Mutation spectrum of ATP7A, the gene defective in Menkes disease

Unraveling the Multifaceted Role of the Golgi Apparatus: Insights into Neuronal Plasticity, Development, Neurogenesis, Alzheimer's Disease, and SARS-CoV-2 Interactions

This article critically evaluates the multifunctional role of the Golgi apparatus within neurological paradigms. We succinctly highlight its influence on neuronal plasticity, development, and the vital trafficking and sorting mechanisms for proteins and lipids. The discourse further navigates to its regulatory prominence in neurogenesis and its implications in Alzheimer's Disease pathogenesis. The emerging nexus between the Golgi apparatus and SARS-CoV-2 underscores its potential in viral replication processes. This consolidation accentuates the Golgi apparatus's centrality in neurobiology and its intersections with both neurodegenerative and viral pathologies. In essence, understanding the Golgi's multifaceted functions harbors profound implications for future therapeutic innovations in neurological and viral afflictions.

Urological Problems in Patients with Menkes Disease

BACKGROUND

Menkes disease (MD) is a rare X-linked hereditary multisystemic disorder that is caused by dysfunction of copper metabolism. Patients with MD typically present with progressive neurodegeneration, some connective tissue abnormalities, and characteristic "kinky" hair. In addition, various types of urological complications are frequent in MD because of underlying connective tissue abnormalities. In this study, we studied the clinical features and outcomes of MD, focusing on urological complications.

METHODS

A total of 14 unrelated Korean pediatric patients (13 boys and 1 girl) with MD were recruited, and their phenotypes and genotypes were analyzed by retrospective review of their medical records.

RESULTS

All the patients had early-onset neurological deficit, including developmental delay, seizures, and hypotonia. The girl patient showed normal serum copper and ceruloplasmin levels as well as milder symptoms. Mutational analysis of the ATP7A gene revealed 11 different mutations in 12 patients. Bladder diverticula was the most frequent urological complication: 8 (57.1%) in the 14 patients or 8 (72.7%) in the 11 patients who underwent urological evaluation. Urological imaging studies were performed essentially for the evaluation of accompanying urinary tract infections. Four patients had stage II chronic kidney disease at the last follow-up.

CONCLUSION

Urologic problems occurred frequently in MD, with bladder diverticula being the most common. Therefore, urological imaging studies and appropriate management of urological complications, which may prevent or reduce the development of urinary tract infections and renal parenchymal damage, are required in all patients with MD.

The Pivotal Role of Copper in Neurodegeneration: A New Strategy for the Therapy of Neurodegenerative Disorders

Copper is an essential trace element for the human body since it is a cofactor of several enzymes and proteins and plays a pivotal role in several biological functions (e.g., respiration, protection from oxidative damage, iron metabolism, etc.), also including the central nervous system development and functioning (e.g., synthesis of neurotransmitters, myelination, activation of neuropeptides, etc.). Therefore, copper dysmetabolism is associated with different toxic effects, mainly represented by oxidative stress, and it has been reported in many neurodegenerative disorders, such as Wilson's disease, Menkes disease, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This paper shows a detailed report of how copper is involved in the pathophysiology of these diseases. Moreover, a hint on novel therapeutic approaches based on restoring copper homeostasis through metal chelators will be pointed out.

The structural flexibility of the human copper chaperone Atox1: Insights from combined pulsed EPR studies and computations

Metallochaperones are responsible for shuttling metal ions to target proteins. Thus, a metallochaperone's structure must be sufficiently flexible both to hold onto its ion while traversing the cytoplasm and to transfer the ion to or from a partner protein. Here, we sought to shed light on the structure of Atox1, a metallochaperone involved in the human copper regulation system. Atox1 shuttles copper ions from the main copper transporter, Ctr1, to the ATP7b transporter in the Golgi apparatus. Conventional biophysical tools such as X-ray or NMR cannot always target the various conformational states of metallochaperones, owing to a requirement for crystallography or low sensitivity and resolution. Electron paramagnetic resonance (EPR) spectroscopy has recently emerged as a powerful tool for resolving biological reactions and mechanisms in solution. When coupled with computational methods, EPR with site-directed spin labeling and nanoscale distance measurements can provide structural information on a protein or protein complex in solution. We use these methods to show that Atox1 can accommodate at least four different conformations in the apo state (unbound to copper), and two different conformations in the holo state (bound to copper). We also demonstrate that the structure of Atox1 in the holo form is more compact than in the apo form. Our data provide insight regarding the structural mechanisms through which Atox1 can fulfill its dual role of copper binding and transfer.

Menkes disease and response to copper histidine: An Indian case series

Background:

Menkes disease (MD) is an X-linked recessive neurodegenerative disorder caused by mutations in ATP7A gene. Depending on the residual ATP7A activity, manifestation may be classical MD, occipital horn syndrome, or distal motor neuropathy. Neurological sparing is expected in female carriers. However, on rare occasions, females may manifest with classical clinical phenotype due to skewed X-chromosome inactivation, X-autosome translocation, and XO genotype. Here, we describe a small series of probands with MD and their response to copper histidine therapy. This series also includes a female with X-13 translocation manifesting neurological symptoms.

Methods:

The clinical profile, laboratory and radiological data, and follow-up of four children with MD were collected from the hospital database and are being presented.

Results:

All the four children in our series had developmental delay, recurrent respiratory tract infections, hair and skeletal changes, axial hypotonia, tortuous vessels on imaging, low serum copper, ceruloplasmin, and elevated lactate. Fetal hypokinesia and fetal growth retardation were present in two cases. Failure to thrive was present in three children and only one child had epilepsy. Subcutaneous copper histidine was administered to all children. The average time lapse in the initiation of treatment was 20.3 months, and average duration of follow-up was 14.3 months.

Conclusion:

We conclude that copper histidine therapy is beneficial in reversing the skin and hair changes, improving appendicular tone, socio-cognitive milestones, and improving weight gain, and immunity. Early diagnosis and management of MD are essential to have a better clinical outcome. More research is needed to explore and devise new strategies in the management of patients with MD.

