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

Syntaxin 5 is required for copper homeostasis in Drosophila and mammals

Copper is essential for aerobic life, but many aspects of its cellular uptake and distribution remain to be fully elucidated. A genome-wide screen for copper homeostasis genes in Drosophila melanogaster identified the SNARE gene Syntaxin 5 (Syx5) as playing an important role in copper regulation; flies heterozygous for a null mutation in Syx5 display increased tolerance to high dietary copper. The phenotype is shown here to be due to a decrease in copper accumulation, a mechanism also observed in both Drosophila and human cell lines. Studies in adult Drosophila tissue suggest that very low levels of Syx5 result in neuronal defects and lethality, and increased levels also generate neuronal defects. In contrast, mild suppression generates a phenotype typical of copper-deficiency in viable, fertile flies and is exacerbated by co-suppression of the copper uptake gene Ctr1A. Reduced copper uptake appears to be due to reduced levels at the plasma membrane of the copper uptake transporter, Ctr1. Thus Syx5 plays an essential role in copper homeostasis and is a candidate gene for copper-related disease in humans.

Zebrafish sod1 and sp1 expression are modulated by the copper ATPase gene atp7a in response to intracellular copper status

Copper is an essential trace metal for physiological functions, whereas copper overload causes cytotoxicity in living organisms. Genetically determined systems regulate acquisition, distribution and storage for copper maintenance and homeostasis. The Human ATP7A copper transport ATPase modulates intracellular copper distribution, which is critical for copper-dependent enzymes such as superoxide dismutase (SOD1). To investigate the role of zebrafish ATP7A in copper homeostasis, zebrafish atp7a gene expression was reduced for analysis of downstream cellular function. The results demonstrated that zebrafish sod1 has lower expression in atp7a-knockdown fish. Similarly, zebrafish sp1, a transcriptional regulator of sod1, also shows reduced expression in atp7a-knockdown fish. The lower expression of sod1 resulting from atp7a knockdown is independent to p53 gene activation. The knockdown of atp7a and copper chelator NeoC results in hypopigmentation and notochord deformation in zebrafish. Addition of exogenous copper alleviated the impaired development. Interestingly, both sod1 and sp1 transcripts are reduced in the presence of NeoC and increased with exogenous copper, suggesting that the expression of sod1 and sp1 are directly affected by copper status. This is the first report to demonstrate a hierarchic gene expression of copper homeostatic genes between atp7a, sp1 and sod1 in zebrafish.

High prevalence of fulminant hepatic failure among patients with mutant alleles for truncation of ATP7B in Wilson's disease

OBJECTIVE

Although many mutations of the Wilson's disease (WD) gene (ATP7B) have been reported, few data exist regarding the occurrence of fulminant hepatic failure (FHF). We sought to determine if genotypic assignment according to type of protein-product could be related to the prevalence of FHF among patients with WD.

MATERIAL AND METHODS

We performed gene analysis in Japanese patients with WD as well as genotype-phenotype analysis in 51 patients. We divided genotypes into two groups according to type of ATP7B product: truncated group [T] consisted of two truncated alleles including nonsense, insertion, deletion, or splice site mutation, and missense group [M] consisted of one or two missense alleles. We also divided phenotypes into two groups: [FHF] group and [non-FHF] group.

RESULTS

We were able to determine genotype in 42 patients. Genotypically, 11 patients were assigned to [T] group and 31 to [M] group. Phenotypically, 4 patients were [FHF] and 38 were [non-FHF]. All patients in [FHF] group belonged to [T] group. The prevalence of [FHF] in [T] group was 36.4% and was significantly higher than in [M] group (p < 0.003).

CONCLUSIONS

These results demonstrated that genotypes for truncation of ATP7B are associated with high prevalence of FHF.

