Elongation factor 1 beta gamma from Artemia. Purification and properties of its subunits

Quaternary organization of the human eEF1B complex reveals unique multi-GEF domain assembly

Protein synthesis in eukaryotic cell is spatially and structurally compartmentalized that ensures high efficiency of this process. One of the distinctive features of higher eukaryotes is the existence of stable multi-protein complexes of aminoacyl-tRNA synthetases and translation elongation factors. Here, we report a quaternary organization of the human guanine-nucleotide exchange factor (GEF) complex, eEF1B, comprising α, β and γ subunits that specifically associate into a heterotrimeric form eEF1B(αβγ)3. As both the eEF1Bα and eEF1Bβ proteins have structurally conserved GEF domains, their total number within the complex is equal to six. Such, so far, unique structural assembly of the guanine-nucleotide exchange factors within a stable complex may be considered as a 'GEF hub' that ensures efficient maintenance of the translationally active GTP-bound conformation of eEF1A in higher eukaryotes.

Mutational analysis reveals potential phosphorylation sites in eukaryotic elongation factor 1A that are important for its activity

Previous studies have suggested that phosphorylation of translation elongation factor 1A (eEF1A) can alter its function, and large‐scale phospho‐proteomic analyses in Saccharomyces cerevisiae have identified 14 eEF1A residues phosphorylated under various conditions. Here, a series of eEF1A mutations at these proposed sites were created and the effects on eEF1A activity were analyzed. The eEF1A‐S53D and eEF1A‐T430D phosphomimetic mutant strains were inviable, while corresponding alanine mutants survived but displayed defects in growth and protein synthesis. The activity of an eEF1A‐S289D mutant was significantly reduced in the absence of the guanine nucleotide exchange factor eEF1Bα and could be restored by an exchange‐deficient form of the protein, suggesting that eEF1Bα promotes eEF1A activity by a mechanism other than nucleotide exchange. Our data show that several of the phosphorylation sites identified by high‐throughput analysis are critical for eEF1A function.

Non-translational Connections of eEF1B in the Cytoplasm and Nucleus of Cancer Cells

The human translation machinery includes three types of supramolecular complexes involved in elongation of the polypeptide chain: the ribosome, complex of elongation factors eEF1B and multienzyme aminoacyl-tRNA synthetase complex. Of the above, eEF1B is the least investigated assembly. Recently, a number of studies provided some insights into the structure of different eEF1B subunits and changes in their expression in cancer and other diseases. There is increasing agreement that possible disease-related functions of eEF1B are not necessarily related to its role in translation. This mini-review focuses on structural and functional features of the eEF1B complex while paying special attention to possible non-canonical functions of its subunits in cancer cells.

An update on the biophysical character of the human eukaryotic elongation factor 1 beta: Perspectives from interaction with elongation factor 1 gamma

The β-subunit of the human eukaryotic elongation factor 1 complex (heEF1β) plays a central role in the elongation step in eukaryotic protein biosynthesis, which essentially involves interaction with the α- and γ-subunits (eEF1γ). To biophysically characterize heEF1β, we constructed 3 Escherichia coli expression vector systems for recombinant expression of the full length (FL-heEF1β), N-terminus (NT-heEF1β), and the C-terminus (CT-heEF1β) regions of the protein. Our results suggest that heEF1β is predominantly alpha-helical and possesses an accessible hydrophobic cavity in the CT-heEF1β. Both FL-heEF1β and NT-heEF1β form dimers of size 62 and 30 kDa, respectively, but the CT-heEF1β is monomeric. FL-heEF1β interacts with the N-terminus glutathione transferase-like domain of heEF1γ (NT-heEF1γ) to form a 195-kDa complex or a 230-kDa complex in the presence of oxidized glutathione. On the other hand, NT-heEF1β forms a 170-kDa complex with NT-heEF1γ and a high molecular weight aggregate of size greater than 670 kDa. Surface plasmon resonance analysis confirmed that (by fitting the Langmuir 1:1 model) FL-heEF1β associated with monomeric or dimeric NT-heEF1γ at a rapid rate and slowly dissociated, suggesting strong functional affinity (K_D  = 9.6 nM for monomeric or 11.3 nM for dimeric NT-heEF1γ). We postulate that the N-terminus region of heEF1β may be responsible for its dimerization and the C-terminus region of heEF1β modulates the formation of an ordered heEF1β-γ oligomer, a structure that may be essential in the elongation step of eukaryotic protein biosynthesis.

eIF2B Mechanisms of Action and Regulation: A Thermodynamic View

Eukaryotic translation initiation factor 2B (eIF2B) is the guanine nucleotide exchange factor of the GTPase eIF2, which brings the initiator Met-tRNA_i to the ribosome in the form of the eIF2-GTP·Met-tRNA_i ternary complex (TC). The activity of eIF2B is inhibited by phosphorylation of its substrate eIF2 by several stress-induced kinases, which triggers the integrated stress response (ISR). The ISR plays a central role in maintaining homeostasis in the cell under various stress conditions, and its dysregulation is a causative factor in the pathology of a number of neurodegenerative disorders. Over the past three decades, virtually every aspect of eIF2B function has been the subject of uncertainty or controversy: from the catalytic mechanism of nucleotide exchange, to whether eIF2B only catalyzes nucleotide exchange on eIF2 or also promotes binding of Met-tRNA_i to eIF2-GTP to form the TC. Here, we provide the first complete thermodynamic analysis of the process of recycling of eIF2-GDP to the TC. The available evidence leads to the conclusion that eIF2 is channeled from the ribosome (as an eIF5·eIF2-GDP complex) to eIF2B, converted by eIF2B to the TC, which is then channeled back to eIF5 and the ribosome. The system has evolved to be regulated by multiple factors, including post-translational modifications of eIF2, eIF2B, and eIF5, as well as directly by the energy balance in the cell, through the GTP:GDP ratio.

Targeted Genetic Screen in Amyotrophic Lateral Sclerosis Reveals Novel Genetic Variants with Synergistic Effect on Clinical Phenotype

Amyotrophic lateral sclerosis (ALS) is underpinned by an oligogenic rare variant architecture. Identified genetic variants of ALS include RNA-binding proteins containing prion-like domains (PrLDs). We hypothesized that screening genes encoding additional similar proteins will yield novel genetic causes of ALS. The most common genetic variant of ALS patients is a G4C2-repeat expansion within C9ORF72. We have shown that G4C2-repeat RNA sequesters RNA-binding proteins. A logical consequence of this is that loss-of-function mutations in G4C2-binding partners might contribute to ALS pathogenesis independently of and/or synergistically with C9ORF72 expansions. Targeted sequencing of genomic DNA encoding either RNA-binding proteins or known ALS genes (n = 274 genes) was performed in ALS patients to identify rare deleterious genetic variants and explore genotype-phenotype relationships. Genomic DNA was extracted from 103 ALS patients including 42 familial ALS patients and 61 young-onset (average age of onset 41 years) sporadic ALS patients; patients were chosen to maximize the probability of identifying genetic causes of ALS. Thirteen patients carried a G4C2-repeat expansion of C9ORF72. We identified 42 patients with rare deleterious variants; 6 patients carried more than one variant. Twelve mutations were discovered in known ALS genes which served as a validation of our strategy. Rare deleterious variants in RNA-binding proteins were significantly enriched in ALS patients compared to control frequencies (p = 5.31E-18). Nineteen patients featured at least one variant in a RNA-binding protein containing a PrLD. The number of variants per patient correlated with rate of disease progression (t-test, p = 0.033). We identified eighteen patients with a single variant in a G4C2-repeat binding protein. Patients with a G4C2-binding protein variant in combination with a C9ORF72 expansion had a significantly faster disease course (t-test, p = 0.025). Our data are consistent with an oligogenic model of ALS. We provide evidence for a number of entirely novel genetic variants of ALS caused by mutations in RNA-binding proteins. Moreover we show that these mutations act synergistically with each other and with C9ORF72 expansions to modify the clinical phenotype of ALS. A key finding is that this synergy is present only between functionally interacting variants. This work has significant implications for ALS therapy development.

