Human copper transporter ATP7B (Wilson disease protein) forms stable dimers in vitro and in cells

Epigallocatechin Gallate Promotes Cuproptosis via the MTF1/ATP7B Axis in Hepatocellular Carcinoma

BACKGROUND

Cuproptosis is a form of copper-dependent non-apoptotic cell death. Cancer cells that prefer to use aerobic glycolysis for energy generation are commonly insensitive to cuproptosis, which hinders its application for cancer treatment. Epigallocatechin gallate (EGCG) possesses diverse pharmacological activities. However, the association between EGCG and cuproptosis has not been studied.

METHODS

The cell viability, proliferation, and cuproptosis-related protein levels were detected to investigate whether EGCG enhances the sensitivity of HCC cells to cuproptosis. The intracellular copper level, related copper metabolism proteins, and gene expression were detected to explore the mechanisms. In addition, a nude mouse xenograft model was established to determine the effects of EGCG on cuproptosis in tumor tissues.

RESULTS

The combination of EGCG and copper ionophores significantly enhanced the mortality of HCC cells and heightened the sensitivity of HCC cells to cuproptosis. There was a notable reduction in the expression of copper export protein copper-transporting P-type ATPase (ATP7B). EGCG effectively suppressed metal regulatory transcription factor (MTF1) expression and subsequently hindered the transcriptional regulation of ATP7B. EGCG also facilitated the intratumoral accumulation of copper and augmented susceptibility to cuproptosis in vivo.

CONCLUSIONS

EGCG can increase the sensitivity of hepatocellular carcinoma cells to cuproptosis by promoting intracellular copper accumulation through the MTF1/ATP7B axis.

Mammalian copper homeostasis: physiological roles and molecular mechanisms

In the past decade, evidence for the numerous roles of copper (Cu) in mammalian physiology has grown exponentially. The discoveries of Cu involvement in cell signaling, autophagy, cell motility, differentiation, and regulated cell death (cuproptosis) have markedly extended the list of already known functions of Cu, such as a cofactor of essential metabolic enzymes, a protein structural component, and a regulator of protein trafficking. Novel and unexpected functions of Cu transporting proteins and enzymes have been identified, and new disorders of Cu homeostasis have been described. Significant progress has been made in the mechanistic studies of two classic disorders of Cu metabolism, Menkes disease and Wilson's disease, which paved the way for novel approaches to their treatment. The discovery of cuproptosis and the role of Cu in cell metastatic growth have markedly increased interest in targeting Cu homeostatic pathways to treat cancer. In this review, we summarize the established concepts in the field of mammalian Cu physiology and discuss how new discoveries of the past decade expand and modify these concepts. The roles of Cu in brain metabolism and in cell functional speciation and a recently discovered regulated cell death have attracted significant attention and are highlighted in this review.

Structure and mechanism of the human copper transporting ATPases: Fitting the pieces into a moving puzzle

Human copper transporters ATP7B and ATP7A deliver copper to biosynthetic pathways and maintain copper homeostasis in the cell. These enzymes combine several challenges for structural biology because they are large low abundance membrane proteins with many highly mobile domains and long disordered loops. No method has yet succeeded in solving the structure of the complete fully functional protein. Still, X-ray crystallography, Cryo-EM and NMR helped to piece together a structure based model of the enzyme activity and regulation by copper. We review the structures of ATP7B and ATP7A with an emphasis on the mechanistic insights into the unique aspects of the transport function and regulation of the human copper ATPases that have emerged from more than twenty years of research.

Epidemiology of Wilson's Disease and Pathogenic Variants of the ATP7B Gene Leading to Diversified Protein Disfunctions

Wilson's disease (WD) is an autosomal recessive disorder characterized by toxic accumulation of copper in the liver, brain, and other organs. The disease is caused by pathogenic variants in the ATP7B gene, which encodes a P-type copper transport ATPase. Diagnosing WD is associated with numerous difficulties due to the wide range of clinical manifestations and its unknown dependence on the physiological characteristics of the patient. This leads to a delay in the start of therapy and the subsequent deterioration of the patient's condition. However, in recent years, molecular genetic testing of patients using next generation sequencing (NGS) has been gaining popularity. This immediately affected the detection speed of WD. If, previously, the frequency of this disease was estimated at 1:35,000-45,000 people, now, when conducting large molecular genetic studies, the frequency is calculated as 1:7026 people. This certainly points to the problem of identifying WD patients. This review provides an update on the performance of epidemiological studies of WD and describes normal physiological functions of the protein and diversified disfunctions depending on pathogenic variants of the ATP7B gene. Future prospects in the development of WD genetic diagnostics are also discussed.