Progressive Movement Disorder in Brothers Carrying a GNAO1 Mutation Responsive to Deep Brain Stimulation

GNAO1, located on chromosome 16q12.2, encodes for 1 of the heterotrimeric guanine binding proteins subunits (G proteins), specifically Gαo, which has been implicated as having an important role in brain function. GNAO1 mutations have been shown to impart oncogene properties as well as cause epileptic encephalopathy. The authors report 2 cases of brothers with a severe movement disorder and hypotonia without epilepsy who have been confirmed by whole exome sequencing to have a novel mutation in GNAO1. Their movement disorder improved significantly with deep brain stimulation.

Twenty-five novel mutations including duplications in the ATP7A gene

Twenty-five novel mutations including duplications in the ATP7A gene. Menkes disease (MD) and occipital horn syndrome (OHS) are allelic X-linked recessive copper deficiency disorders resulting from ATP7A gene mutations. MD is a severe condition leading to progressive neurological degeneration and death in early childhood, whereas OHS has a milder phenotype with mainly connective tissue abnormalities. Until now, molecular analyses have revealed only deletions and point mutations in both diseases. This study reports new molecular data in a series of 40 patients referred for either MD or OHS. We describe 23 point mutations (9 missense mutations, 7 splice site variants, 4 nonsense mutations, and 3 small insertions or deletions) and 7 intragenic deletions. Of these, 18 point mutations and 3 deletions are novel. Furthermore, our finding of four whole exon duplications enlarges the mutation spectrum in the ATP7A gene. ATP7A alterations were found in 85% of cases. Of these alterations, two thirds were point mutations and the remaining one third consisted of large rearrangements. We found that 66.6% of point mutations resulted in impaired ATP7A transcript splicing, a phenomenon more frequent than expected. This finding enabled us to confirm the pathogenic role of ATP7A mutations, particularly in missense and splice site variants.

Copper mediated neurological disorder: visions into amyotrophic lateral sclerosis, Alzheimer and Menkes disease

Copper (Cu) is a vital redox dynamic metal that is possibly poisonous in superfluous. Metals can traditionally or intricately cause propagation in reactive oxygen species (ROS) accretion in cells and this may effect in programmed cell death. Accumulation of Cu causes necrosis that looks to be facilitated by DNA damage, followed by activation of P53. Cu dyshomeostasis has also been concerned in neurodegenerative disorders such as Alzheimer, Amyotrophic lateral sclerosis (ALS) or Menkes disease and is directly related to neurodegenerative syndrome that usually produces senile dementia. These mortal syndromes are closely related with an immense damage of neurons and synaptic failure in the brain. This review focuses on copper mediated neurological disorders with insights into amyotrophic lateral sclerosis, Alzheimer and Menkes disease.

Probing the structural flexibility of the human copper metallochaperone Atox1 dimer and its interaction with the CTR1 c-terminal domain

Both the essentiality and the toxicity of copper in human, yeast, and bacteria cells require precise mechanisms for acquisition, intimately linked to controlled distribution, which have yet to be fully understood. This work explores one aspect in the copper cycle, by probing the interaction between the human copper chaperone Atox1 and the c-terminal domain of the copper transporter, CTR1, using electron paramagnetic resonance (EPR) spectroscopy and circular dichroism (CD). The data collected here shows that the Atox1 keeps its dimer nature also in the presence of the CTR1 c-terminal domain; however, two geometrical states are assumed by the Atox1. One is similar to the geometrical state reported by the crystal structure, while the latter has not yet been constructed. In the presence of the CTR1 c-terminal domain, both states are assumed; however, the structure of Atox1 is more restricted in the presence of the CTR1 c-terminal domain. This study also shows that the last three amino acids of the CTR1 c-terminal domain, HCH, are important for maintaining the crystal structure of the Atox1, allowing less structural flexibility and improved thermal stability of Atox1.

An overview and update of ATP7A mutations leading to Menkes disease and occipital horn syndrome

Menkes disease (MD) is a lethal multisystemic disorder of copper metabolism. Progressive neurodegeneration and connective tissue disturbances, together with the peculiar "kinky" hair, are the main manifestations. MD is inherited as an X-linked recessive trait, and as expected the vast majority of patients are males. MD occurs because of mutations in the ATP7A gene and the vast majority of ATP7A mutations are intragenic mutations or partial gene deletions. ATP7A is an energy-dependent transmembrane protein, which is involved in the delivery of copper to the secreted copper enzymes and in the export of surplus copper from cells. Severely affected MD patients die usually before the third year of life. A cure for the disease does not exist, but very early copper-histidine treatment may correct some of the neurological symptoms. This study reviews 274 published and 18 novel disease causing mutations identified in 370 unrelated MD patients, nonpathogenic variants of ATP7A, functional studies of the ATP7A mutations, and animal models of MD.

Congenital abnormalities in Japanese patients with Menkes disease

Menkes disease (MNK) is an X-linked recessive disorder. Incidence of live-born infants with MNK is 2.8 per million live births in Japan. The aim of this study was to observe congenital malformations (CMs) in MNK patients. Subjects comprised 35 Japanese male patients with classical MNK who received copper histidine treatment. Patient clinical data were obtained anonymously from medical records or medical record summaries by pediatrician's retrospective review through a survey. We observed 21 different CMs in 14 patients. Eight of these had a single CM, while six had multiple CMs. The most frequent CM was higher arched palate with other CMs found in five patients. There was no relationship between CMs and mutations in the ATP7A gene. Using Mann-Whitney U tests, age at death was also significantly lower in MNK patients with CMs (P<0.05), compared to those without CMs, even though there was no significant difference of age onset, age at diagnosis and age at start of treatment with copper histidine between both groups of patients. Sudden death occurred in three MNK patients with CMs only: two with congenital heart disease, and one with microphallus.

Infantile spasms (West syndrome) in children with inborn errors of metabolism: a review of the literature

West syndrome (infantile spasms) is an epileptic encephalopathy that includes psychomotor deterioration. In rare cases, it is due to an inherited, progressive metabolic disease. More than 25 inborn errors of metabolism have been considered etiologic or predisposing factors for infantile spasms. This is a review of the literature on reported cases of children diagnosed with a metabolic disease who developed infantile spasms. This article presents in brief the most frequent inborn errors of metabolism that have been associated with West syndrome and also illustrates the importance of screening for inborn errors of metabolism in infantile spasms.