Molecular characterization, expression analysis and RNAi knock-down of elongation factor 1α and 1γ from Nilaparvata lugens and its yeast-like symbiont

In the present paper, four cDNAs encoding the alpha and gamma subunits of elongation factor 1 (EF-1) were cloned and sequenced from Nilaparvata lugens, named NlEF-1α, NlEF-1γ, and its yeast-like symbiont (YLS), named YsEF-1α and YsEF-1γ, respectively. Comparisons with sequences from other species indicated a greater conservation for EF-1α than for EF-1γ. NlEF-1α has two identical copies. The deduced amino acid sequence homology of NlEF-1α and NlEF-1γ is 96 and 64%, respectively, compared with Homalodisca vitripennis and Locusta migratoria. The deduced amino acid sequence homology of YsEF-1α and YsEF-1γ is 96 and 74%, respectively, compared with Metarhizium anisopliae and Ophiocordyceps sinensis. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis revealed that the expression level of NlEF-1α and NlEF-1γ mRNA in hemolymph, ovary, fat body and salivary glands were higher than the midgut and leg tissue. YsEF-1α and YsEF-1γ was highly expressed in fat body. The expression level of NlEF-1α was higher than that of NlEF-1γ. Through RNA interference (RNAi) of the two genes, the mortality of nymph reached 92.2% at the 11th day after treatment and the ovarian development was severely hindered. The RT-qPCR analysis verified the correlation between mortality, sterility and the down-regulation of the target genes. The expression and synthesis of vitellogenin (Vg) protein in insects injected with NlEF-1α and NlEF-1γ double-stranded RNA (dsRNA) was significantly lower than control groups. Attempts to knockdown the YsEF-1 genes in the YLS was unsuccessful. However, the phenotype of N. lugens injected with YsEF-1α dsRNA was the same as that injected with NlEF-1α dsRNA, possibly due to the high similarity (up to 71.9%) in the nucleotide sequences between NlEF-1α and YsEF-1α. We demonstrated that partial silencing of NlEF-1α and NlEF-1γ genes caused lethal and sterility effect on N. lugens. NlEF-1γ shares low identity with that of other insects and therefore it could be a potential target for RNAi-based pest management.

Energetics of Glutathione Binding to Human Eukaryotic Elongation Factor 1 Gamma: Isothermal Titration Calorimetry and Molecular Dynamics Studies

The energetics of ligand binding to human eukaryotic elongation factor 1 gamma (heEF1γ) was investigated using reduced glutathione (GSH), oxidised glutathione (GSSG), glutathione sulfonate and S-hexylglutathione as ligands. The experiments were conducted using isothermal titration calorimetry, and the findings were supported using computational studies. The data show that the binding of these ligands to heEF1γ is enthalpically favourable and entropically driven (except for the binding of GSSG). The full length heEF1γ binds GSSG with lower affinity (K _d = 115 μM), with more hydrogen-bond contacts (ΔH = -73.8 kJ/mol) and unfavourable entropy (-TΔS = 51.7 kJ/mol) compared to the glutathione transferase-like N-terminus domain of heEF1γ, which did not show preference to any specific ligand. Computational free binding energy calculations from the 10 ligand poses show that GSSG and GSH consistently bind heEF1γ, and that both ligands bind at the same site with a folded bioactive conformation. This study reveals the possibility that heEF1γ is a glutathione-binding protein.

Multiple Parallel Pathways of Translation Initiation on the CrPV IRES

The complexity of eukaryotic translation allows fine-tuned regulation of protein synthesis. Viruses use internal ribosome entry sites (IRESs) to minimize or, like the CrPV IRES, eliminate the need for initiation factors. Here, by exploiting the CrPV IRES, we observed the entire process of initiation and transition to elongation in real time. We directly tracked the CrPV IRES, 40S and 60S ribosomal subunits, and tRNA using single-molecule fluorescence spectroscopy and identified multiple parallel initiation pathways within the system. Our results distinguished two pathways of 80S:CrPV IRES complex assembly that produce elongation-competent complexes. Following 80S assembly, the requisite eEF2-mediated translocation results in an unstable intermediate that is captured by binding of the elongator tRNA. Whereas initiation can occur in the 0 and +1 frames, the arrival of the first tRNA defines the reading frame and strongly favors 0 frame initiation. Overall, even in the simplest system, an intricate reaction network regulates translation initiation.

A non-catalytic N-terminal domain negatively influences the nucleotide exchange activity of translation elongation factor 1Bα

Eukaryotic translation elongation factor 1Bα (eEF1Bα) is a functional homolog of the bacterial factor EF-Ts, and is a component of the macromolecular eEF1B complex. eEF1Bα functions as a catalyst of guanine nucleotide exchange on translation elongation factor 1A (eEF1A). The C-terminal domain of eEF1Bα is necessary and sufficient for its catalytic activity, whereas the N-terminal domain interacts with eukaryotic translation elongation factor 1Bγ (eEF1Bγ) to form a tight complex. However, eEF1Bγ has been shown to enhance the catalytic activity of eEF1Bα attributed to the C-terminal domain of eEF1Bα. This suggests that the N-terminal domain of eEF1Bα may in some way influence the guanine nucleotide exchange process. We have shown that full-length recombinant eEF1Bα and its truncated forms are non-globular proteins with elongated shapes. Truncation of the N-terminal domain of eEF1Bα, which is dispensable for catalytic activity, resulted in acceleration of the rate of guanine nucleotide exchange on eEF1A compared to full-length eEF1Bα. A similar effect on the catalytic activity of eEF1Bα was observed after its interaction with eEF1Bγ. We suggest that the non-catalytic N-terminal domain of eEF1Bα may interfere with eEF1A binding to the C-terminal catalytic domain, resulting in a decrease in the overall rate of the guanine nucleotide exchange reaction. Formation of a tight complex between the eEF1Bγ and eEF1Bα N-terminal domains abolishes this inhibitory effect.

Characterisation of translation elongation factor eEF1B subunit expression in mammalian cells and tissues and co-localisation with eEF1A2

Translation elongation is the stage of protein synthesis in which the translation factor eEF1A plays a pivotal role that is dependent on GTP exchange. In vertebrates, eEF1A can exist as two separately encoded tissue-specific isoforms, eEF1A1, which is almost ubiquitously expressed, and eEF1A2, which is confined to neurons and muscle. The GTP exchange factor for eEF1A1 is a complex called eEF1B made up of subunits eEF1Bα, eEF1Bδ and eEF1Bγ. Previous studies have cast doubt on the ability of eEF1B to interact with eEF1A2, suggesting that this isoform might use a different GTP exchange factor. We show that eEF1B subunits are all widely expressed to varying degrees in different cell lines and tissues, and at different stages of development. We show that ablation of any of the subunits in human cell lines has a small but significant impact on cell viability and cycling. Finally, we show that both eEF1A1 and eEF1A2 colocalise with all eEF1B subunits, in such close proximity that they are highly likely to be in a complex.

