Elongation factor T from Bacillus stearothermophilus and Escherichia coli. Purification and some properties of EF-Tu and EF-Ts from Bacillus stearothermophilus

Thermostability of multidomain proteins: elongation factors EF-Tu from Escherichia coli and Bacillus stearothermophilus and their chimeric forms

Recombinant mesophilic Escherichia coli (Ec) and thermophilic Bacillus stearothermophilus (Bst) elongation factors EF-Tus, their isolated G-domains, and six chimeric EF-Tus composed of domains of either EF-Tu were prepared, and their GDP/GTP binding activities and thermostability were characterized. BstEF-Tu and BstG-domain bound GDP and GTP with affinities in nanomolar and submicromolar ranges, respectively, fully comparable with those of EcEF-Tu. In contrast, the EcG-domain bound the nucleotides with much lower, micromolar affinities. The exchange of domains 2 and 3 had essentially no effect on the GDP-binding activity; all complexes of chimeric EF-Tus with GDP retained K(d) values in the nanomolar range. The final thermostability level of either EF-Tu was the result of a cooperative interaction between the G-domains and domains 2 + 3. The G-domains set up a "basic" level of the thermostability, which was approximately 20 degrees C higher with the BstG-domain than with the EcG-domain. This correlated with the growth temperature optimum difference of both bacteria and two distinct thermostabilization features of the BstG-domain: an increase of charged residues at the expense of polar uncharged residues (CvP bias), and a decrease in the nonpolar solvent-accessible surface area. Domains 2 + 3 contributed by further stabilization of alpha-helical regions and, in turn, the functions of the G-domains to the level of the respective growth temperature optima. Their contributions were similar irrespective of their origin but, with Ecdomains 2 + 3, dependent on the guanine nucleotide binding state. It was lower in the GTP conformation, and the mechanism involved the destabilization of the alpha-helical regions of the G-domain by Ecdomain 2.

Mg2+ is not catalytically required in the intrinsic and kirromycin-stimulated GTPase action of Thermus thermophilus EF-Tu

The influence of divalent metal ions on the intrinsic and kirromycin-stimulated GTPase activity in the absence of programmed ribosomes and on nucleotide binding affinity of elongation factor Tu (EF-Tu) from Thermus thermophilus prepared as the nucleotide- and Mg(2+)-free protein has been investigated. The intrinsic GTPase activity under single turnover conditions varied according to the series: Mn(2+) (0.069 min(-1)) > Mg(2+) (0.037 min(-1)) approximately no Me(2+) (0.034 min(-1)) > VO(2+) (0.014 min(-1)). The kirromycin-stimulated activity showed a parallel variation. Under multiple turnover conditions (GTP/EF-Tu ratio of 10:1), Mg(2+) retarded the rate of hydrolysis in comparison to that in the absence of divalent metal ions, an effect ascribed to kinetics of nucleotide exchange. In the absence of added divalent metal ions, GDP and GTP were bound with equal affinity (K(d) approximately 10(-7) m). In the presence of added divalent metal ions, GDP affinity increased by up to two orders of magnitude according to the series: no Me(2+) < VO(2+) < Mn(2+) approximately Mg(2+) whereas the binding affinity of GTP increased by one order of magnitude: no Me(2+) < Mg(2+) < VO(2+) < Mn(2+). Estimates of equilibrium (dissociation) binding constants for GDP and GTP by EF-Tu on the basis of Scatchard plot analysis, together with thermodynamic data for hydrolysis of triphosphate nucleotides (Phillips, R. C., George, P., and Rutman, R. J. (1969) J. Biol. Chem. 244, 3330-3342), showed that divalent metal ions stabilize the EF-Tu.Me(2+).GDP complex over the protein-free Me(2+).GDP complex in solution, with the effect greatest in the presence of Mg(2+) by approximately 10 kJ/mol. These combined results show that Mg(2+) is not a catalytically obligatory cofactor in intrinsic and kirromycin-stimulated GTPase action of EF-Tu in the absence of programmed ribosomes, which highlights the differential role of Mg(2+) in EF-Tu function.

