Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0022716 (Menkes)
 1,057 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The genes responsible for Wilson disease and Menkes syndrome have been cloned and identified as copper ATPases. These enzymes form part of a large family of transporters, the P-type ATPases. Although copper ATPases share strong structural similarities with these other pumps, comparatively little is known about their physiologic function. In this review, we examine data relating to the Wilson disease protein, ATP7B, in the liver. We present evidence suggesting that ATP7B is located intracellularly, together with data suggesting that, at least in part, ATP7B may also be found on the canalicular membrane. We also examine the form of copper that the transporter recognizes. We then review data on the Long-Evans Cinnamon rat, a model for Wilson disease, and discuss what effect the Wilson disease mutation has on copper transport. Finally, we conclude that, although we have made major advances in our understanding of copper metabolism in the liver, there are still many questions awaiting answers.
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PMID:Physiologic function of the Wilson disease gene product, ATP7B. 958 40

The movement of copper ions across membrane barriers of vital organs and tissues is a priority topic in nutrition and one for which there continues to be little understanding of the mechanism. Reports of membrane-bound, copper-transporting adenosine triphosphatases (Cu-ATPases) selective for copper ions have brought new focus to the problem and prompted fresh ideas. Using a cell culture model approach, we attempted to learn whether transport into and out of cells depends on a Cu-ATPase. Measurement of transport kinetics in fibroblasts, brain glial cells, neuroblastoma cells, and placental cells showed differences in the rates of copper uptake and response to sulfhydryl reagents. BeWo cells, a human choriocarcinoma placental cell line, behaved as did Menkes fibroblasts by avidly absorbing copper but not releasing copper to the immediate environment. Further tests showed that BeWo cells did not express the transcript for the membrane-bound Cu-ATPase that has been identified with Menkes syndrome. Transcript induction, however, was achieved by growing BeWo cells on porous filters that allowed apical and basolateral surfaces to form. With transcript expression, the cells showed a capacity to release copper into the medium. BeWo cells also synthesized a form of ceruloplasmin whose structure differed from that of the plasma protein and hence may be a product of a different gene. BeWo cells may also express the gene for Wilson disease, thus linking Menkes and Wilson proteins to maternal delivery of copper. We constructed a model in which both ATPases work in concert in a vesicle-based transport mechanism. The vesicle model may help us understand the transport of copper across the placenta and all cells in general.
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PMID:Functional analysis of copper homeostasis in cell culture models: a new perspective on internal copper transport. 958 41

A series of reports in the 1960s highlighted nutritional copper deficiencies in infants and children recovering from malnutrition in Peru; since that time, a cascade of additional cases in premature infants, in patients receiving total parenteral nutrition, and in those receiving special diets or unmodified cow milk have been reported. The identification by Danks that Menkes syndrome, a genetically determined defect in copper absorption and utilization, is responsible for the observed clinical manifestations provided further insight into the physiopathologic effects of copper deficiency. New information on the metabolism and physiologic role of copper, plus the identification of additional copper metalloenzymes and improvement in how to determine copper status, has fueled interpretation and speculation on how and why the classic signs of copper deficiency occur, as well as on the possible effects of mild deficiencies. Also under scrutiny are potential interactions between other elements and the effects of other elements, even when given in acceptable amounts, on copper status. There should be no constraints in thinking on other possible effects of impaired copper status in humans. I review some of the history of nutritional copper deficiency in infants and children and attempt to interpret some of the clinical manifestations in light of newly acquired information.
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PMID:Clinical manifestations of nutritional copper deficiency in infants and children. 958 44