Copper in diseases and treatments, and copper-based anticancer strategies

Copper is found in all living organisms and is a crucial trace element in redox chemistry, growth and development. It is important for the function of several enzymes and proteins involved in energy metabolism, respiration, and DNA synthesis, notably cytochrome oxidase, superoxide dismutase, ascorbate oxidase, and tyrosinase. The major functions of copper-biological molecules involve oxidation-reduction reactions in which they react directly with molecular oxygen to produce free radicals. Therefore, copper requires tightly regulated homeostatic mechanisms to ensure adequate supplies without any toxic effects. Overload or deficiency of copper is associated, respectively, with Wilson disease (WD) and Menkes disease (MD), which are of genetic origin. Researches on Menkes and Wilson disorders have provided useful insights in the field of copper homeostasis and in particular into the understanding of intracellular trafficking and distribution of copper at molecular levels. Therapies based on metal supplementation with copper histidine or removal of copper excess by means of specific copper chelators are currently effective in treating MD and WD, respectively. Copper chelation therapy is now attracting much attention for the investigation and treatment of various neurodegenerative disorders such as Alzheimer, Parkinson and CreutzfeldtJakob. An excess of copper appears to be an essential co-factor for angiogenesis. Moreover, elevated levels of copper have been found in many types of human cancers, including prostate, breast, colon, lung, and brain. On these basis, the employment of copper chelators has been reported to be of therapeutic value in the treatment of several types of cancers as anti-angiogenic molecules. More recently, mixtures of copper chelators with copper salts have been found to act as efficient proteasome inhibitors and apoptosis inducers, specifically in cancer cells. Moreover, following the worldwide success of platinum(II) compounds in cancer chemotherapy, several families of individual copper complexes have been studied as potential antitumor agents. These investigations, revealing the occurrence of mechanisms of action quite different from platinum drugs, head toward the development of new anticancer metallodrugs with improved specificity and decreased toxic side effects.

Alterations in the expression of the Atp7a gene in the early postnatal development of the mosaic mutant mice (Atp7a mo-ms) - An animal model for Menkes disease

Copper is a trace element that is essential for the normal growth and development of all living organisms. In mammals, the ATP7A Cu-transporting ATPase is a key protein that is required for the maintenance of copper homeostasis. In both humans and mice, the ATP7A protein is coded by the X-linked ATP7A/Atp7a gene. Disturbances in copper metabolism caused by mutations in the ATP7A/Atp7a gene lead to severe metabolic syndromes Menkes disease in humans and the lethal mottled phenotype in mice. Mosaic is one of numerous mottled mutations and may serve as a model for a severe Menkes disease variant. In Menkes patients, mutations in the ATP7A gene often result in a decreased level of the normal ATP7A protein. The aim of this study was to analyse the expression of the Atp7a gene in mosaic mutants in early postnatal development, a critical period for starting copper supplementation therapy in both Menkes patients and mutant mice. Using real-time quantitative RT-PCR, we analysed the expression of the Atp7a gene in the brain, kidney and liver of newborn (P0.5) and suckling (P14) mice. Our results indicate that in mosaic P0.5 mutants, the Atp7a mRNA level is decreased in all analysed organs in comparison with wild-type animals. In two week-old mutants, a significant decrease was observed only in the kidney. In contrast, their hepatic level of Atp7a tended to be higher than in wild-type mice. We speculate that disturbance in the expression of the Atp7a gene and, consequently, change in the copper concentration of the organs, may contribute to the early fatal outcome of mosaic males.

Genetics of Wilsons disease

Wilson's disease is a rare autosomal recessive disorder of copper transport due to mutations in the ATP7B gene, responsible for transport of copper into bile from hepatocytes and its incorporation into apoceruloplasmin to form ceruloplasmin resulting in excessive accumulation of copper in the liver and extrahepatic tissues. Clinical features of WD result from toxic accumulation of copper in liver, brain and kidney. Early diagnosis is mandatory to initiate early treatment to prevent morbidity and mortality. More than 400 mutations have been reported, some of which are rather characteristic of geographical regions and ethnic population. Genetic testing is not useful as a routine procedure, but has its role in at risk individuals such as siblings and children of probands and in individuals with suggestive symptoms but where other tests are contradictory.

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.