Protein kinase Darkener of apricot and its substrate EF1γ regulate organelle transport along microtubules

Regulation of organelle transport along microtubules is important for proper distribution of membrane organelles and protein complexes in the cytoplasm. RNAi-mediated knockdown in cultured Drosophila S2 cells demonstrates that two microtubule-binding proteins, a unique isoform of Darkener of apricot (DOA) protein kinase, and its substrate, translational elongation factor EF1γ, negatively regulate transport of several classes of membrane organelles along microtubules. Inhibition of transport by EF1γ requires its phosphorylation by DOA on serine 294. Together, our results indicate a new role for two proteins that have not previously been implicated in regulation of the cytoskeleton. These results further suggest that the biological role of some of the proteins binding to the microtubule track is to regulate cargo transport along these tracks.

Elongation factor 1β' gene from Spodoptera exigua: characterization and function identification through RNA interference

Elongation factor (EF) is a key regulation factor for translation in many organisms, including plants, bacteria, fungi, animals and insects. To investigate the nature and function of elongation factor 1β′ from Spodoptera exigua (SeEF-1β′), its cDNA was cloned. This contained an open reading frame of 672 nucleotides encoding a protein of 223 amino acids with a predicted molecular weight of 24.04 kDa and pI of 4.53. Northern blotting revealed that SeEF-1β′ mRNA is expressed in brain, epidermis, fat body, midgut, Malpighian tubules, ovary and tracheae. RT-PCR revealed that SeEF-1β′ mRNA is expressed at different levels in fat body and whole body during different developmental stages. In RNAi experiments, the survival rate of insects injected with SeEF-1β′ dsRNA was 58.7% at 36 h after injection, which was significantly lower than three control groups. Other elongation factors and transcription factors were also influenced when EF-1β′ was suppressed. The results demonstrate that SeEF-1β′ is a key gene in transcription in S. exigua.

Regulation of translation by hydrogen peroxide

Cells must be able to maintain their intracellular homeostasis in the face of changing conditions. Typically, they respond by invoking complex regulatory mechanisms, including a global inhibition of translation. This reduction in protein synthesis may prevent continued gene expression during potentially error-prone conditions as well as allow for the turnover of existing mRNAs and proteins, whilst gene expression is directed toward the production of new molecules required to protect against or detoxify the stress. However, it is becoming increasingly recognized that not all translation is inhibited and translational control of specific mRNAs is required for survival under stress conditions. Control of protein levels via translational regulation offers a significant advantage to the cell due to the immediacy of the regulatory effect. This review describes how protein synthesis is regulated in response to oxidative stress conditions induced by exposure to hydrogen peroxide. Translational control can be mediated via direct oxidative regulation of translation factors as well via mRNA-specific regulatory mechanisms. Additionally, increasing evidence suggests that oxidative damage to the translational apparatus can itself alter the proteomic output. The resulting translational reprogramming is fundamental for adaptation to the oxidative stress.

The eEF1γ subunit contacts RNA polymerase II and binds vimentin promoter region

Here, we show that the eukaryotic translation elongation factor 1 gamma (eEF1γ) physically interacts with the RNA polymerase II (pol II) core subunit 3 (RPB3), both in isolation and in the context of the holo-enzyme. Importantly, eEF1γ has been recently shown to bind Vimentin mRNA. By chromatin immunoprecipitation experiments, we demonstrate, for the first time, that eEF1γ is also physically present on the genomic locus corresponding to the promoter region of human Vimentin gene. The eEF1γ depletion causes the Vimentin protein to be incorrectly compartmentalised and to severely compromise cellular shape and mitochondria localisation. We demonstrate that eEF1γ partially colocalises with the mitochondrial marker Tom20 and that eEF1γ depletion increases mitochondrial superoxide generation as well as the total levels of carbonylated proteins. Finally, we hypothesise that eEF1γ, in addition to its role in translation elongation complex, is involved in regulating Vimentin gene by contacting both pol II and the Vimentin promoter region and then shuttling/nursing the Vimentin mRNA from its gene locus to its appropriate cellular compartment for translation.

Elongation factors are involved in cytokinesis of sea urchin eggs

Cleavage furrows (CFs) have been isolated from dividing sea urchin eggs and the protein constituents have been analyzed by two-dimensional gel electrophoresis (Fujimoto & Mabuchi, J. Biochem. 122, 518-524, 1997). Two proteins of 51 and 32 kDa, respectively, have been found to be enriched in the CF preparation. Here, we show that these proteins are identical to the protein elongation factor 1alpha (EF-1alpha) and 1beta (EF-1beta), respectively. Furthermore, the CF 51-kDa protein is identical to the 51-kDa protein which had been isolated as a component of the microtubule organizing granules of mitotic sea urchin eggs. The 51-kDa protein bundles F-actin in vitro. This activity is suppressed by Ca(2+)/calmodulin or GTPgammaS. The 32-kDa protein binds EF-1alpha both in vitro and in cell extract, and is shown to suppress the F-actin-bundling activity of the 51-kDa protein. Microinjection of a monoclonal antibody against the 51-kDa protein or that of His-tagged 32-kDa protein into dividing sea urchin eggs at the onset of cleavage leads to failure of cytokinesis. These results strongly suggest that EF-1alpha is involved in maintenance of the structure of the contractile ring and EF-1beta regulates the F-actin-bundling activity of EF-1alpha.

Drosophila translational elongation factor-1gamma is modified in response to DOA kinase activity and is essential for cellular viability

Drosophila translational elongation factor-1gamma (EF1gamma) interacts in the yeast two-hybrid system with DOA, the LAMMER protein kinase of Drosophila. Analysis of mutant EF1gamma alleles reveals that the locus encodes a structurally conserved protein essential for both organismal and cellular survival. Although no genetic interactions were detected in combinations with mutations in EF1alpha, an EF1gamma allele enhanced mutant phenotypes of Doa alleles. A predicted LAMMER kinase phosphorylation site conserved near the C terminus of all EF1gamma orthologs is a phosphorylation site in vitro for both Drosophila DOA and tobacco PK12 LAMMER kinases. EF1gamma protein derived from Doa mutant flies migrates with altered mobility on SDS gels, consistent with it being an in vivo substrate of DOA kinase. However, the aberrant mobility appears to be due to a secondary protein modification, since the mobility of EF1gamma protein obtained from wild-type Drosophila is unaltered following treatment with several nonspecific phosphatases. Expression of a construct expressing a serine-to-alanine substitution in the LAMMER kinase phosphorylation site into the fly germline rescued null EF1gamma alleles but at reduced efficiency compared to a wild-type construct. Our data suggest that EF1gamma functions in vital cellular processes in addition to translational elongation and is a LAMMER kinase substrate in vivo.

Elongation factor eEF1B modulates functions of the release factors eRF1 and eRF3 and the efficiency of translation termination in yeast

BACKGROUND

Termination of translation in eukaryotes is controlled by two interacting polypeptide chain release factors, eRF1 and eRF3. While eRF1 recognizes nonsense codons, eRF3 facilitates polypeptide chain release from the ribosome in a GTP-dependent manner. Besides termination, both release factors have essential, but poorly characterized functions outside of translation.