Structure and expression of elongation factor Tu from Bacillus stearothermophilus

The tuf gene coding for elongation factor Tu (EF-Tu) of Bacillus stearothermophilus was cloned and sequenced. This gene maps in the same context as the tufA gene of Escherichia coli str operon. Northern-blot analysis and primer extension experiments revealed that the transcription of the tuf gene is driven from two promoter regions. One of these is responsible for producing a 4.9-kb transcript containing all the genes of B. stearothermophilus str operon and the other, identified adjacent to the stop codon of the fus gene and designated tufp, for producing a 1.3-kb transcript of the tuf gene only. In contrast to the situation in E. coli, the ratio between the transcription products was found to be about 10:1 in favour of the tuf gene transcript. This high transcription activity from the tufp promoter might be accounted for by the presence of an extremely A+T-rich block consisting of 29 nucleotides which immediately precedes the consensus -35 region of the promoter. A very similar tuf gene transcription strategy and the same tufp promoter organization with the identical A/T block were found in Bacillus subtilis. The tuf gene specifies a protein of 395 amino acid residues with a molecular mass of 43,290 Da, including the N-terminal methionine. A computer-generated three-dimensional homology model shows that all the structural elements essential for binding guanine nucleotides and aminoacyl-tRNA are conserved. The presence of serine at position 376 and a low affinity for kirromycin determined by zone-interference gel electrophoresis (Kd approximately 8 microM) and by polyacrylamide gel electrophoresis under non-denaturing conditions are in agreement with the reported resistance of this EF-Tu to the antibiotic. The replacement of the highly conserved Leu211 by Met was identified as a possible cause of pulvomycin resistance.

Characterization of the interaction between the restriction endonuclease McrBC from E. coli and its cofactor GTP

McrBC, a GTP-dependent restriction enzyme from E. coli K-12, cleaves DNA containing methylated cytosine residues 40 to 80 residues apart and 3'-adjacent to a purine residue (PumCN40-80PumC). The presence of the three consensus sequences characteristic for guanine nucleotide binding proteins in one of the two subunits of McrBC suggests that this subunit is responsible for GTP binding and hydrolysis. We show here that (i) McrB binds GTP with an affinity of 10(6) M-1 and that GTP binding stabilizes McrB against thermal denaturation. (ii) McrB binds GDP about 50-fold and ATP at least three orders of magnitude more weakly than GTP. (iii) McrB hydrolyzes GTP in the presence of Mg2+ with a steady-state rate of approximately 0.5 min-1. (iv) McrC stimulates GTP hydrolysis 30-fold, but substrate DNA has no detectable effect on the GTPase activity of McrB, neither by itself nor in the presence of McrC. (v) Substitution of N339 and N376 with alanine allowed us to identify NTAD (339 to 342) rather than NKKA (376 to 379) as the equivalent of the third consensus sequence motif characteristic for guanine nucleotide binding proteins, NKXD.

Stoichiometry of the EF-Tu.GTP complex with aminoacyl-tRNA: ternary of quinternary?

The stoichiometry of the complex formed between the Escherichia coli polypeptide elongation factor EF-Tu, GTP and valyl-tRNA(val) has been determined by non-enzymatic deacylation studies on mixtures of the components at well-defined concentrations. A titration end-point was found corresponding to a 1:1 complex of EF-Tu.GTP with the aminoacylated-tRNA i.e. formation of a ternary complex. The result conforms to the classical model of the elongation step and not to the revolutionary proposition of the formation of a 2:2:1 complex; quinternary complex (EF-Tu.GTP)2.aa-RNA.

NMR study of the phosphate-binding elements of Escherichia coli elongation factor Tu catalytic domain

The phosphoryl-binding elements in the GDP-binding domain of elongation factor Tu were studied by heteronuclear proton observe methods. Five proton resonances were found below 10.5 ppm. Two of these were assigned to the amide groups of Lys 24 and Gly 83. These are conserved residues in each of the consensus sequences. Their uncharacteristic downfield proton shifts are attributed to strong hydrogen bonds to phosphate oxygens as for resonances in N-ras-p21 [Redfield, A. G., & Papastavros, M. Z. (1990) Biochemistry 29, 3509-3514]. The Lys 24 of the EF-Tu G-domain has nearly the same proton and nitrogen shifts as the corresponding Lys 16 in p21. These results suggest that this conserved lysine has a similar structural role in proteins in this class. The tentative Gly 83 resonance has no spectral analogue in p21. A mutant protein with His 84 changed to glycine was fully 15N-labeled and the proton resonance assigned to Gly 83 shifted downfield by 0.3 ppm, thereby supporting the assignment.