The copper-transporting capacity of ATP7A mutants associated with Menkes disease is ameliorated by COMMD1 as a result of improved protein expression

Menkes disease (MD) is an X-linked recessive disorder characterized by copper deficiency resulting in a diminished function of copper-dependent enzymes. Most MD patients die in early childhood, although mild forms of MD have also been described. A diversity of mutations in the gene encoding of the Golgi-resident copper-transporting P_1B-type ATPase ATP7A underlies MD. To elucidate the molecular consequences of the ATP7A mutations, various mutations in ATP7A associated with distinct phenotypes of MD (L873R, C1000R, N1304S, and A1362D) were analyzed in detail. All mutants studied displayed changes in protein expression and intracellular localization parallel to a dramatic decline in their copper-transporting capacity compared to ATP7A the wild-type. We restored these observed defects in ATP7A mutant proteins by culturing the cells at 30°C, which improves the quality of protein folding, similar to that which as has recently has been demonstrated for misfolded ATP7B, a copper transporter homologous to ATP7A. Further, the effect of the canine copper toxicosis protein COMMD1 on ATP7A function was examined as COMMD1 has been shown to regulate the proteolysis of ATP7B proteins. Interestingly, in addition to adjusted growth temperature, binding of COMMD1 partially restored the expression, subcellular localization, and copper-exporting activities of the ATP7A mutants. However, no effect of pharmacological chaperones was observed. Together, the presented data might provide a new direction for developing therapies to improve the residual exporting activity of unstable ATP7A mutant proteins, and suggests a potential role for COMMD1 in this process.

Transition metal homeostasis: from yeast to human disease

Transition metal ions are essential nutrients to all forms of life. Iron, copper, zinc, manganese, cobalt and nickel all have unique chemical and physical properties that make them attractive molecules for use in biological systems. Many of these same properties that allow these metals to provide essential biochemical activities and structural motifs to a multitude of proteins including enzymes and other cellular constituents also lead to a potential for cytotoxicity. Organisms have been required to evolve a number of systems for the efficient uptake, intracellular transport, protein loading and storage of metal ions to ensure that the needs of the cells can be met while minimizing the associated toxic effects. Disruptions in the cellular systems for handling transition metals are observed as a number of diseases ranging from hemochromatosis and anemias to neurodegenerative disorders including Alzheimer's and Parkinson's disease. The yeast Saccharomyces cerevisiae has proved useful as a model organism for the investigation of these processes and many of the genes and biological systems that function in yeast metal homeostasis are conserved throughout eukaryotes to humans. This review focuses on the biological roles of iron, copper, zinc, manganese, nickel and cobalt, the homeostatic mechanisms that function in S. cerevisiae and the human diseases in which these metals have been implicated.

Distorted copper homeostasis with decreased sensitivity to cisplatin upon chaperone Atox1 deletion in Drosophila

Copper is an integral part of a number of proteins and thus an essential trace metal. However, free copper ions can be highly toxic and every organism has to carefully control its bioavailability. Eukaryotes contain three copper chaperones; Atx1p/Atox1 which delivers copper to ATP7 transporters located in the trans-Golgi network, Cox17 which provides copper to the mitochondrial cytochrome c oxidase, and CCS which is a copper chaperone for superoxide dismutase 1. Here we describe the knockout phenotype of the Drosophila homolog of mammalian Atox1 (ATX1 in yeast). Atox1-/- flies develop normally, though at reduced numbers, and the eclosing flies are fertile. However, the mutants are unable to develop on low-copper food. Furthermore, the intestinal copper importer Ctr1B, which is regulated by copper demand, fails to be induced upon copper starvation in Atox1-/- larvae. At the same time, intestinal metallothionein is upregulated. This phenotype, which resembles the one of the ATP7 mutant, is best explained by intestinal copper accumulation, combined with insufficient delivery to the rest of the body. In addition, compared to controls, Drosophila Atox1 mutants are relatively insensitive to the anticancer drug cisplatin, a compound which is also imported via Ctr1 copper transporters and was recently found to bind mammalian Atox1.

Menkes disease

Menkes disease (MD) is a lethal multisystemic disorder of copper metabolism. Progressive neurodegeneration and connective tissue disturbances, together with the peculiar 'kinky' hair are the main manifestations. MD is inherited as an X-linked recessive trait, and as expected the vast majority of patients are males. MD occurs due to mutations in the ATP7A gene and the vast majority of ATP7A mutations are intragenic mutations or partial gene deletions. ATP7A is an energy dependent transmembrane protein, which is involved in the delivery of copper to the secreted copper enzymes and in the export of surplus copper from cells. Severely affected MD patients die usually before the third year of life. A cure for the disease does not exist, but very early copper-histidine treatment may correct some of the neurological symptoms.

The pathobiology of splicing

Ninety-four percent of human genes are discontinuous, such that segments expressed as mRNA are contained within exons and separated by intervening segments, called introns. Following transcription, genes are expressed as precursor mRNAs (pre-mRNAs), which are spliced co-transcriptionally, and the flanking exons are joined together to form a continuous mRNA. One advantage of this architecture is that it allows alternative splicing by differential use of exons to generate multiple mRNAs from individual genes. Regulatory elements located within introns and exons guide the splicing complex, the spliceosome, and auxiliary RNA binding proteins to the correct sites for intron removal and exon joining. Misregulation of splicing and alternative splicing can result from mutations in cis-regulatory elements within the affected gene or from mutations that affect the activities of trans-acting factors that are components of the splicing machinery. Mutations that affect splicing can cause disease directly or contribute to the susceptibility or severity of disease. An understanding of the role of splicing in disease expands potential opportunities for therapeutic intervention by either directly addressing the cause or by providing novel approaches to circumvent disease processes.

