RESUMO
Myxoma virus (MYXV) is a Leporipoxvirus (genus) belonging to the family Poxviridae; it is characterised by a genome of approximately 161 kb dsDNA encoding for several proteins that play an essential role in both host spectrum determination and immunomodulation. The healthy reservoir of the virus is Sylvilagus spp. At the same time, in wild and domestic European rabbits (Oryctolagus cuniculus), MYXV is the etiologic agent of myxomatosis, a disease with an extremely high mortality rate. In 2014, an interspecies jump of MYXV was reported in Lepus europaeus in the UK. In 2018, myxomatosis induced by a new recombinant strain called MYXV-To was identified during a large outbreak in Iberian hares (Lepus granatensis) in Spain. Here, we describe the case of myxomatosis in another hare species: an adult male Italian hare (Lepus corsicanus) found dead in 2018 in Sicily with lesions suggestive of myxomatosis and treponema infection. Laboratory tests, e.g., end-point PCR and negative staining electron microscopy, confirmed the presence of both pathogens. MYXV was then isolated from tissue samples in permissive cells and sequenced using NGS technology. Main genomic differences concerning known MYXV strains are discussed.
Assuntos
Lebres , Myxoma virus , Vírus , Animais , Masculino , Coelhos , Myxoma virus/genética , Genoma , Vírus/genética , Itália/epidemiologiaRESUMO
BACKGROUND: . The occurrence of trans-placental transmission of severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) infection remains highly debated. Placental positivity for SARS-CoV-2 has been reported in selected cases, but infection or virus-associated disease of fetal tissues or newborns remains to be demonstrated. METHODS: We screened for SARS-CoV-2 spike (S) protein expression placentas from 101 women who delivered between February 7 and May 15, 2020, including 15 tested positive for SARS-CoV-2 RNA, 34 tested negative, and 52 not evaluated as they did not meet testing criteria (32), or delivered before COVID-19 pandemic declaration (20). Immunostain for SARS-CoV-2 nucleocapsid (N) was performed in the placentas of all COVID-19 positive women. One placenta resulted positive for the SARS-CoV-2 S and N proteins, which was further studied by RNA-in situ hybridization and RT-PCR for S transcripts, and by electron microscopy. A comprehensive immunohistochemical and immunofluorescence analysis of the placental inflammatory infiltrate completed the investigations. FINDINGS: SARS-CoV-2 S and N proteins were strongly expressed in the placenta of a COVID-19 pregnant woman whose newborn tested positive for viral RNA and developed COVID-19 pneumonia soon after birth. SARS-CoV-2 antigens, RNA and/or particles morphologically consistent with coronavirus were identified in villous syncytiotrophoblast, endothelial cells, fibroblasts, in maternal macrophages, and in Hofbauer cells and fetal intravascular mononuclear cells. The placenta intervillous inflammatory infiltrate consisted of neutrophils and monocyte-macrophages expressing activation markers. Absence of villitis was associated with an increase in the number of Hofbauer cells, which expressed PD-L1. Scattered neutrophil extracellular traps (NETs) were identified by immunofluorescence. INTERPRETATION: We provide first-time evidence for maternal-fetal transmission of SARS-CoV-2, likely propagated by circulating virus-infected fetal mononuclear cells. Placenta infection was associated with recruitment of maternal inflammatory cells in the intervillous space, without villitis. PD-L1 expression in syncytiotrophoblast and Hofbaeur cells, together with limited production of NETs, may have prevented immune cell-driven placental damage, ensuring sufficient maternal-fetus nutrient exchanges.
Assuntos
Infecções por Coronavirus/transmissão , Placenta/virologia , Pneumonia Viral/transmissão , Adulto , Betacoronavirus/genética , Betacoronavirus/isolamento & purificação , COVID-19 , Infecções por Coronavirus/patologia , Infecções por Coronavirus/virologia , Proteínas do Nucleocapsídeo de Coronavírus , Armadilhas Extracelulares/metabolismo , Feminino , Humanos , Imuno-Histoquímica , Recém-Nascido , Macrófagos/virologia , Microscopia Eletrônica , Nasofaringe/virologia , Proteínas do Nucleocapsídeo/genética , Proteínas do Nucleocapsídeo/metabolismo , Pandemias , Fosfoproteínas , Placenta/citologia , Placenta/patologia , Pneumonia Viral/patologia , Pneumonia Viral/virologia , Gravidez , RNA Viral/metabolismo , SARS-CoV-2 , Glicoproteína da Espícula de Coronavírus/genética , Glicoproteína da Espícula de Coronavírus/metabolismoRESUMO
Lagovirus is an emerging genus of Caliciviridae, which includes the Rabbit Hemorrhagic Disease Virus (RHDV) of rabbits and the European brown hare syndrome virus (EBHSV) of hares that cause lethal hepatitis. In 2010, a new RHDV related virus (RHDV2) with a unique genetic and antigenic profile and lower virulence was identified in France in rabbits. Here we report the identification of RHDV2 as the cause in Sardinia of several outbreaks of acute hepatitis in rabbits and Cape hare (Lepus capensis mediterraneus). This is the first account of a lagovirus that causes fatal hepatitis in both rabbits and hares.