Copper in Gynecological Diseases

Copper (Cu) is an essential micronutrient for the correct development of eukaryotic organisms. This metal plays a key role in many cellular and physiological activities, including enzymatic activity, oxygen transport, and cell signaling. Although the redox activity of Cu is crucial for enzymatic reactions, this property also makes it potentially toxic when found at high levels. Due to this dual action of Cu, highly regulated mechanisms are necessary to prevent both the deficiency and the accumulation of this metal since its dyshomeostasis may favor the development of multiple diseases, such as Menkes' and Wilson's diseases, neurodegenerative diseases, diabetes mellitus, and cancer. As the relationship between Cu and cancer has been the most studied, we analyze how this metal can affect three fundamental processes for tumor progression: cell proliferation, angiogenesis, and metastasis. Gynecological diseases are characterized by high prevalence, morbidity, and mortality, depending on the case, and mainly include benign and malignant tumors. The cellular processes that promote their progression are affected by Cu, and the mechanisms that occur may be similar. We analyze the crosstalk between Cu deregulation and gynecological diseases, focusing on therapeutic strategies derived from this metal.

Copper binding leads to increased dynamics in the regulatory N-terminal domain of full-length human copper transporter ATP7B

ATP7B is a human copper-transporting P_1B-type ATPase that is involved in copper homeostasis and resistance to platinum drugs in cancer cells. ATP7B consists of a copper-transporting core and a regulatory N-terminal tail that contains six metal-binding domains (MBD1-6) connected by linker regions. The MBDs can bind copper, which changes the dynamics of the regulatory domain and activates the protein, but the underlying mechanism remains unknown. To identify possible copper-specific structural dynamics involved in transport regulation, we constructed a model of ATP7B spanning the N-terminal tail and core catalytic domains and performed molecular dynamics (MD) simulations with (holo) and without (apo) copper ions bound to the MBDs. In the holo protein, MBD2, MBD3 and MBD5 showed enhanced mobilities, which resulted in a more extended N-terminal regulatory region. The observed separation of MBD2 and MBD3 from the core protein supports a mechanism where copper binding activates the ATP7B protein by reducing interactions among MBD1-3 and between MBD1-3 and the core protein. We also observed an increased interaction between MBD5 and the core protein that brought the copper-binding site of MBD5 closer to the high-affinity internal copper-binding site in the core protein. The simulation results assign specific, mechanistic roles to the metal-binding domains involved in ATP7B regulation that are testable in experimental settings.

Living organisms depend upon active transport against gradients across biological membranes for survival. Such transport can be accomplished by ATP-dependent membrane protein transporters for which the activity must be regulated to maintain optimal concentrations in the cellular compartments. The regulatory mechanisms often involve structural responses inherent to the protein structure, which because of their dynamic nature can be hard to assess experimentally. A prime example is regulation of cellular copper levels by a copper-binding tail in the human copper transporter ATP7B. Dysregulation can cause severe diseases, for example the copper metabolism disorder Wilson’s disease, which is caused by mutations in ATP7B regulation machinery. Due to the practical difficulties in working with membrane proteins, most studies of ATP7B have been conducted in the absence of the membrane-bound protein core. Here, we used computer simulations of full-length ATP7B to study how structural dynamics in the regulatory tail differ between copper-bound and copper-free states. Copper induced increased dynamics in the tail, resulting in an overall movement towards the ion-binding site in the protein core. The simulations identified several, hitherto not reported, interactions between the regulatory tail and the protein core that can be targeted experimentally to enhance our understanding of this medically relevant regulatory mechanism.

Wilson Disease: Update on Pathophysiology and Treatment

Wilson disease (WD) is a potentially fatal genetic disorder with a broad spectrum of phenotypic presentations. Inactivation of the copper (Cu) transporter ATP7B and Cu overload in tissues, especially in the liver, are established causes of WD. However, neither specific ATP7B mutations nor hepatic Cu levels, alone, explain the diverse clinical presentations of WD. Recently, the new molecular details of WD progression and metabolic signatures of WD phenotypes began to emerge. Studies in WD patients and animal models revealed the contributions of non-parenchymal liver cells and extrahepatic tissues to the liver phenotype, and pointed to dysregulation of nuclear receptors (NR), epigenetic modifications, and mitochondria dysfunction as important hallmarks of WD pathogenesis. This review summarizes recent advances in the characterization of WD pathophysiology and discusses emerging targets for improving WD diagnosis and treatment.

Structure of the Wilson disease copper transporter ATP7B

ATP7A and ATP7B, two homologous copper-transporting P1B-type ATPases, play crucial roles in cellular copper homeostasis, and mutations cause Menkes and Wilson diseases, respectively. ATP7A/B contains a P-type ATPase core consisting of a membrane transport domain and three cytoplasmic domains, the A, P, and N domains, and a unique amino terminus comprising six consecutive metal-binding domains. Here, we present a cryo-electron microscopy structure of frog ATP7B in a copper-free state. Interacting with both the A and P domains, the metal-binding domains are poised to exert copper-dependent regulation of ATP hydrolysis coupled to transmembrane copper transport. A ring of negatively charged residues lines the cytoplasmic copper entrance that is presumably gated by a conserved basic residue sitting at the center. Within the membrane, a network of copper-coordinating ligands delineates a stepwise copper transport pathway. This work provides the first glimpse into the structure and function of ATP7 proteins and facilitates understanding of disease mechanisms and development of rational therapies.

