RESUMO
The classic view is that iron regulatory proteins operate at the post-transcriptional level. Iron Regulatory Protein 1 (IRP1) shifts between an apo-form that binds mRNAs and a holo-form that harbors a [4Fe4S] cluster. The latter form is not considered relevant to iron regulation, but rather thought to act as a non-essential cytosolic aconitase. Recent work in Drosophila, however, shows that holo-IRP1 can also translocate to the nucleus, where it appears to downregulate iron metabolism genes, preparing the cell for a decline in iron uptake. The shifting of IRP1 between states requires a functional mitoNEET pathway that includes a glycogen branching enzyme for the repair or disassembly of IRP1's oxidatively damaged [3Fe4S] cluster. The new findings add to the notion that glucose metabolism is modulated by iron metabolism. Furthermore, we propose that ferritin ferroxidase activity participates in the repair of the IRP1 [3Fe4S] cluster leading to the hypothesis that cytosolic ferritin directly contributes to cellular iron sensing.
Assuntos
Proteína 1 Reguladora do Ferro/genética , Proteínas Reguladoras de Ferro/genética , Proteínas Ferro-Enxofre/genética , Ferro/metabolismo , Aconitato Hidratase/genética , Núcleo Celular/genética , Ceruloplasmina/genética , Citosol/metabolismo , Ferritinas/genética , Regulação da Expressão Gênica/genética , Proteínas Ferro-Enxofre/química , Oxirredução , RNA Mensageiro/genéticaRESUMO
Bacterial type IV secretion systems (T4SS) are a highly diversified but evolutionarily related family of macromolecule transporters that can secrete proteins and DNA into the extracellular medium or into target cells. It was recently shown that a subtype of T4SS harboured by the plant pathogen Xanthomonas citri transfers toxins into target cells. Here, we show that a similar T4SS from the multi-drug-resistant opportunistic pathogen Stenotrophomonas maltophilia is proficient in killing competitor bacterial species. T4SS-dependent duelling between S. maltophilia and X. citri was observed by time-lapse fluorescence microscopy. A bioinformatic search of the S. maltophilia K279a genome for proteins containing a C-terminal domain conserved in X. citri T4SS effectors (XVIPCD) identified twelve putative effectors and their cognate immunity proteins. We selected a putative S. maltophilia effector with unknown function (Smlt3024) for further characterization and confirmed that it is indeed secreted in a T4SS-dependent manner. Expression of Smlt3024 in the periplasm of E. coli or its contact-dependent delivery via T4SS into E. coli by X. citri resulted in reduced growth rates, which could be counteracted by expression of its cognate inhibitor Smlt3025 in the target cell. Furthermore, expression of the VirD4 coupling protein of X. citri can restore the function of S. maltophilia ΔvirD4, demonstrating that effectors from one species can be recognized for transfer by T4SSs from another species. Interestingly, Smlt3024 is homologous to the N-terminal domain of large Ca2+-binding RTX proteins and the crystal structure of Smlt3025 revealed a topology similar to the iron-regulated protein FrpD from Neisseria meningitidis which has been shown to interact with the RTX protein FrpC. This work expands our current knowledge about the function of bacteria-killing T4SSs and increases the panel of effectors known to be involved in T4SS-mediated interbacterial competition, which possibly contribute to the establishment of S. maltophilia in clinical and environmental settings.
Assuntos
Proteínas de Bactérias/fisiologia , Stenotrophomonas maltophilia/fisiologia , Stenotrophomonas maltophilia/patogenicidade , Sistemas de Secreção Tipo IV/fisiologia , Sequência de Aminoácidos , Antibiose/genética , Antibiose/fisiologia , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Sequência Conservada , Cristalografia por Raios X , Escherichia coli/genética , Escherichia coli/crescimento & desenvolvimento , Genes Bacterianos , Infecções por Bactérias Gram-Negativas/microbiologia , Humanos , Proteínas Reguladoras de Ferro/química , Proteínas Reguladoras de Ferro/genética , Proteínas Reguladoras de Ferro/fisiologia , Modelos Moleculares , Infecções Oportunistas/microbiologia , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Especificidade da Espécie , Stenotrophomonas maltophilia/genética , Sistemas de Secreção Tipo IV/química , Sistemas de Secreção Tipo IV/genética , Xanthomonas/genética , Xanthomonas/crescimento & desenvolvimentoRESUMO
Entamoeba histolytica is a human parasite that causes amoebiasis, a disease that affects the colon and liver and is prevalent worldwide. This protozoan requires a high concentration of iron to survive and reproduce. Iron modulates the expression of parasite virulence factors, including hemoglobinases, hemoglobin-binding proteins and cysteine proteases, as well as proteins related to the amoebic cytoskeleton. This review summarizes the virulence factors that are affected by iron, resulting in upregulation or downregulation of E. histolytica genes. This review also discusses the functionality of iron in the mechanisms of pathogenesis.
