Mitochondria function in cytoplasmic FeS protein biogenesis.

Iron­sulfur (FeS) clusters are cofactors of numerous proteins involved in essential cellular functions including respiration, protein translation, DNA synthesis and repair, ribosome maturation, anti-viral responses, and isopropylmalate isomerase activity. Novel FeS proteins are still being discovered due to the widespread use of cryogenic electron microscopy (cryo-EM) and elegant genetic screens targeted at protein discovery. A complex sequence of biochemical reactions mediated by a conserved machinery controls biosynthesis of FeS clusters. In eukaryotes, a remarkable epistasis has been observed: the mitochondrial machinery, termed ISC (Iron-Sulfur Cluster), lies upstream of the cytoplasmic machinery, termed CIA (Cytoplasmic Iron­sulfur protein Assembly). The basis for this arrangement is the production of a hitherto uncharacterized intermediate, termed X-S or (Fe-S)int, produced in mitochondria by the ISC machinery, exported by the mitochondrial ABC transporter Atm1 (ABCB7 in humans), and then utilized by the CIA machinery for the cytoplasmic/nuclear FeS cluster assembly. Genetic and biochemical findings supporting this sequence of events are herein presented. New structural views of the Atm1 transport phases are reviewed. The key compartmental roles of glutathione in cellular FeS cluster biogenesis are highlighted. Finally, data are presented showing that every one of the ten core components of the mitochondrial ISC machinery and Atm1, when mutated or depleted, displays similar phenotypes: mitochondrial and cytoplasmic FeS clusters are both rendered deficient, consistent with the epistasis noted above.

Child Neurology: Progressive Cerebellar Atrophy and Retinal Dystrophy: Clues to an Ultrarare ACO2-Related Neurometabolic Diagnosis.

Pathogenic biallelic variants in ACO2, which encodes the enzyme mitochondrial aconitase, are associated with the very rare diagnosis of ACO2-related infantile cerebellar retinal degeneration (OMIM 614559). We describe the diagnostic odyssey of a 4-year-old female patient with profound global developmental delays, microcephaly, severe hypotonia, retinal dystrophy, seizures, and progressive cerebellar atrophy. Whole-exome sequencing revealed 2 variants in ACO2; c.2105_2106delAG (p.Gln702ArgfsX9), a likely pathogenic variant, and c.988C>T (p.Pro330Ser) which was classified as a variant of uncertain significance (VUS). While the VUS was confirmed to be maternally inherited, the phase of the other variant could not be confirmed due to lack of a paternal sample. Functional biochemical studies were performed on a research basis to clarify the interpretation of the VUS, which enabled clinical confirmation of the diagnosis of ACO2-related infantile cerebellar retinal degeneration for our patient.

Essential mitochondrial role in iron-sulfur cluster assembly of the cytoplasmic isopropylmalate isomerase Leu1 in Saccharomyces cerevisiae.

Iron-sulfur (Fe-S) cluster assembly in mitochondria and cytoplasm is essential for cell viability. In the yeast S. cerevisiae, Leu1 [4Fe-4S] is the cytoplasmic isopropylmalate isomerase involved in leucine biosynthesis. Using permeabilized Δleu1 cells and recombinant apo-Leu1R, here we show that the [4Fe-4S] cluster assembly on Leu1R can be reconstituted in a physiologic manner requiring both mitochondria and cytoplasm, as judged by conversion of the inactive enzyme to an active form. The mitochondrial contribution to this reconstitution assay is abrogated by inactivating mutations in the mitochondrial ISC (iron-sulfur cluster assembly) machinery components (such as Nfs1 cysteine desulfurase and Ssq1 chaperone) or the mitochondrial exporter Atm1. Likewise, depletion of a CIA (cytoplasmic iron-sulfur protein assembly) component Dre2 leads to impaired Leu1R reconstitution. Mitochondria likely make and export an intermediate, called X-S or (Fe-S)int, that is needed for cytoplasmic Fe-S cluster biosynthesis. Here we show that once exported, the same intermediate can be used for both [2Fe-2S] and [4Fe-4S] cluster biogenesis in the cytoplasm, with no further requirement of mitochondria. Our data also suggest that the exported intermediate can activate defective/latent CIA components in cytoplasm isolated from nfs1 or Δatm1 mutant cells. These findings may provide a way to isolate X-S or (Fe-S)int.

