Initiation factor eIF2B mediates a key regulatory step in the initiation of mRNA translation, i.e. the regeneration of active eIF2.GTP complexes. It is composed of five subunits, alpha-epsilon. The largest of these (epsilon) displays catalytic activity in the absence of the others. The catalytic mechanism of eIF2B and the functions of the other subunits remain to be clarified. Here we show that, when present at similar concentrations to eIF2, mammalian eIF2B can mediate release of eIF2-bound GDP even in the absence of free nucleotide, indicating that it acts as a GDP dissociation stimulator protein. Consistent with this, addition of GDP to purified eIF2.eIF2B complexes causes them to dissociate. The alternative sequential mechanism would require that eIF2Bepsilon itself bind GTP. However, we show that it is the beta-subunit of eIF2B that interacts with GTP. This indicates that binding of GTP to eIF2B is not an essential element of its mechanism. eIF2B preparations that lack the alpha-subunit display reduced activity compared with the holocomplex. Supplementation of such preparations with recombinant eIF2Balpha markedly enhances activity, indicating that eIF2Balpha is required for full activity of mammalian eIF2B.
Initiation factor eIF2B mediates a key regulatory step in the initiation of mRNA translation, i.e. the regeneration of active eIF2.GTP complexes. It is composed of five subunits, alpha-epsilon. The largest of these (epsilon) displays catalytic activity in the absence of the others. The catalytic mechanism of eIF2B and the functions of the other subunits remain to be clarified. Here we show that, when present at similar concentrations to eIF2, mammalian eIF2B can mediate release of eIF2-bound GDP even in the absence of free nucleotide, indicating that it acts as a GDP dissociation stimulator protein. Consistent with this, addition of GDP to purified eIF2.eIF2B complexes causes them to dissociate. The alternative sequential mechanism would require that eIF2Bepsilon itself bind GTP. However, we show that it is the beta-subunit of eIF2B that interacts with GTP. This indicates that binding of GTP to eIF2B is not an essential element of its mechanism. eIF2B preparations that lack the alpha-subunit display reduced activity compared with the holocomplex. Supplementation of such preparations with recombinant eIF2Balpha markedly enhances activity, indicating that eIF2Balpha is required for full activity of mammalian eIF2B.
Stimulates the exchange of guanyl nucleotides associated with a GTPase. Under normal cellular physiological conditions, the concentration of GTP is higher than that of GDP, favoring the replacement of GDP by GTP in association with the GTPase.
Evidence
1:
Inferred from Mutant PhenotypeUniProtKB
Mutations in each of the five eucaryotic initiation factor 2B (eIF2B) subunits have been found in leukodystrophies of various severity: Cree leukoencephalopathy, childhood ataxia with central hypomyelination/leukodystrophy with vanishing white matter and ovarioleukodystrophy. A continuum was observed from fatal infantile forms to adult forms without neurological deterioration. Disease severity was found to correlate with the age at disease onset and the specific amino-acid substitution. In order to analyze the functional consequences of eIF2B mutations, we measured the guanine nucleotide exchange factor (GEF) activity of eIF2B in transformed lymphocytes from 30 affected patients carrying mutations in eIF2B compared to 10 unaffected heterozygotes and 22 controls without eIF2B mutations. A significant decrease of 20-70% in GEF activity was observed in all mutated cells. The severity of this decrement of GEF activity correlated with age at onset of the disease. These results suggest that a deficiency in GEF activity underlies the encephalopathy associated eIF2B-related disease. Our study demonstrates that the evaluation of the GEF activity in transformed lymphocytes represents an interesting alternative test to the systematic screening of the five EIF2B genes. This relevant cellular model may also be used to test the functional impact of different molecules on the GEF activity for future therapeutic strategies.