Assuntos
Infecções por Caliciviridae/veterinária , Lebres , Vírus da Doença Hemorrágica de Coelhos/fisiologia , Animais , Anticorpos Monoclonais/sangue , Anticorpos Antivirais/sangue , Infecções por Caliciviridae/epidemiologia , Infecções por Caliciviridae/genética , Infecções por Caliciviridae/virologia , Citocromos b/genética , Citocromos b/metabolismo , Complexo IV da Cadeia de Transporte de Elétrons/genética , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Ensaio de Imunoadsorção Enzimática/veterinária , Vírus da Doença Hemorrágica de Coelhos/genética , Vírus da Doença Hemorrágica de Coelhos/metabolismo , Itália/epidemiologia , Dados de Sequência Molecular , Filogenia , Análise de Sequência de Proteína/veterinária , Proteínas Estruturais Virais/genética , Proteínas Estruturais Virais/metabolismoRESUMO
Since summer 2010, numerous cases of Rabbit Haemorrhagic Disease (RHD) have been reported in north-western France both in rabbitries, affecting RHD-vaccinated rabbits, and in wild populations. We demonstrate that the aetiological agent was a lagovirus phylogenetically distinct from other lagoviruses and which presents a unique antigenic profile. Experimental results show that the disease differs from RHD in terms of disease duration, mortality rates, higher occurrence of subacute/chronic forms and that partial cross-protection occurs between RHDV and the new RHDV variant, designated RHDV2. These data support the hypothesis that RHDV2 is a new member of the Lagovirus genus. A molecular epidemiology study detected RHDV2 in France a few months before the first recorded cases and revealed that one year after its discovery it had spread throughout the country and had almost replaced RHDV strains. RHDV2 was detected in continental Italy in June 2011, then four months later in Sardinia.
Assuntos
Infecções por Caliciviridae/veterinária , Vírus da Doença Hemorrágica de Coelhos/classificação , Vírus da Doença Hemorrágica de Coelhos/genética , Coelhos , Proteínas Estruturais Virais/genética , Sequência de Aminoácidos , Animais , Infecções por Caliciviridae/epidemiologia , Infecções por Caliciviridae/virologia , Ensaio de Imunoadsorção Enzimática/veterinária , França/epidemiologia , Testes de Hemaglutinação/veterinária , Vírus da Doença Hemorrágica de Coelhos/química , Vírus da Doença Hemorrágica de Coelhos/metabolismo , Dados de Sequência Molecular , Filogenia , Reação em Cadeia da Polimerase Via Transcriptase Reversa/veterinária , Alinhamento de Sequência/veterinária , Proteínas Estruturais Virais/química , Proteínas Estruturais Virais/metabolismoRESUMO
Myxoma virus is a poxvirus responsible for myxomatosis in European Rabbits (Oryctolagus cuniculus). The entire genome of the myxoma virus has been sequenced, allowing a systemic survey of the functions of a large number of putative pathogenic factors that this virus expresses to subvert the immune and inflammatory pathways of infected rabbit hosts. In Italy, industrial rabbits are mostly vaccinated against myxomatosis using the attenuated myxoma virus strains Borghi or SG33. We have identified genetic markers specific for Borghi or SG33 vaccine strains and established a PCR-based assay that could be used to: (a) rapidly diagnose the presence of myxoma virus in infected organs; (b) discriminate between field strain-infected and vaccinated rabbits and (c) differentiate between Borghi or SG33 vaccine strain.