Molecular genetic approaches to understanding the roles and regulation of iron in brain health and disease

Iron is essential in the brain, yet too much iron can be toxic. Tight regulation of iron in the brain may involve intrinsic mechanisms that control internal homeostasis independent of systemic iron status. Iron abnormalities occur in various neurological disorders, usually with symptoms or neuropathology associated with movement impairment or behavioral disturbances rather than cognitive impairment or dementia. Consistent with this, polymorphisms in the HFE gene, associated with the iron overload disorder hemochromatosis, show stronger associations with the movement disorder amyotrophic lateral sclerosis (motor neuron disease) than with cognitive impairment. Such associations may arise because certain brain regions involved in movement or executive control are particularly iron-rich, notably the basal ganglia, and may be highly reliant on iron. Various mechanisms, including iron redistribution causing functional iron deficiency, lysosomal and mitochondrial abnormalities or oxidative damage, could underlie iron-related neuropathogenesis. Clarifying how iron contributes causatively to neurodegeneration may improve treatment options in a range of neurodegenerative disorders. This review considers how modern molecular genetic approaches can be applied to resolve the complex molecular systems and pathways by which brain iron homeostasis is regulated and the molecular changes that occur with iron dyshomeostasis and neuropathogenesis.

Missense mutations in the copper transporter gene ATP7A cause X-linked distal hereditary motor neuropathy

Distal hereditary motor neuropathies comprise a clinically and genetically heterogeneous group of disorders. We recently mapped an X-linked form of this condition to chromosome Xq13.1-q21 in two large unrelated families. The region of genetic linkage included ATP7A, which encodes a copper-transporting P-type ATPase mutated in patients with Menkes disease, a severe infantile-onset neurodegenerative condition. We identified two unique ATP7A missense mutations (p.P1386S and p.T994I) in males with distal motor neuropathy in two families. These molecular alterations impact highly conserved amino acids in the carboxyl half of ATP7A and do not directly involve the copper transporter's known critical functional domains. Studies of p.P1386S revealed normal ATP7A mRNA and protein levels, a defect in ATP7A trafficking, and partial rescue of a S. cerevisiae copper transport knockout. Although ATP7A mutations are typically associated with severe Menkes disease or its milder allelic variant, occipital horn syndrome, we demonstrate here that certain missense mutations at this locus can cause a syndrome restricted to progressive distal motor neuropathy without overt signs of systemic copper deficiency. This previously unrecognized genotype-phenotype correlation suggests an important role of the ATP7A copper transporter in motor-neuron maintenance and function.

Child and adolescent psychiatric genetics

The current status of child and adolescent psychiatric genetics appears promising in light of the initiation of genome-wide association studies (GWAS) for diverse polygenic disorders and the molecular elucidation of monogenic Rett syndrome, for which recent functional studies provide hope for pharmacological treatment strategies. Within the last 50 years, tremendous progress has been made in linking genetic variation to behavioral phenotypes and psychiatric disorders. We summarize the major findings of the Human Genome Project and dwell on largely unsuccessful candidate gene and linkage studies. GWAS for the first time offer the possibility to detect single nucleotide polymorphisms and copy number variants without a priori hypotheses as to their molecular etiology. At the same time it is becoming increasingly clear that very large sample sizes are required in order to enable genome wide significant findings, thus necessitating further large-scaled ascertainment schemes for the successful elucidation of the molecular genetics of childhood and adolescent psychiatric disorders. We conclude by reflecting on different scenarios for future research into the molecular basis of early onset psychiatric disorders. This review represents the introductory article of this special issue of the European Child and Adolescent Psychiatry.

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.

A Drosophila model of Menkes disease reveals a role for DmATP7 in copper absorption and neurodevelopment

Human Menkes disease is a lethal neurodegenerative disorder of copper metabolism that is caused by mutations in the ATP7A copper-transporting gene. In the present study, we attempted to construct a Drosophila model of Menkes disease by RNA interference (RNAi)-induced silencing of DmATP7, the Drosophila orthologue of mammalian ATP7A, in the digestive tract. Here, we show that a lowered level of DmATP7 mRNA in the digestive tract results in a reduced copper content in the head and the rest of the body of surviving adults, presumably owing to copper entrapment in the gut. Similar to Menkes patients, a majority of flies exhibit an impaired neurological development during metamorphosis and die before eclosion. In addition, we show that survival to the adult stage is highly dependent on the copper content of the food and that overexpression of the copper homeostasis gene, metal-responsive transcription factor-1 (MTF-1), enhances survival to the adulthood stage. Taken together, these results highlight the role of DmATP7-mediated copper uptake in the neurodevelopment of Drosophila melanogaster and provide a framework for the analysis of potential gene interactions influencing Menkes disease.