Stereochemistry and lifetime of the GTP hydrolysis intermediate at the active site of elongation factor Tu from Bacillus stearothermophilus as inferred from the 17O-55Mn superhyperfine interaction

Electron paramagnetic resonance spectroscopy has been used to obtain information on the structure and stability of the products of GTP cleavage at the active site of elongation factor Tu (EF-Tu) from Bacillus stearothermophilus. Using stereospecifically labelled (Sp)-(Rp)-[beta-17O]GTP (prepared by modification of a previously published procedure which is now also suitable for guanine nucleotides), it was found that only one of the two possible diastereomers (Sp) led to detectable line-broadening of the EPR spectrum of Mn2+ at the active site of EF-Tu (linewidth 1.5 mT), whereas the Rp isomer caused the same linewidth as unlabelled nucleotide (1.3 mT). From our earlier work and from a demonstration that the lifetime of the state giving the broadened spectrum is too long to be assigned to the EF-Tu.GDP.Mn complex [the rate constant for decay as measured by displacement of GDP by the fluorescent 2'(3')-O-(N-methylanthraniloyl)-GDP is 6.2 x 10(-3) s-1 at 25 degrees C and pH 6.8], we conclude that the broadened signal arises from the EF-Tu.Mn.GDP.Pi complex, the predominant steady-state species. During the hydrolysis of GTP the Mn2+ remains bound to the beta-phosphate oxygen of GDP which arises from the beta pro-S oxygen of GTP, possibly until GDP dissociates and certainly until Pi dissociates. Addition of elongation factor Ts (EF-Ts) to this intermediate leads to rapid reduction of the linewidth to that expected for random distribution of interactions of one 17O and two 16O atoms of GDP with Mn2+, and is not distinguishable from that exhibited by (Rp)-[beta-17O]GTP in the corresponding complex in the presence of EF-Ts.

Preparation of Escherichia coli elongation factor Tu-guanosine 5'-triphosphate analogs

A simple procedure for the bulk preparation of 20 mg of Escherichia coli elongation factor (EF)-Tu-GTP analogs is described. The protocol is based upon the preparation and stabilization of nucleotide-free EF-Tu using an EF-Ts affinity chromatographic resin. The procedure is a general one for the preparation of any GTP analog of EF-Tu.

Molecular properties of elongation factor Tu from Streptomyces aureofaciens and Escherichia coli

Some molecular properties of the elongation factor Tu of protein synthesis purified in an aggregated state from gram-positive Streptomyces aureofaciens were studied and compared with those of Tu from gram-negative Escherichia coli. Electrofocussing under reducing conditions showed that the molecule of EF-Tu from S. aureofaciens has an isoelectric point shifted more to the acidic side compared with EF-Tu from E. coli. A comparison of amino acid composition revealed minor differences in the content of several amino acids in the two factors and showed that EF-Tu from S. aureofaciens contains four half-cystines per molecule. Under denaturing conditions only two mercapto groups reacted with 5,5'-dithiobis(2-nitrobenzoic acid). Limited tryptic digestion of aggregated EF-Tu from S. aureofaciens yields six fragments: the four main fragments are of a similar size as those of the E. coli factor. All fragments detected after trypsin digestion of S. aureofaciens EF-Tu were immunologically cross-reactive with antibodies against E. coli EF-Tu. However, even after 2 h of the reaction there still remains a small part of streptomycete factor uncleaved, which documents high resistance of aggregated EF-Tu towards trypsin.

