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R Leberman

Publications and source records attributed to R Leberman.

At least 55 records · Page 3Linked to original sources
PubMed1986

Small-angle neutron scattering study of the ternary complex formed between bacterial elongation factor Tu, guanosine 5'-triphosphate, and valyl-tRNAVal.

The formation of the ternary complex between bacterial elongation factor Tu, GTP, and valyl-tRNAVal has been studied by small-angle neutron scattering. Titrations of the protein with amino-acyl-tRNA solutions in both H2O and 70% D2O confirm the expected stoichiometry. The molecular weight obtained for the protein alone is significantly higher than expected and can be explained by postulating a monomer-dimer equilibrium. The titration data are then internally consistent with a dissociation of the dimer on ternary complex formation. The radius of gyration for the ternary complex and the calculation of the separation of the centers of mass of the protein and tRNA components suggest a compact model for the ternary complex.

Escherichia coli↗
PubMed1986

31P-NMR spectra of the Ha-ras p21.nucleotide complexes.

Phosphorus nuclear magnetic resonance spectra of the Ha-ras oncogene product p21 and its nucleotide complexes have been obtained. It is shown that the 31P nuclear magnetic resonance spectra of a number of nucleotide-enzyme complexes show some common features. In particular, the chemical shift values of the beta-phosphorus resonance of enzyme-bound NTP and NDP (N = A, G) of hydrolases exhibit a downfield shift virtually identical for myosin, elongation factor Tu, and the Ha-ras oncogene product p21. This suggests that the stereochemistry around the beta-phosphorus might be similar in these compounds.

Guanosine Diphosphate↗
PubMed1985

Homologies and anomalies in primary structural patterns of nucleotide binding proteins.

In searches for homology among nucleotide binding proteins, recent reports have described primary structure alignments for stretches of 30 or so amino acid residues among a variety of proteins including the ras and src oncogene products. The significance of these sequence matches has been tested by searching in available data banks for certain conserved residue patterns resulting from the alignments. The tests suggest that alignments over these limited stretches are not necessarily justifiable and any implications for residues involved in nucleotide binding must be viewed with caution.

Amino Acid Sequence↗
PubMed1984

Modification of amino groups in EF-Tu.GTP and the ternary complex EF-Tu.GTP.valyl-tRNAVal.

In an attempt to describe the binding region of EF-Tu . GTP for aminoacyl-tRNA, the epsilon-amino groups of the lysine residues of the protein molecule in the GTP and ternary complexes were modified with ethyl acetimidate. Using [14C]ethyl acetimidate, tryptic digestion, fractionation of peptides by high-performance liquid chromatography, and amino acid analysis, all reactive lysine residues could be unambiguously identified. 19 of the 23 lysine residues of EF-Tu were labelled under conditions for ternary complex stability. Of these only 8 showed differences in reactivity between free and complexed EF-Tu . GTP. In the ternary complex lysine residues 208 and 390 [Jones, M. D., Petersen, T. E., Nielsen, K. M., Magnusson, S., Sotterup-Jensen, L., Gausing, K. and Clark, B. F. C. (1980) Eur. J. Biochem. 108, 507-526] showed an increase in reactivity (60% and 30% respectively) and residues 2, 4, 237, 248, 263, and 282 showed a decrease in reactivity (between 85% and 37%) compared to the values observed with EF-Tu . GTP. The greatest changes in reactivity were observed for lysine residues 2, 4 and 263. These data can be combined with the available structural information to identify possible areas of contact between the protein and nucleic acid moieties in the ternary complex.

Amino Acids↗
PubMed1984

Homologies in the primary structure of GTP-binding proteins: the nucleotide-binding site of EF-Tu and p21.

An examination of the available amino acid sequences of GTP-binding proteins has revealed that each contains a polypeptide essentially homologous for all of them. These sequences for elongation factor-Tu (EF-Tu) and the human bladder protein p21 exhibit a singular degree of homology (50%). Chemical and structural evidence indicates that this sequence in EF-Tu constitutes part of the nucleotide-binding site. The homologous sequences may therefore contribute to the GTP-binding sites of the other proteins.

Amino Acid Sequence↗
PubMed1983

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.

Guanosine Diphosphate↗
PubMed1980

Composition and properties of trypsin-cleaved elongation factor Tu.

Native elongation factor Tu from Escherichia coli, EF-Tu, is initially attacked by trypsin at three adjacent sites in the primary structure. These are arginine-44, arginine-58, and lysine-56. The rates of hydrolysis at the two arginine residues are about the same but that at the lysine residue is much slower. The products of the tryptic digestion have been analysed by Edman degradation and polyacrylamide gel electrophoresis. The peptide from alanine-45 to arginine-58 is eventually excised and does not complex with the remaining polypeptides (fragments A and D). The loss of this peptide does not lead to a concomitant loss of activity in stimulating polyphenylalanine synthesis. The latter is closely correlated with the further hydrolysis of the remaining fragment (A + D) complex. This complex resembles native EF-Tu in its ability to stimulate both polyphenylalanine synthesis and the binding of aminoacyl-tRNA to 70-S ribosomes, but does not form so stable a ternary complex with aminoacyl-tRNA and GTP as the native protein.

Amino Acid Sequence↗
PubMed1979

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.

Calcium↗