The CopA2-Type P1B-Type ATPase CcoI Serves as Central Hub for cbb 3-Type Cytochrome Oxidase Biogenesis

Copper (Cu)-transporting P_1B-type ATPases are ubiquitous metal transporters and crucial for maintaining Cu homeostasis in all domains of life. In bacteria, the P_1B-type ATPase CopA is required for Cu-detoxification and exports excess Cu(I) in an ATP-dependent reaction from the cytosol into the periplasm. CopA is a member of the CopA1-type ATPase family and has been biochemically and structurally characterized in detail. In contrast, less is known about members of the CopA2-type ATPase family, which are predicted to transport Cu(I) into the periplasm for cuproprotein maturation. One example is CcoI, which is required for the maturation of cbb ₃-type cytochrome oxidase (cbb ₃-Cox) in different species. Here, we reconstituted purified CcoI of Rhodobacter capsulatus into liposomes and determined Cu transport using solid-supported membrane electrophysiology. The data demonstrate ATP-dependent Cu(I) translocation by CcoI, while no transport is observed in the presence of a non-hydrolysable ATP analog. CcoI contains two cytosolically exposed N-terminal metal binding sites (N-MBSs), which are both important, but not essential for Cu delivery to cbb ₃-Cox. CcoI and cbb ₃-Cox activity assays in the presence of different Cu concentrations suggest that the glutaredoxin-like N-MBS1 is primarily involved in regulating the ATPase activity of CcoI, while the CopZ-like N-MBS2 is involved in Cu(I) acquisition. The interaction of CcoI with periplasmic Cu chaperones was analyzed by genetically fusing CcoI to the chaperone SenC. The CcoI-SenC fusion protein was fully functional in vivo and sufficient to provide Cu for cbb ₃-Cox maturation. In summary, our data demonstrate that CcoI provides the link between the cytosolic and periplasmic Cu chaperone networks during cbb ₃-Cox assembly.

Diagnosis of Wilson Disease and Its Phenotypes by Using Artificial Intelligence

WD is caused by ATP7B variants disrupting copper efflux resulting in excessive copper accumulation mainly in liver and brain. The diagnosis of WD is challenged by its variable clinical course, onset, morbidity, and ATP7B variant type. Currently it is diagnosed by a combination of clinical symptoms/signs, aberrant copper metabolism parameters (e.g., low ceruloplasmin serum levels and high urinary and hepatic copper concentrations), and genetic evidence of ATP7B mutations when available. As early diagnosis and treatment are key to favorable outcomes, it is critical to identify subjects before the onset of overtly detrimental clinical manifestations. To this end, we sought to improve WD diagnosis using artificial neural network algorithms (part of artificial intelligence) by integrating available clinical and molecular parameters. Surprisingly, WD diagnosis was based on plasma levels of glutamate, asparagine, taurine, and Fischer's ratio. As these amino acids are linked to the urea-Krebs' cycles, our study not only underscores the central role of hepatic mitochondria in WD pathology but also that most WD patients have underlying hepatic dysfunction. Our study provides novel evidence that artificial intelligence utilized for integrated analysis for WD may result in earlier diagnosis and mechanistically relevant treatments for patients with WD.

Nanobodies against the metal binding domains of ATP7B as tools to study copper transport in the cell

Nanobodies are genetically engineered single domain antibodies derived from the unusual heavy-chain only antibodies found in llamas and camels. The small size of the nanobodies and flexible selection schemes make them uniquely versatile tools for protein biochemistry and cell biology. We have developed a panel of nanobodies against the metal binding domains of the human copper transporter ATP7B, a multidomain membrane protein with a complex regulation of enzymatic activity and intracellular localization. To enable the use of the nanobodies as tools to investigate copper transport in the cell, we characterized their binding sites and affinity by isothermal titration calorimetry and NMR. We have identified nanobodies against each of the first four metal binding domains of ATP7B, with a wide affinity range, as evidenced by dissociation constants from below 10-9 to 10-6 M. We found both the inhibitory and activating nanobodies among those tested. The diverse properties of the nanobodies make the panel useful for the structural studies of ATP7B, immunoaffinity purification of the protein, modulation of its activity in the cell, protein dynamics studies, and as mimics of copper chaperone ATOX1, the natural interaction partner of ATP7B.

