Amino acid sequence of elongation factor Tu. Characterization and alignment of the cyanogen bromide fragments and location of the cysteine residues

Structure of the GDP domain of EF-Tu and location of the amino acids homologous to ras oncogene proteins

A 2.7 angstrom resolution x-ray diffraction analysis of a trypsin-modified form of the Escherichia coli elongation factor Tu reveals that the GDP-binding domain has a structure similar to that of other nucleotide-binding proteins. The GDP ligand is located at the COOH-terminal end of the beta sheet and is linked to the protein via a Mg2+ ion salt bridge. The location of the guanine ring is unusual; the purine ring is located on the outer edge of the domain, not deep within a hydrophobic pocket. The amino acids from Pro10 to Arg44 and from Gly59 to Glu190 have been assigned to the electron density with computer graphic techniques, and the resulting model is consistent with all known biochemical data. An analysis of the structure reveals that four regions of the amino acid sequence that are homologous with the family of ras oncogene proteins, termed p21, are located in the vicinity of the GDP-binding site, and most of the invariant amino acids shared by the proteins interact directly with the GDP ligand.

The complete amino-acid sequence of elongation factor Tu from Escherichia coli

The complete primary structure of elongation factor Tu from Escherichia coli has been elucidated. The protein, which is a mixture of two gene products, consists of a single polypeptide chain of 393 residues. After tryptic digestion of S-carboxymethylated protein, 50 tryptic peptides were isolated covering the complete protein chain. Their alignment was established with overlapping peptides obtained by chemical cleavage with cyanogen bromide and subsequent enzymic subdigestion with Staphylococcus aureus protease, chymotrypsin, elastase and thermolysin. Peptides were sequenced by manual dansyl-Edman and direct Edman degradation procedures. The N-terminal amino acid of EF-Tu is serine and is N-acetylated. The lysine residue at positon 56, in the polypeptide chain is partly methylated. The C-terminal residue is a mixture of serine and glycine, and this was the only heterogeneity found in the EF-Tu preparation used in this study.

Primary structure of elongation factor Tu from Escherichia coli

The amino acid sequence of elongation factor Tu (EF-Tu) from Escherichia coli has been determined. EF-Tu is a single-chain polypeptide composed of 393 amino acids (Mr 43,225 for the species bearing COOH-terminal serine). The NH2-terminal serine is acetylated, and lysine-56 is partially methylated. The sites of facile tryptic cleavage are at arginines 44 and 58 and at lysine-263. The cysteinyl residues associated with aminoacyl-tRNA and guanosine nucleotide binding activities are residues 81 and 137, respectively. The COOH-terminal amino acid is heterogenous in that analyses of the COOH-terminal peptides isolated from different EF-Tu preparations gave position 393 as glycine and serine in ratios (Gly/Ser) ranging from about 0.7 to 3.

Magnesium ion dependent rabbit skeletal muscle myosin guanosine and thioguanosine triphosphatase mechanism and a novel guanosine diphosphatase reaction

The mechanism of the Mg2+-dependent myosin subfragment 1 catalyzed hydrolysis of GTP and 2-amino-6-mercapto-9-beta-ribofuranosylpurine 5'-triphosphate (thioGTP) has been investigated by rapid-reaction techniques. The myosin was isolated from rabbit skeletal muscle. The steady-state intermediate of these reactions consists pre-dominantly of a protein-substrate complex unlike the myosin subfragment 1 ATPase reaction which has a protein-products complex as the principal steady-state component. The mechanism of GTP hydrolysis catalyzed by subfragment 1 has other marked differences from the ATPase mechanism. The second-order rate constant of binding of GTP to subfragment 1 is tenfold greater than that for GDP binding. The dissociation rate constant of GDP from subfragment 1 is 0.06 s-1 compared with the subfragment 1 catalytic center activity for GTP hydrolysis of 0.5 s-1 at pH 8.0 and 20 degrees C. This shows that GDP bound to subfragment 1 forms a complex which is not kinetically competent to be an intermediate of the GTPase mechanism. GDP is hydrolyzed in the presence of subfragment 1 to GMP and Pi. The subfragment 1 GTPase mechanism has a nuber if features in common with that of the elongation factor Tu GTPase of the protein biosynthetic system of Escherichia coli.

Genetic and biochemical characterization of kirromycin resistance mutations in Bacillus subtilis

Spontaneous mutations causing resistance to the EF-Tu-specific antibiotic kirromycin have been isolated and mapped in Bacillus subtilis. Three-factor transductional and transformational crosses have placed the kir locus proximal to ery-1 and distal to strA (rpsL) and several mutations affecting elongation factors EF-G and EF-Tu, in the order: cysA strA [fus-1/ts-6(EF-G)] [ts-5(EF-Tu)] kir ery-1 spcA. Purified EF-Tu from mutant strains is more resistant to kirromycin as measured by in vitro protein synthesis and also shows a more acidic isoelectric point than wild-type EF-Tu. This indicates that the kir locus is the genetic determinant (tuf) for EF-Tu and that there is a single active gene for this enzyme in B. subtilis.

Paracrystalline arrays of protein-synthesis elongation factor Tu. Comparison with polymerized actin

Homogeneous protein synthesis elongation factor Tu from Escherichia coli forms aggregates at high concentrations of ammonium sulfate which have a filamentous appearance in the light microscope. Electron microscopy of negatively stained preparations shows that these aggregates are paracrystalline, including three different forms. On the basis of analyses by optical diffraction, this polymorphism can be explained in terms of three different tubular foldings of the same basic two-dimensional surface lattice. This can be compared with that underlying the structure of actin filaments, thus providing a crucial test of the putative relationship between the elongation factor and actin [Rosenbusch, J. P. et al. (1976) J. Supramol. Struct. 5, 391-396]. The differences between the surface lattices, in conjunction with the negative results of sensitive immunochemical tests for possible cross-reactivities between the two proteins, suggest that any such relationship is very remote.

A comparison of the activities of the products of the two genes for elongation factor Tu

The two species of Elongation Factor Tu coded for by the tufA and tufB genes were synthesized in UV-irradiated E coli infected by transducing phages bearing the separate genes. Both proteins interact similarly with EFTs, GDP, and phe-tRNA. Although the phe-tRNA.EFTu.GMP.PNP complex containing the tufA gene product binds somewhat more tightly to ribosomes, both proteins promote the complete process of binding phe tRNA to ribosomes at similar rates.