Characteristics of the Isu1 C-terminus in relation to [2Fe-2S] cluster assembly and ISCU Myopathy.

Mitochondrial [2Fe-2S] cluster biosynthesis is driven by the coordinated activities of the Iron-Sulfur Cluster (ISC) pathway protein machinery. Within the ISC machinery, the protein that provides a structural scaffold on which [2Fe-2S] clusters are assembled is the ISCU protein in humans; this protein is referred to as the "Scaffold" protein. Truncation of the C-terminal portion of ISCU causes the fatal disease "ISCU Myopathy", which exhibits phenotypes of reduced Fe-S cluster assembly in cells. In this report, the yeast ISCU ortholog "Isu1" has been characterized to gain a better understanding of the role of the scaffold protein in relation to [2Fe-2S] assembly and ISCU Myopathy. Here we explored the biophysical characteristics of the C-terminal region of Isu1, the segment of the protein that is truncated on the human ortholog during the disease ISCU Myopathy. We characterized the role of this region in relation to iron binding, protein stability, assembly of the ISC multiprotein complex required to accomplish Fe-S cluster assembly, and finally on overall cell viability. We determined the Isu1 C-terminus is essential for the completion of the Fe-S cluster assembly but serves a function independent of protein iron binding.

Inhibition of mitochondrial LonP1 protease by allosteric blockade of ATP binding and hydrolysis via CDDO and its derivatives.

The mitochondrial protein LonP1 is an ATP-dependent protease that mitigates cell stress and calibrates mitochondrial metabolism and energetics. Biallelic mutations in the LONP1 gene are known to cause a broad spectrum of diseases, and LonP1 dysregulation is also implicated in cancer and age-related disorders. Despite the importance of LonP1 in health and disease, specific inhibitors of this protease are unknown. Here, we demonstrate that 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) and its -methyl and -imidazole derivatives reversibly inhibit LonP1 by a noncompetitive mechanism, blocking ATP-hydrolysis and thus proteolysis. By contrast, we found that CDDO-anhydride inhibits the LonP1 ATPase competitively. Docking of CDDO derivatives in the cryo-EM structure of LonP1 shows these compounds bind a hydrophobic pocket adjacent to the ATP-binding site. The binding site of CDDO derivatives was validated by amino acid substitutions that increased LonP1 inhibition and also by a pathogenic mutation that causes cerebral, ocular, dental, auricular and skeletal (CODAS) syndrome, which ablated inhibition. CDDO failed to inhibit the ATPase activity of the purified 26S proteasome, which like LonP1 belongs to the AAA+ superfamily of ATPases Associated with diverse cellular Activities, suggesting that CDDO shows selectivity within this family of ATPases. Furthermore, we show that noncytotoxic concentrations of CDDO derivatives in cultured cells inhibited LonP1, but not the 26S proteasome. Taken together, these findings provide insights for future development of LonP1-specific inhibitors with chemotherapeutic potential.

Exome sequencing and characterization of 49,960 individuals in the UK Biobank.