Structural Role of the First Four Transmembrane Helices in ZntA, a P1B-Type ATPase from Escherichia coli

ZntA from Escherichia coli confers resistance to toxic concentrations of Pb²⁺, Zn²⁺, and Cd²⁺. It is a member of the P_1B-ATPase transporter superfamily, which includes the human Cu⁺-transporting proteins ATP7A and ATP7B. P_1B-type ATPases typically have a hydrophilic N-terminal metal-binding domain and eight transmembrane helices. A splice variant of ATP7B was reported, which has 100-fold higher night-specific expression in the pineal gland; it lacks the entire N-terminal domain and the first four transmembrane helices. Here, we report our findings with Δ231-ZntA, a similar truncation we created in ZntA. Δ231-ZntA has no in vivo and greatly reduced in vitro activity. It binds one metal ion per dimer at the transmembrane site, with a 15-19000-fold higher binding affinity, indicating highly significant changes in the dimer structure of Δ231-ZntA relative to that of ZntA. Cd²⁺ has the highest affinity for Δ231-ZntA, in contrast to ZntA, which has the highest affinity for Pb²⁺. Site-specific mutagenesis of the metal-binding residues, ³⁹²Cys, ³⁹⁴Cys, and ⁷¹⁴Asp, showed that there is considerable flexibility at the metal-binding site, with any two of these three residues able to bind Zn²⁺ and Pb²⁺ unlike in ZntA. However, Cd²⁺ binds to only ³⁹²Cys and ⁷¹⁴Asp, with ³⁹⁴Cys not involved in Cd²⁺ binding. Three-dimensional homology models show that there is a dramatic difference between the ZntA and Δ231-ZntA dimer structures, which help to explain these observations. Therefore, the first four transmembrane helices in ZntA and P_1B-type ATPases play an important role in maintaining the correct dimer structure.

Dimerization of SERCA2a Enhances Transport Rate and Improves Energetic Efficiency in Living Cells

The type 2a sarco/endoplasmic reticulum (ER) Ca²⁺-ATPase (SERCA2a) plays a key role in intracellular Ca²⁺ regulation in the heart. We have previously shown evidence of stable homodimers of SERCA2a in heterologous cells and cardiomyocytes. However, the functional significance of the pump dimerization remains unclear. Here, we analyzed how SERCA2a dimerization affects ER Ca²⁺ transport. Fluorescence resonance energy transfer experiments in HEK293 cells transfected with fluorescently labeled SERCA2a revealed increasing dimerization of Ca²⁺ pumps with increasing expression level. This concentration-dependent dimerization provided means of comparison of the functional characteristics of monomeric and dimeric pumps. SERCA-mediated Ca²⁺ uptake was measured with the ER-targeted Ca²⁺ sensor R-CEPIA1er in cells cotransfected with SERCA2a and ryanodine receptor. For each individual cell, the maximal ER Ca²⁺ uptake rate and the maximal Ca²⁺ load, together with the pump expression level, were analyzed. This analysis revealed that the ER Ca²⁺ uptake rate increased as a function of SERCA2a expression, with a particularly steep, nonlinear increase at high expression levels. Interestingly, the maximal ER Ca²⁺ load also increased with an increase in the pump expression level, suggesting improved catalytic efficiency of the dimeric species. Reciprocally, thapsigargin inhibition of a fraction of the population of SERCA2a reduced not only the maximal ER Ca²⁺ uptake rate but also the maximal Ca²⁺ load. These data suggest that SERCA2a dimerization regulates Ca²⁺ transport by improving both the SERCA2a turnover rate and catalytic efficacy. Analysis of ER Ca²⁺ uptake in cells cotransfected with human wild-type SERCA2a (SERCA2a^WT) and SERCA2a mutants with different catalytic activity revealed that an intact catalytic cycle in both protomers is required for enhancing the efficacy of Ca²⁺ transport by a dimer. The data are consistent with the hypothesis of functional coupling of two SERCA2a protomers in a dimer that reduces the energy barrier of rate-limiting steps of the catalytic cycle of Ca²⁺ transport.

Analysis of Wilson disease mutations revealed that interactions between different ATP7B mutants modify their properties

Wilson disease (WD) is an autosomal-recessive disorder caused by mutations in the copper (Cu)-transporter ATP7B. Thus far, studies of WD mutations have been limited to analysis of ATP7B mutants in the homozygous states. However, the majority of WD patients are compound-heterozygous, and how different mutations on two alleles impact ATP7B properties is unclear. We characterized five mutations identified in Indian WD patients, first by expressing each alone and then by co-expressing two mutants with dissimilar properties. Mutations located in the regulatory domains of ATP7B-A595T, S1362A, and S1426I-do not affect ATP7B targeting to the trans-Golgi network (TGN) but reduce its Cu-transport activity. The S1362A mutation also inhibits Cu-dependent trafficking from the TGN. The G1061E and G1101R mutations, which are located within the ATP-binding domain, cause ATP7B retention in the endoplasmic reticulum, inhibit Cu-transport, and lower ATP7B protein abundance. Co-expression of the A595T and G1061E mutations, which mimics the compound-heterozygous state of some WD patients, revealed an interaction between these mutants that altered their intracellular localization and trafficking under both low and high Cu conditions. These findings highlight the need to study WD variants in both the homozygous and compound-heterozygous states to better understand the genotype-phenotype correlations and incomplete penetrance observed in WD.