Initiation factor eIF2B mediates a key regulatory step in the initiation of mRNA translation, i.e. the regeneration of active eIF2.GTP complexes. It is composed of five subunits, alpha-epsilon. The largest of these (epsilon) displays catalytic activity in the absence of the others. The catalytic mechanism of eIF2B and the functions of the other subunits remain to be clarified. Here we show that, when present at similar concentrations to eIF2, mammalian eIF2B can mediate release of eIF2-bound GDP even in the absence of free nucleotide, indicating that it acts as a GDP dissociation stimulator protein. Consistent with this, addition of GDP to purified eIF2.eIF2B complexes causes them to dissociate. The alternative sequential mechanism would require that eIF2Bepsilon itself bind GTP. However, we show that it is the beta-subunit of eIF2B that interacts with GTP. This indicates that binding of GTP to eIF2B is not an essential element of its mechanism. eIF2B preparations that lack the alpha-subunit display reduced activity compared with the holocomplex. Supplementation of such preparations with recombinant eIF2Balpha markedly enhances activity, indicating that eIF2Balpha is required for full activity of mammalian eIF2B.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionUniProtKB
Leukoencephalopathy with vanishing white matter (VWM) is a severe inherited human neurodegenerative disorder that is caused by mutations in the genes for the subunits of eukaryotic initiation factor 2B (eIF2B), a heteropentameric guanine nucleotide exchange factor that regulates both global and mRNA-specific translation. Marked variability is evident in the clinical severity and time course of VWM in patients. Here we have studied the effects of VWM mutations on the function of human eIF2B. All the mutations tested cause partial loss of activity. Frameshift mutations in genes for eIF2Bepsilon or eIF2Bbeta lead to truncated polypeptides that fail to form complexes with the other subunits and are effectively null mutations. Certain point mutations also impair the ability of eIF2Bbeta or -epsilon to form eIF2B holocomplexes and also diminish the intrinsic nucleotide exchange activity of eIF2B. A point mutation in the catalytic domain of eIF2Bepsilon impairs its ability to bind the substrate, while two mutations in eIF2Bbeta actually enhance eIF2 binding. We provide evidence that expression of VWM mutant eIF2B may enhance the translation of specific mRNAs. The variability of the clinical phenotype in VWM may reflect the multiple ways in which VWM mutations affect eIF2B function.
Development of an efficient cell-free translation system from mammalian cells is an important goal. We examined whether supplementation of HeLa cell extracts with any translation initiation factor or translational regulator could enhance protein synthesis. eIF2 (eukaryotic translation initiation factor 2) and eIF2B augmented translation of capped, uncapped and encephalomyocarditis virus-internal ribosome entry site-promoted mRNAs. eIF4E specifically stimulated capped mRNA translation, while p97, a homologue to the C-terminal two-thirds of eIF4G, increased uncapped mRNA translation. When the HeLa cell extract was supplemented with a combination of eIF2, eIF2B, and p97, the capacity to synthesize a protein from an uncapped mRNA became comparable to that from the capped counterpart stimulated with a combination of eIF2, eIF2B, and eIF4E. A dialysis method rendered the HeLa cell extract capable of synthesizing proteins for 36h, and the yield was augmented when supplemented with initiation factors. In contrast, the productivity of a rabbit reticulocyte lysate was not enhanced by this method. Collectively, the translation factor-supplemented HeLa cell extract should become an important tool for the production of recombinant proteins.
Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a stimulus. The process begins with detection of the stimulus by a cell and ends with a change in state or activity or the cell.
J. Biol. Chem. 271, 11410-11413 (1996)[PubMed:8626696]
Mitogenic stimulation of T-lymphocytes causes a rapid activation or protein synthesis, which reflects in part increased expression of many translation components. Their levels, however, rise more slowly than the rate of protein synthesis, indicating an enhancement of the efficiency of their utilization. Initiation factor eIF2B catalyzes a key regulatory step in the initiation of translation, and we have therefore studied its activity following T-cell activation. eIF2B activity rises quickly, increasing as early as 5 min after cell stimulation. This initial phase is followed by an additional slow but substantial increase in eIF2B activity. The level of eIF2B subunits did not change over the initial rapid phase but did increase at later time points. Northern analysis revealed that levels of eIF2B mRNA only rose during the later phase. The rapid activation of EIF2B following mitogenic stimulation of T-cells is therefore mediated by factors other than its own concentration. The largest (epsilon) subunit of eIF2B is a substrate for glycogen synthase kinase-3 (GSK-3), the activity of which rapidly decreases following T-cell activation. Since phosphorylation of eIF2B by GSK-3 appears to inhibit nucleotide exchange in vitro, this provides a potential mechanism by which eIF2B may be activated.
The process whose specific outcome is the progression of the central nervous system over time, from its formation to the mature structure. The central nervous system is the core nervous system that serves an integrating and coordinating function. In vertebrates it consists of the brain, spinal cord and spinal nerves. In those invertebrates with a central nervous system it typically consists of a brain, cerebral ganglia and a nerve cord.