The UK Biobank is a prospective study of 502,543 individuals, combining extensive phenotypic and genotypic data with streamlined access for researchers around the world1. Here we describe the release of exome-sequence data for the first 49,960 study participants, revealing approximately 4 million coding variants (of which around 98.6% have a frequency of less than 1%). The data include 198,269 autosomal predicted loss-of-function (LOF) variants, a more than 14-fold increase compared to the imputed sequence. Nearly all genes (more than 97%) had at least one carrier with a LOF variant, and most genes (more than 69%) had at least ten carriers with a LOF variant. We illustrate the power of characterizing LOF variants in this population through association analyses across 1,730 phenotypes. In addition to replicating established associations, we found novel LOF variants with large effects on disease traits, including PIEZO1 on varicose veins, COL6A1 on corneal resistance, MEPE on bone density, and IQGAP2 and GMPR on blood cell traits. We further demonstrate the value of exome sequencing by surveying the prevalence of pathogenic variants of clinical importance, and show that 2% of this population has a medically actionable variant. Furthermore, we characterize the penetrance of cancer in carriers of pathogenic BRCA1 and BRCA2 variants. Exome sequences from the first 49,960 participants highlight the promise of genome sequencing in large population-based studies and are now accessible to the scientific community.

Mitochondria export iron-sulfur and sulfur intermediates to the cytoplasm for iron-sulfur cluster assembly and tRNA thiolation in yeast.

Iron-sulfur clusters are essential cofactors of proteins. In eukaryotes, iron-sulfur cluster biogenesis requires a mitochondrial iron-sulfur cluster machinery (ISC) and a cytoplasmic iron-sulfur protein assembly machinery (CIA). Here we used mitochondria and cytoplasm isolated from yeast cells, and [35S]cysteine to detect cytoplasmic Fe-35S cluster assembly on a purified apoprotein substrate. We showed that mitochondria generate an intermediate, called (Fe-S)int, needed for cytoplasmic iron-sulfur cluster assembly. The mitochondrial biosynthesis of (Fe-S)int required ISC components such as Nfs1 cysteine desulfurase, Isu1/2 scaffold, and Ssq1 chaperone. Mitochondria then exported (Fe-S)int via the Atm1 transporter in the inner membrane, and we detected (Fe-S)int in active form. When (Fe-S)int was added to cytoplasm, CIA utilized it for iron-sulfur cluster assembly without any further help from the mitochondria. We found that both iron and sulfur for cytoplasmic iron-sulfur cluster assembly originate from the mitochondria, revealing a surprising and novel mitochondrial role. Mitochondrial (Fe-S)int export was most efficient in the presence of cytoplasm containing an apoprotein substrate, suggesting that mitochondria respond to the cytoplasmic demand for iron-sulfur cluster synthesis. Of note, the (Fe-S)int is distinct from the sulfur intermediate called Sint, which is also made and exported by mitochondria but is instead used for cytoplasmic tRNA thiolation. In summary, our findings establish a direct and vital role of mitochondria in cytoplasmic iron-sulfur cluster assembly in yeast cells.

Splitting the functions of Rim2, a mitochondrial iron/pyrimidine carrier.

Rim2 is an unusual mitochondrial carrier protein capable of transporting both iron and pyrimidine nucleotides. Here we characterize two point mutations generated in the predicted substrate-binding site, finding that they yield disparate effects on iron and pyrimidine transport. The Rim2 (E248A) mutant was deficient in mitochondrial iron transport activity. By contrast, the Rim2 (K299A) mutant specifically abrogated pyrimidine nucleotide transport and exchange, while leaving iron transport activity largely unaffected. Strikingly, E248A preserved TTP/TTP homoexchange but interfered with TTP/TMP heteroexchange, perhaps because proton coupling was dependent on the E248 acidic residue. Rim2-dependent iron transport was unaffected by pyrimidine nucleotides. Rim2-dependent pyrimidine transport was competed by Zn2+ but not by Fe2+, Fe3+ or Cu2+. The iron and pyrimidine nucleotide transport processes displayed different salt requirements; pyrimidine transport was dependent on the salt content of the buffer whereas iron transport was salt independent. In mitochondria containing Rim2 (E248A), iron proteins were decreased, including aconitase (Fe-S), pyruvate dehydrogenase (lipoic acid containing) and cytochrome c (heme protein). Additionally, the rate of Fe-S cluster synthesis in isolated and intact mitochondria was decreased compared with the K299A mutant, consistent with the impairment of iron-dependent functions in that mutant. In summary, mitochondrial iron transport and pyrimidine transport by Rim2 occur separately and independently. Rim2 could be a bifunctional carrier protein.