The co-occurrence of Wilson disease and X-linked agammaglobulinemia in one family highlights the promising diagnostic potential of proteolytic analysis

BACKGROUND

We report the first case of a family with co-occurrence of Wilson disease (WD), an autosomal recessive disorder of copper metabolism, and X-linked agammaglobulinemia (XLA), a primary immunodeficiency disorder (PIDD) that features marked reduction in circulating B lymphocytes and serum immunoglobulins.

METHODS AND RESULTS

Through utilization of a multiplexed biomarker peptide quantification method known as the immuno-SRM assay, we were able to simultaneously and independently identify which family members are affected with WD and which are affected with XLA using dried blood spots (DBS).

CONCLUSION

Being able to delineate multiple diagnoses using proteolytic analysis from a single DBS provides support for implementation of this methodology for clinical diagnostic use as well as large-scale population screening, such as newborn screening (NBS). This could allow for early identification and treatment of affected individuals with WD or XLA, which have been shown to reduce morbidity and decrease mortality in these two populations.

Copper homeostasis as target of both consolidated and innovative strategies of anti-tumor therapy

BACKGROUND

Copper was reported to be involved in the onset and progression of cancer. Proteins in charge of copper uptake and distribution, as well as cuproenzymes, are altered in cancer. More recently, proteins involved in signaling cascades, regulating cell proliferation, and anti-apoptotic protein factors were found to interact with copper. Therefore, therapeutic strategies using copper complexing molecules have been proposed for cancer therapy and used in clinical trials.

OBJECTIVES

This review will focus on novel findings about the involvement of copper and cupro-proteins in cancer dissemination process, epithelium to mesenchymal transition and vascularization. Particularly, implication of well-established (e.g. lysil oxidase) or newly identified copper-binding proteins (e.g. MEMO1), as well as their interplay, will be discussed. Moreover, we will describe recently synthesized copper complexes, including plant-derived ones, and their efficacy in contrasting cancer development.

CONCLUSIONS

The research on the involvement of copper in cancer is still an open field. Further investigation is required to unveil the mechanisms involved in copper delivery to the novel copper-binding proteins, which may identify other possible gene and protein targets for cancer therapy.

Improving Editing Efficiency for the Sequences with NGH PAM Using xCas9-Derived Base Editors

The development of CRISPR/Cas9-mediated base editors (BEs) provided a versatile tool for precise genome editing. The recently developed xCas9-derived base editors (xBEs) that recognize the NG PAM substantially expand the targeting scope in the genome, while their editing efficiency needs to be improved. Here, we described an improved version of xBEs by fusing the BPNLS and Gam to the N terminus of xBEs (BPNLS-Gam-xBE3 and BPNLS-xABE), and this version of base editor displayed higher targeting efficiency for the majority of detected sites. By using this improved version of xBEs, we successfully created and corrected pathogenic mutations at genomic sites with the NGN protospacer-adjacent motif in human cells. Lastly, we used BPNLS-Gam-xBE3 to model pathogenic mutations in discarded human tripronuclear (3PN) zygotes, and no obvious off-targets and indels were detected. Taken together, the data in our study offer an efficient tool for precise genome editing and, thus, an enriched base editing toolkit.

Liver Expression of a MiniATP7B Gene Results in Long-Term Restoration of Copper Homeostasis in a Wilson Disease Model in Mice

Gene therapy with an adeno-associated vector (AAV) serotype 8 encoding the human ATPase copper-transporting beta polypeptide (ATP7B) complementary DNA (cDNA; AAV8-ATP7B) is able to provide long-term copper metabolism correction in 6-week-old male Wilson disease (WD) mice. However, the size of the genome (5.2 kilobases [kb]) surpasses the optimal packaging capacity of the vector, which resulted in low-yield production; in addition, further analyses in WD female mice and in animals with a more advanced disease revealed reduced therapeutic efficacy, as compared to younger males. To improve efficacy of the treatment, an optimized shorter AAV vector was generated, in which four out of six metal-binding domains (MBDs) were deleted from the ATP7B coding sequence, giving rise to the miniATP7B protein (Δ57-486-ATP7B). In contrast to AAV8-ATP7B, AAV8-miniATP7B could be produced at high titers and was able to restore copper homeostasis in 6- and 12-week-old male and female WD mice. In addition, a recently developed synthetic AAV vector, AAVAnc80, carrying the miniATP7B gene was similarly effective at preventing liver damage, restoring copper homeostasis, and improving survival 1 year after treatment. Transduction of approximately 20% of hepatocytes was sufficient to normalize copper homeostasis, suggesting that corrected hepatocytes are acting as a sink to eliminate excess of copper. Importantly, administration of AAVAnc80-miniATP7B was safe in healthy mice and did not result in copper deficiency. Conclusion: In summary, gene therapy using an optimized therapeutic cassette in different AAV systems provides long-term correction of copper metabolism regardless of sex or stage of disease in a clinically relevant WD mouse model. These results pave the way for the implementation of gene therapy in WD patients.