RESULTS

To characterize further the functions of yeast eRF1 and eRF3, a genetic screen for their novel partner proteins was performed. As a result, the genes for gamma (TEF4 and TEF3/CAM1) and alpha (TEF5/EFB1) subunits of the translation elongation factor eEF1B, known to catalyze the exchange of bound GDP for GTP on eEF1A, were revealed. These genes act as dosage suppressors of a synthetic growth defect caused by some mutations in the SUP45 and SUP35 genes encoding eRF1 and eRF3, respectively. Extra copies of TEF5 and TEF3 can also suppress the temperature sensitivity of some sup45 and sup35 mutants and reduce nonsense codon readthrough caused by these omnipotent suppressors. Besides, overproduction of eEF1Balpha reduces nonsense codon readthrough in the strain carrying suppressor tRNA. Such effects were not shown for extra copies of TEF2, which encodes eEF1A, thus indicating that they were not due to eEF1A activation.

CONCLUSION

The data obtained demonstrate involvement of the translation elongation factor eEF1B in modulating the functions of translation termination factors and suggest its possible role in GDP for GTP exchange on eRF3.

Elongation factor 1Bgamma (eEF1Bgamma) expression during the molting cycle and cold acclimation in the crayfish Procambarus clarkii

Eukaryotic elongation factor 1Bgamma (eEF1Bgamma) is a subunit of elongation factor 1 (EF1), which regulates the recruitment of amino acyl-tRNAs to the ribosome during protein synthesis in eukaryotes. In addition to structural roles within eEF1, eEF1Bgamma has properties which suggest sensory or regulatory activities. We have cloned eEF1Bgamma from axial abdominal muscle of freshwater crayfish, Procambarus clarkii. The predicted amino acid sequence has 66% identity to Locusta migratoria eEF1Bgamma and 65% identity to Artemia salina eEF1Bgamma. We measured eEF1Bgamma expression by real-time PCR, using the relative quantification method with 18s ribosomal RNA as an internal calibrator. eEF1Bgamma expression was lowest in gill, axial abdominal muscle, and hepatopancreas, and was highest in the antennal gland (5.7-fold above hepatopancreas) and cardiac muscle (7.8-fold above hepatopancreas). In axial abdominal muscle, eEF1Bgamma expression was 4.4-fold higher in premolt and 11.9 higher in postmolt compared to intermolt. In contrast, eEF1Bgamma was decreased or unchanged in epithelial tissues during pre- and postmolt. eEF1Bgamma expression in the hepatopancreas was 3.5-fold higher during intermolt compared to premolt and was unchanged in gill and antennal gland. No significant differences in eEF1Bgamma were found after 1 week of acclimation to 4 degrees C. These results show that eEF1Bgamma is regulated at the mRNA level with tissue-specific differences in expression patterns.

Kinetics of the interactions between yeast elongation factors 1A and 1Balpha, guanine nucleotides, and aminoacyl-tRNA

The interactions of elongation factor 1A (eEF1A) from Saccharomyces cerevisiae with elongation factor 1Balpha (eEF1Balpha), guanine nucleotides, and aminoacyl-tRNA were studied kinetically by fluorescence stopped-flow. eEF1A has similar affinities for GDP and GTP, 0.4 and 1.1 microm, respectively. Dissociation of nucleotides from eEF1A in the absence of the guanine nucleotide exchange factor is slow (about 0.1 s(-1)) and is accelerated by eEF1Balpha by 320-fold and 250-fold for GDP and GTP, respectively. The rate constant of eEF1Balpha binding to eEF1A (10(7)-10(8) M (-1) s(-1)) is independent of guanine nucleotides. At the concentrations of nucleotides and factors prevailing in the cell, the overall exchange rate is expected to be in the range of 6 s(-1), which is compatible with the rate of protein synthesis in the cell. eEF1A.GTP binds Phe-tRNA(Phe) with a K(d) of 3 nm, whereas eEF1A.GDP shows no significant binding, indicating that eEF1A has similar tRNA binding properties as its prokaryotic homolog, EF-Tu.

Antitumor activity of CTFB, a novel anticancer agent, is associated with the down-regulation of nuclear factor-kappaB expression and proteasome activation in head and neck squamous carcinoma cell lines

This study aimed to characterize the antitumor activity of 5-Chloro-N-[2-[2-(4-chloro-phenyl)-3-methyl-butoxy]-5-trifluoromethyl-phenyl]-2-hydroxy-benzamide (CTFB), a novel anticancer agent, in head and neck cancer cell lines, FaDu, SCC-25 and cisplatin-resistant CAL-27. CTFB was generated as a result of an extensive medicinal chemistry effort on a lead compound series discovered in a high-throughput screen for inducers of apoptosis. All cell lines showed significant growth delay in response to CTFB treatment at a concentration of 1 micromol/L with 17.16 +/- 2.08%, 10.92 +/- 1.22%, and 27.03 +/- 1.86% of cells surviving at 120 h in FaDu, CAL-27, and SCC-25, respectively. To define proteins involved in the mechanism of action of CTFB, we determined differences in the proteome profile of cell lines before and after treatment with CTFB using two-dimensional difference gel electrophoresis followed by computational image analysis and mass spectrometry. Eight proteins were found to be regulated by CTFB in all cell lines. All these proteins are involved in cytoskeleton formation and function and/or in cell cycle regulation. We showed that CTFB-induced cell growth delay was accompanied by cell cycle arrest at the G(0)-G(1) phase that was associated with the up-regulation of p21/WAF1 and p27/Kip1 expression and the down-regulation of cyclin D1. Furthermore, we showed that activity of CTFB depended on the down-regulation of nuclear factor-kappaB (NF-kappaB) and NF-kappaB p65 phosphorylated at Ser(536). The level of proteasome activity correlated with the response to CTFB treatment, and the down-regulation of NF-kappaB is accompanied by enhanced proteasome activity in all investigated head and neck cancer cell lines. In this report, we show that CTFB reveals multiple effects that lead to delayed cell growth. Our data suggest that this compound should be studied further in the treatment of head and neck cancer.

Kinectin-dependent assembly of translation elongation factor-1 complex on endoplasmic reticulum regulates protein synthesis

Kinectin is an integral membrane protein with many isoforms primarily found on the endoplasmic reticulum. It has been found to bind kinesin, Rho GTPase, and translation elongation factor-1delta. None of the existing models for the quaternary organization of the elongation factor-1 complex in higher eukaryotes involves kinectin. We have investigated here the assembly of the elongation factor-1 complex onto endoplasmic reticulum via kinectin using in vitro and in vivo assays. We established that the entire elongation factor-1 complex can be anchored to endoplasmic reticulum via kinectin, and the interacting partners are as follows. Kinectin binds EF-1delta, which in turn binds EF-1gamma but not EF-1beta; EF-1gamma binds EF-1delta and EF-1beta but not kinectin. In vivo splice blocking of the kinectin exons 36 and 37 produced kinectin lacking the EF-1delta binding domain, which disrupted the membrane localization of EF-1delta, EF-1gamma, and EF-1beta on endoplasmic reticulum, similar to the disruptions seen with the overexpression of kinectin fragments containing the EF-1delta binding domain. The disruptions of the EF-1delta/kinectin interaction inhibited expression of membrane proteins but enhanced synthesis of cytosolic proteins in vivo. These findings suggest that anchoring the elongation factor-1 complex onto endoplasmic reticulum via EF-1delta/kinectin interaction is important for regulating protein synthesis in eukaryotic cells.