Bi-allelic mutations of LONP1 encoding the mitochondrial LonP1 protease cause pyruvate dehydrogenase deficiency and profound neurodegeneration with progressive cerebellar atrophy.

LonP1 is crucial for maintaining mitochondrial proteostasis and mitigating cell stress. We identified a novel homozygous missense LONP1 variant, c.2282 C > T, (p.Pro761Leu), by whole-exome and Sanger sequencing in two siblings born to healthy consanguineous parents. Both siblings presented with stepwise regression during infancy, profound hypotonia and muscle weakness, severe intellectual disability and progressive cerebellar atrophy on brain imaging. Muscle biopsy revealed the absence of ragged-red fibers, however, scattered cytochrome c oxidase-negative staining and electron dense mitochondrial inclusions were observed. Primary cultured fibroblasts from the siblings showed normal levels of mtDNA and mitochondrial transcripts, and normal activities of oxidative phosphorylation complexes I through V. Interestingly, fibroblasts of both siblings showed glucose-repressed oxygen consumption compared to their mother, whereas galactose and palmitic acid utilization were similar. Notably, the siblings' fibroblasts had reduced pyruvate dehydrogenase (PDH) activity and elevated intracellular lactate:pyruvate ratios, whereas plasma ratios were normal. We demonstrated that in the siblings' fibroblasts, PDH dysfunction was caused by increased levels of the phosphorylated E1α subunit of PDH, which inhibits enzyme activity. Blocking E1α phosphorylation activated PDH and reduced intracellular lactate concentrations. In addition, overexpressing wild-type LonP1 in the siblings' fibroblasts down-regulated phosphoE1α. Furthermore, in vitro studies demonstrated that purified LonP1-P761L failed to degrade phosphorylated E1α, in contrast to wild-type LonP1. We propose a novel mechanism whereby homozygous expression of the LonP1-P761L variant leads to PDH deficiency and energy metabolism dysfunction, which promotes severe neurologic impairment and neurodegeneration.

A Whole Methylome Study of Ethanol Exposure in Brain and Blood: An Exploration of the Utility of Peripheral Blood as Proxy Tissue for Brain in Alcohol Methylation Studies.

BACKGROUND: Recent reviews have highlighted the potential use of blood-based methylation biomarkers as diagnostic and prognostic tools of current and future alcohol use and addiction. Due to the substantial overlap that often exists between methylation patterns across different tissues, including blood and brain, blood-based methylation may track methylation changes in brain; however, little work has explored the overlap in alcohol-related methylation in these tissues. METHODS: To study the effects of alcohol on the brain methylome and identify possible biomarkers of these changes in blood, we performed a methylome-wide association study in brain and blood from 40 male DBA/2J mice that received either an acute ethanol (EtOH) or saline intraperitoneal injection. To investigate all 22 million CpGs in the mouse genome, we enriched for the methylated genomic fraction using methyl-CpG binding domain (MBD) protein capture followed by next-generation sequencing (MBD-seq). We performed association tests in blood and brain separately followed by enrichment testing to determine whether there was overlapping alcohol-related methylation in the 2 tissues. RESULTS: The top result for brain was a CpG located in an intron of Ttc39b (p = 5.65 × 10-08 ), and for blood, the top result was located in Espnl (p = 5.11 × 10-08 ). Analyses implicated pathways involved in inflammation and neuronal differentiation, such as CXCR4, IL-7, and Wnt signaling. Enrichment tests indicated significant overlap among the top results in brain and blood. Pathway analyses of the overlapping genes converge on MAPKinase signaling (p = 5.6 × 10-05 ) which plays a central role in acute and chronic responses to alcohol and glutamate receptor pathways, which can regulate neuroplastic changes underlying addictive behavior. CONCLUSIONS: Overall, we have shown some methylation changes in brain and blood after acute EtOH administration and that the changes in blood partly mirror the changes in brain suggesting the potential for DNA methylation in blood to be biomarkers of alcohol use.