Quantitative relationship between mutated amino-acid sequence of human copper-transporting ATPases and their related diseases

Copper-transporting ATPase 1 and 2 (ATP7A and ATP7B) are two highly homologous P-type copper ATPase exporters. Mutations in ATP7A can lead to Menkes disease which is an X-linked disorder of copper deficiency. Mutations in ATP7B can cause Wilson disease which is an autosomal recessive disorder of copper toxicity. In this study, we attempt to build a quantitative relationship between mutated ATPase and Menkes/Wilson disease. First, we use the amino-acid distribution probability as a measure to quantify the difference in ATPase before and after mutation. Second, we use the cross-impact analysis to define the quantitative relationship between mutant ATPase protein and Menkes/Wilson disease, and compute various probabilities. Finally, we use the Bayesian equation to determine the probability that Menkes/Wilson disease is diagnosed under a mutation. The results show (i) the vast majority of mutations lead to the amino-acid distribution probability increase in mutant ATP7As and decrease in ATP7Bs, and (ii) the probability that a mutation causes Menkes/Wilson disease is about nine tenth. Thus we provide a way to use the descriptively probabilistic method to couple the mutation with its clinical outcome after quantifying mutations in proteins.

Sequence variation in the ATP-binding domain of the Wilson disease transporter, ATP7B, affects copper transport in a yeast model system

ATP7B is a copper transporting P-type ATPase defective in the autosomal recessive copper storage disorder, Wilson disease (WND). Functional assessment of variants helps to distinguish normal from disease-causing variants and provides information on important amino acid residues. A total of 11 missense variants of ATP7B, originally identified in WND patients, were examined for their capacity to functionally complement a yeast mutant strain in which the yeast gene ortholog, CCC2, was disrupted. Solution structures of ATP7B domains were used to predict the effects of each variant on ATP7B structure. Three variants lie within the copper-binding domain and eight within the ATP-binding domain of ATP7B. All three ATP7B variants within the copper-binding domain and four within the ATP-binding domain showed full complementation of the yeast ccc2 phenotype. For the remaining four located in the ATP-binding domain, p.Glu1064Lys and p.Val1106Asp were unable to complement the yeast ccc2 high-affinity iron uptake deficiency phenotype, apparently due to mislocalization and/or change in conformation of the variant protein. p.Leu1083Phe exhibited a temperature-sensitive phenotype with partial complementation at 30 degrees C and a severe deficit at 37 degrees C. p.Met1169Val only partially complemented the ccc2 phenotype at 30 degrees C and 37 degrees C. Therefore, four variant positions were identified as important for copper transport and as disease-causing changes. Since the yeast assay specifically evaluates copper transport function, variants with normal transport could be defective in some other aspect of ATP7B function, particularly trafficking in mammalian cells. Functional assessment is critical for reliable use of mutation analysis as an aid to diagnosis of this clinically variable condition.

Transport of cisplatin by the copper efflux transporter ATP7B

ATP7B is a P-type ATPase that mediates the efflux of copper. Recent studies have demonstrated that ATP7B regulates the cellular efflux of cisplatin (DDP) and controls sensitivity to the cytotoxic effects of this drug. To determine whether DDP is a substrate for ATP7B, DDP transport was assayed in vesicles isolated from Sf9 cells infected with a baculovirus that expressed either the wild-type ATP7B or a mutant ATP7B that was unable to transport copper as a result of conversion of the transmembrane metal binding CPC motif to CPA. Only the wild-type ATP7B-expressing vesicles exhibited copper-dependent ATPase activity, copper-induced acyl-phosphate formation, and ATP-dependent transport of copper. The amount of DDP that became bound was higher for vesicles expressing either type of ATP7B than for those not expressing either form of ATP7B, but only the vesicles expressing wild-type ATP7B mediated ATP-dependent accumulation of the drug. At pH 4.6, the vesicles expressing the wild-type ATP7B exhibited ATP-dependent accumulation of DDP with an apparent K(m) of 1.2 +/- 0.5 (S.E.M.) muM and V(max) of 0.03 +/- 0.002 (S.E.M.) nmol/mg of protein/min. DDP also induced the acyl-phosphorylation of ATP7B but at a much slower rate than copper. Copper and DDP each inhibited the ATP-dependent transport of the other. These results establish that DDP is a substrate for ATP7B but is transported at a much slower rate than copper.

Molecular pathogenesis of Wilson and Menkes disease: correlation of mutations with molecular defects and disease phenotypes

The trace metal copper is essential for a variety of biological processes, but extremely toxic when present in excessive amounts. Therefore, concentrations of this metal in the body are kept under tight control. Central regulators of cellular copper metabolism are the copper-transporting P-type ATPases ATP7A and ATP7B. Mutations in ATP7A or ATP7B disrupt the homeostatic copper balance, resulting in copper deficiency (Menkes disease) or copper overload (Wilson disease), respectively. ATP7A and ATP7B exert their functions in copper transport through a variety of interdependent mechanisms and regulatory events, including their catalytic ATPase activity, copper-induced trafficking, post-translational modifications and protein-protein interactions. This paper reviews the extensive efforts that have been undertaken over the past few years to dissect and characterise these mechanisms, and how these are affected in Menkes and Wilson disease. As both disorders are characterised by an extensive clinical heterogeneity, we will discus how the underlying genetic defects correlate with the molecular functions of ATP7A and ATP7B and with the clinical expression of these disorders.

Dynamics of endogenous ATP7A (Menkes protein) in intestinal epithelial cells: copper-dependent redistribution between two intracellular sites

We report for the first time on the copper-dependent behavior of endogenous ATP7A in two types of polarized intestinal epithelia, rat enterocytes in vivo and filter-grown Caco-2 cells, an accepted in vitro model of human small intestine. We used high-resolution, confocal immunofluorescence combined with quantitative cell surface biotinylation and found that the vast majority of endogenous ATP7A was localized intracellularly under all copper conditions. In copper-depleted cells, virtually all of the ATP7A localized to a post-TGN compartment, with <3% of the total protein detectable at the basolateral cell surface. When copper levels were elevated, ATP7A dispersed to the cell periphery in punctae whose pattern did not overlap with the steady-state distributions of post-Golgi, endosomal, or basolateral membrane markers; only approximately 8-10% of the recovered ATP7A was detected at the basolateral cell surface. These results raise several questions regarding prevailing models of ATP7A dynamics and the mechanism of copper efflux.