Myoblast attachment and spreading are regulated by different patterns by ubiquitous calpains

The calcium-dependent proteolytic system is a large family of well-conserved ubiquitous and tissue-specific proteases, known as calpains, and an endogenous inhibitor, calpastatin. Ubiquitous calpains are involved in many physiological phenomena, such as the cell cycle, muscle cell differentiation, and cell migration. This study investigates the regulation of crucial steps of cell motility, myoblast adhesion and spreading, by calpains. Inhibition of each ubiquitous calpain isoform by antisense strategy pinpointed the involvement of each of these proteases in myoblast adhesion and spreading. Moreover, the actin cytoskeleton and microtubules were observed in transfected cells, demonstrating that each ubiquitous calpain could be involved in the actin fiber organization. C2C12 cells with reduced mu- or m-calpain levels have a rounded morphology and disorganized stress fibers, but no modification in the microtubule cytoskeleton. Antisense strategy directed against MARCKS, a calpain substrate during C2C12 migration, showed that this protein could play a role in stress fiber polymerization. A complementary proteomic analysis using C2C12 cells over-expressing calpastatin indicated that two proteins were under-expressed, while six, which are involved in the studied phenomena, were overexpressed after calpain inhibition. The possible role of these proteins in adhesion, spreading, and migration was discussed.

Mg2+ and a key lysine modulate exchange activity of eukaryotic translation elongation factor 1B alpha

To sustain efficient translation, eukaryotic elongation factor B alpha (eEF1B alpha) functions as the guanine nucleotide exchange factor for eEF1A. Stopped-flow kinetics using 2'-(or 3')-O-N-methylanthraniloyl (mant)-GDP showed spontaneous release of nucleotide from eEF1A is extremely slow and accelerated 700-fold by eEF1B alpha. The eEF1B alpha-stimulated reaction was inhibited by Mg2+ with a K(1/2) of 3.8 mM. Previous structural studies predicted the Lys-205 residue of eEF1B alpha plays an important role in promoting nucleotide exchange by disrupting the Mg2+ binding site. Co-crystal structures of the lethal K205A mutant in the catalytic C terminus of eEF1B alpha with eEF1A and eEF1A.GDP established that the lethality was not due to a structural defect. Instead, the K205A mutant drastically reduced the nucleotide exchange activity even at very low concentrations of Mg2+. A K205R eEF1B alpha mutant on the other hand was functional in vivo and showed nearly wild-type nucleotide dissociation rates but almost no sensitivity to Mg2+. These results indicate the significant role of Mg2+ in the nucleotide exchange reaction by eEF1B alpha and establish the catalytic function of Lys-205 in displacing Mg2+ from its binding site.

eEF1B: At the dawn of the 21st century

Translational regulation of gene expression in eukaryotes can rapidly and accurately control cell activity in response to stimuli or when rapidly dividing. There is increasing evidence for a key role of the elongation step in this process. Elongation factor-1 (eEF1), which is responsible for aminoacyl-tRNA transfer on the ribosome, is comprised of two entities: a G-protein named eEF1A and a nucleotide exchange factor, eEF1B. The multifunctional nature of eEF1A, as well as its oncogenic potential, is currently the subject of a number of studies. Until recently, less work has been done on eEF1B. This review describes the macromolecular complexity of eEF1B, its multiple phosphorylation sites and numerous cellular partners, which lead us to suggest an essential role for the factor in the control of gene expression, particularly during the cell cycle.

The 110kDa glutathione transferase of Yarrowia lipolytica is encoded by a homologue of the TEF3 gene from Saccharomyces cerevisiae: Cloning, expression, and homology modeling of the recombinant protein

The TEF4 gene of the non-saccharomyces yeast Yarrowia lipolytica encodes an EF1Bgamma protein with structural similarity to the glutathione transferases (GSTs). This 1203bp gene was cloned, over-expressed in Escherichia coli, and the recombinant protein characterized. DNA sequencing of the cloned gene agreed with the recently completed Y. lipolytica genome and showed 100% identity to a previously reported 30-residue N-terminal sequence for a 110kDa Y. lipolytica GST, except that it encoded two additional N-terminal residues (N-Met-Ser-). The recombinant protein (subunit M(r) 52kDa) was found not to possess GST activity with 1-chloro-2,4-dinitrobenzene. Partial tryptic digestion released two fragments of M(r) 22 and 18kDa, which we interpret as N- and C-terminal domains. Homology modeling confirmed that the N-terminal domain of Y. lipolytica TEF4 encodes a GST-like protein.

Regulation of elongation factor-1 expression by vitamin E in diabetic rat kidneys

Translation elongation factor-1 (EF-1) forms a primary site of regulation of protein synthesis and has been implicated amongst others in tumorigenesis, diabetes and cell death. To investigate whether diabetes-induced oxidative stress affects EF-1 gene expression, we used a free radical scavenger, vitamin E. The following groups of rats (5/group) were studied: control, vitamin E control, diabetic and diabetic treated with vitamin E. Markers of hyperglycemia, kidney function, oxidative stress, and kidney hypertrophy were elevated in diabetic rats. Increased urinary protein excretion indicated early signs of glomerular and tubular dysfunction. The mRNA and protein levels of the three EF-1 subunits (A, Balpha, and Bgamma) were determined in renal cortex extracts using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), northern blot analysis and western blotting. EF-1A mRNA expression in renal cortex extracts was significantly increased by at least 2-fold (p < 0.002) in diabetic rats; however, there was no change in the mRNA levels of EF-1Balpha and EF-1Bgamma subunits. Similar results were observed at the protein level. Treatment of diabetic rats with vitamin E for 10 days suppressed both glycemic and oxidative stresses in renal cortex and kidney hypertrophy. EF-1A mRNA and protein levels were also reduced to control levels. In conclusion, EF-1A but not EF-1Balpha and EF-1Bgamma gene expression is significantly enhanced in the renal cortex of diabetic rats. Normalization of enhanced EF-1A expression by vitamin E treatment suggests a role for EF-1A during diabetes-induced oxidative stress.

Leishmania major elongation factor 1B complex has trypanothione S-transferase and peroxidase activity

In the Trypanosomatidae, trypanothione has subsumed many of the roles of glutathione in defense against chemical and oxidant stress. Crithidia fasciculata lacks glutathione S-transferase, but contains an unusual trypanothione S-transferase activity that is associated with eukaryotic translation elongation factor 1B (eEF1B). Here we describe the cloning, expression, and reconstitution of the purified alpha, beta, and gamma subunits of eEF1B from Leishmania major. Individual subunits lacked trypanothione S-transferase activity. Only eEF1B, formed by reconstitution or co-expression of the three subunits, was able to conjugate a variety of electrophilic substrates to trypanothione or glutathionylspermidine, but not glutathione. In contrast to the C. fasciculata eEF1B, the L. major enzyme also displayed peroxidase activity against a variety of organic hydroperoxides. The enzyme showed no activity with hydrogen peroxide and greatest activity with linoleic acid hydroperoxide (1 unit mg(-1)). Kinetic studies suggest a ternary complex mechanism, with Km values of 140 mum for trypanothione and 7.4 mm for cumene hydroperoxide and kcat=25 s(-1). Immunofluorescence studies indicate that the enzyme may be localized to the surface of the endoplasmic reticulum. These results suggest that, in addition to its role in protein synthesis, the Leishmania eEF1B may help protect the parasite from lipid peroxidation.