Acetylation and phosphorylation of human TFAM regulate TFAM-DNA interactions via contrasting mechanisms.

Mitochondrial transcription factor A (TFAM) is essential for the maintenance, expression and transmission of mitochondrial DNA (mtDNA). However, mechanisms for the post-translational regulation of TFAM are poorly understood. Here, we show that TFAM is lysine acetylated within its high-mobility-group box 1, a domain that can also be serine phosphorylated. Using bulk and single-molecule methods, we demonstrate that site-specific phosphoserine and acetyl-lysine mimics of human TFAM regulate its interaction with non-specific DNA through distinct kinetic pathways. We show that higher protein concentrations of both TFAM mimics are required to compact DNA to a similar extent as the wild-type. Compaction is thought to be crucial for regulating mtDNA segregation and expression. Moreover, we reveal that the reduced DNA binding affinity of the acetyl-lysine mimic arises from a lower on-rate, whereas the phosphoserine mimic displays both a decreased on-rate and an increased off-rate. Strikingly, the increased off-rate of the phosphoserine mimic is coupled to a significantly faster diffusion of TFAM on DNA. These findings indicate that acetylation and phosphorylation of TFAM can fine-tune TFAM-DNA binding affinity, to permit the discrete regulation of mtDNA dynamics. Furthermore, our results suggest that phosphorylation could additionally regulate transcription by altering the ability of TFAM to locate promoter sites.

Mitochondria Export Sulfur Species Required for Cytosolic tRNA Thiolation.

In eukaryotes, mitochondria have been hypothesized to generate sulfur species required for tRNA thiolation in the cytosol, although no direct evidence thus far exists. Here we have detected these sulfur species, making use of our observation that isolated yeast cytosol alone is unable to thiolate tRNAs but can do so upon addition of mitochondria. Mitochondria were found to utilize the cysteine desulfurase Nfs1 to produce sulfur-containing species with masses ranging from 700 to 1,100 Da. Mitochondria exported these species via the Atm1 transporter in the inner membrane. Once exported to the cytosol, these sulfur species promoted cytosolic tRNA thiolation with no further requirement of mitochondria. Furthermore, we found that the Isu1/2 scaffolds but not the Ssq1 chaperone of the mitochondrial iron-sulfur cluster machinery were required for cytosolic tRNA thiolation, and thus the sulfur utilization pathway bifurcates at the Isu1/2 site for intra-organellar use in mitochondria or export to the cytosol.

Effect of elevated ozone and varying levels of soil nitrogen in two wheat (Triticum aestivum L.) cultivars: Growth, gas-exchange, antioxidant status, grain yield and quality.