Evidence
1:
Inferred from Mutant PhenotypeUniProtKB
Autosomal recessive inherited mutations in each of the five eukaryotic initiation factor 2B (eIF2B) subunits are known to cause white matter abnormalities with a wide continuum of clinical signs and severity leading to the concept of eIF2B-related disorders. The clinical spectrum extends from fatal infantile forms to adult forms with slow or absent neurological deterioration. In this study 15 well-characterised patients with the classical form of leukoencephalopathy with vanishing white matter (VWM) or with phenotypic variants like ovarioleukodystrophy were investigated for mutations in the genes EIF2B1, EIF2B2, EIF2B3, EIF2B4, and EIF2B5 encoding eIF2B. We identified one novel nonsense mutation (EIF2B4, c.625C>T, p.Arg209X), one novel frameshift mutation (EIF2B5, c.453_454del, p.Tyr152fsX12), eight novel missense muations (EIF2B1, c.547G>T, p.Val183Phe; EIF2B2, c. 586C>T, p.Pro196Ser; EIF2B4, c.806T>G, p.Leu269Arg; EIF2B5, c.203T>C, p.Leu68Ser; EIF2B5, c.220G>A, p.Ala74Thr; EIF2B5, c.805C>G, p.Arg269Gly; EIF2B5, c.929G>T, p.Cys310Phe; EIF2B5, c.1003T>C, p.Cys335Arg), and eight previously described alterations.
The process in which myelin sheaths are formed and maintained around neurons. Oligodendrocytes in the brain and spinal cord and Schwann cells in the peripheral nervous system wrap axons with compact layers of their plasma membrane. Adjacent myelin segments are separated by a non-myelinated stretch of axon called a node of Ranvier.
Evidence
1:
Inferred from Mutant PhenotypeUniProtKB
Leukoencephalopathy with vanishing white matter, also called "childhood ataxia with central nervous system hypomyelination," is the first human disease related to mutations in any of the five genes encoding subunits of eukaryotic initiation factor eIF2B or any translation factor at all. eIF2B is essential in all cells of the body for protein synthesis and the regulation of this protein synthesis under different stress conditions. It is surprising that mutations in the eIF2B genes have been reported to lead to abnormalities of the white matter of the brain only, although it has been shown recently that ovarian failure may accompany the leukoencephalopathy. Another surprising observation is that the onset of the disease varies from early childhood to adulthood, with the exception of Cree leukoencephalopathy, a disease related to a particular mutation in one of the eIF2B genes, which invariably has its onset within the first year of life. We analyzed the eIF2B genes of nine patients with an antenatal- or early-infantile-onset encephalopathy and an early demise and found mutations in eight of the patients. In addition to signs of a serious encephalopathy, we found oligohydramnios, intrauterine growth retardation, cataracts, pancreatitis, hepatosplenomegaly, hypoplasia of the kidneys, and ovarian dysgenesis. Until now, no evidence had been found for a genotype-phenotype correlation, but the consistently severe phenotype in affected siblings among our patients and in Cree encephalopathy patients suggests an influence of the genotype on the phenotype.
The process aimed at the progression of an oligodendrocyte over time, from initial commitment of the cell to a specific fate, to the fully functional differentiated cell. An oligodendrocyte is a type of glial cell involved in myelinating the axons in the central nervous system.
Evidence
1:
Inferred from Mutant PhenotypeUniProtKB
J. Neuropathol. Exp. Neurol. 63, 618-630 (2004)[PubMed:15217090]
Vanishing white matter disease (VWM) is a progressive cavitating disease of central white matter due to a deficiency of the translation initiation factor eIF2B. Oligodendrocytes appear to be numerically increased in some white matter areas, while decreased in others. We compared oligodendrocytes of cerebral, cerebellar, and pontine white matter from 5 VWM patients with those of age-matched controls by light microscopy and immunohistochemistry using antibodies to activated caspase-3, bak, bax, bcl-2, survivin, and Ki-67, as well as by the TUNEL technique. Oligodendrocytes were identified morphologically and quantified using an ocular grid. We observed statistically significant increases in their densities at all sites; Ki-67-labeled oligodendrocytes were identified in 2 of 5 patients. Apoptotic oligodendrocytes were documented in 3 of 5 patients, while bcl-2 and survivin labeling was observed in 2 of 5 and 2 of 2 patients, respectively. There was a trend toward an increase in apoptotic labeling of oligodendrocytes that was strongest in the cerebrum, the major locus of VWM, in the youngest and most severely affected patients. These data conclusively demonstrate increased oligodendrocytic densities in VWM; the increase is not an artifact of white matter contraction. Our data also document that oligodendrocytes undergo apoptosis, perhaps in conjunction with major neurologic crises, and that a subset of oligodendrocytes are able to persist and proliferate. Conflicting proliferative, cell-death, and survival signals impact the oligodendrocytes of VWM.
