RESUMEN
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.
Asunto(s)
Proteína 1 Reguladora de Hierro/genética , Proteínas Reguladoras del Hierro/genética , Proteínas Hierro-Azufre/genética , Hierro/metabolismo , Aconitato Hidratasa/genética , Núcleo Celular/genética , Ceruloplasmina/genética , Citosol/metabolismo , Ferritinas/genética , Regulación de la Expresión Génica/genética , Proteínas Hierro-Azufre/química , Oxidación-Reducción , ARN Mensajero/genéticaRESUMEN
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.
Asunto(s)
Proteínas Bacterianas/fisiología , Stenotrophomonas maltophilia/fisiología , Stenotrophomonas maltophilia/patogenicidad , Sistemas de Secreción Tipo IV/fisiología , Secuencia de Aminoácidos , Antibiosis/genética , Antibiosis/fisiología , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Secuencia Conservada , Cristalografía por Rayos X , Escherichia coli/genética , Escherichia coli/crecimiento & desarrollo , Genes Bacterianos , Infecciones por Bacterias Gramnegativas/microbiología , Humanos , Proteínas Reguladoras del Hierro/química , Proteínas Reguladoras del Hierro/genética , Proteínas Reguladoras del Hierro/fisiología , Modelos Moleculares , Infecciones Oportunistas/microbiología , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Especificidad de la Especie , Stenotrophomonas maltophilia/genética , Sistemas de Secreción Tipo IV/química , Sistemas de Secreción Tipo IV/genética , Xanthomonas/genética , Xanthomonas/crecimiento & desarrolloRESUMEN
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.
Asunto(s)
Amebiasis/parasitología , Entamoeba histolytica/patogenicidad , Hierro/metabolismo , Factores de Virulencia/metabolismo , Animales , Proteasas de Cisteína/genética , Proteasas de Cisteína/metabolismo , Entamoeba histolytica/genética , Hemoglobinas/metabolismo , Interacciones Huésped-Parásitos , Humanos , Proteínas Reguladoras del Hierro/genética , Proteínas Reguladoras del Hierro/metabolismo , Ratones , Estructura Molecular , Proteínas Protozoarias/genética , Proteínas Protozoarias/metabolismo , Factores de Virulencia/genéticaRESUMEN
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.
Asunto(s)
Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Grupo Citocromo b/genética , Ferritinas/genética , Regulación Bacteriana de la Expresión Génica , Proteínas Reguladoras del Hierro/metabolismo , Hierro/metabolismo , ARN Bacteriano/metabolismo , Sinorhizobium meliloti/metabolismo , Factores de Transcripción/metabolismo , Proteínas Bacterianas/biosíntesis , Grupo Citocromo b/biosíntesis , Ferritinas/biosíntesis , Proteínas Reguladoras del Hierro/genética , Mutación , ARN Bacteriano/genética , Sinorhizobium meliloti/genética , Factores de Transcripción/genéticaRESUMEN
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.
Asunto(s)
Homeostasis , Proteínas Reguladoras del Hierro/metabolismo , Hierro/metabolismo , Transcripción Genética , Trichomonas vaginalis/fisiología , Animales , Secuencia de Bases , Moléculas de Adhesión Celular/genética , Moléculas de Adhesión Celular/metabolismo , Proteasas de Cisteína/genética , Proteasas de Cisteína/metabolismo , ADN Protozoario/análisis , ADN Protozoario/genética , Femenino , Regulación de la Expresión Génica , Genoma de Protozoos , Humanos , Hierro/química , Proteínas Reguladoras del Hierro/genética , Datos de Secuencia Molecular , Proteínas Protozoarias/genética , Proteínas Protozoarias/metabolismo , Vaginitis por Trichomonas/metabolismo , Vaginitis por Trichomonas/parasitología , Trichomonas vaginalis/química , Trichomonas vaginalis/patogenicidad , VirulenciaRESUMEN
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.
Asunto(s)
Regiones no Traducidas 3'/fisiología , Ceruloplasmina/fisiología , Proteínas Reguladoras del Hierro/fisiología , Hierro/metabolismo , Biosíntesis de Proteínas/fisiología , Regiones no Traducidas 3'/genética , Animales , Ceruloplasmina/genética , Regulación de la Expresión Génica/genética , Regulación de la Expresión Génica/fisiología , Homeostasis/genética , Homeostasis/fisiología , Humanos , Inflamación/metabolismo , Interferón gamma/metabolismo , Proteínas Reguladoras del Hierro/genética , Biosíntesis de Proteínas/genética , ARN MensajeroRESUMEN
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.
Asunto(s)
Ferritinas/biosíntesis , Homeostasis , Proteínas Reguladoras del Hierro/metabolismo , Hierro/metabolismo , Oxígeno/metabolismo , Animales , ADN/metabolismo , Regulación de la Expresión Génica , Humanos , Proteínas Reguladoras del Hierro/genética , ARN Mensajero/metabolismo , Transcripción GenéticaRESUMEN
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.
Asunto(s)
Animales , Humanos , /fisiología , Ceruloplasmina/fisiología , Proteínas Reguladoras del Hierro/fisiología , Hierro/metabolismo , Biosíntesis de Proteínas/fisiología , /genética , Ceruloplasmina/genética , Regulación de la Expresión Génica/genética , Regulación de la Expresión Génica/fisiología , Homeostasis/genética , Homeostasis/fisiología , Inflamación/metabolismo , Interferón gamma/metabolismo , Proteínas Reguladoras del Hierro/genética , Biosíntesis de Proteínas/genética , ARN MensajeroRESUMEN
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.
Asunto(s)
Animales , Humanos , Ferritinas/biosíntesis , Homeostasis , Proteínas Reguladoras del Hierro/metabolismo , Hierro/metabolismo , Oxígeno/metabolismo , ADN , Regulación de la Expresión Génica , Proteínas Reguladoras del Hierro/genética , ARN Mensajero/metabolismo , Transcripción GenéticaRESUMEN
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.