The first reported case of Menkes disease caused by an Alu insertion mutation

We present the first reported case of Menkes disease caused by an Alu element insertion mutation that interfered with splicing regulatory elements. A whole young AluYa5a2 element, which was 382-bp long, was identified within exon 9 of the ATP7A gene, and all of exon 9 was aberrantly skipped in the cDNA, resulting in severely truncated proteins. To confirm whether the aberrant skipping resulted in Alu insertion, an exonic splicing enhancer finder was used. The Alu element created two new high-score exonic splicing enhancer sequences in the mutation located near the site of the insertion. Exon 9, which encodes the first and second transmembrane domains, is necessary for the normal function of the ATP7A protein.

Copper binding to the N-terminal metal-binding sites or the CPC motif is not essential for copper-induced trafficking of the human Wilson protein (ATP7B)

The Wilson protein (ATP7B) is a copper-translocating P-type ATPase that mediates the excretion of excess copper from hepatocytes into bile. Excess copper causes the protein to traffic from the TGN (trans-Golgi network) to subapical vesicles. Using site-directed mutagenesis, mutations known or predicted to abrogate catalytic activity (copper translocation) were introduced into ATP7B and the effect of these mutations on the intracellular trafficking of the protein was investigated. Mutation of the critical aspartic acid residue in the phosphorylation domain (DKTGTIT) blocked copper-induced redistribution of ATP7B from the TGN, whereas mutation of the phosphatase domain [TGE (Thr-Gly-Glu)] trapped ATP7B at cytosolic vesicular compartments. Our findings demonstrate that ATP7B trafficking is regulated with its copper-translocation cycle, with cytosolic vesicular localization associated with the acyl-phosphate intermediate. In addition, mutation of the six N-terminal metal-binding sites and/or the trans-membrane CPC (Cys-Pro-Cys) motif did not suppress the constitutive vesicular localization of the ATP7B phosphatase domain mutant. These results suggested that copper co-ordination by these sites is not essential for trafficking. Importantly, copper-chelation studies with these mutants clearly demonstrated a requirement for copper in ATP7B trafficking, suggesting the presence of an additional copper-binding site(s) within the protein. The results presented in this report significantly advance our understanding of the regulatory mechanism that links copper-translocation activity with copper-induced intracellular trafficking of ATP7B, which is central to hepatic and hence systemic copper homoeostasis.

The Cadmium Transport Sites of CadA, the Cd2+-ATPase from Listeria monocytogenes

CadA, the Cd(2+)-ATPase from Listeria monocytogenes, belongs to the Zn(2+)/Cd(2+)/Pb(2+)-ATPase bacterial subfamily of P(1B)-ATPases that ensure detoxification of the bacteria. Whereas it is the major determinant of Listeria resistance to Cd(2+), CadA expressed in Saccharomyces cerevisiae severely decreases yeast tolerance to Cd(2+) (Wu, C. C., Bal, N., Pérard, J., Lowe, J., Boscheron, C., Mintz, E., and Catty, P. (2004) Biochem. Biophys. Res. Commun. 324, 1034-1040). This phenotype, which reflects in vivo Cd(2+)-transport activity, was used to select from 33 point mutations, shared out among the eight transmembrane (TM) segments of CadA, those that affect the activity of the protein. Six mutations affecting CadA were found: M149A in TM3; E164A in TM4; C354A, P355A, and C356A in TM6; and D692A in TM8. Functional studies of the six mutants produced in Sf9 cells revealed that Cys(354) and Cys(356) in TM6 as well as Asp(692) in TM8 and Met(149) in TM3 could participate at the Cd(2+)-binding site(s). In the canonical Cys-Pro-Cys motif of P(1B)-ATPases, the two cysteines act at distinct steps in the transport mechanism, Cys(354) being directly involved in Cd(2+) binding, while Cys(356) seems to be required for Cd(2+) occlusion. This confirms an earlier observation that the two equivalent Cys of Ccc2, the yeast Cu(+)-ATPase, also act at different steps. In TM4, Glu(164), which is conserved among P(1B)-ATPases, may be required for Cd(2+) release. Finally, analysis of the role of Cd(2+) in the phosphorylation from ATP and from P(i) of the mutants suggests that two Cd(2+) ions are involved in the reaction cycle of CadA.

Identification and analysis of 21 novel disease-causing amino acid substitutions in the conserved part of ATP7A

ATP7A encodes a copper-translocating ATPase that belongs to the large family of P-type ATPases. Eight conserved regions define the core of the P-type ATPase superfamily. We report here the identification of 21 novel missense mutations in the conserved part of ATP7A that encodes the residues p.V842-p.S1404. Using the coordinates of X-ray crystal structures of the sarcoplasmic reticulum Ca(2+)-ATPase, as determined in the presence and absence of Ca(2+), we created structural homology models of ATP7A. By mapping the substituted residues onto the models, we found that these residues are more clustered three-dimensionally than expected from the primary sequence. The location of the substituted residues in conserved regions supports the functional similarities between the two types of P-type ATPases. An immunofluorescence analysis of Menkes fibroblasts suggested that the localization of a large number of the mutated ATP7A protein variants was correct. In the absence of copper, they were located in perinuclear regions of the cells, just like the wild type. However, two of the mutated ATP7A variants showed only partly correct localization, and in five cultures no ATP7A protein could be detected. These findings suggest that although a disease-causing mutation may indicate a functional significance of the affected residue, this is not always the case.

Epilepsy in Menkes Disease: Analysis of Clinical Stages

PURPOSE

Epilepsy is one of the main features of Menkes disease (MD), although it is not described in depth. To determine the spectrum of epilepsy, we studied its main characteristics.

METHODS

Based on clinical charts, we retrospectively analyzed the evolution of electroclinical features of 12 patients with confirmed MD.