Assuntos
Myxoma virus/genética , Mixomatose Infecciosa/genética , Vacinas Virais/genética , Animais , Marcadores Genéticos/imunologia , Myxoma virus/imunologia , Mixomatose Infecciosa/imunologia , Mixomatose Infecciosa/prevenção & controle , Coelhos , Especificidade da Espécie , Vacinas Virais/imunologia , Vacinas Virais/farmacologiaRESUMO
Pantothenate kinase 2 (Pank2) is a mitochondrial enzyme that catalyses the first regulatory step of Coenzyme A synthesis and that is responsible for a genetic movement disorder named Pank-associated neurodegeneration (PKAN). This is characterized by abnormal iron accumulation in the brain, particularly in the globus pallidus. We downregulated Pank2 in some cell lines by using specific siRNAs to study its effect on iron homeostasis. In HeLa cells this caused a reduction of cell proliferation and of aconitase activity, signs of cytosolic iron deficiency without mitochondrial iron deposition, and a 12-fold induction of ferroportin mRNA. Pank2 silencing caused a strong induction of ferroportin mRNA also in hepatoma HepG2, a modest one in neuroblastoma SH-SY5Y and none in glioma U373 cells. A reduction of cell growth was observed in all these cell types. The strong Pank2-mediated alteration of ferroportin expression in some cell types might alter iron transfer to the brain and be connected with brain iron accumulation.
Assuntos
Proteínas de Transporte de Cátions/metabolismo , Proliferação de Células/efeitos dos fármacos , Regulação da Expressão Gênica/fisiologia , Ferro/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , RNA Interferente Pequeno/farmacologia , Aconitato Hidratase/metabolismo , Proteínas de Transporte de Cátions/genética , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/genética , Ativação Enzimática/efeitos dos fármacos , Ativação Enzimática/genética , Regulação da Expressão Gênica/efeitos dos fármacos , Humanos , Mitocôndrias/genética , Mitocôndrias/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Protoporfirinas/metabolismo , RNA Mensageiro/metabolismo , Superóxido Dismutase/metabolismoRESUMO
Ferritins are characterized by highly conserved three-dimensional structures similar to spherical shells, designed to accommodate large amounts of iron in a safe, soluble and bioavailable form. They can have different architectures with 12 or 24 equivalent or non-equivalent subunits, all surrounding a large cavity. All ferritins readily interact with Fe(II) to induce its oxidation and deposition in the cavity in a mineral form, in a reaction that is catalyzed by a ferroxidase center. This is an anti-oxidant activity that consumes Fe(II) and peroxides, the reagents that produce toxic free radicals in the Fenton reaction. The mechanism of ferritin iron incorporation has been characterized in detail, while that of iron release and recycling has been less thoroughly studied. Generally ferritin expression is regulated by iron and by oxidative damage, and in vertebrates it has a central role in the control of cellular iron homeostasis. Ferritin is mostly cytosolic but is found also in mammalian mitochondria and nuclei, in plant plastids and is secreted in insects. In vertebrates the cytosolic ferritins are composed of H and L subunit types and their assembly in a tissues specific ratio that permits flexibility to adapt to cell needs. The H-ferritin can translocate to the nuclei in some cell types to protect DNA from iron toxicity, or can be actively secreted, accomplishing various functions. The mitochondrial ferritin is found in mammals, it has a restricted tissue distribution and it seems to protect the mitochondria from iron toxicity and oxidative damage. The various functions attributed to the cytosolic, nuclear, secretory and mitochondrial ferritins are discussed.
Assuntos
Ferritinas/fisiologia , Ferro/metabolismo , Animais , Antioxidantes/metabolismo , Ferritinas/química , Ferritinas/genética , Ferritinas/imunologia , Humanos , Imunoterapia , Neoplasias/tratamento farmacológico , OxirreduçãoRESUMO
X-linked sideroblastic anemia with ataxia (XLSA/A) is caused by defects of the transporter ABCB7 and is characterized by mitochondrial iron deposition and excess of protoporphyrin in erythroid cells. We describe ABCB7 silencing in HeLa cells by performing sequential transfections with siRNAs. The phenotype of the ABCB7-deficient cells was characterized by a strong reduction in proliferation rate that was not rescued by iron supplementation, by evident signs of iron deficiency, and by a large approximately 6-fold increase of iron accumulation in the mitochondria that was poorly available to mitochondrial ferritin. The cells showed an increase of protoporphyrin IX, a higher sensitivity to H(2)O(2) toxicity, and a reduced activity of mitochondrial superoxide dismutase 2 (SOD2), while the activity of mitochondrial enzymes, such as citrate synthase or succinate dehydrogenase, and ATP content were not decreased. In contrast, aconitase activity, particularly that of the cytosolic, IRP1 form, was reduced. The results support the hypothesis that ABCB7 is involved in the transfer of iron from mitochondria to cytosol, and in the maturation of cytosolic Fe/S enzymes. In addition, the results indicate that anemia in XLSA/A is caused by the accumulation of iron in a form that is not readily usable for heme synthesis.
