherwise high electrophilicity and redox activity of its free ions. In recent years, however, this concept has been contradicted by new evidence revealing that, rather than stabilizing free copper ions, its binding to GSH leads to the formation of a Cu(I)-[GSH]2 complex capable of reducing molecular oxygen into superoxide. It is now understood that, under conditions leading to the removal of such radicals, the Cu(I)-[GSH]2 complex is readily oxidized into Cu(II)-GSSG. Interestingly, in the presence of a GSH excess, the latter complex is able to regenerate the superoxide-generating capacity of the complex it originated from, opening the possibility that a GSH-dependent interplay exists between the reduced and the oxidized glutathione forms of these copper-complexes. Furthermore, recent evidence obtained from experiments conducted in non-cellular systems and intact mitochondria indicates that the Cu(II)-GSSG complex is also able to function in a catalytic manner as an efficient superoxide dismutating- and catalase-like molecule. Here we review and discuss the most relevant chemical and biological evidence on the formation of the Cu(I)-[GSH]2 and Cu(II)-GSSG complexes and on the potential redox implications associated with their intracellular occurrence.

Structure and vibrations of glutathione studied by vibrational spectroscopy and density functional theory

The vibrational properties of glutathione have been investigated by infrared absorption and Raman spectroscopic techniques, and density functional theory calculations at the B3LYP/6-31+G(d,p) level. Assignments of all the experimentally observed vibrational bands have been done with the help of simulated vibrational spectra and potential energy distribution calculations of glutathione water cluster, which includes the effect of hydrogen bonding. Optimized molecular parameters of energy minimized structure have been compared with the available experimental values. Calculated molecular parameters of glutathione-water cluster match well with the experimental values. Some of the calculated molecular parameters and vibrational frequencies of vapor phase glutathione-water cluster suggest participation of some atoms of glutathione in hydrogen bonding. Experimentally observed UV-Visible absorption spectrum of glutathione has also been reported. Observed band at 203 nm has been assigned to electronic transitions calculated with time dependent density functional theory.

Synthetic fluorescent probes for studying copper in biological systems

The potent redox activity of copper is required for sustaining life. Mismanagement of its cellular pools, however, can result in oxidative stress and damage connected to aging, neurodegenerative diseases, and metabolic disorders. Therefore, copper homeostasis is tightly regulated by cells and tissues. Whereas copper and other transition metal ions are commonly thought of as static cofactors buried within protein active sites, emerging data points to the presence of additional loosely bound, labile pools that can participate in dynamic signalling pathways. Against this backdrop, we review advances in sensing labile copper pools and understanding their functions using synthetic fluorescent indicators. Following brief introductions to cellular copper homeostasis and considerations in sensor design, we survey available fluorescent copper probes and evaluate their properties in the context of their utility as effective biological screening tools. We emphasize the need for combined chemical and biological evaluation of these reagents, as well as the value of complementing probe data with other techniques for characterizing the different pools of metal ions in biological systems. This holistic approach will maximize the exciting opportunities for these and related chemical technologies in the study and discovery of novel biology of metals.

Formation constants of copper(i) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye

Speciation modelling incorporating redox equilibria provides a plausible explanation for copper deposition in the human eye associated with Wilson's disease.

Subcellular metal imaging identifies dynamic sites of Cu accumulation in Chlamydomonas

We identified a Cu-accumulating structure with a dynamic role in intracellular Cu homeostasis. During Zn limitation, Chlamydomonas reinhardtii hyperaccumulates Cu, a process dependent on the nutritional Cu sensor CRR1, but it is functionally Cu deficient. Visualization of intracellular Cu revealed major Cu accumulation sites coincident with electron-dense structures that stained positive for low pH and polyphosphate, suggesting that they are lysosome-related organelles. Nano-secondary ion MS showed colocalization of Ca and Cu, and X-ray absorption spectroscopy was consistent with Cu(+) accumulation in an ordered structure. Zn resupply restored Cu homeostasis concomitant with reduced abundance of these structures. Cu isotope labeling demonstrated that sequestered Cu(+) became bioavailable for the synthesis of plastocyanin, and transcriptome profiling indicated that mobilized Cu became visible to CRR1. Cu trafficking to intracellular accumulation sites may be a strategy for preventing protein mismetallation during Zn deficiency and enabling efficient cuproprotein metallation or remetallation upon Zn resupply.

Copper is an endogenous modulator of neural circuit spontaneous activity

For reasons that remain insufficiently understood, the brain requires among the highest levels of metals in the body for normal function. The traditional paradigm for this organ and others is that fluxes of alkali and alkaline earth metals are required for signaling, but transition metals are maintained in static, tightly bound reservoirs for metabolism and protection against oxidative stress. Here we show that copper is an endogenous modulator of spontaneous activity, a property of functional neural circuitry. Using Copper Fluor-3 (CF3), a new fluorescent Cu(+) sensor for one- and two-photon imaging, we show that neurons and neural tissue maintain basal stores of loosely bound copper that can be attenuated by chelation, which define a labile copper pool. Targeted disruption of these labile copper stores by acute chelation or genetic knockdown of the CTR1 (copper transporter 1) copper channel alters the spatiotemporal properties of spontaneous activity in developing hippocampal and retinal circuits. The data identify an essential role for copper neuronal function and suggest broader contributions of this transition metal to cell signaling.

Dendrimer–folate–copper conjugates as bioprobes for synchrotron X-ray fluorescence imaging

We present a bioprobe for synchrotron X-ray fluorescence imaging based on dendrimer–folate–copper conjugates, which exhibit excellent FR-targeting properties in KB cells.

Letter: Mass spectrometric approach of high pH- and copper-induced glutathione oxidation

The interaction between copper ions and gamma-L-glutamyl-L-cysteinyl-glycine [glutathione (GSH)] molecules may lead to the formation of the physiologically occurring Cu[I)-[GSH]2 and Cu(II)-GSSG complexes. Since glutathione depletion in neurons and aberrant copper metabolism have been implicated in several neurodegenerative disorders, we studied here the interaction of GSH with copper ions (Cu2+) by electrospray ionization ion trap mass spectrometry (ESI-IT-MS). Besides, we extended this approach to pH in excess of 10 by adding ethanolamine to the solution being investigated. As a result, the ESI-IT-MS spectra revealed novel aspects regarding the speciation of copper-glutathione complex.

A novel glutathione-hydroxycinnamic acid product generated in oxidative wine conditions

This study characterizes a novel glutathione-substituted dihydroxyphenyl compound formed during the oxidation of white wine and model wine solutions, which may contribute to the synergistic role of glutathione and hydroxycinnamic acids in delaying oxidative coloration. The critical components for the formation of the compound were found to be hydroxycinnamic acids and glutathione, while ascorbic acid enabled the product to accumulate to higher concentrations. The presence of the wine components important in other wine oxidation mechanisms, (+)-catechin, ethanol and/or tartaric acid, was not essential for the formation of this new compound. Via LC-MS/MS, HR-MS and (1)H NMR (1D and 2D NMR) analyses, the major isomer of the compound formed from glutathione and caffeic acid was found to be 4-[(E)-2'-(S)-glutathionyl ethenyl]-catechol (GEC). Equivalent products were also confirmed via LC-MS/MS for other hydroxycinnamic acids (i.e., ferulic and coumaric acids). Only trace amounts of GEC were formed with the quinic ester of caffeic acid (i.e., chlorogenic acid), and no equivalent product was found for cinnamic acid. GEC was detected in a variety of white wines supplemented with glutathione and caffeic acid. A radical mechanism for the formation of the styrene-glutathione derivatives is proposed.