Update on the Diagnosis and Management of Wilson Disease

PURPOSE OF REVIEW

Exciting developments relating to Wilson disease (WD) have taken place with respect to both basic biological and clinical research. This review critically examines some of these findings and considers their implications for current thinking about WD. It is not a comprehensive review of WD as a clinical disorder.

RECENT FINDINGS

The structure of the gene product of ATP7B, abnormal in WD, is being worked out in detail, along with a broader description of how the protein ATP7B (Wilson ATPase) functions in cells including enterocytes, not only in relation to copper disposition but also to lipid synthesis. Recent population studies raise the possibility that WD displays incomplete penetrance. Innovative screening techniques may increase ascertainment. New strategies for diagnosing and treating WD are being developed. Several disorders have been identified which might qualify as WD-mimics. WD can be difficult to diagnose and treat. Insights from its pathobiology are providing new options for managing WD.

ATP7A and ATP7B copper transporters have distinct functions in the regulation of neuronal dopamine-β-hydroxylase

The copper (Cu) transporters ATPase copper-transporting alpha (ATP7A) and ATPase copper-transporting beta (ATP7B) are essential for the normal function of the mammalian central nervous system. Inactivation of ATP7A or ATP7B causes the severe neurological disorders, Menkes disease and Wilson disease, respectively. In both diseases, Cu imbalance is associated with abnormal levels of the catecholamine-type neurotransmitters dopamine and norepinephrine. Dopamine is converted to norepinephrine by dopamine-β-hydroxylase (DBH), which acquires its essential Cu cofactor from ATP7A. However, the role of ATP7B in catecholamine homeostasis is unclear. Here, using immunostaining of mouse brain sections and cultured cells, we show that DBH-containing neurons express both ATP7A and ATP7B. The two transporters are located in distinct cellular compartments and oppositely regulate the export of soluble DBH from cultured neuronal cells under resting conditions. Down-regulation of ATP7A, overexpression of ATP7B, and pharmacological Cu depletion increased DBH retention in cells. In contrast, ATP7B inactivation elevated extracellular DBH. Proteolytic processing and the specific activity of exported DBH were not affected by changes in ATP7B levels. These results establish distinct regulatory roles for ATP7A and ATP7B in neuronal cells and explain, in part, the lack of functional compensation between these two transporters in human disorders of Cu imbalance.

Mass spectrometric studies of Cu(I)-binding to the N-terminal domains of B. subtilis CopA and influence of bacillithiol

CopA is a Cu(I)-exporting transmembrane P_1B-type ATPase from Bacillus subtilis. It contains two N-terminal cytoplasmic domains, CopAab, which bind Cu(I) with high affinity and to form higher-order complexes with multiple Cu(I) ions. To determine the precise nature of these species, electrospray ionisation mass spectrometry (ESI-MS) under non-denaturing conditions was employed. Up to 1 Cu per CopAab resulted in Cu coordination to one or both CopAab domains. At >1 Cu/CopAab, two distinct dimeric charge state envelopes were observed, corresponding to distinct conformations, each with Cu₆(CopAab)₂ as its major form. The influence of the physiologically relevant low molecular weight thiol bacillithiol (BSH) on Cu(I)-binding to CopAab was assessed. Dimeric CopAab persisted in the presence of BSH, with previously undetected Cu₇(CopAab)₂ and Cu₆(CopAab)₂(BSH) forms apparent.

Sex Differences in Clinical Characteristics and Brain MRI Change in Patients With Wilson's Disease in a Chinese Population

Background: Wilson’s disease (WD) is an inborn copper metabolism disease. Sex differences in clinical features of WD patients have been reported; however, the effect of sex on brain MRI is still unclear, especially for Chinese WD patients. Therefore, we aimed to examine sex differences in clinical correlates and brain MRI changes in WD patients in a Chinese Han population.

Methods: 535 WD patients were enrolled and underwent MRI scanning. These patients were subdivided by the clinical symptoms, Kayser–Fleischer (K–F) rings, laboratory tests and sex. The mean age of onset and diagnosis, disease latency, localization of brain MRI lesions, and the level of copper metabolism were compared between male and female patients.