Study of the interaction between uncharged yeast tRNAPhe and elongation factor Tu from Bacillus stearothermophilis

Proton NMR studies are presented on the interaction of nonaminoacylated yeast tRNAPhe and elongation factor Tu X GTP from Bacillus stearothermophilis. From experiments in which transfer of magnetization is observed between proton spins of tRNA and the protein, it is concluded that complex formation takes place. Amino acid residues of the protein come into close contact with the base pair A5U68 and/or U52A62 of the acceptor T psi C limb of the tRNA molecule. From the line broadening of tRNA resonances, associated with complex formation, an association constant of 10(3)-10(4) M-1 is estimated. The NMR experiments do not monitor a significant conformational change of the tRNA molecule upon interaction with the protein. However, at times long after the onset of complex formation, spectral changes indicate that the upper part of the acceptor helix becomes distorted.

Structural homology between elongation factors EF-Tu from Bacillus stearothermophilus and Escherichia coli in the binding site for aminoacyl-tRNA

Elongation factor EF-Tu (Mr approximately equal to 50 000) and elongation factor EF-G (Mr approximately equal to 78 000) were isolated from Bacillus stearothermophilus in a homogeneous form. The ability of EF-Tu to participate in protein synthesis is rapidly inactivated by N-tosyl-L-phenyl-alanylchloromethane (Tos-PheCH2Cl). EF-Tu X GTP is more susceptible to the inhibition by Tos-PheCH2Cl than is EF-Tu X GDP. Tos-PheCH2Cl forms a covalent equimolar complex with the factor by reacting with a cysteine residue in its molecule. The labelling of EF-Tu by the reagent irreversibly destroys its ability to bind aminoacyl-tRNA, which in turn protects the protein from this inactivation. This indicates that the modification of EF-Tu by Tos-PheCH2Cl occurs at the aminoacyl-tRNA binding site of the protein. To identify and characterize the site of aminoacyl-tRNA binding in EF-Tu, the factor was labelled with [14C]Tos-PheCH2Cl, digested with trypsin, the resulting peptides were separated by high-performance liquid chromatography and the sequence of the radioactive peptide was determined. The peptide has identical structure with an Escherichia coli EF-Tu tryptic peptide comprising the residues 75-89 and the Tos-PheCH2Cl-reactive cysteine at position 81 [Jonák, J., Petersen, T. E., Clark, B. F. C. and Rychlík, I. (1982) FEBS Lett. 150, 485-488]. Experiments on photo-oxidation of EF-Tu by visible light in the presence of rose bengal dye showed that there are apparently two histidine residues in elongation factor Tu from B. stearothermophilus which are essential for the interaction with aminoacyl-tRNA. This is clearly reminiscent of a similar situation in E. coli EF-Tu [Jonák, J., Petersen, T. E., Meloun, B. and Rychlík, I. (1984) Eur. J. Biochem. 144, 295-303]. Our results provide further evidence for the conserved nature of the site of aminoacyl-tRNA binding in elongation factor EF-Tu and show that Tos-PheCH2Cl reagent might be a favourable tool for the identification of the site in the structure of prokaryotic EF-Tus.

Bulk preparation and crystallization of the Escherichia coli elongation factor Tu-Ts complex

A simple procedure for the preparation of 10-500 mg of the Escherichia coli elongation Tu-Ts complex is described. The protocol is based on the separate purification and quantitation of EF-Tu-GDP and EF-Ts, followed by mixing of equimolar amounts of each protein and removal of the displaced GDP by dialysis. Single crystals grown from the final product have been analyzed by X-ray diffraction techniques. The procedure is also applicable to the bulk preparation and crystallization of the trypsin-modified Tu-Ts complex. Quantitation of the elongation factors by three methods is presented.

Structural details of the binding of guanosine diphosphate to elongation factor Tu from E. coli as studied by X-ray crystallography

Structural details of the guanosine diphosphate binding to a modified form of elongation factor Tu from Escherichia coli, resulting from X-ray crystallographic studies, are reported. The protein elements that take part in the nucleotide binding are located in four loops connecting beta-strands with alpha-helices. These loops correspond to regions in primary sequences which show a high degree of homology when compared with other prokaryotic and eukaryotic elongation factors and initiation factor 2.