RESULTS

Epilepsy could be divided into three periods: (a) an early stage (median age, 3 months), characterized by focal clonic status epilepticus, usually triggered by fever (10 patients). Ictal EEG showed runs of slow spike-waves and slow waves in the posterior regions, and interictal EEG multifocal and polymorphic slow waves (three cases), or mixed slow spike-waves and slow waves (seven cases). Partial seizure control was obtained in nine patients during 5.9 months; (b) an intermediate stage (median age, 10 months) with intractable infantile spasms (11 patients) in which interictal EEG demonstrated modified hypsarrhythmia (seven cases), diffuse irregular slow waves and spike-waves (four cases). Six patients died at the median age of 15 months; and (c) a late stage in the six remaining patients (median age, 25 months), with multifocal seizures, tonic spasms, and myoclonus in four patients, whereas two patients became seizure free. Interictal EEG showed multifocal high-amplitude activity, mixed with irregular slow waves in all six cases. These patients died at the median age of 3.6 years.

CONCLUSIONS

Based on a relatively large series of MD patients with a quite prolonged survival, we individualized three successive periods in the course of epilepsy: early focal status, then infantile spasms, and then myoclonic and multifocal epilepsy after age 2 years.

Alteration of copper physiology in mice overexpressing the human Menkes protein ATP7A

The Menkes protein (ATP7A) is defective in the Cu deficiency disorder Menkes disease and is an important contributor to the maintenance of physiological Cu homeostasis. To investigate more fully the role of ATP7A, transgenic mice expressing the human Menkes gene ATP7A from chicken beta-actin composite promoter (CAG) were produced. The transgenic mice expressed ATP7A in lung, heart, liver, kidney, small intestine, and brain but displayed no overt phenotype resulting from expression of the human protein. Immunohistochemical analysis revealed that ATP7A was found primarily in the cardiac muscle, smooth muscle of the lung, distal tubules of the kidney, intestinal enterocytes, and patches of hepatocytes, as well as in the hippocampus, cerebellum, and choroid plexus of the brain. In 60-day- and 300-day-old mice, Cu concentrations were reduced in most tissues, consistent with ATP7A playing a role in Cu efflux. The reduction in Cu was most pronounced in the hearts of older T22#2 females (24%), T22#2 males (18%), and T25#5 females (23%), as well as in the brains of 60-day-old T22#2 females and males (23% and 30%, respectively).

An Atomic-level Investigation of the Disease-causing A629P Mutant of the Menkes Protein, ATP7A

Menkes disease is a fatal disease that can be induced by various mutations in the ATP7A gene, leading to unpaired uptake of dietary copper. The ATP7A gene encodes a copper(I)-translocating ATPase. Here the disease-causing A629P mutation, which occurs in the last of the six copper(I)-binding soluble domains of the ATPase (hereafter MNK6), was investigated. To understand why this apparently minor amino acid replacement is pathogenic, the solution structures and dynamics on various time-scales of wild-type and A629P-MNK6 were determined both in the apo- and copper(I)-loaded forms. The interaction in vitro with the physiological ATP7A copper(I)-donor (HAH1) was additionally studied. The A629P mutation makes the protein beta-sheet more solvent accessible, possibly resulting in an enhanced susceptibility of ATP7A to proteolytic cleavage and/or in reduced capability of copper(I)-translocation. A small reduction of the affinity for copper(I) is also observed. Both effects could concur to pathogenicity.

Variable clinical expression of an identical mutation in the ATP7A gene for Menkes disease/occipital horn syndrome in three affected males in a single family

Two maternal half-brothers presented with huge cephalic hematoma, fatal in one. Skin morphology disclosed lack of elastic fibres. Their maternal uncle is moderately mentally handicapped and has extensive connective tissue disorders. In all these patients, an identical missense mutation in the ATP7A gene was found and confirmed Menkes' disease.

A mutational study in the transmembrane domain of Ccc2p, the yeast Cu(I)-ATPase, shows different roles for each Cys-Pro-Cys cysteine

Ccc2p is homologous to the human Menkes and Wilson copper ATPases and is herein studied as a model for human copper transport. Most studies to date have sought to understand how mutations in the human Menkes or Wilson genes impair copper homeostasis and induce disease. Here we analyze whether eight conserved amino acids of the transmembrane domain are important for copper transport. Wild-type Ccc2p and variants were expressed in a ccc2-Delta yeast strain to check whether they were able to restore copper transport by complementation. Wild-type Ccc2p and variants were also expressed in Sf9 cells using baculovirus to study their enzymatic properties on membrane preparations. The latter system allowed us to measure a copper-activated ATPase activity of about 20 nmol/mg/min for the wild-type Ccc2p at 37 degrees C. None of the variants was as efficient as the wild type in restoring copper homeostasis. The mutation of each cysteine of the (583)CPC(585) motif into a serine resulted in nonfunctional proteins that could not restore copper homeostasis in yeast and had no ATPase activity. Phosphorylation by ATP was still possible with the C583S variant, although it was not possible with the C585S variant, suggesting that the cysteines of the CPC motif have a different role in copper transport. Cys(583) would be necessary for copper dissociation and/or enzyme dephosphorylation and Cys(585) would be necessary for ATP phosphorylation, suggesting a role in copper binding.

Screening of 383 unrelated patients affected with Menkes disease and finding of 57 gross deletions inATP7A

Menkes disease (MD) is an X-linked multisystemic lethal disorder of copper metabolism dominated by neurodegenerative symptoms and connective tissue disturbances. MD results from mutations in the ATP7A gene, which encodes a membrane-bound copper transporting P-type ATPase located in the trans-Golgi network. In this study we describe screening of 383 unrelated patients affected with Menkes disease for gross deletions in ATP7A gene and finding of 57 patients. The present data suggests that gross deletion of ATP7A is the disease-causing mutation in 14.9% of the Menkes disease patients. Except for a few cases, gross gene deletions result in the classical form of Menkes disease with death in early childhood.