Tropospheric ozone (O3) is a phytotoxic air pollutant causing a substantial damage to plants and agriculture worldwide. Plant productivity is affected by several environmental factors, which interact with each other. Studies related to interactions involving O3 and different levels of nitrogen (N) are still rare and elusive. In the present study we grew two wheat cultivars (HD2967 and Sonalika) in open top chambers (OTC) under ambient (AO) and elevated O3 (EO) (ambient + 20 ppb O3) and provided two levels of N fertilization; (a) recommended nitrogen (RN), (b) 1.5 times the recommended N (HN). Growth (root/shoot ratio, leaf number and leaf area), biomass, gas-exchange (stomatal conductance (gs), photosynthesis (A), transpiration (E), chlorophyll fluorescence (Fv/Fm), physiological (chlorophyll and carotenoids), biochemical [antioxidant activity, lipid peroxidation (MDA)] parameters and leaf N content were measured at the vegetative and reproductive phases. Yield attributes (spike weight plant-1, grain weight plant-1, grain numbers plant-1, husk weight plant-1, straw weight plant-1, 1000 grain weight, harvest index) and seed N content were analyzed at the final harvest stage. Grain yield plant-1 was decreased in Sonalika under EO irrespective of different levels of N fertilization. Seed N content decreased by 3.9% and 5.6% in HD2967 and Sonalika, respectively, under EO at RN treatment. Antioxidant defense played an important role in protecting the plants against O3 stress which was enhanced under HN treatment. Response of antioxidants varied between the cultivar, growth phase (at the vegetative or reproductive phase) and the N levels (RN or HN). Cultivar HD2967 was characterized by higher biomass, gs and stronger antioxidant protection system, while, Sonalika showed early senescence response (decreased leaf number plant-1, gs) and greater resources allocation towards eco-physiological parameters (increased A and Fv/Fm) at the vegetative phase, resulting in the significant decrease in the yield attributes. Further study warrants the need to screen a large number of cultivars in relation to their response to various levels of N fertilization to minimize the yield losses under highly O3 polluted areas.

The ß1'-ß2' Motif of the RNase H Domain of Human Immunodeficiency Virus Type 1 Reverse Transcriptase Is Responsible for Conferring Open Conformation to the p66 Subunit by Displacing the Connection Domain from the Polymerase Cleft.

The heterodimeric human immunodeficiency virus type 1 reverse transcriptase is composed of p66 and p51 subunits. While in the p51 subunit, the connection domain is tucked in the polymerase cleft; it is effectively displaced from the cleft of the catalytically active p66 subunit. How is the connection domain relocated from the polymerase cleft of p66? Does the RNase H domain have any role in this process? To answer this question, we extended the C-terminal region of p51 by stepwise addition of N-terminal motifs of RNase H domain to generate p54, p57, p60, and p63 derivatives. We found all of the C-terminal extended derivatives of p51 assume open conformation, bind to the template-primer, and catalyze the polymerase reaction. Glycerol gradient ultracentrifugation analysis showed that only p54 sedimented as a monomer, while other derivatives were in a homodimeric conformation. We proposed a model to explain the monomeric conformation of catalytically active p54 derivative carrying additional 21-residues long ß1'-ß2' motif from the RNase H domain. Our results indicate that the ß1'-ß2' motif of the RNase H domain may be responsible for displacing the connection domain from the polymerase cleft of putative monomeric p66. The unstable elongated p66 molecule may then readily dimerize with p51 to assume a stable dimeric conformation.

Conserved effect of aging on DNA methylation and association with EZH2 polycomb protein in mice and humans.

In humans, DNA methylation at specific CpG sites can be used to estimate the 'epigenetic clock', a biomarker of aging and health. The mechanisms that regulate the aging epigenome and level of conservation are not entirely clear. We performed affinity-based enrichment with methyl-CpG binding domain protein followed by high-throughput sequencing (MBD-seq) to assay DNA methylation in mouse samples. Consistent with previous reports, aging is associated with increase in methylation at CpG islands that likely overlap regulatory regions of genes that have been implicated in cancers (e.g., C1ql3, Srd5a2 and Ptk7). The differentially methylated regions in mice have high sequence conservation in humans and the pattern of methylation is also largely conserved between the two species. Based on human ENCODE data, these sites are targeted by polycomb proteins, including EZH2. Chromatin immunoprecipitation confirmed that these regions interact with EZH2 in mice as well, and there may be reduction in EZH2 occupancy with age at C1ql3. This adds to the growing evidence that EZH2 is part of the protein machinery that shapes the aging epigenome. The conservation in both sequence and methylation patterns of the age-dependent CpGs indicate that the epigenetic clock is a fundamental feature of aging in mammals.