Anion-exchange chromatography of proteins on AG MP-1 using high-performance liquid chromatography equipment

That the macroporous anion-exchange resin AG MP-1 can be used with HPLC equipment and common aqueous buffers for the chromatography of proteins is shown. The utility of this system is illustrated by the partial purification and complete resolution of the three protein synthesis elongation factors from each other, starting with a crude extract of Escherichia coli. The factors were purified 10- to 30-fold in a yield of 50 to 90% with a single 60-min chromatographic program of increasing NaCl concentration. Other proteins from various biological sources were purified with similar results. Thus, it appears that AG MP-1 is useful, at least in some applications, for the rapid, reproducible, and economical purification of proteins using HPLC equipment.

An improved bulk purification method for Escherichia coli elongation factor, Ts

A bulk purification procedure has been designed to maximize the yield of Escherichia coli elongation factor, Ts, with a minimum of effort and time. The enzyme purification is achieved by DEAE-Sepharose and elongation factor Tu-affinity chromatographies. The typical yield is 150 mg/kg of E. coli (B) cells.

Two tuf genes in the cyanobacterium Spirulina platensis

Probes derived from the tufA gene of Escherichia coli have been utilized to detect homologous sequences on Spirulina platensis DNA. A 6-kilobase-pair fragment of S. platensis DNA appears to contain two sequences homologous to the E. coli gene. Thus, as reported for gram-negative bacteria, the cyanobacterium presumably contains two tuf genes.

Purification of the elongation factor Tu (EF-Tu) from the cyanobacterium Spirulina platensis

Elongation factor Tu (EF-Tu) has been purified from the cyanobacterium Spirulina platensis. By gel electrophoresis the Mr of the purified protein appears to be 49 000, a value close to that reported for the EF-Tu isolated from a number of bacteria but higher than that reported for the protein isolated from Escherichia coli (43 000). Functionally, however, S. platensis EF-Tu may replace the E. coli protein in a protein-synthesizing system in vitro. In addition, its activity is affected by kirromycin, an antibiotic that specifically interacts with eubacterial EF-Tu.

Bacterial elongation factor Ts: isolation and reactivity with elongation factor Tu

An improved method for the purification of bacterial polypeptide elongation factor Ts (EF-Ts) from one mesophile (Escherichia coli) and two thermophiles (Bacillus stearothermophilus and PS3) is described. The improvements are both in the facility of isolation and in increased yields. The purified factors were used for cross-reactivity studies with elongation factor Tu (EF-Tu) obtained from the same bacterial strains. In all combinations studied, the efficiency of EF-Ts in catalyzing the exchange of EF-Tu-bound GDP was proportional to the strength of the protein-protein complex. Whereas the factors from the two thermophiles were interchangeable, the mesophilic EF-Ts formed a very weak complex with thermophilic EF-Tu; however, thermophilic EF-Ts formed very strong complexes with mesophilic EF-Tu. Thus, e.g., EF-Tu from E. coli formed a complex with EF-Ts from B. stearothermophilus which was 10 times more stable than the corresponding homologous complex.

Properties of native and nicked elongation factor Tu from Thermus thermophilus HB 8

Two alternative procedures for the isolation of the elongation factor Tu from Thermus thermophilus were compared and the properties of a specifically nicked EF-Tu . GDP were examined in detail. Although the native elongation factor possessed similar catalytic activities in all reactions investigated as the protein isolated by Arai et al. [Eur. J. Biochem. 92, 509-519 and 521-531 (1978)] it could not be crystallized. The nicked EF-Tu, consisting of two associated fragments with molecular weights of 41000 and 8000 respectively, was active in binding GDP, GTP and in the formation of Phe-tRNAPhe . EF-Tu . GTP ternary complex. However, it did not promote poly(U)-dependent synthesis of polyphenylalanine on Escherichia coli ribosomes. The isolated fragment of a molecular weight of about 41000 did not bind GDP. This activity could be reconstituted with the supplement of the small 8000-Mr fragment. It is demonstrated that, in contrast to the native EF-Tu, the nicked EF-Tu forms high-molecular-weight aggregates. Cleavage of the polypeptide chain of EF-Tu from T. thermophilus stimulates the crystallization of this protein.