Trypanothione S-transferase activity in a trypanosomatid ribosomal elongation factor 1B

Trypanothione is a thiol unique to the Kinetoplastida and has been shown to be a vital component of their antioxidant defenses. However, little is known as to the role of trypanothione in xenobiotic metabolism. A trypanothione S-transferase activity was detected in extracts of Leishmania major, L. infantum, L. tarentolae, Trypanosoma brucei, and Crithidia fasciculata, but not Trypanosoma cruzi. No glutathione S-transferase activity was detected in any of these parasites. Trypanothione S-transferase was purified from C. fasciculata and shown to be a hexadecameric complex of three subunits with a relative molecular weight of 650,000. This enzyme complex was specific for the thiols trypanothione and glutathionylspermidine and only used 1-chloro-2,4-dinitrobenzene from a range of glutathione S-transferase substrates. Peptide sequencing revealed that the three components were the alpha, beta, and gamma subunits of ribosomal eukaryotic elongation factor 1B (eEF1B). Partial dissociation of the complex suggested that the S-transferase activity was associated with the gamma subunit. Moreover, Cibacron blue was found to be a tight binding inhibitor and reactive blue 4 an irreversible time-dependent inhibitor that covalently modified only the gamma subunit. The rate of inactivation by reactive blue 4 was increased more than 600-fold in the presence of trypanothione, and Cibacron blue protected the enzyme from inactivation by 1-chloro-2,4-dinitrobenzene, confirming that these dyes interact with the active site region. Two eEF1Bgamma genes were cloned from C. fasciculata, but recombinant C. fasciculata eEF1Bgamma had no S-transferase activity, suggesting that eEF1Bgamma is unstable in the absence of the other subunits.

The crystal structure of the glutathione S-transferase-like domain of elongation factor 1Bgamma from Saccharomyces cerevisiae

The crystal structure of the N-terminal 219 residues (domain 1) of the conserved eukaryotic translation elongation factor 1Bgamma (eEF1Bgamma), encoded by the TEF3 gene in Saccharomyces cerevisiae, has been determined at 3.0 A resolution by the single wavelength anomalous dispersion technique. The structure is overall very similar to the glutathione S-transferase proteins and contains a pocket with architecture highly homologous to what is observed in glutathione S-transferase enzymes. The TEF3-encoded form of eEF1Bgamma has no obvious catalytic residue. However, the second form of eEF1Bgamma encoded by the TEF4 gene contains serine 11, which may act catalytically. Based on the x-ray structure and gel filtration studies, we suggest that the yeast eEF1 complex is organized as an [eEF1A.eEF1Balpha.eEF1Bgamma]2 complex. A 23-residue sequence in the middle of eEF1Bgamma is essential for the stable dimerization of eEF1Bgamma and the quaternary structure of the eEF1 complex.

Solution structure of the 162 residue C-terminal domain of human elongation factor 1Bgamma

The multisubunit elongation factor 1 (eEF1) is required for the elongation step of eukaryotic protein synthesis. The eEF1 complex consists of four subunits: eEF1A, a G-protein that shuttles aminoacylated tRNAs to the ribosome; eEF1Balpha and eEF1Bbeta, two guanine nucleotide exchange factors, and eEF1Bgamma. Although its exact function remains unknown, this latter subunit is present in all eukaryotes. Recombinant human eEF1Bgamma has been purified and shown to consist of two independent domains. We have utilized high resolution NMR to determine the three-dimensional structure of the 19 kDa C-terminal fragment (domain 2). The structure consists of a five-stranded anti-parallel beta-sheet surrounded by alpha-helices and resembles a contact lens. Highly conserved residues are mainly located on the concave face, suggesting thereby that this side of the molecule might be involved in some biologically relevant interface(s). Although the isolated domain 2 appears to be mostly monomeric in solution, biochemical and structural data indicate a potential homodimer. The proposed dimer model can be further positioned within the quaternary arrangement of the whole eEF1 assembly.

Direct and biochemical interaction between dopamine D3 receptor and elongation factor-1Bbetagamma

Novel signaling components of dopamine D3 receptor (D3R) were searched using yeast two-hybrid system, and the gamma subunit of elongation Factor-1B (eEF1Bgamma) was found to interact with D3R. This interaction was observed specifically between eEF1Bgamma and D3R but not with D2R or D4R. Immunocytochemical studies showed that D3R and eEF1Bgamma form clusters on the plasma membrane and their co-localization was evident in these clusters. The beta subunit of eEF1B (eEF1Bbeta), which forms a tight complex with eEF1Bgamma, was phosphorylated on serine residues in response to the stimulation of D3R. Phosphorylation of eEF1Bbeta was insensitive to pertussis toxin or wortmannin, however, stimulation of cellular protein kinase C (PKC) directly phosphorylated eEF1Bbeta and depletion of PKC abolished D3R-mediated phosphorylation of eEF1Bbeta. These results suggest the involvement of PKC, but not Gi/o proteins or phosphatidylinositol 3-kinase, in D3R-mediated phosphorylation of eEF1Bbeta. Stimulation of D3R did not activate PKC, but the activation of PKC resulted in the phosphorylation of D3R. These results show that PKC has a permissive role for the D3R-mediated phosphorylation of eEF1Bbeta, and suggest that PKC could modulate the mutual interaction between two protein by phosphorylating both D3R and eEF1Bbeta. Therefore, the cellular PKC level would be important for the D3R-mediated modulation of eEF1B, and for their cellular regulations such as protein synthesis or cellular proliferation.

Mutation of a conserved CDK site converts a metazoan Elongation Factor 1Bbeta subunit into a replacement for yeast eEF1Balpha

Elongation factor subunit eEF1Bbeta (formerly EF-1beta in plants and EF-1delta in animals) was identified and cloned in a screen for proteins from pea that interact with a cyclin-dependent kinase (CDK). CDKs are enzymes that regulate progression through meiotic and mitotic cell cycles in eukaryotes. eEF1Bbeta and the related protein eEF1Balpha (formerly EF-1beta' in plants and EF-1beta in animals and fungi) can catalyze GTP/GDP exchange on the G-protein eEF1A (formerly EF-1alpha in plants, animals and fungi) during the elongation phase of protein synthesis in eukaryotes. Recombinant Cdc2 and its native homologues from pea extracts associated both in vitro and in vivo with eEF1Bbeta. A Cdc2-cyclin B complex phosphorylated recombinant plant eEF1Bbetas, but not eEF1Balpha. These interactions between CDK and eEF1Bbeta prompted investigations into the in vivo consequences of this relationship. Expression of cDNAs encoding rice or pea eEF1Bbeta subunits failed to complement a Saccharomyces cerevisiae mutant deleted for the eEF1Balpha gene, as was previously observed for the human eEF1Bbeta. However, replacement of Thr91, the sole consensus CDK phosphorylation site in pea eEF1Bbeta, with alanine allowed the pea protein to substitute for eEF1Balpha function in vivo. In addition, this rescued strain was severely cold sensitive, and more sensitive to translational inhibitors than wild-type yeast. Taken together, these results suggest a physiological connection between the cyclin-dependent class of kinases and a translational elongation factor in mitotic cells, and provide the first in vivo evidence that an altered form of eEF1Bbeta can serve as the guanine nucleotide exchange factor for eEF1A.