Reduced expression of ATP7B affected by Wilson disease-causing mutations is rescued by pharmacological folding chaperones 4-phenylbutyrate and curcumin

Wilson disease (WD) is an autosomal recessive copper overload disorder of the liver and basal ganglia. WD is caused by mutations in the gene encoding ATP7B, a protein localized to the trans-Golgi network that primarily facilitates hepatic copper excretion. Current treatment comprises reduction of circulating copper by zinc supplementation or copper chelation. Despite treatment, a significant number of patients have neurological deterioration. The aim of this study was to investigate the possibility that defects arising from some WD mutations are ameliorated by drug treatment aimed at improvement of protein folding and restoration of protein function. This necessitated systematic characterization of the molecular consequences of distinct ATP7B missense mutations associated with WD. With the exception of p.S1363F, all mutations tested (p.G85V, p.R778L, p.H1069Q, p.C1104F, p.V1262F, p.G1343V, and p.S1363F) resulted in reduced ATP7B protein expression, whereas messenger RNA abundance was unaffected. Retention of mutant ATP7B in the endoplasmic reticulum, increased protein expression, and normalization of localization after culturing cells at 30 degrees C, and homology modeling suggested that these proteins were misfolded. Four distinct mutations exhibited residual copper export capacity, whereas other mutations resulted in complete disruption of copper export by ATP7B. Treatment with pharmacological chaperones 4-phenylbutyrate (4-PBA) and curcumin, a clinically approved compound, partially restored protein expression of most ATP7B mutants.

CONCLUSION

These findings might enable novel treatment strategies in WD by directly enhancing the protein expression of mutant ATP7B with residual copper export activity. 1795.).

Association mapping of cadmium, copper and hydrogen peroxide tolerance of roots and translocation capacities of cadmium and copper in Arabidopsis thaliana

Association mapping analysis of Cd, Cu and H (2)O (2) tolerance, judged by relative root length (RRL: % of root length in stress condition relative to that in control condition), and Cd and Cu translocation ratios (amount of metal in the shoot to the total) were performed using 90 accessions of Arabidopsis thaliana. Using 140 SNPs that were distributed across the genome, association mapping analysis was performed with a haploid setting by the Q + K method, which minimizes detection of false associations by combining the Q-matrix of the structured association (Q) with kinship (K) to control for the population structure. Six, five and five significant (-log (10)P-value is 1.3 > or =) linkages were detected between the SNPs and Cd, Cu and H(2)O(2) resistant RRLs, respectively. In addition, six significant linkages were identified with translocation capacities of Cd and Cu. Among those detected loci, two each of Cu and Cd tolerance RRLs were collocated with those of H(2)O(2) tolerance RRL, while one locus each was detected by Cu and Cd tolerance RRLs that collocated with their translocation ratios. These results suggested that these factors might partly explain the phenotypic variation of tolerance RRLs to Cd and Cu of Arabidopsis thaliana. Finally, using a different approach to analyze interactions between individual phenotypes, namely clustering analysis, we found an expected segregation of resistant SNPs (single-nucleotide polymorphisms) of the multiple RRLs in the typical accession groups carrying multiple traits. Almost none of the loci detected by association mapping analysis were linked to the loci of previously identified critical genes regulating the traits, suggesting that this could be useful to identify complex architecture of genetic factors determining variation among multiple accessions.

Copper redistribution in Atox1-deficient mouse fibroblast cells

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

Structural basis for autoregulation of the zinc transporter YiiP

Zinc transporters play critical roles in cellular zinc homeostatic control. The 2.9-Å resolution structure of the zinc transporter YiiP from Escherichia coli reveals a richly charged dimer-interface stabilized by zinc binding. Site-directed fluorescent resonance energy transfer (FRET) measurements and mutation-activity analysis suggest that zinc binding triggers hinge movements of two electrically repulsive cytoplasmic domains pivoting around four salt-bridges situated at the juncture of the cytoplasmic and transmembrane domains. These highly conserved salt-bridges interlock transmembrane helices at the dimer-interface, well positioned to transmit zinc-induced inter-domain movements to reorient transmembrane helices, thereby modulating coordination geometry of the active-site for zinc transport. The cytoplasmic domain of YiiP is a structural mimic of metal trafficking proteins and the metal-binding domains of metal-transporting P-type ATPases. The use of this common structural module to regulate metal coordination chemistry may enable a tunable transport activity in response to cytoplasmic metal fluctuations.