Menkes syndrome is an X-linked genetic copper deficiency that is usually fatal in early childhood. Milder variants exist, including occipital horn syndrome, which is primarily a connective tissue disorder. Mutations of the mottled locus in mice produce a wide range of copper-deficient phenotypes that are good models for human diseases. Understanding the nature of the defects has been greatly increased as a result of the identification of the gene affected in Menkes syndrome. The gene spans approximately 140 kilobases, contains 23 exons, and encodes a copper-transporting ATPase termed MNK that is thought to be involved in copper efflux from cells. More recent studies show that MNK is located primarily in the trans-Golgi compartment of Chinese hamster ovary cells. Copper-resistant cells overexpress MNK and can efflux more copper than parental cells, consistent with the copper efflux role proposed for MNK. Patients with Menkes syndrome are predicted to have little or no MNK activity, whereas patients with occipital horn syndrome have less severe mutations and some residual MNK activity is predicted. Similarly, the mottled mice mutants have a range of mutations in the MNK gene homologue. Complete loss of MNK, however, produces a fetal lethal phenotype in mice. A model is proposed to explain the wide range of phenotypes exhibited by the different mouse mutants. Further research into the cell biology of copper transport is expected to reveal more about the molecular basis of copper homeostasis.
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PMID:Menkes syndrome and animal models. 958 46

In the 25 y since copper deficiency was first delineated in persons with Menkes syndrome, advances in our understanding of the clinical, biochemical, and molecular aspects of this rare disorder have surpassed progress in the design of effective therapies. In contrast with purely nutritional copper deficiency, in which copper replacement can be curative, the nature of the basic defect in Menkes syndrome suggests that corrective efforts are likely to be more complicated, a point supported by the cumulative literature on this topic as well as by emerging molecular data. In this paper, certain clinical, biochemical, and molecular aspects of copper histidine treatment in 25 Menkes syndrome patients at the National Institutes of Health are reviewed. The delineation of a distinctive neurochemical pattern in plasma and cerebrospinal fluid, reflecting deficiency of the copper enzyme dopamine beta-monooxygenase, is arguably the most important finding in the study of Menkes syndrome. This abnormal pattern has proven extremely reliable as a rapid diagnostic test, enabling early identification of affected infants--a fundamental requirement for improving clinical outcomes. Of 11 patients identified by prenatal or prompt postnatal testing and treated within the first 10 d of age, one walked at 14 mo of age and has normal neurodevelopment at age 3 y and another infant's early progress appears promising. However, five patients died in infancy and neurodevelopmental outcome was suboptimal in four others. Consideration of additional therapeutic strategies seems necessary, therefore, for most patients and families facing this troublesome form of copper deficiency.
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PMID:Diagnosis and therapy of Menkes syndrome, a genetic form of copper deficiency. 958 47

Menkes disease arises from a genetic impairment in copper transport. The gene responsible for the phenotype has been identified as a copper transporting ATPase ( ATP7A ). Recently, the protein encoded by the ATP7A gene has been localized to the Golgi complex. In order to investigate the role of the Menkes disease protein in copper transport, recombinant constructs containing both the full-length open reading frame and an alternatively spliced form have been successfully expressed and localized in mammalian cells. Other studies of a patient with occipital horn syndrome, an allelic variant of Menkes disease, have demonstrated that only this alternatively spliced isoform and not the full-length form is expressed in this patient. The milder form of this patient's phenotype suggests that the alternatively spliced isoform has some functional role in copper transport. In the present study the full-length recombinant Menkes protein was shown by immunofluorescence to localize to the Golgi apparatus and the alternatively spliced form, lacking sequences for transmembrane domains 3 and 4 encoded by exon 10, was shown to localize to the endoplasmic reticulum. Using sequences from exon 10 fused to a non-Golgi reporter molecule, a 38 amino acid sequence containing transmembrane domain 3 of the Menkes protein was found to be sufficient for localization to the Golgi complex. Therefore, the protein sequence encoded by exon 10 may be responsible for this differential localization and both isoforms may be required for comprehensive transport of copper within the cell.
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PMID:A Golgi localization signal identified in the Menkes recombinant protein. 966 66