Kinectin anchors the translation elongation factor-1 delta to the endoplasmic reticulum

Kinectin has been proposed to be a membrane anchor for kinesin on intracellular organelles. A kinectin isoform that lacks a major portion of the kinesin-binding domain does not bind kinesin but interacts with another resident of the endoplasmic reticulum, the translation elongation factor-1 delta (EF-1 delta). This was shown by yeast two-hybrid analysis and a number of in vitro and in vivo assays. EF-1 delta provides the guanine nucleotide exchange activities on EF-1 alpha during elongation step of protein synthesis. The minimal EF-1 delta-binding domain on kinectin resides within a conserved region present in all the kinectin isoforms. Overexpression of the kinectin fragments in vivo disrupted the intracellular localization of EF-1 delta proteins. This report provides evidence of an alternative kinectin function as the membrane anchor for EF-1 delta on the endoplasmic reticulum and provides clues to the EF-1 complex assembly and anchorage on the endoplasmic reticulum.

Steady-state and pre-steady-state kinetic analysis of halopropane conversion by a rhodococcus haloalkane dehalogenase

Haloalkane dehalogenase from Rhodococcus rhodochrous NCIMB 13064 (DhaA) catalyzes the hydrolysis of carbon-halogen bonds in a wide range of haloalkanes. We examined the steady-state and pre-steady-state kinetics of halopropane conversion by DhaA to illuminate mechanistic details of the dehalogenation pathway. Steady-state kinetic analysis of DhaA with a range of halopropanes showed that bromopropanes had higher k(cat) and lower K(M) values than the chlorinated analogues. The kinetic mechanism of dehalogenation was further studied using rapid-quench-flow analysis of 1,3-dibromopropane conversion. This provided a direct measurement of the chemical steps in the reaction mechanism, i.e., cleavage of the carbon-halogen bond and hydrolysis of the covalent alkyl-enzyme intermediate. The results lead to a minimal mechanism consisting of four main steps. The occurrence of a pre-steady-state burst, both for bromide and 3-bromo-1-propanol, suggests that product release is rate-limiting under steady-state conditions. Combining pre-steady-state burst and single-turnover experiments indicated that the rate of carbon-bromine bond cleavage was indeed more than 100-fold higher than the steady-state k(cat). Product release occurred with a rate constant of 3.9 s(-1), a value close to the experimental k(cat) of 2.7 s(-1). Comparing the kinetic mechanism of DhaA with that of the corresponding enzyme from Xanthobacter autotrophicus GJ10 (DhlA) shows that the overall mechanisms are similar. However, whereas in DhlA the rate of halide release represents the slowest step in the catalytic cycle, our results suggest that in DhaA the release of 3-bromo-1-propanol is the slowest step during 1,3-dibromopropane conversion.

Apoptosis-like death in trypanosomatids: search for putative pathways and genes involved

Members of the Trypanosomatidae family comprises species that are causative of important human diseases such as Chagas'disease, Leishmaniasis and sleeping sickness. A wealth of evidence has accumulated that illustrates the ability of these unicellular organisms to undergo, with or without induction (stress conditions), a cell death with some features resembling apoptosis-like phenomenon. However, despite the apparent phenotypic similarities between the apoptosis-like death of kinetoplastids and mammalian nucleated cell programmed cell death (PCD), the pathways seem to differ significantly. This review analyses some of the current data related to the cell death in trypanosomatids. Special attention is given to members of conserved protein families demonstrating remarkable diversity and plasticity of function [i.e. elongation factor-1 subunits alpha and gamma; and the Silent Information Regulator (SIR2)-related gene, showed to be associated with resistance to apoptosis-like death in Leishmania]. The elucidation of the molecular events which tightly regulated the processes of growth arrest, differentiation and death of Trypanosoma cruzi, Leishmania spp and African trypanosomes, might allow not only to define a more comprehensive view of the cell death machinery in term of evolutionary origin but may also be useful to identify new target molecules for chemotherapeutic drug development and therapeutic intervention.

The 3' untranslated region of human vimentin mRNA interacts with protein complexes containing eEF-1gamma and HAX-1

Previously, we have shown that the vimentin 3' untranslated region (3'UTR) contains a highly conserved region, which is sufficient for the perinuclear localization of a reporter mRNA. This region was shown to specifically bind protein(s) by band shift analyses. UV-cross-linking studies suggest these proteins are 46- and 35-kDa in mass. Here, we have used this sequence as 'bait' to isolate RNA binding proteins using the yeast three-hybrid method. This technique relies on a functional assay detecting bona fide RNA-protein interaction in vivo. Three cDNA isolates, HAX-1, eEF-1gamma and hRIP, code for proteins of a size consistent with in vitro cross- linking studies. In all cases, recombinant proteins were capable of binding RNA in vitro. Although hRIP is thought to be a general mRNA binding protein, this represents an unreported activity for eEF-1gamma and HAX-1. Moreover, HAX-1 binding appears to be specific to vimentin's 3'UTR. Both in vivo synthesized eEF-1gamma and HAX-1 proteins were 'pulled out' of HeLa whole cell extracts by binding to a RNA affinity column comprised of vimentin's 3'UTR. Moreover, size-fractionation of extracts results in the separation of large complexes containing either eEF-1gamma or HAX-1. Thus, in addition to their known functions, both eEF-1gamma and HAX-1 are RNA binding proteins, which suggests new roles in mRNA translation and/or perinuclear localization.

Isolation and proteomic characterization of human Parvulin-associating preribosomal ribonucleoprotein complexes

Human parvulin (hParvulin; Par14/EPVH) belongs to the third family of peptidylprolyl cis-trans isomerases that exhibit an enzymatic activity of interconverting the cis-trans conformation of the prolyl peptide bond, and shows sequence similarity to the regulator enzyme for cell cycle transitions, human Pin1. However, the cellular function of hParvulin is entirely unknown. Here, we demonstrate that hParvulin associates with the preribosomal ribonucleoprotein (pre-rRNP) complexes, which contain preribosomal RNAs, at least 26 ribosomal proteins, and 26 trans-acting factors involved in rRNA processing and assembly at an early stage of ribosome biogenesis. Since an amino-terminal domain of hParvulin, which is proposed to be a putative DNA-binding domain, was alone sufficient to associate in principle with the pre-rRNP complexes, the association is probably through protein-RNA interaction. In addition, hParvulin co-precipitated at least 10 proteins not previously known to be involved in ribosome biogenesis. Coincidentally, most of these proteins are implicated in regulation of microtubule assembly or nucleolar reformation during the mitotic phase of the cell. Thus, these results, coupled with the preferential nuclear localization of hParvulin, suggest that hParvulin may be involved in ribosome biogenesis and/or nucleolar re-assembly of mammalian cells.

Isolation and characterization of Leishmania infantum cDNA encoding a protein homologous to eukaryotic elongation factor 1 gamma

This paper reports the isolation and characterization of a complementary deoxyribonucleic acid clone showing sequence homology with genes coding for the eukaryotic elongation factor 1 gamma (EF-1 gamma). The clone encodes an open reading frame of 404 amino acids corresponding to a deduced molecular mass of 46.2 kDa. Database searches revealed 30-64% sequence identity between the Leishmania infantum EF-1 gamma and several eukaryotic homologues. Southern blot analysis indicated that 2 genes tandemly organized were present in the L. infantum genome. The 3' untranslated regions of these 2 genes differed in size. Southern hybridization and pulsed field gel electrophoresis showed that EF-1 gamma genes are highly conserved among members of the Leishmania genus and must be clustered in a single chromosomal locus.