Assuntos
Amebíase/parasitologia , Entamoeba histolytica/patogenicidade , Ferro/metabolismo , Fatores de Virulência/metabolismo , Animais , Cisteína Proteases/genética , Cisteína Proteases/metabolismo , Entamoeba histolytica/genética , Hemoglobinas/metabolismo , Interações Hospedeiro-Parasita , Humanos , Proteínas Reguladoras de Ferro/genética , Proteínas Reguladoras de Ferro/metabolismo , Camundongos , Estrutura Molecular , Proteínas de Protozoários/genética , Proteínas de Protozoários/metabolismo , Fatores de Virulência/genéticaRESUMO
In this work we found that the bfr gene of the rhizobial species Ensifer meliloti, encoding a bacterioferritin iron storage protein, is involved in iron homeostasis and the oxidative stress response. This gene is located downstream of and overlapping the smc03787 open reading frame (ORF). No well-predicted RirA or Irr boxes were found in the region immediately upstream of the bfr gene although two presumptive RirA boxes and one presumptive Irr box were present in the putative promoter of smc03787 We demonstrate that bfr gene expression is enhanced under iron-sufficient conditions and that Irr and RirA modulate this expression. The pattern of bfr gene expression as well as the response to Irr and RirA is inversely correlated to that of smc03787 Moreover, our results suggest that the small RNA SmelC759 participates in RirA- and Irr-mediated regulation of bfr expression and that additional unknown factors are involved in iron-dependent regulation.IMPORTANCEE. meliloti belongs to the Alphaproteobacteria, a group of bacteria that includes several species able to associate with eukaryotic hosts, from mammals to plants, in a symbiotic or pathogenic manner. Regulation of iron homeostasis in this group of bacteria differs from that found in the well-studied Gammaproteobacteria In this work we analyzed the effect of rirA and irr mutations on bfr gene expression. We demonstrate the effect of an irr mutation on iron homeostasis in this bacterial genus. Moreover, results obtained indicate a complex regulatory circuit where multiple regulators, including RirA, Irr, the small RNA SmelC759, and still unknown factors, act in concert to balance bfr gene expression.
Assuntos
Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Grupo dos Citocromos b/genética , Ferritinas/genética , Regulação Bacteriana da Expressão Gênica , Proteínas Reguladoras de Ferro/metabolismo , Ferro/metabolismo , RNA Bacteriano/metabolismo , Sinorhizobium meliloti/metabolismo , Fatores de Transcrição/metabolismo , Proteínas de Bactérias/biossíntese , Grupo dos Citocromos b/biossíntese , Ferritinas/biossíntese , Proteínas Reguladoras de Ferro/genética , Mutação , RNA Bacteriano/genética , Sinorhizobium meliloti/genética , Fatores de Transcrição/genéticaRESUMO
Trichomonas vaginalis has high iron-dependency, favoring its growth and multiplication in culture. Iron also regulates some of the trichomonal virulence properties by yet unknown mechanisms. Iron is an essential but potentially toxic metal for the majority of organisms. Thus, its concentration must be tightly regulated within the cell. In mammals, the iron homeostasis is mainly regulated at the post-transcriptional level by a well known mechanism mediated by the binding of iron regulatory proteins (IRP1 and IRP2) to hairpin-loop structures, dubbed iron-responsive elements (IREs), localized in the untranslated regions (UTRs) of target mRNAs. The knowledge of iron regulation in T. vaginalis is still very limited. An iron-responsive promoter and other regulatory elements in the 5'-UTR of the ap65-1 gene were identified as a mechanism for the positive transcriptional regulation of trichomonad genes by iron. Recently, two IRE-like hairpin-loop structures in mRNAs of differentially iron-regulated TVCP4 and TVCP12 cysteine proteinases, as well as IRP-like trichomonad proteins were identified in T. vaginalis, suggesting the existence in this protozoan of a post-transcriptional iron regulatory mechanism by an IRE/IRP-like system. The responsiveness of T. vaginalis to distinct iron concentrations was examined here. Also, the comparison of the atypical IRE-like sequences of T. vaginalis with the consensus IRE and other putative IRE sequences present in parasite and bacteria mRNAs suggest that these trichomonad IRE-like sequences might be the ancestral forms of the RNA stem-loop structures of the IRE/IRP system.