Assuntos
Transportadores de Cassetes de Ligação de ATP/genética , Anemia Ferropriva/genética , Anemia Sideroblástica/genética , Ataxia/genética , Doenças Genéticas Ligadas ao Cromossomo X/genética , Sobrecarga de Ferro/genética , Mitocôndrias/genética , Interferência de RNA , Transportadores de Cassetes de Ligação de ATP/antagonistas & inibidores , Anemia Ferropriva/metabolismo , Anemia Sideroblástica/metabolismo , Ataxia/metabolismo , Transporte Biológico/genética , Citoplasma/genética , Citoplasma/metabolismo , Doenças Genéticas Ligadas ao Cromossomo X/metabolismo , Células HeLa , Heme/biossíntese , Heme/genética , Humanos , Ferro/metabolismo , Sobrecarga de Ferro/metabolismo , Mitocôndrias/metabolismo , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismo , Fenótipo , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/farmacologiaRESUMO
Adaptor protein-3 (AP-3) is an ubiquitous cytoplasmic complex that shuttles cargo proteins from the trans-Golgi and a tubular-endosomal compartment to endosome-lysosome-related organelles. Lack of the beta3A subunit of this complex causes Hermansky-Pudlak syndrome type 2, an autosomal recessive disease characterized by partial albinism, prolonged bleeding tendency, and immunodeficiency. To investigate the pathogenesis of immunodeficiency, we studied natural killer (NK) cells and neutrophil functions in 2 previously unreported siblings affected by Hermansky-Pudlak type 2 syndrome. In both patients we observed a dramatic reduction of cytolytic activity of freshly isolated and of IL-2-activated NK cells. Levels of perforin were reduced in unstimulated NK cells, thereby accounting for the impairment of NK cytolitic activity. In addition, analysis of neutrophils in these patients demonstrated that intracellular elastase content was largely reduced while CD63 expression on plasma membrane was substantially increased. Taken together, these observations suggest that type 2 Hermansky-Pudlak syndrome is characterized by defects of innate immunity.
Assuntos
Complexo 3 de Proteínas Adaptadoras/imunologia , Subunidades beta do Complexo de Proteínas Adaptadoras/imunologia , Antígenos CD/imunologia , Síndrome de Hermanski-Pudlak/imunologia , Imunidade Inata/imunologia , Células Matadoras Naturais/imunologia , Neutrófilos/imunologia , Glicoproteínas da Membrana de Plaquetas/imunologia , Adulto , Criança , Pré-Escolar , Feminino , Regulação da Expressão Gênica/imunologia , Síndrome de Hermanski-Pudlak/patologia , Humanos , Imunidade Celular/imunologia , Síndromes de Imunodeficiência/imunologia , Síndromes de Imunodeficiência/patologia , Lactente , Células Matadoras Naturais/patologia , Elastase de Leucócito/imunologia , Masculino , Neutrófilos/patologia , Tetraspanina 30 , Rede trans-Golgi/imunologiaRESUMO
Hepcidin is a small peptide that acts as a regulator of systemic iron homeostasis. To study some of its functional properties, a synthetic cDNA for the minimal, 20-amino-acid, form of human hepcidin was cloned into different constructs for expression in Escherichia coli. The fusion ferritin-hepcidin produced molecules retaining most of ferritin structural and functional properties, including ferroxidase and iron incorporation activities. However, it showed spectroscopic properties compatible with the presence of iron-sulfur complexes on the hepcidin moiety, which was buried into protein cavity. Similar complexes were reconstituted by in vitro incubation of the iron-free protein with iron and sulfide salts. Two other unrelated fusion products were constructed, which, when expressed in E. coli, formed insoluble aggregates retaining a large proportion of total bacterial iron. Analysis of the solubilized preparations showed them to contain iron-sulfur complexes. We concluded that the cysteine-rich hepcidin acts as an iron-sequestering molecule during expression in E. coli. This may have implications for the biological functions of this key protein of iron metabolism.