Downregulation of oligodendrocyte transcripts is associated with impaired prefrontal cortex function in rats

Abnormalities of brain white matter and oligodendroglia are among the most consistent findings in schizophrenia (Sz) research. Various gene expression microarray studies of post-mortem Sz brains showed a downregulation of myelin transcripts, while imaging and microscopy studies demonstrated decreases in prefrontal cortical (PFC) white matter volume and oligodendroglia density. Currently, the extent to which reduced oligodendrocyte markers contribute to pathophysiological domains of Sz is unknown. We exposed adolescent rats to cuprizone (CPZ), a copper chelator known to cause demyelination in mice, and examined expression of oligodendrocyte mRNA transcripts and PFC-mediated behavior. Rats on the CPZ diet showed decreased expression of mRNA transcripts encoding oligodendroglial proteins within the medial PFC, but not in the hippocampus or the striatum. These rats also displayed a specific deficit in the ability to shift between perceptual dimensions in the attentional set-shifting task, a PFC-mediated behavioral paradigm modeled after the Wisconsin Card Sorting Test (WCST). The inability to shift strategies corresponds to the deficits exhibited by Sz patients in the WCST. The results demonstrate that a reduction in oligodendrocyte markers is associated with impaired PFC-mediated behaviors. Thus, CPZ exposure of rats can serve as a model to examine the contribution of oligodendrocyte perturbation to cognitive deficits observed in Sz.

Hepatocyte GP73 expression in Wilson disease

BACKGROUND/AIMS

Wilson disease (WD) is a disorder of copper transport caused by mutations within the ATP7B gene. WD is phenotypically variable and can present with predominantly hepatic or neurologic manifestations. The mechanisms responsible for this variability are unknown. GP73, a Golgi membrane protein, is expressed in hepatocytes in response to acute and chronic liver disease.

METHODS

Hepatocyte GP73 expression was examined in the livers of WD patients by semiquantitative immunohistochemistry. GP73 mRNA levels were measured in mice with a deletion of the WD gene (Atp7b(-/-)) by real-time PCR, and these values were compared to the concomitant histological abnormalities and previously reported copper levels.

RESULTS

Hepatocyte GP73 expression was more frequently observed in patients with hepatic versus neurologic presentation (79% vs. 30%, p<0.05). Furthermore, GP73 expression was significantly higher (44.7+/-14.0 vs. 2.0+/-0.81, p<0.05) in patients with hepatic phenotype. In Atp7b(-/-) mice, GP73 mRNA was significantly elevated at 20-46 weeks of age, coincident with extensive hepatic inflammation and fibrosis, but not at 6 weeks, when hepatic histology was normal despite significant copper overload. GP73 mRNA levels normalized concomitantly with the resolution of hepatic injury at 60-weeks. However, in tumor-like nodules GP73 was strikingly elevated.

CONCLUSION

Increased hepatocyte GP73 expression is more commonly a feature of hepatic than neurologic WD, and is triggered in response to inflammation, fibrosis, and dysplasia, rather than copper overload.

Looking past the lump: genetic aspects of inguinal hernia in children

Inguinal hernia is associated with a multitude of genetic syndromes. Disorders of the microfibril, elastin, collagen, and the glycosaminoglycan component of the extracellular matrix can result in an increase in the likelihood of inguinal hernia. In addition, inguinal hernia may be the presenting feature of disorders of sexual differentiation. Inguinal hernia of unknown etiology also occurs more commonly in several other groups of genetic diseases including chromosomal disorders, microdeletion disorders such as 22q11.2 microdeletion, and in single gene disorders. We review the genetics of connective tissue formation and focus on a series of genetic conditions that may present with or are characterized by a higher risk of inguinal hernia. A comprehensive review of the literature aims to provide a diagnostic framework to aid in the identification of patients with inguinal hernia as part of underlying genetic disease.