Estimation of deuteration levels in whole cells and cellular proteins by 1H n.m.r. spectroscopy and neutron scattering

Methods using conventional Fourier transform 1H n.m.r. spectroscopy at 250 MHz for the determination of the overall deuteration levels of cells cultured in media containing 2H2O or deuterated carbon sources are described. These were developed for Escherichia coli as a model, and extended to Neurospora crassa hyphae and mouse myeloma cells P815. The results were investigated by 1H n.m.r. and neutron scattering measurements on deuterated proteins that were obtained from E. coli. It is concluded that 1H n.m.r. is able to observe the soluble proteins of E. coli in certain cases, that deuteration levels can be determined by 1H n.m.r. for small quantities of proteins in their native state, and that glycerol is a more efficient carbon source than glucose for the deuteration of E. coli proteins.

Two elongation factors from the extremely halophilic archaebacterium Halobacterium cutirubrum. Assay systems and purification at high salt concentrations

Two peptide chain elongation factors from Halobacterium cutirubrum were purified nearly to homogeneity. They were identified and characterized by three assay systems working at very high salt concentrations: poly(Phe) synthesis, GDP binding and ADP-ribosylation. The purification procedure consisted of Sepharose 4B chromatography with a decreasing ammonium sulfate gradient, gel filtration on Sephadex G-100 in the presence of (NH4)2SO4 and, for each of the two separated factors, an independent adsorption chromatography on hydroxyapatite. The factors were absolutely dependent on high salt concentrations for stability and activity. Both factors (I and II) complement each other to give fully active poly(Phe) synthesis, which is totally inhibited by puromycin and anisomycin. Factor I (Mr 51 000) is a major protein of the cell-free extract. It binds GDP, which can be displaced by GTP only to a small extent. The function of factor I in poly(Phe) synthesis is not impaired by high concentrations of kirromycin. The observed characteristics resemble partly those of prokaryotic EF-Tu and partly those of eukaryotic EF-1. Factor II (Mr 111 000) can be ADP-ribosylated by diphtheria toxin, and thus was identified as an EF-2-type elongation factor.

Protein synthesis elongation factors Tu and Tu.Ts from Caulobacter crescentus: sensitivity to kirromycin and activity in Q beta replicase

The protein synthesis elongation factors Tu and Ts are responsible for binding aminoacyl-transfer ribonucleic acid (RNA) to the ribosome. In addition, they perform an undefined function, as the EF-Tu.Ts complex, in the RNA phage RNA replicases. In an effort to obtain insight into these two apparently unrelated roles, we purified the elongation factors from Caulobacter crescentus and compared them to the analogous Escherichia coli polypeptides. Although most physical and functional characteristics were found to be similar, significant differences were found in the molecular weight of EF-Ts and relative affinities of guanine nucleotides, sensitivity to trypsin cleavage, and rate of heat denaturation of EF-Tu. The antibiotic kirromycin was active with EF-Tu from both bacterial species. When C. crescentus EF-Tu.Ts was substituted for the E. coli elongation factors in Q beta phage RNA replicase, an enzyme capable of apparently normal RNA synthetic activity was formed.

The effect of Mg2+ on some properties of nucleotide-free elongation factor Tu from Bacillus stearothermophilus

The nucleotide-free elongation factor from Bacillus stearothermophilus provides a means to study the effect of Mg2+ ions on various reactions of the protein. The binding of GDP to the protein is stimulated by Mg2+. From comparative studies with other metal ions, particularly Mn2+, it appears that this stimulation is due to the formation of a metal - GDP complex which is bound to the protein. Protection against proteolysis by trypsin is afforded by both Mg2+ and Mg - GDP, but not by GDP alone. The rate of substitution of the sulphydryl group associated with aminoacyl-tRNA binding, either 5,5'-dithio-bis(2-nitrobenzoic acid) or N-ethylmaleimide is reduced in the presence of Mg2+ - All these observations show that Mg2+ not only is involved in GDP binding but also has a direct effect on the tertiary structure of the protein.

