Precursor for elongation factor Tu from Escherichia coli

Analysis of thePasteurella multocida outer membrane sub-proteome and its response to thein vivo environment of the natural host

This study describes the identification of outer membrane proteins (OMPs) of the bacterial pathogen Pasteurella multocida and an analysis of how the expression of these proteins changes during infection of the natural host. We analysed the sarcosine-insoluble membrane fractions, which are highly enriched for OMPs, from bacteria grown under a range of conditions. Initially, the OMP-containing fractions were resolved by 2-DE and the proteins identified by MALDI-TOF MS. In addition, the OMP-containing fractions were separated by 1-D SDS-PAGE and protein identifications were made using nano LC MS/MS. Using these two methods a total of 35 proteins was identified from samples obtained from organisms grown in rich culture medium. Six of the proteins were identified only by 2-DE MALDI-TOF MS, whilst 17 proteins were identified only by 1-D LC MS/MS. We then analysed the OMPs from P. multocida which had been isolated from the bloodstream of infected chickens (a natural host) or grown in iron-depleted medium. Three proteins were found to be significantly up-regulated during growth in vivo and one of these (Pm0803) was also up-regulated during growth in iron-depleted medium. After bioinformatic analysis of the protein matches, it was predicted that over one third of the combined OMPs predicted by the bioinformatics sub-cellular localisation tools PSORTB and Proteome Analyst, had been identified during this study. This is the first comprehensive proteomic analysis of the P. multocida outer membrane and the first proteomic analysis of how a bacterial pathogen modifies its outer membrane proteome during infection.

Structural constraints on the complex of elongation factor Tu with magnesium guanosine diphosphate from rotational-echo double-resonance NMR

Rotational-echo, double-resonance (REDOR) NMR measurements of 31P-15N dipolar couplings have been made on a complex of Mg guanosine diphosphate (MgGDP) with uniformly 15N-labeled elongation factor Tu. The complex was embedded in a lyophilized buffer glass. The observed 15N REDOR dephasing by 31P was accounted for quantitatively by distances from 15N of Gly23 and Lys24 to P alpha and P beta of MgGDP as determined by X-ray crystallography of MgGDP complex formed using an elongation factor Tu that is missing a 15 residue loop in the vicinity of the binding site.

Correlation between temperature-dependent cytoplasmic solubility and periplasmic export of a heterologous protein in Escherichia coli

The coding sequence of mature human tumor necrosis factor (hTNF) was fused to the signal-encoding sequence of beta-lactamase (Bla). Mature hTNF was exported into the periplasm of Escherichia coli. A mutant hTNF [Van Ostade et al., FEBS Lett. 238 (1988) 347-352], which displays a temperature-dependent intracellular solubility, was fused to the same Bla signal-encoding sequence. We found that the export competence of the mutated hTNF was correlated with the intracellular solubility of this protein. We postulate that the secretion proficiency of eukaryotic proteins, when fused to a prokaryotic export signal, depends on the ability of the mature protein to readily fold into a soluble conformation.

Control of the tRNA-tufB operon in Escherichia coli. 3. Feedback inhibition of tufB expression by an EF-Tu with a deletion in the guanine-nucleotide-binding domain

The expression of tufB, one of the two EF-Tu-encoding genes in Escherichia coli, is under autogenous control. Feedback inhibition of tufB expression by plasmid-borne EF-Tu has been used to answer the question of whether or not the integrity of the guanine-nucleotide-binding domain of EF-Tu is required for the autoregulatory role of the factor protein. We show that a large deletion of tufB, causing the elimination of an 81-amino-acid segment from the plasmid-borne EF-Tu, does not abolish tufB repression. We conclude that the autoregulation of the cellular EF-Tu level is not dependent on an intact guanine-nucleotide-binding domain and does not require binding of GTP to EF-Tu. The repressor activity of the deletion derivative of EF-Tu can be measured despite a rapid disappearance of the (altered) mutant protein from the soluble cytoplasmic fraction of the cell. Degradation and assembly in larger complexes are responsible for this disappearance.

Overproduction of the proFhuA outer membrane receptor protein of Escherichia coli K-12: isolation, properties, and immunocytochemical localization at the inner side of the cytoplasmic membrane

The fhu operon of Escherichia coli K-12 comprises four genes, termed fhuA,C,D,B, which are involved in the uptake of iron-hydroxamate compounds. The fhuA gene encodes the outer membrane receptor protein. Cells that contained three copies of the fhuACD fragment on the thermoamplifiable plasmid pHK232 accumulated at 37 degrees C large amounts of the proFhuA protein. Most of the overproduced proFhuA protein was not translocated into the outer membrane but instead precipitated at the cytoplasmic side of the inner membrane, presumably at the sites of synthesis. Despite inhibition of export proFhuA synthesis continued. The precipitate formed was sedimented by centrifugation at 8,000 x g. The proFhuA protein could be solubilized in 1% sodium dodecyl sulfate. Replacement of sodium dodecyl sulfate by Triton X-100 resulted in a proFhuA protein which exhibited 10% of the phage T5 binding activity of renatured mature FhuA protein. Binding of the phage T5 was inhibited by the FhuA-specific ligands ferrichrome, albomycin and colicin M. Limited proteolysis of the isolated pro- and mature form of the FhuA protein with trypsin yielded similar oligopeptide patterns. Addition of ferrichrome affected trypsin cleavage of both proteins in the same way. The common proteolytic intermediates together with phage inactivation indicate a similar conformation of the pro- and mature form.