P-type ATPases as drug targets: tools for medicine and science

P-type ATPases catalyze the selective active transport of ions like H+, Na+, K+, Ca2+, Zn2+, and Cu2+ across diverse biological membrane systems. Many members of the P-type ATPase protein family, such as the Na+,K+-, H+,K+-, Ca2+-, and H+-ATPases, are involved in the development of pathophysiological conditions or provide critical function to pathogens. Therefore, they seem to be promising targets for future drugs and novel antifungal agents and herbicides. Here, we review the current knowledge about P-type ATPase inhibitors and their present use as tools in science, medicine, and biotechnology. Recent structural information on a variety of P-type ATPase family members signifies that all P-type ATPases can be expected to share a similar basic structure and a similar basic machinery of ion transport. The ion transport pathway crossing the membrane lipid bilayer is constructed of two access channels leading from either side of the membrane to the ion binding sites at a central cavity. The selective opening and closure of the access channels allows vectorial access/release of ions from the binding sites. Recent structural information along with new homology modeling of diverse P-type ATPases in complex with known ligands demonstrate that the most proficient way for the development of efficient and selective drugs is to target their ion transport pathway.

[From gene to disease: copper-transporting P ATPases alteration]

Copper is a trace metal, essential for many biological processes. Copper is also toxic if in excessive amounts; its homeostatic balance requires a delicate regulation. Several severe hereditary human disorders of copper regulatory mechanisms have been identified; they are related to mutations in gene ATP7A and ATP7B coding for copper-transporting proteins. Those mutations result in copper deficiency for ATP7A (Menkes disease) and copper overload for ATP7B (Wilson disease). Usually, clinical and biochemical phenotypes of these diseases are disparate. This article focuses on the molecular pathogenesis of Wilson and Menkes disease, and discusses how causing mutations are correlated with molecular defects and disease phenotypes.

Three-dimensional structure of the human copper transporter hCTR1

Copper uptake proteins (CTRs), mediate cellular acquisition of the essential metal copper in all eukaryotes. Here, we report the structure of the human CTR1 protein solved by electron crystallography to an in plane resolution of 7 A. Reminiscent of the design of traditional ion channels, trimeric hCTR1 creates a pore that stretches across the membrane bilayer at the interface between the subunits. Assignment of the helices identifies the second transmembrane helix as the key element lining the pore, and reveals how functionally important residues on this helix could participate in Cu(I)-coordination during transport. Aligned with and sealing both ends of the pore, extracellular and intracellular domains of hCTR1 appear to provide additional metal binding sites. Consistent with the existence of distinct metal binding sites, we demonstrate that hCTR1 stably binds 2 Cu(I)-ions through 3-coordinate Cu-S bonds, and that mutations in one of these putative binding sites results in a change of coordination chemistry.

Metallothionein Toxicology: Metal Ion Trafficking and Cellular Protection

The literature is replete with reports about the involvement of metallothionein in host defense against injurious chemical, biological, and physical agents. Yet, metallothionein's functional roles are still being debated. This review addresses the issues that have left the physiological significance of metallothionein in doubt and moves on to assess the MT's importance in cell toxicology. It is evident that the protein is broadly involved in protecting cells from injury due to toxic metal ions, oxidants, and electrophiles. Attention is focused on MT's structural and chemical properties that confer this widespread role in cell protection. Particular emphasis is placed on the implications of finding that metal ion unsaturated metallothionein is commonly present in many cells and tissues and the question, how does selectivity of reaction with metallothionein take place in the cellular environment that includes large numbers of competing metal binding sites and high concentrations of protein and glutathione sulfhydryl groups?

Amino acid polymorphisms in strictly conserved domains of a P-type ATPase HMA5 are involved in the mechanism of copper tolerance variation in Arabidopsis