A comparison of the mutation spectra of Menkes disease and Wilson disease

The genes for two copper-transporting ATPases, ATP7A and ATP7B, are defective in the heritable disorders of copper imbalance, Menkes disease (MNK) and Wilson disease (WND), respectively. A comparison of the two proteins shows extensive conservation in the signature domains, with amino acid identities outside of the conserved domains being limited. The mutation spectra of MNK and WND were compared to confirm and refine further regions critical for normal function. Mutations were found to be relatively widespread; however, the majority was concentrated within defined functional domains and membrane-spanning segments, reinforcing the importance of these regions for protein function. Of the total published point mutations in ATP7A, 23.0% are splice-site, 20.7% nonsense, 17.2% missense, and 39.1% small insertions/deletions. There is a high prevalence (58.2%) of missense mutations in ATP7B. For the other mutations in ATP7B, 7.4% are splice-site, 7.4% nonsense, and 27.0% small insertions/deletions. A region of possible importance is the intervening sequence between the last copper-binding domain and the first transmembrane helix, as this region has a high percentage of MNK mutations. Similarly, the region containing the ATP-binding domain has 24.6% of all WND mutations. The study of mutation locations is useful for defining critical regions or residues and for efficient molecular diagnosis.

Rapid and robust screening of the Menkes disease/occipital horn syndrome gene

Menkes disease and occipital horn syndrome (OHS) are allelic neurogenetic disorders of copper transport associated with mutations in an X-linked gene, ATP7A. This gene encodes a copper-transporting P-type ATPase. The spectrum of mutations at the Menkes/OHS locus is estimated to include 1% chromosomal rearrangements and 15-20% large deletions, with the remaining defects involving small alterations. There is a compelling need for a rapid and reliable molecular diagnostic approach for patients and families impacted by these conditions. In addition to testing suspected affected males, carrier screening of females in Menkes/OHS families and prenatal evaluation of at-risk pregnancies will be enhanced by the wider availability of robust mutation analysis for this large (23-exon) locus. Here we describe a stepwise approach to mutation screening for these disorders that successfully identified molecular alterations in over 95% of our patient population (n = 49). This genomic DNA-based technique employs multiplex PCR, heteroduplex analysis, and direct sequencing, in a serial fashion. This approach should find application in molecular diagnostic laboratories in the United States and other countries. Currently, only a single European center provides commercial testing for unknown mutations in Menkes/OHS patients, even though these disorders occur worldwide.

Cd2+ and the N-terminal metal-binding domain protect the putative membranous CPC motif of the Cd2+-ATPase of Listeria monocytogenes

CadA, the Cd(2+)-ATPase of Listeria monocytogenes, contains four cysteine residues: two in the CTNC (Cys-Thr-Asn-Cys) sequence in the cytoplasmic metal-binding domain (MBD), and two in the CPC (Cys-Pro-Cys) sequence in the membrane domain. Taking advantage of DeltaMBD, a truncated version of CadA that lacks the MBD but which still acts as a functional Cd(2+)-ATPase [Bal, Mintz, Guillain and Catty (2001) FEBS Lett. 506, 249-252], we analysed the role of the membrane cysteine residues (studied using DeltaMBD) separately from that of the cysteine residues of the MBD, which were studied using full-length CadA. The role of the cysteines was assessed by reacting DeltaMBD and CadA with N -ethylmaleimide (NEM), an SH-specific reagent, in the presence or absence of Cd(2+). We show here that (i) in both DeltaMBD and CadA, the cysteine residues in the CPC motif are essential for phosphorylation; (ii) in both proteins, Cd(2+) protects against alkylation by NEM; and (iii) in the absence of Cd(2+), the MBD of CadA also protects against alkylation by NEM. Our results suggest that the CPC motif is present in the membrane Cd(2+) transport site(s) and that the MBD protects these site(s).

X-linked recessive Menkes disease: identification of partial gene deletions in affected males

Menkes disease is an X-linked recessive lethal disorder of copper metabolism, caused by defects in the ATP7A gene. Partial gene deletions comprise about 15% of the mutations causing Menkes disease. We have previously demonstrated identification of partial ATP7A deletions in patients by Southern blot analysis. In the present study, we report the use of three fast and reliable polymerase chain reaction (PCR)-based methods for the identification of partial ATP7A deletions in Menkes disease patients. First we demonstrate the use of multiplex PCR, a fast method for identification and rough localization of partial gene deletions, in which two exons of ATP7A are coamplified. Second, we present PCR amplification of genomic DNA across the deletion junctions, a method enabling identification of the deletion breakpoints and hence the exact size of the deletion. Finally, application of reverse transcription PCR (RT-PCR) for identification and localization of gene deletions at the cDNA level is demonstrated. By studying the mutation at the cDNA level the predicted effect of the mutation on the amino acid sequence and consequently the protein structure and function can be inferred. We demonstrate characterization of partial gene deletions in five patients, and in three of these we were able to determine the breakpoint sequences.

Copper-regulated trafficking of the Menkes disease copper ATPase is associated with formation of a phosphorylated catalytic intermediate

The Menkes protein (MNK; ATP7A) is a copper-transporting P-type ATPase that is defective in the copper deficiency disorder, Menkes disease. MNK is localized in the trans-Golgi network and transports copper to enzymes synthesized within secretory compartments. However, in cells exposed to excessive copper, MNK traffics to the plasma membrane where it functions in copper efflux. A conserved feature of all P-type ATPases is the formation of an acyl-phosphate intermediate, which occurs as part of the catalytic cycle during cation transport. In this study we investigated the effect of mutations within conserved catalytic regions of MNK on intracellular localization and trafficking from the trans-Golgi network (TGN). Our findings suggest that mutations that block formation of the phosphorylated catalytic intermediate also prevent copper-induced relocalization of MNK from the TGN. Furthermore, mutations in the phosphatase domain, which resulted in hyperphosphorylation of MNK, caused constitutive trafficking from the TGN to the plasma membrane. A similar effect on trafficking was observed with a phosphatase mutation in the closely related copper ATPase, ATP7B, affected in Wilson disease. These findings suggest that the copper-induced trafficking of the Menkes and Wilson disease copper ATPases is associated with the phosphorylated intermediate that is formed during the catalysis of these pumps. Our findings describe a novel mechanism for regulating the subcellular location of a transport protein involving the recognition of intermediate conformations during catalysis.