Assuntos
Homeostase , Proteínas Reguladoras de Ferro/metabolismo , Ferro/metabolismo , Transcrição Gênica , Trichomonas vaginalis/fisiologia , Animais , Sequência de Bases , Moléculas de Adesão Celular/genética , Moléculas de Adesão Celular/metabolismo , Cisteína Proteases/genética , Cisteína Proteases/metabolismo , DNA de Protozoário/análise , DNA de Protozoário/genética , Feminino , Regulação da Expressão Gênica , Genoma de Protozoário , Humanos , Ferro/química , Proteínas Reguladoras de Ferro/genética , Dados de Sequência Molecular , Proteínas de Protozoários/genética , Proteínas de Protozoários/metabolismo , Vaginite por Trichomonas/metabolismo , Vaginite por Trichomonas/parasitologia , Trichomonas vaginalis/química , Trichomonas vaginalis/patogenicidade , VirulênciaRESUMO
Translational control is a common regulatory mechanism for the expression of iron-related proteins. For example, three enzymes involved in erythrocyte development are regulated by three different control mechanisms: globin synthesis is modulated by heme-regulated translational inhibitor, erythroid 5-aminolevulinate synthase translation is inhibited by binding of the iron regulatory protein to the iron response element in the 5'-untranslated region (UTR); and 15-lipoxygenase is regulated by specific proteins binding to the 3'-UTR. Ceruloplasmin (Cp) is a multi-functional, copper protein made primarily by the liver and by activated macrophages. Cp has important roles in iron homeostasis and in inflammation. Its role in iron metabolism was originally proposed because of its ferroxidase activity and because of its ability to stimulate iron loading into apo-transferrin and iron efflux from liver. We have shown that Cp mRNA is induced by interferon (IFN)-gamma in U937 monocytic cells, but synthesis of Cp protein is halted by translational silencing. The silencing mechanism requires binding of a cytosolic inhibitor complex, IFN-Gamma-Activated Inhibitor of Translation (GAIT), to a specific GAIT element in the Cp 3'-UTR. Here, we describe our studies that define and characterize the GAIT element and elucidate the specific trans-acting proteins that bind the GAIT element. Our experiments describe a new mechanism of translational control of an iron-related protein and may shed light on the role that macrophage-derived Cp plays at the intersection of iron homeostasis and inflammation.
Assuntos
Regiões 3' não Traduzidas/fisiologia , Ceruloplasmina/fisiologia , Proteínas Reguladoras de Ferro/fisiologia , Ferro/metabolismo , Biossíntese de Proteínas/fisiologia , Regiões 3' não Traduzidas/genética , Animais , Ceruloplasmina/genética , Regulação da Expressão Gênica/genética , Regulação da Expressão Gênica/fisiologia , Homeostase/genética , Homeostase/fisiologia , Humanos , Inflamação/metabolismo , Interferon gama/metabolismo , Proteínas Reguladoras de Ferro/genética , Biossíntese de Proteínas/genética , RNA MensageiroRESUMO
Bioiron - central to respiration, photosynthesis and DNA synthesis and complicated by radical chemistry with oxygen - depends on ferritin, the super family of protein nanocages (maxi-ferritins in humans, animals, plant, and bacteria, and mini-ferritins, also called DPS proteins, in bacteria) for iron and oxygen control. Regulation of ferritin synthesis, best studied in animals, uses DNA transcription and mRNA translation check points. Ferritin is a member of both the "oxidant stress response" gene family that includes thioredoxin reductase and quinine reductase, and a member of the iron responsive gene family that includes ferroportin and mt-aconitase ferritin DNA regulation responds preferentially to oxidant response inducers and ferritin mRNA to iron inducers: heme confers regulator synergy. Ferritin proteins manage iron and oxygen, with ferroxidase sites and iron + oxygen substrates to form mineral of both Fe and O atoms; maxi-ferritins contribute more to cellular iron metabolism and mini-ferritins to stress responses. Iron recovery from ferritin is controlled by gated protein pores, possibly contributing to iron absorption from ferritin, a significant dietary iron source. Ferritin gene regulation is a model for integrating DNA/mRNA controls, while ferritin protein function is central to molecular nutrition cellular metabolism at the crossroads of iron and oxygen in biology.