BACKGROUND: Premature Ovarian Failure (POF), defined as the development of hypergonadotropic amenorrhea before the age of 40 years, occurs in about 1% of all women. Other than karyotype abnormalities, very few genes are known to be associated with this ovarian dysfunction. Recently, in seven patients who presented with POF and white matter abnormalities on MRI (ovarioleukodystrophy) eight mutationswere found in EIF2B2, 4 and 5. METHODS: To further test the involvement of known mutations of EIF2B genes in POF, we screened 93 patients with POF who did not have identified leukodystrophy or neurological symptoms. We evaluated these eight mutations and two additional mutations that had been found in patients with milder forms of eIF2B-related disorders. We used restriction enzymes and direct sequencing. RESULTS: None of the known mutations in EIF2B genes, either homozygous or heterozygous, were identified in our 93 patients with pure 46,XX POF. The upper 95 % confidence limit of the proportion 0/93 is 3.2%. CONCLUSIONS: We conclude that eIF2B mutations, already described in cases of POF associated with white matter abnormalities, are an uncommon cause of pure spontaneous premature ovarian failure.
Leukoencephalopathy with vanishing white matter (VWM) is a severe inherited human neurodegenerative disorder that is caused by mutations in the genes for the subunits of eukaryotic initiation factor 2B (eIF2B), a heteropentameric guanine nucleotide exchange factor that regulates both global and mRNA-specific translation. Marked variability is evident in the clinical severity and time course of VWM in patients. Here we have studied the effects of VWM mutations on the function of human eIF2B. All the mutations tested cause partial loss of activity. Frameshift mutations in genes for eIF2Bepsilon or eIF2Bbeta lead to truncated polypeptides that fail to form complexes with the other subunits and are effectively null mutations. Certain point mutations also impair the ability of eIF2Bbeta or -epsilon to form eIF2B holocomplexes and also diminish the intrinsic nucleotide exchange activity of eIF2B. A point mutation in the catalytic domain of eIF2Bepsilon impairs its ability to bind the substrate, while two mutations in eIF2Bbeta actually enhance eIF2 binding. We provide evidence that expression of VWM mutant eIF2B may enhance the translation of specific mRNAs. The variability of the clinical phenotype in VWM may reflect the multiple ways in which VWM mutations affect eIF2B function.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a glucose stimulus.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a heat stimulus, a temperature stimulus above the optimal temperature for that organism.
Childhood ataxia with central hypomyelination (CACH)/vanishing white matter (VWM) leukoencephalopathy is related to mutations in all five genes of the eukaryotic translation initiation factor (eIF2B). In a fatal infantile leukoencephalopathy, which the authors previously classified as a severe variant of CACH/VWM, a new homozygous missense mutation in the EIF2B5 gene was found. Abnormal decrease in blood uric acid and increase of erythrocyte guanosine 5'-diphosphate sugars found in two siblings may contribute to the explanation of this particularly severe condition.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a peptide hormone stimulus. A peptide hormone is any of a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.
The process preceding formation of the peptide bond between the first two amino acids of a protein. This includes the formation of a complex of the ribosome, mRNA, and an initiation complex that contains the first aminoacyl-tRNA.
Development of an efficient cell-free translation system from mammalian cells is an important goal. We examined whether supplementation of HeLa cell extracts with any translation initiation factor or translational regulator could enhance protein synthesis. eIF2 (eukaryotic translation initiation factor 2) and eIF2B augmented translation of capped, uncapped and encephalomyocarditis virus-internal ribosome entry site-promoted mRNAs. eIF4E specifically stimulated capped mRNA translation, while p97, a homologue to the C-terminal two-thirds of eIF4G, increased uncapped mRNA translation. When the HeLa cell extract was supplemented with a combination of eIF2, eIF2B, and p97, the capacity to synthesize a protein from an uncapped mRNA became comparable to that from the capped counterpart stimulated with a combination of eIF2, eIF2B, and eIF4E. A dialysis method rendered the HeLa cell extract capable of synthesizing proteins for 36h, and the yield was augmented when supplemented with initiation factors. In contrast, the productivity of a rabbit reticulocyte lysate was not enhanced by this method. Collectively, the translation factor-supplemented HeLa cell extract should become an important tool for the production of recombinant proteins.
Protein involved in the biosynthesis of proteins from mRNA molecules. This process, called translation, is carried out by ribosomes, where activated amino acids are added to the nascent polypeptide chain.
Protein which plays an important role in initiating the translation of a mRNA molecule into a polypeptide. Initiation factors help to form the complex between the mRNA and a ribosome.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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