We have optimised the overexpression and purification of the N-terminal end of the Menkes disease protein expressed in Escherichia coli, containing one, two and six metal binding domains (MBD), respectively. The domain(s) have been characterised using circular dichroism (CD) and fluorescence spectroscopy, and their copper(I) binding properties have been determined. Structure prediction derived from far-UV CD indicates that the secondary structure is similar in the three proteins and dominated by beta-sheet. The tryptophan fluorescence maximum is blue-shifted in the constructs containing two and six MBDs relative to the monomer, suggesting more structurally buried tryptophan(s), compared to the single MBD construct. Copper(I) binding has been studied by equilibrium dialysis under anaerobic conditions. We show that the copper(I) binding to constructs containing two and six domains is cooperative, with Hill coefficients of 1.5 and 4, respectively. The apparent affinities are described by K(0.5), determined to be 65 microM and 19 microM for constructs containing two and six domains, respectively. Our data reveal a unique regulation of Menkes protein upon a change in copper(I) concentration. The regulation does not occur as an 'all-or-none' cooperativity, suggesting that the copper(I) binding domains have a basal low affinity for binding and release of copper(I) at low concentrations but are able to respond to higher copper levels by increasing the affinity, thereby contributing to prevent the copper concentration from reaching toxic levels in the cell.
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PMID:Cooperative binding of copper(I) to the metal binding domains in Menkes disease protein. 1055 64

Copper (Cu) is a potentially toxic yet essential element. MENKES DISEASE, a copper deficiency disorder, and WILSON DISEASE, a copper toxicosis condition, are two human genetic disorders, caused by mutations of two closely related Cu-transporting ATPases. Both molecules efflux copper from cells. Quite diverse clinical phenotypes are produced by different mutations of these two Cu-transporting proteins. The understanding of copper homeostasis has become increasingly important in clinical medicine as the metal could be involved in the pathogenesis of some important neurological disorders such as Alzheimer's disease, motor neurone diseases and prion diseases.
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PMID:The molecular basis of copper-transport diseases. 1128 57

The Menkes disease protein (ATP7A or MNK) is a P-type transmembrane ATPase that regulates translocation of cytosolic copper ions across intracellular membranes of compartments along the secretory pathway. In this study, we show that endogenous MNK in cultured cell lines is localized to the distal Golgi apparatus and translocates to the plasma membrane in response to exogenous copper ions. This transport event is not blocked by expression of a dominant-negative mutant protein kinase D, an enzyme implicated in regulating constitutive trafficking from the trans-Golgi network (TGN) to the plasma membrane, whereas constitutive transport of CD4 is inhibited. In contrast, protein kinase A inhibitors block copper-stimulated MNK delivery to the plasma membrane. Expression of constitutively active Rho GTPases such as Cdc42, Rac1 and RhoA reveals a requirement for Cdc42 in the trafficking of MNK, to the cell surface. Furthermore, overexpression of WASp inhibits anterograde transport of MNK, further supporting regulation by the Cdc42 GTPase. These findings define a novel step in TGN-to-plasma membrane traffic required to export MNK to the cell surface.
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PMID:Novel membrane traffic steps regulate the exocytosis of the Menkes disease ATPase. 1239 97

Copper is essential for brain metabolism, serving as a cofactor to superoxide dismutase, dopamine-beta-hydroxylase, amyloid precursor protein, ceruloplasmin, and other proteins required for normal brain function. The copper-transporting ATPases ATP7A and ATP7B play a central role in distribution of copper in the central nervous system; genetic mutations in ATP7A and ATP7B lead to severe neurodegenerative disorders, Menkes disease and Wilson disease, respectively. Although both ATP7A and ATP7B are required, their specific roles and regulation in the brain remain poorly understood. Using high-resolution imaging and functional assays, we demonstrate that ATP7A and ATP7B show cell-specific distribution in adult cerebellum, have distinct enzymatic characteristics, and are regulated differently during development. ATP7B is continuously expressed in Purkinje neurons (PN) where it delivers copper to the ferroxidase ceruloplasmin. ATP7A is a faster copper transporter than Wilson disease protein as evidenced by faster rates of catalytic reactions. The expression of ATP7A switches during development from PN to Bergmann glia, the cells supporting PN function in adult brain. Inactivation of ATP7B (Wilson disease protein) by gene knock-out induces a striking shift in the expression of the ATP7B target protein, ceruloplasmin, from PN to Bergmann glia, where ATP7A (Menkes disease protein) is present. The induced cell-specific change in expression restores copper delivery to ceruloplasmin via ATP7A. Overall, the results provide evidence for distinct functions of ATP7A and ATP7B in the cerebellum and illustrate a tight link between copper homeostasis in PN and Bergmann glia.
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PMID:The copper-transporting ATPases, menkes and wilson disease proteins, have distinct roles in adult and developing cerebellum. 1563 71


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