Studies on polypeptide-chain-elongation factors from an extreme thermophile, Thermus thermophilus HB8. 1. Purification and some properties of the purified factors

Polypeptide chain elongation factors have been purified from an extreme thermophile, Thermus thermophilus HB8. By chromatography on a DEAE-Sephadex column, the factors were separated into two peaks; peak I contained a complex of EF-Tu and EF-Ts, while peak II was composed of EF-Tu.gdp and EF-G. These factors were subsequently purified to homogeneous states and crystallized. The EF-Tu . EF-Ts complex could be resolved into EF-Tu and EF-Ts by chromatography on a Sephadex G-200 column in the presence of 8 M guanidine-HCl. The complex could be reconstituted from EF-Tu and the renatured EF-Ts. No immunological cross-reaction was detected between EF-Tu, EF-Ts, and EF-G from T. thermophilus and the antibodies to their corresponding Escherichia coli factors. The molecular weight of EF-Tu . GDP determined by sedimentation equilibrium and sodium dodecylsulfate/polyacrylamide gel electrophoresis was 49000 and 51000 respectively. On the other hand, the molecular weight of EF-Ts was estimated as 27000 and 64000, respectively, by sodium dodecylsulfate/polyacrylamide gel electrophoresis and Sephadex gel filtration, suggesting that the protein existed probably as a dimer. The molecular weight of the EF-Tu . EF-Ts complex determined by sedimentation equilibrium and by gel filtration, was 142000 and 220000, respectively. Since the molar ratio of EF-Tu to EF-Ts in the EF-Tu . EF-Ts complex was one to one, it was suggested that the complex was composed of 2 mol each of EF-Tu and EF-Ts. The molecular weight of EF-G was estimated as 85000, 80000 and 78000 by equilibrium centrifugation, gel filtration, and sodium dodecylsulfate/polyacrylamide gel electrophoresis respectively.

Studies on polypeptide-chain-elongation factors from an extreme thermophile, Thermus thermophilus HB8. 3. Molecular properties

Molecular properties of the polypeptide chain elongation factors from Thermus thermophilus HB8 have been investigated and compared with those from Escherichia coli. 1. As expected, the factors purified from T. thermophilus were exceedingly heat-stable. Even free EF-Tu not complexed with GDP was stable after heating for 5 min at 60 degrees C. 2. GDP binding activity of T. thermophilus EF-Tu was also stable in various protein denaturants, such as 5.5 M urea, 1.5 M guanidine-HCl, and 4 M LiCl. 3. Amino acid compositions of EF-Tu and EF-G from T. thermophilus were similar to those from E. coli. On the other hand, amino acid composition of T. thermophilus EF-Ts was considerably different from that of E. coli EF-Ts. 4. In contrast to E. coli EF-Tu, T. thermophilus EF-Tu contained no free sulfhydryl group, but one disulfide bond. The disulfide bond was cleaved by sodium borohydride or sodium sulfite under native conditions. The heat stability of the reduced EF-Tu . GDP, as measured by GDP binding activity, did not differ from that of the untreated EF-Tu . GDP. 5. T. thermophilus EF-Ts contained, in addition to one disulfide bond, a sulfhydryl group which could be titrated only after complete denaturation of the protein. 6. Under native conditions one sulfhydryl group of T. thermophilus EF-G was titrated with p-chloromercuribenzoate, while the rate of reaction was very sluggish. The sulfhydryl group appears to be essential for interaction with ribosomes, whereas the ability to form a binary GDP . EF-G complex was not affected by its modification. The protein contained also one disulfide bond. 7. Circular dichroic spectra of EF-Tu from T. thermophilus and E. coli were very similar. Binding of GDP or GTP caused a similar spectral change in both. T. thermophilus and E. coli EF-Tu. On the other hand, the spectra of T. thermophilus EF-G and E. coli EF-G were significantly different, the content of ordered structure being higher in the former as compared to the latter.