Detection and characterization of glutathione S-transferase activity in rice EF-1betabeta'gamma and EF-1gamma expressed in Escherichia coli

Plant elongation factor EF-1 consists of four subunits (EF-1alphabetabeta'gamma). EF-1alpha. GTP catalyses the binding of aminoacyl-tRNA to the ribosome. EF-1beta and EF-1beta' catalyze the GDP/GTP exchange on EF-1alpha. GDP. However, the function of EF-1gamma, a subunit detected in eukaryotes, but not in prokaryotes remained unknown. This report demonstrates that rice EF-1betabeta'gamma and recombinant EF-1gamma possess glutathione S-transferase (GST) activity. The EF-1betabeta'gamma- or EF-1gamma-dependent GST activity is about one-fiftieth of the rice GST activity. The Km values of EF-1betabeta'gamma, EF-1gamma, and rice GST for glutathione and 1-chloro-2,4-dinitrobenzene are of about the same order. Although recombinant EF-1gamma is heat labile, active EF-1gamma was obtained by purifying it in the presence of 20% glycerol.

FEZ1/LZTS1 gene at 8p22 suppresses cancer cell growth and regulates mitosis

The FEZ1/LZTS1 gene maps to chromosome 8p22, a region that is frequently deleted in human tumors. Alterations in FEZ1/LZTS1 expression have been observed in esophageal, breast, and prostate cancers. Here, we show that introduction of FEZ1/LZTS1 into Fez1/Lzts1-negative cancer cells results in suppression of tumorigenicity and reduced cell growth with accumulation of cells at late S-G(2)/M stage of the cell cycle. Fez1/Lzts1 protein is hyperphosphorylated by cAMP-dependent kinase during cell-cycle progression. We found that Fez1/Lzts1 is associated with microtubule components and interacts with p34(cdc2) at late S-G(2)/M stage in vivo. Present data show that FEZ1/LZTS1 inhibits cancer cell growth through regulation of mitosis, and that its alterations result in abnormal cell growth.

Elongation factor 1beta is an actin-binding protein

A 17 kDa polypeptide found in association with actin in cellular extracts of Dictyostelium discoideum was identified as a proteolytic fragment of eEF1beta. Antibody elicited against the 17 kDa protein reacted with a single 29 kDa polypeptide in Dictyostelium, indicating that the 17 kDa peptide arises from degradation of a larger precursor. The cDNA isolated from a Dictyostelium library using this antibody as a probe encodes Dictyostelium elongation factor 1beta. Amino acid degradation of the 17 kDa protein fragment confirmed the identity of the protein as eEF1beta. Direct interaction of eEF1beta with actin in vitro was further demonstrated in mixtures of actin with the 17 kDa protein fragment of Dictyostelium eEF1beta, recombinant preparations of Dictyostelium eEF1beta expressed in Escherichia coli, and the intact eEF1betagamma complex purified from wheat germ. Localization of eEF1beta in Dictyostelium by immunofluorescence microscopy reveals both diffuse cytoplasmic staining, and some concentration in the cortical and hyaline cytoplasm. The results support the existence of physical and functional interactions of the translation apparatus with the cytoskeleton, and suggest that eEF1beta may function in a dual role both to promote the elongation phase of protein synthesis, and to interact with cytoplasmic actin.

Competition between a sterol biosynthetic enzyme and tRNA modification in addition to changes in the protein synthesis machinery causes altered nonsense suppression

The Saccharomyces cerevisiae Mod5 protein catalyzes isopentenylation of A to i(6)A on tRNAs in the nucleus, cytosol, and mitochondria. The substrate for Mod5p, dimethylallyl pyrophosphate, is also a substrate for Erg20p that catalyzes an essential step in sterol biosynthesis. Changing the distribution of Mod5p so that less Mod5p is present in the cytosol decreases i(6)A on cytosolic tRNAs and alters tRNA-mediated nonsense suppression. We devised a colony color/growth assay to assess tRNA-mediated nonsense suppression and used it to search for genes, which, when overexpressed, affect nonsense suppression. We identified SAL6, TEF4, and YDL219w, all of which likely affect nonsense suppression via alteration of the protein synthesis machinery. We also identified ARC1, whose product interacts with aminoacyl synthetases. Interestingly, we identified ERG20. Midwestern analysis showed that yeast cells overproducing Erg20p have reduced levels of i(6)A on tRNAs. Thus, Erg20p appears to affect nonsense suppression by competing with Mod5p for substrate. Identification of ERG20 reveals that yeast have a limited pool of dimethylallyl pyrophosphate. It also demonstrates that disrupting the balance between enzymes that use dimethylallyl pyrophosphate as substrate affects translation.

Haloalkane dehalogenases: structure of a Rhodococcus enzyme

The hydrolytic haloalkane dehalogenases are promising bioremediation and biocatalytic agents. Two general classes of dehalogenases have been reported from Xanthobacter and Rhodococcus. While these enzymes share 30% amino acid sequence identity, they have significantly different substrate specificities and halide-binding properties. We report the 1.5 A resolution crystal structure of the Rhodococcus dehalogenase at pH 5.5, pH 7.0, and pH 5.5 in the presence of NaI. The Rhodococcus and Xanthobacter enzymes have significant structural homology in the alpha/beta hydrolase core, but differ considerably in the cap domain. Consistent with its broad specificity for primary, secondary, and cyclic haloalkanes, the Rhodococcus enzyme has a substantially larger active site cavity. Significantly, the Rhodococcus dehalogenase has a different catalytic triad topology than the Xanthobacter enzyme. In the Xanthobacter dehalogenase, the third carboxylate functionality in the triad is provided by D260, which is positioned on the loop between beta7 and the penultimate helix. The carboxylate functionality in the Rhodococcus catalytic triad is donated from E141. A model of the enzyme cocrystallized with sodium iodide shows two iodide binding sites; one that defines the normal substrate and product-binding site and a second within the active site region. In the substrate and product complexes, the halogen binds to the Xanthobacter enzyme via hydrogen bonds with the N(eta)H of both W125 and W175. The Rhodococcusenzyme does not have a tryptophan analogous to W175. Instead, bound halide is stabilized with hydrogen bonds to the N(eta)H of W118 and to N(delta)H of N52. It appears that when cocrystallized with NaI the Rhodococcus enzyme has a rare stable S-I covalent bond to S(gamma) of C187.

Eukaryotic translation elongation factor 1 alpha: structure, expression, functions, and possible role in aminoacyl-tRNA channeling

This review offers a comprehensive analysis of eukaryotic translation elongation factor 1 (eEF-1 alpha) in comparison with its bacterial counterpart EF-Tu. Altogether, the data presented indicate some variances in the elongation process in prokaryotes and eukaryotes. The differences may be attributed to translational channeling and compartmentalization of protein synthesis in higher eukaryotic cells. The functional importance of the EF-1 multisubunit complex and expression of its subunits under miscellaneous cellular conditions are reviewed. A number of novel functions of EF-1 alpha, which may contribute to the coordinate regulation of multiple cellular processes including growth, division, and transformation, are characterized.