Assuntos
Peptídeos Catiônicos Antimicrobianos/genética , Peptídeos Catiônicos Antimicrobianos/fisiologia , Ferro/metabolismo , Ferroproteínas não Heme/fisiologia , Peptídeos Catiônicos Antimicrobianos/isolamento & purificação , Clonagem Molecular/métodos , Escherichia coli/genética , Ferritinas/genética , Hepcidinas , Humanos , Ferroproteínas não Heme/genética , Proteínas Recombinantes de Fusão , Proteínas Recombinantes , SolubilidadeRESUMO
Omenn syndrome is a severe primary immunodeficiency with putative autoimmune manifestations of the skin and gastrointestinal tract. The disease is caused by hypomorphic mutations in recombination-activating genes that impair but do not abolish the process of VDJ recombination, leading to the generation of autoreactive T cells with a highly restricted receptor repertoire. Loss of central tolerance in genetically determined autoimmune diseases, e.g., autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy, is associated with defective expression by medullary thymic epithelial cells of AIRE, the transcription activator that induces thymic expression of tissue-specific antigens. Analysis of AIRE expression in the thymi of 2 Omenn syndrome patients and 1 SCID patient, by real-time RT-PCR and immunohistochemistry, demonstrated a profound reduction in the levels of AIRE mRNA and protein in patients as compared with a normal control subject. Lack of AIRE was associated with normal or even increased levels of keratin and lymphotoxin-beta receptor mRNAs, while mRNAs of the self-antigens insulin, cytochrome P450 1a2, and fatty acid-binding protein were undetectable in thymi from immunodeficiency patients. These results demonstrate that deficiency of AIRE expression is observed in severe immunodeficiencies characterized by abnormal T cell development and suggest that in Omenn syndrome, the few residual T cell clones that develop may escape negative selection and thereafter expand in the periphery, causing massive autoimmune reactions.
Assuntos
Trato Gastrointestinal/imunologia , Síndromes de Imunodeficiência/genética , Pele/imunologia , Timo/metabolismo , Fatores de Transcrição/deficiência , Animais , Células COS , Chlorocebus aethiops , Feminino , Humanos , Síndromes de Imunodeficiência/imunologia , Síndromes de Imunodeficiência/patologia , Lactente , Receptor beta de Linfotoxina , Receptores do Fator de Necrose Tumoral/genética , Receptores do Fator de Necrose Tumoral/metabolismo , Linfócitos T/imunologia , Linfócitos T/fisiologia , Timo/citologia , Timo/patologia , Proteína AIRERESUMO
The chemokine receptor CXCR4 and its functional ligand, CXCL12, are essential regulators of development and homeostasis of hematopoietic and lymphoid organs. Heterozygous truncating mutations in the CXCR4 intracellular tail cause a rare genetic disease known as WHIM syndrome (warts, hypogammaglobulinemia, infections, myelokathexis), whose pathophysiology remains unclear. We report CXCR4 function in 3 patients with WHIM syndrome carrying heterozygous truncating mutations of CXCR4. We show that CXCR4 gene mutations in WHIM patients do not affect cell surface expression of the chemokine receptor and its internalization upon stimulation with CXCL12. Moreover, no significant differences in calcium mobilization in response to CXCL12 are found. However, the chemotactic response of both polymorphonuclear cells and T lymphocytes in response to CXCL12 is increased. Furthermore, immunophenotypic analysis of circulating T and B lymphocytes reveals a decreased number of memory B cells and of naive T cells and an accumulation of effector memory T cells associated with a restricted T-cell repertoire. Based on our results, we suggest that the altered leukocyte response to CXCL12 may account for the pathologic retention of mature polymorphonuclear cells in the bone marrow (myelokathexis) and for an altered lymphocyte trafficking, which may cause the immunophenotyping abnormalities observed in WHIM patients.
Assuntos
Agamaglobulinemia/imunologia , Infecções Bacterianas/imunologia , Quimiocinas CXC/genética , Neutropenia/imunologia , Verrugas/imunologia , Adolescente , Adulto , Agamaglobulinemia/genética , Linfócitos B/citologia , Linfócitos B/imunologia , Infecções Bacterianas/genética , Medula Óssea/imunologia , Cálcio/metabolismo , Quimiocina CXCL12 , Criança , Análise Mutacional de DNA , Feminino , Citometria de Fluxo , Expressão Gênica/imunologia , Humanos , Imunofenotipagem , Neutropenia/genética , Neutrófilos/citologia , Neutrófilos/imunologia , Síndrome , Linfócitos T/citologia , Linfócitos T/imunologia , Verrugas/genéticaRESUMO
Three peptidases are responsible for the proteolytic processing of both nuclearly and mitochondrially encoded precursor polypeptides targeted to the various subcompartments of the mitochondria. Mitochondrial processing peptidase (MPP) cleaves the vast majority of mitochondrial proteins, while inner membrane peptidase (IMP) and mitochondrial intermediate peptidase (MIP) process specific subsets of precursor polypeptides. All three enzymes are structurally and functionally conserved across species, and their human homologues begin to be recognized as potential players in mitochondrial disease.