Purification of the elongation factors present in spinach chloroplasts

Elongation factor G (EF-Gchl) and elongation factor Tu (EF-TUchl) have been purified from isolated spinach chloroplasts. On polyacrylamide gel electrophoresis the purifed proteins appear to be at least 70% pure. The molecular weight has been estimated to be 77000 and 45500 for EF-Gchl and EF-TUchl respectively. Chloroplast elongation factor T (EF-Tchl) has been only partially purified. Gel electrophoresis under non-denaturing and denaturing conditons indicate that EF-T-chl is most probably composed of two polypeptides, one of which has an electrophoretic mobility identical to that of EF-TUchl. EF-TUchl appears to represent approximately 7% of the chloroplast soluble protein while EF-Gchl accounts for less than 1%. Just as in the case of the bacterial factors, EF-TUchl appears to be in excess as compared to EF-Gchl. Although no data were obtained on the concentration of EF-Tchl, it may be assumed that the three elongation factors represent approximately 10% of the chloroplast soluble protein.

A small angle X-ray study of the elongation factor complex Tu . GDP from Escherichia coli

The protein elongation factor complex Tu. GDP from Escherichia coli was investigated in the presence of 0.01 mM GDP using the small-angle X-ray method. The overall shape and the molecular parameters of the Tu . GDP complex were determined using a least-squares method where the experimental data were used directly without desmearing. The best fit to the experimental data was obtained assuming the molecule to be an ellipsoid of revolution with the semiaxes A = B = 4.08 nm, and C = 1.18nm. Determination of the molecular weight gave the result Mr = 46 000, which corresponds to a water content equal to 26% (by weight).

Structural fluctuation of the polypeptide-chain elongation factor Tu. A comparison of factors from Escherichia coli and Thermus thermophilus HB8

The kinetics of hydrogen-deuterium exhcange in the polypeptide chain elongation factor Tu (EF Tu) from Escherichia coli and that from Thermus thermophilus HB8 has been examined in aqueous solutions at various pH and temperatures by means of infrared absorption measurements. The free EF-Tu from E. Coli has a greater reaction rate at all pH values and at every temperature than that of the GTP-bound or GDP-bound EF-Tu. The free EF-Tu from T. thermophilus, on the other hand, has an alomst equal reaction rate to that of EF-Tu-GDP in the temperature range 38-55 degrees C. For the peptide NH groups belonging to a medium-labile kinetic class, a small but definite difference in the rate of exchange reaction was observed between EF-Tu-GDP and EF-Tu-GTP for both E. coli and T. thermophilus. For less labile peptide NH groups, on the other hand, the rate of the exchange reaction with EF-Tu-GDP from T. thermophilus is only slightly affected by the pH of the solution at 38 degrees C and 45 degrees C, while the rate constant(k) with E. coli EF-Tu-GDP is pH-dependent (log k oc pH). For T. thermophilus EF-Tu, heat stability measurements, kinetics of the rates of GDP and GTP dissociation, and circular dichroic measurements have also been made. The molecular basis for the thermostability of T. thermophilus EF-Tu is discussed.

Ternary complex formation between elongation factor Tu, GTP and aminoacyl-tRNA: an equilibrium study

The equilibria between the elongation factor Tu-GTP complex (EF-Tu-GTP) from Escherichia coli and tyrosyl-tRNATyr from E. coli as well as phenylalanyl-tRNAPhe and seryl-tRNASer from yeast were studied using a novel procedure, which takes advantage of the protective effect of ternary complex formation on the stability of theaminoacyl bond against non-enzymatic hydrolysis. At 25 degrees C and at pH 7.4 tyrosyl-tRNATyr, phenylalanyl-tRNAPhe and seryl-tRNASer are bound with binding constants of 0.7 X 10(7) M-1, 5.0 X 10(7) M-1 and 0.5 X 10(7) M-1 respectively. The binding of aminoacyl-tRNA to EF-Tu-GTP has a negative deltaH of the order of 10 kcal/mol (42 kJ/mol). Complex formation is dependent on ionic strength: with 0.1 M KCl Kass = 0.8 X 10(7) M-1, with 0.5 M KCl Kass = 0.2 X 10(7) M-1 was determined for the binding of Tyr-tRNATyr.