Results: The neuropsychiatric form (452 and 84.5%) was the most common subtype. Compared to female patients, male patients had a higher percentage in three clinical forms: neuropsychiatric form (263 and 58.2%), hepatic form (41 and 59.4%), and presymptomatic form (10 and 71.4%). In the neuropsychiatric form, male patients had the earlier age of onset and definitive diagnosis, and shorter time of disease latency than female patients. Putamen was the most common site for lesions in brain MRI of three groups. In the hepatic form, more male patients showed the ventricular widening than female patients (14/41 vs. 3/28; p < 0.05). The level of serum ceruloplasmin and copper of WD patients with neuropsychiatric form was higher than that of male patients with hepatic or presymptomatic form. In women, however, patients of presymptomatic form have the highest level of the ceruloplasmin, and the level of serum copper in hepatic patients was highest.

Conclusion: Our findings suggest sex differences in the percentage of three clinical forms. Meanwhile, the mean age of onset and diagnosis of female was higher than male, also happened in the disease latency. Only in the hepatic form, there was a sex difference in the ventricular widening.

A Luminal Loop of Wilson Disease Protein Binds Copper and Is Required for Protein Activity

The copper-transporting ATPase ATP7B is essential for loading of copper ions to copper-dependent enzymes in the secretory pathway; its inactivation results in Wilson disease. In contrast to copper-ion uptake by the cytoplasmic domains, ATP7B-mediated copper-ion release in the Golgi has not been explored yet. We demonstrate here that a luminal loop in ATP7B, rich in histidine/methionine residues, binds reduced copper (Cu(I)) ions, and identified copper-binding residues play an essential role in ATP7B-mediated metal ion release. NMR experiments on short-peptide models demonstrate that three methionine and two histidine residues are specifically involved in Cu(I) ion binding; with these residues replaced by alanines, no Cu(I) ion interaction is detected. Although more than one Cu(I) ion can interact with the wild-type peptide, removing either all histidine or all methionine residues reduces the stoichiometry to one Cu(I) ion binding per peptide. Using a yeast complementation assay, we show that for efficient copper transport by full-length ATP7B, the complete set of histidine and methionine residues in the lumen loop are required. The replacement of histidine/methionine residues by alanines does not perturb overall ATP7B structure, as the localization of ATP7B variants in yeast cells matches that of the wild-type protein. Thus, in similarity to ATP7A, ATP7B also appears to have a luminal “exit” copper ion site.

Modulating Chemosensitivity of Tumors to Platinum-Based Antitumor Drugs by Transcriptional Regulation of Copper Homeostasis

Platinum (Pt)-based antitumor agents have been effective in treating many human malignancies. Drug importing, intracellular shuffling, and exporting—carried out by the high-affinity copper (Cu) transporter (hCtr1), Cu chaperone (Ato x1), and Cu exporters (ATP7A and ATP7B), respectively—cumulatively contribute to the chemosensitivity of Pt drugs including cisplatin and carboplatin, but not oxaliplatin. This entire system can also handle Pt drugs via interactions between Pt and the thiol-containing amino acid residues in these proteins; the interactions are strongly influenced by cellular redox regulators such as glutathione. hCtr1 expression is induced by acute Cu deprivation, and the induction is regulated by the transcription factor specific protein 1 (Sp1) which by itself is also regulated by Cu concentration variations. Copper displaces zinc (Zn) coordination at the zinc finger (ZF) domains of Sp1 and inactivates its DNA binding, whereas Cu deprivation enhances Sp1-DNA interactions and increases Sp1 expression, which in turn upregulates hCtr1. Because of the shared transport system, chemosensitivity of Pt drugs can be modulated by targeting Cu transporters. A Cu-lowering agent (trientine) in combination with a Pt drug (carboplatin) has been used in clinical studies for overcoming Pt-resistance. Future research should aim at further developing effective Pt drug retention strategies for improving the treatment efficacy.

Characterization of the most frequent ATP7B mutation causing Wilson disease in hepatocytes from patient induced pluripotent stem cells

H1069Q substitution represents the most frequent mutation of the copper transporter ATP7B causing Wilson disease in Caucasian population. ATP7B localizes to the Golgi complex in hepatocytes but moves in response to copper overload to the endo-lysosomal compartment to support copper excretion via bile canaliculi. In heterologous or hepatoma-derived cell lines, overexpressed ATP7B-H1069Q is strongly retained in the ER and fails to move to the post-Golgi sites, resulting in toxic copper accumulation. However, this pathogenic mechanism has never been tested in patients' hepatocytes, while animal models recapitulating this form of WD are still lacking. To reach this goal, we have reprogrammed skin fibroblasts of homozygous ATP7B-H1069Q patients into induced pluripotent stem cells and differentiated them into hepatocyte-like cells. Surprisingly, in HLCs we found one third of ATP7B-H1069Q localized in the Golgi complex and able to move to the endo-lysosomal compartment upon copper stimulation. However, despite normal mRNA levels, the expression of the mutant protein was only 20% compared to the control because of endoplasmic reticulum-associated degradation. These results pinpoint rapid degradation as the major cause for loss of ATP7B function in H1069Q patients, and thus as the primary target for designing therapeutic strategies to rescue ATP7B-H1069Q function.