Assuntos
Membranas Intracelulares/enzimologia , Metaloendopeptidases/metabolismo , Mitocôndrias/enzimologia , Precursores de Proteínas/metabolismo , Sequência de Aminoácidos , Animais , Sítios de Ligação , Escherichia coli , Humanos , Metaloendopeptidases/química , Metaloendopeptidases/genética , Proteínas Mitocondriais/química , Proteínas Mitocondriais/metabolismo , Dados de Sequência Molecular , Filogenia , Saccharomyces cerevisiae , Alinhamento de Sequência , Relação Estrutura-Atividade , Especificidade por Substrato , Peptidase de Processamento MitocondrialRESUMO
Most mitochondrial proteins are synthesized in the cytoplasm as larger precursors carrying N-terminal matrix-targeting presequences, and are subsequently transported to the mitochondria. The presequence mediates the interaction between the precursor polypeptide and components of the mitochondrial protein import machinery, a complex apparatus that is responsible for translocation of the precursor across the two mitochondrial membranes. Once the precursor has reached the mitochondrial matrix, the presequence is removed by the general mitochondrial processing peptidase (MPP). Some precursors undergo additional processing steps carried out by specialized processing peptidases. For most mitochondrial proteins, however, cleavage by MPP is the step that precedes folding and assembly into the native form. We describe methods to isolate import-competent mitochondria from rat liver and to perform import reactions with precursor proteins synthesized in vitro by coupled transcription-translation. We also describe methods to perform in vitro processing reactions of mitochondrial precursors by recombinant MPP and to identify the cleavage sites used by this enzyme.
Assuntos
Bioquímica/métodos , Metaloendopeptidases/metabolismo , Mitocôndrias Hepáticas/metabolismo , Animais , Escherichia coli/metabolismo , Masculino , Metaloendopeptidases/química , Modelos Biológicos , Neurospora crassa/metabolismo , Ligação Proteica , Biossíntese de Proteínas , Estrutura Terciária de Proteína , Transporte Proteico , Ratos , Ratos Sprague-Dawley , Proteínas Recombinantes/metabolismo , Saccharomyces cerevisiae/metabolismo , Fatores de Tempo , Transcrição Gênica , Peptidase de Processamento MitocondrialRESUMO
Friedreich ataxia (FRDA) is an autosomal recessive degenerative disease caused by a deficiency of frataxin, a conserved mitochondrial protein of unknown function. Mitochondrial iron accumulation, loss of iron-sulfur cluster-containing enzymes and increased oxidative damage occur in yeast and mouse frataxin-depleted mutants as well as tissues and cell lines from FRDA patients, suggesting that frataxin may be involved in export of iron from the mitochondria, synthesis of iron-sulfur clusters and/or protection from oxidative damage. We have previously shown that yeast frataxin has structural and functional features of an iron storage protein. In this study we have investigated the function of human frataxin in Escherichia coli and Saccharomyces cerevisiae. When expressed in E.coli, the mature form of human frataxin assembles into a stable homopolymer that can bind approximately 10 atoms of iron per molecule of frataxin. The iron-loaded homopolymer can be detected on non-denaturing gels by either protein or iron staining demonstrating a stable association between frataxin and iron. As analyzed by gel filtration and electron microscopy, the homopolymer consists of globular particles of approximately 1 MDa and ordered rod-shaped polymers of these particles that accumulate small electron-dense cores. When the human frataxin precursor is expressed in S.cerevisiae, the mitochondrially generated mature form is separated by gel filtration into monomer and a high molecular weight pool of >600 kDa. A high molecular weight pool of frataxin is also present in mouse heart indicating that frataxin can assemble under native conditions. In radiolabeled yeast cells, human frataxin is recovered by immunoprecipitation with approximately five atoms of (55)Fe bound per molecule. These findings suggest that FRDA results from decreased mitochondrial iron storage due to frataxin deficiency which may impair iron metabolism, promote oxidative damage and lead to progressive iron accumulation.