Copper transporting P-type ATPases and human disease

Copper transporting P-type ATPases, designated ATP7A and ATP7B, play an essential role in mammalian copper balance. Impaired intestinal transport of copper, resulting from mutations in the ATP7A gene, lead to Menkes disease in humans. Defects in a similar gene, the copper transporting ATPase ATP7B, result in Wilson disease. This ATP7B transporter has two functions: transport of copper into the plasma protein ceruloplasmin, and elimination of copper through the bile. Variants of ATP7B can be functionally assayed to identify defects in each of these functions. Tissue expression studies of the copper ATPases and their copper chaperone ATOX1 indicate that there is not complete overlap in expression. Other chaperones may be important for the transport of copper into ATP7A and ATP7B.

Prenatal diagnosis of Menkes disease by genetic analysis and copper measurement

Carrier detection for 12 women and prenatal diagnosis for six fetuses in Japanese families with a patient with Menkes disease (MNK) were performed by gene analysis and/or measurement of the copper concentration in cultured cells. Six out of eight mothers of MNK patients were carriers while two (25%) were not carriers. Two unrelated patients showed the same mutation (R986X): one patient's mother was a carrier while the other was not. One male and three female fetuses did not have the same mutant allele as the respective MNK proband and have been healthy since birth. One female fetus had the same mutant allele as her affected brother. Gene analysis is very useful and reliable, although such examination is only indicated in families in which a mutation has been identified. In one family in which a mutation in ATP7A was not found, cultured amniocytes from a male fetus had a high copper concentration. Thus after his birth, the biochemical findings confirmed the presence of MNK and early treatment was started. As his early treatment with parenteral copper-histidine prevented the neurological disorders effectively, prenatal diagnosis is very important.

Menkes copper-translocating P-type ATPase (ATP7A): biochemical and cell biology properties, and role in Menkes disease

The Menkes copper-translocating P-type ATPase (ATP7A; MNK) is a ubiquitous protein that regulates the absorption of copper in the gastrointestinal tract. Inside cells the protein has a dual function: it delivers copper to cuproenzymes in the Golgi compartment and effluxes excess copper. The latter property is achieved through copper-dependent vesicular trafficking of the Menkes protein to the plasma membrane of the cell. The trafficking mechanism and catalytic activity combine to facilitate absorption and intercellular transport of copper. The mechanism of catalysis and copper-dependent trafficking of the Menkes protein are the subjects of this review. Menkes disease, a systemic copper deficiency disorder, is caused by mutations in the gene encoding the Menkes protein. The effect of these mutations on the catalytic cycle and the cell biology of the Menkes protein, as well as predictions of the effect of particular mutant MNKs on observed Menkes disease symptoms will also be discussed.

Drug targets in Menkes disease - prospective developments

Menkes disease (MNK) is an X-linked recessive disorder characterised by a copper-transporting ATPase defect. In the affected cells, copper transport from the cytosol to the Golgi apparatus is disturbed, resulting in a reduction of copper efflux. Orally-administered copper, which accumulates in the intestine, cannot be absorbed and thus a copper deficiency arises. The characteristic features of MNK are progressive neurological degeneration, connective tissue disorders and hair abnormalities, which are caused by a reduction in the activity of several copper-dependent enzymes, due to concomitant copper deficiency. Subcutaneous injections of copper-histidine complex, which currently forms the accepted mode of treatment, prevent the neurological degeneration in some patients when the treatment is initiated soon after birth. However, when the treatment is started later, the neurological degenerative processes are not prevented. Moreover, the treatment does not improve the connective tissue disorders that are caused by the low activity of lysyl oxidase. In order to solve these problems, a form of the treatment aimed at delivering copper into the Golgi apparatus should be studied. An attempt is made in this review to present what is currently known about MNK and its variants, the efficacy and problems of currently accepted treatments and finally therapeutic targets in MNK.

Structure-function analysis of purified Enterococcus hirae CopB copper ATPase: effect of Menkes/Wilson disease mutation homologues

The Enterococcus hirae CopB ATPase (EC 3.6.1.3) confers copper resistance to the organism by expelling excess copper. Two related human ATPase genes, ATP7A (EC 3.6.1.36) and ATP7B (EC 3.6.1.36), have been cloned as the loci of mutations causing Menkes and Wilson diseases, diseases of copper metabolism. Many mutations in these genes have been identified in patients. Since it has not yet been possible to purify the human copper ATPases, it has proved difficult to test the impact of mutations on ATPase function. Some mutations occur in highly conserved sequence motifs, suggesting that their effect on function can be tested with a homologous enzyme. Here, we used the E. hirae CopB ATPase to investigate the impact of such mutations on enzyme function in vivo and in vitro. The Menkes disease mutation of Cys-1000-->Arg, changing the conserved Cys-Pro-Cys ('CPC') motif, was mimicked in CopB. The corresponding Cys-396-->Ser CopB ATPase was unable to restore copper resistance in a CopB knock-out mutant in vivo. The purified mutant ATPase still formed an acylphosphate intermediate, but possessed no detectable ATP hydrolytic activity. The most frequent Wilson disease mutation, His-1069-->Gln, was introduced into CopB as His-480-->Gln (H480Q). This mutant CopB also failed to confer copper resistance to a CopB knock-out strain. Purified H480Q CopB formed an acylphosphate intermediate and retained a small, but significant, ATPase activity. Our results reveal that Cys-396 and His-480 of CopB are key residues for ATPase function, and similar roles are suggested for Cys-1000 and His-1069 of Menkes and Wilson ATPases respectively.

Expression of the human Menkes ATPase in Xenopus laevis oocytes

Menkes disease is an X-linked disorder of copper metabolism that is usually fatal. The affected gene has recently been cloned and encodes one of the two human copper ATPases. If the Menkes ATPase is defective, copper is trapped in the intestinal mucosa, leading to systemic copper deficiency. In order to study copper transport by this ATPase and the effects of disease mutations on its function, we developed a Xenopus laevis oocyte expression system. Wild-type Menkes ATPase cDNA and a fusion of this gene with the green fluorescent protein (GFP) gene was transcribed in vitro and the mRNA injected into oocytes. Expression in oocytes was analyzed by Western blotting and fluorescence microscopy. The Menkes ATPase-GFP chimera appeared to localize primarily to the plasma membrane as assessed by confocal microscopy. This system should thus provide an interesting new tool to study the function of the Menkes ATPase.