A glimpse into the regulation of the Wilson disease protein, ATP7B, sheds light on the complexity of mammalian apical trafficking pathways

Wilson disease (WD), a Mendelian disorder of copper metabolism caused by mutations in the ATP7B gene, manifests a large spectrum of phenotypic variability. This phenomenon of extensive symptom variation is not frequently associated with a monogenic disorder. We hypothesize that the phenotypic variability in WD is primarily driven by the variations in interacting proteins that regulate the ATP7B function and localization in the cell. Based on existing literature, we delineated a potential molecular mechanism for ATP7B mediated copper transport in the milieu of its interactome, its dysfunction in WD and the resulting variability in the phenotypic manifestation. Understanding the copper-induced apical trafficking of ATP7B also significantly contributes to the appreciation of the complexities of the ligand-induced transport pathway. We believe that this holistic view of WD will pave the way for a better opportunity for rational drug design and therapeutics.

Cu+-specific CopB transporter: Revising P1B-type ATPase classification

The copper-transporting P_1B-ATPases, which play a key role in cellular copper homeostasis, have been divided traditionally into two subfamilies, the P_1B-1-ATPases or CopAs and the P_1B-3-ATPases or CopBs. CopAs selectively export Cu⁺ whereas previous studies and bioinformatic analyses have suggested that CopBs are specific for Cu²⁺ export. Biochemical and spectroscopic characterization of Sphaerobacter thermophilus CopB (StCopB) show that, while it does bind Cu²⁺, the binding site is not the prototypical P_1B-ATPase transmembrane site and does not involve sulfur coordination as proposed previously. Most important, StCopB exhibits metal-stimulated ATPase activity in response to Cu⁺, but not Cu²⁺, indicating that it is actually a Cu⁺ transporter. X-ray absorption spectroscopic studies indicate that Cu⁺ is coordinated by four sulfur ligands, likely derived from conserved cysteine and methionine residues. The histidine-rich N-terminal region of StCopB is required for maximal activity, but is inhibitory in the presence of divalent metal ions. Finally, reconsideration of the P_1B-ATPase classification scheme suggests that the P_1B-1- and P_1B-3-ATPase subfamilies both comprise Cu⁺ transporters. These results are completely consistent with the known presence of only Cu⁺ within the reducing environment of the cytoplasm, which should eliminate the need for a Cu²⁺ P_1B-ATPase.

All Organic Label-like Copper(II) Ions Fluorescent Film Sensors with High Sensitivity and Stretchability

Deep learning and analysis of heavy metal concentration are very crucial to our life, for it plays an essential role in both environmental and human health. In this paper, we developed a new Cu (II) ions sensor made by all organic material with bending and stretching properties. The new sensor consists of chlorophyll-a extracted from fresh leaves of Common Garcinia, plant fiber and with the use of PDMS as a substrate. Fluorescence spectra study shows that chlorophyll-a is significantly much more sensitive to Cu (II) ions than any other heavy metal ions and the device sensitivity outperforms all the Cu (II) ions sensors ever reported. The result fully shows the selectivity of chlorophyll-a toward Cu (II) ions. Bending and stretching tests show that the sensor has an outstanding durability, which can be used to develop accompanying applications, such as real-time sampling and the analysis of Cu (II) concentration specified in athlete's sweat or patients with brain death and Parkinson's disease.

The six metal binding domains in human copper transporter, ATP7B: molecular biophysics and disease-causing mutations

Wilson Disease (WD) is a hereditary genetic disorder, which coincides with a dysfunctional copper (Cu) metabolism caused by mutations in ATP7B, a membrane-bound P1B-type ATPase responsible for Cu export from hepatic cells. The N-terminal part (~ 600 residues) of the multi-domain 1400-residue ATP7B constitutes six metal binding domains (MBDs), each of which can bind a copper ion, interact with other ATP7B domains as well as with different proteins. Although the ATP7B's MBDs have been investigated in vitro and in vivo intensively, it remains unclear how these domains modulate overall structure, dynamics, stability and function of ATP7B. The presence of six MBDs is unique to mammalian ATP7B homologs, and many WD causing missense mutations are found in these domains. Here, we have summarized previously reported in vitro biophysical data on the MBDs of ATP7B and WD point mutations located in these domains. Besides the demonstration of where the research field stands today, this review showcasts the need for further biophysical investigation about the roles of MBDs in ATP7B function. Molecular mechanisms of ATP7B are important not only in the development of new WD treatment but also for other aspects of human physiology where Cu transport plays a role.