Genetic divergence in the transcriptional engram of chronic alcohol abuse: A laser-capture RNA-seq study of the mouse mesocorticolimbic system.

Genetic factors that influence the transition from initial drinking to dependence remain enigmatic. Recent studies have leveraged chronic intermittent ethanol (CIE) paradigms to measure changes in brain gene expression in a single strain at 0, 8, 72 h, and even 7 days following CIE. We extend these findings using LCM RNA-seq to profile expression in 11 brain regions in two inbred strains - C57BL/6J (B6) and DBA/2J (D2) - 72 h following multiple cycles of ethanol self-administration and CIE. Linear models identified differential expression based on treatment, region, strain, or interactions with treatment. Nearly 40% of genes showed a robust effect (FDR < 0.01) of region, and hippocampus CA1, cortex, bed nucleus stria terminalis, and nucleus accumbens core had the highest number of differentially expressed genes after treatment. Another 8% of differentially expressed genes demonstrated a robust effect of strain. As expected, based on similar studies in B6, treatment had a much smaller impact on expression; only 72 genes (p < 0.01) are modulated by treatment (independent of region or strain). Strikingly, many more genes (415) show a strain-specific and largely opposite response to treatment and are enriched in processes related to RNA metabolism, transcription factor activity, and mitochondrial function. Over 3 times as many changes in gene expression were detected in D2 compared to B6, and weighted gene co-expression network analysis (WGCNA) module comparison identified more modules enriched for treatment effects in D2. Substantial strain differences exist in the temporal pattern of transcriptional neuroadaptation to CIE, and these may drive individual differences in risk of addiction following excessive alcohol consumption.

Modulation of HCV replication and translation by ErbB3 binding protein1 isoforms.

We recently identified a cell-factor, ErbB3 binding protein 1 (Ebp-1), which specifically interacts with the viral RNA genome and modulates HCV replication and translation. Ebp1 has two isoforms, p48, and p42, that result from differential splicing. We found that both isoforms interact with HCV proteins NS5A and NS5B, as well as cell-factor PKR. The p48 isoform, which localizes in the cytoplasm and nuclei, promoted HCV replication, whereas the shorter p42 isoform, which resides exclusively in the cytoplasm, strongly inhibited HCV replication. Transient expression of individual isoforms in Ebp1-knockdown MH14 cells confirmed that the p48 isoform promotes HCV replication, while the p42 isoform inhibits it. We found that Ebp1-p42 significantly enhanced autophosphorylation of PKR, while Ebp1-p48 isoform strongly inhibited it. We propose that modulation of autophosphorylation of PKR by p48 isoform is an important mechanism whereby the HCV virus escapes innate antiviral immune responses by circumventing p42-mediated inhibition of its replication.

Organ Specific Proteomic Dissection of Selaginella bryopteris Undergoing Dehydration and Rehydration.

To explore molecular mechanisms underlying the physiological response of Selaginella bryopteris, a comprehensive proteome analysis was carried out in roots and fronds undergoing dehydration and rehydration. Plants were dehydrated for 7 days followed by 2 and 24 h of rehydration. In roots out of 59 identified spots, 58 protein spots were found to be up-regulated during dehydration stress. The identified proteins were related to signaling, stress and defense, protein and nucleotide metabolism, carbohydrate and energy metabolism, storage and epigenetic control. Most of these proteins remained up-regulated on first rehydration, suggesting their role in recovery phase also. Among the 90 identified proteins in fronds, about 49% proteins were up-regulated during dehydration stress. Large number of ROS scavenging proteins was enhanced on dehydration. Many other proteins involved in energy, protein turnover and nucleotide metabolism, epigenetic control were also highly upregulated. Many photosynthesis related proteins were upregulated during stress. This would have helped plant to recover rapidly on rehydration. This study provides a comprehensive picture of different cellular responses elucidated by the proteome changes during dehydration and rehydration in roots and fronds as expected from a well-choreographed response from a resurrection plant.