Assuntos
Ferritinas/biossíntese , Homeostase , Proteínas Reguladoras de Ferro/metabolismo , Ferro/metabolismo , Oxigênio/metabolismo , Animais , DNA/metabolismo , Regulação da Expressão Gênica , Humanos , Proteínas Reguladoras de Ferro/genética , RNA Mensageiro/metabolismo , Transcrição GênicaRESUMO
Translational control is a common regulatory mechanism for the expression of iron-related proteins. For example, three enzymes involved in erythrocyte development are regulated by three different control mechanisms: globin synthesis is modulated by heme-regulated translational inhibitor; erythroid 5-aminolevulinate synthase translation is inhibited by binding of the iron regulatory protein to the iron response element in the 5'-untranslated region (UTR); and 15-lipoxygenase is regulated by specific proteins binding to the 3'-UTR. Ceruloplasmin (Cp) is a multi-functional, copper protein made primarily by the liver and by activated macrophages. Cp has important roles in iron homeostasis and in inflammation. Its role in iron metabolism was originally proposed because of its ferroxidase activity and because of its ability to stimulate iron loading into apo-transferrin and iron efflux from liver. We have shown that Cp mRNA is induced by interferon (IFN)-ã in U937 monocytic cells, but synthesis of Cp protein is halted by translational silencing. The silencing mechanism requires binding of a cytosolic inhibitor complex, IFN-Gamma-Activated Inhibitor of Translation (GAIT), to a specific GAIT element in the Cp 3'-UTR. Here, we describe our studies that define and characterize the GAIT element and elucidate the specific trans-acting proteins that bind the GAIT element. Our experiments describe a new mechanism of translational control of an iron-related protein and may shed light on the role that macrophage-derived Cp plays at the intersection of iron homeostasis and inflammation.
Assuntos
Animais , Humanos , /fisiologia , Ceruloplasmina/fisiologia , Proteínas Reguladoras de Ferro/fisiologia , Ferro/metabolismo , Biossíntese de Proteínas/fisiologia , /genética , Ceruloplasmina/genética , Regulação da Expressão Gênica/genética , Regulação da Expressão Gênica/fisiologia , Homeostase/genética , Homeostase/fisiologia , Inflamação/metabolismo , Interferon gama/metabolismo , Proteínas Reguladoras de Ferro/genética , Biossíntese de Proteínas/genética , RNA MensageiroRESUMO
Bioiron _ central to respiration, photosynthesis and DNA synthesis and complicated by radical chemistry with oxygen _ depends on ferritin, the super family of protein nanocages (maxi-ferritins in humans, animals, plants and bacteria, and mini-ferritins, also called DPS proteins, in bacteria) for iron and oxygen control. Regulation of ferritin synthesis, best studied in animals, uses DNA transcription and mRNA translation check points. Ferritin is a member of both the "oxidant stress response" gene family that includes thioredoxin reductase and quinine reductase, and a member of the iron responsive gene family that includes ferroportin and mt-aconitase ferritin DNA regulation responds preferentially to oxidant response inducers and ferritin mRNA to iron inducers; heme confers regulator synergy. Ferritin proteins manage iron and oxygen, with ferroxidase sites and iron + oxygen substrates to form mineral of both Fe and O atoms; maxi-ferritins contribute more to cellular iron metabolism and mini-ferritins to stress responses. Iron recovery from ferritin is controlled by gated protein pores, possibly contributing to iron absorption from ferritin, a significant dietary iron source. Ferritin gene regulation is a model for integrating DNA/mRNA controls, while ferritin protein function is central to molecular nutrition cellular metabolism at the crossroads of iron and oxygen in biology.
Assuntos
Animais , Humanos , Ferritinas/biossíntese , Homeostase , Proteínas Reguladoras de Ferro/metabolismo , Ferro/metabolismo , Oxigênio/metabolismo , DNA , Regulação da Expressão Gênica , Proteínas Reguladoras de Ferro/genética , RNA Mensageiro/metabolismo , Transcrição GênicaRESUMO
White-rot fungus Phanerochaete chrysosporium, a ligninolytic basidiomycete, was studied to identify iron-responsive genes. Using the differential display reverse transcription PCR technique (DDRT-PCR), a total of 97 differentially expressed cDNA fragments were identified by comparing band intensities among fingerprints obtained from mycelia cultivated in iron-deficient and iron-replete media. Transcripts induced under iron-starvation exhibited homologies to: a modular polyketide synthase, a TonB protein, a probable transmembrane protein, a putative ABC transporter permease and a HSP70-related heat-shock protein. Modular polyketide synthase and TonB proteins are normally expressed under iron-starvation and are known to be involved in biosynthesis and transport of siderophores respectively. Also, a deduced protein with 96% similarity to a precursor of the well-known P. chrysosporium lignin peroxidase was identified under iron-deficiency. Two DDRT-PCR products confirmed their iron-induced expression. One was homologue to the CNOT3, which is a global regulator of RNA polymerase II transcription and has been implicated in multiple roles in the control of mRNA metabolism. The other was similar to the Schizosaccharomyces pombe putative proteasome maturation factor upm1. In conclusion, the majority of iron-responsive P. chrysosporium transcripts isolated in the DDRT-PCR encode proteins involved in iron acquisition, especially members of biosynthesis and transport of iron chelators.