Copper (Cu) is an essential element in plant nutrition, but it inhibits the growth of roots at low concentrations. Accessions of Arabidopsis (Arabidopsis thaliana) vary in their tolerance to Cu. To understand the molecular mechanism of Cu tolerance in Arabidopsis, we performed quantitative trait locus (QTL) analysis and accession studies. One major QTL on chromosome 1 (QTL1) explained 52% of the phenotypic variation in Cu tolerance in roots in a Landsberg erecta/Cape Verde Islands (Ler/Cvi) recombinant inbred population. This QTL regulates Cu translocation capacity and involves a Cu-transporting P(1B-1)-type ATPase, HMA5. The Cvi allele carries two amino acid substitutions in comparison with the Ler allele and is less functional than the Ler allele in Cu tolerance when judged by complementation assays using a T-DNA insertion mutant. Complementation assays of the ccc2 mutant of yeast using chimeric HMA5 proteins revealed that N923T of the Cvi allele, which was identified in the tightly conserved domain N(x)(6)YN(x)(4)P (where the former asparagine was substituted by threonine), is a cause of dysfunction of the Cvi HMA5 allele. Another dysfunctional HMA5 allele was identified in Chisdra-2, which showed Cu sensitivity and low capacity of Cu translocation from roots to shoots. A unique amino acid substitution of Chisdra-2 was identified in another strictly conserved domain, CPC(x)(6)P, where the latter proline was replaced with leucine. These results indicate that a portion of the variation in Cu tolerance of Arabidopsis is regulated by the functional integrity of the Cu-translocating ATPase, HMA5, and in particular the amino acid sequence in several strictly conserved motifs.

Unusual magnetic resonance imaging features in Menkes disease

We present a case of an inherited disorder of copper metabolism, Menkes disease in which MRI studies revealed the coexistence of T2 hypersignal in the temporal white matter with an increase of apparent diffusion coefficient indicative of vasogenic oedema combined with T2 hypersignal of the putamen and head of the caudate and decreased apparent diffusion coefficient indicative of cytotoxic oedema. These unusual MRI features emphasize the interest of newly developed techniques in early diagnosis in Menkes disease. The acute cerebral damage might result from the combined effects of acute metabolic stress due to infectious disease and prolonged status epilepticus, acting on a highly susceptible developing brain. Vasogenic oedema in the temporal white matter could be related to prolonged status epilepticus and vascular abnormalities. Cytotoxic oedema of the putamen and head caudate could result from energetic failure.

Stability and ATP binding of the nucleotide-binding domain of the Wilson disease protein: effect of the common H1069Q mutation

Perturbation of the human copper-transporter Wilson disease protein (ATP7B) causes intracellular copper accumulation and severe pathology, known as Wilson disease (WD). Several WD mutations are clustered within the nucleotide-binding subdomain (N-domain), including the most common mutation, H1069Q. To gain insight into the biophysical behavior of the N-domain under normal and disease conditions, we have characterized wild-type and H1069Q recombinant N-domains in vitro and in silico. The mutant has only twofold lower ATP affinity compared to that of the wild-type N-domain. Both proteins unfold in an apparent two-state reaction at 20 degrees C and ATP stabilizes the folded state. The thermal unfolding reactions are irreversible and, for the same scan rate, the wild-type protein is more resistant to perturbation than the mutant. For both proteins, ATP increases the activation barrier towards thermal denaturation. Molecular dynamics simulations identify specific differences in both ATP orientation and protein structure that can explain the absence of catalytic activity for the mutant N-domain. Taken together, our results provide biophysical characteristics that may be general to N-domains in other P(1B)-ATPases as well as identify changes that may be responsible for the H1069Q WD phenotype in vivo.

"Pulling the plug" on cellular copper: the role of mitochondria in copper export

Mitochondria contain two enzymes, Cu,Zn superoxide dismutase (Sod1) and cytochrome c oxidase (CcO), that require copper as a cofactor for their biological activity. The copper used for their metallation originates from a conserved, bioactive pool contained within the mitochondrial matrix, the size of which changes in response to either genetic or pharmacological manipulation of cellular copper status. Its dynamic nature implies molecular mechanisms exist that functionally couple mitochondrial copper handling with other, extramitochondrial copper trafficking pathways. The recent finding that mitochondrial proteins with established roles in CcO assembly can also effect changes in cellular copper levels by modulating copper efflux from the cell supports a mechanistic link between organellar and cellular copper metabolism. However, the proteins and molecular mechanisms that link trafficking of copper to and from the organelle with other cellular copper trafficking pathways are unknown. This review documents our current understanding of copper trafficking to, and within, the mitochondrion for metallation of CcO and Sod1; the pathways by which the two copper centers in CcO are formed; and, the interconnections between mitochondrial function and the regulation of cellular copper homeostasis.