Project description:Lysine acetylation in proteins has recently been globally identified in bacteria and eukaryotes. Even though acetylproteins are known to be involved in various cellular processes, its physiological significance has not yet been resolved. Using a proteomics approach in combination with immunoprecipitation, we identified 197 lysine acetylation sites and 4 N-terminal acetylation sites from 128 proteins in Thermus thermophilus HB8, an extremely thermophilic eubacterium. Our analyses revealed that identified acetylproteins are well conserved across all three domains of life and are mainly involved in central metabolism and translation. To further characterize functional significance, we successfully mapped 113 acetylation sites on their 54 authentic and 59 homologous protein structures. The acetylation in the majority of proteins occurs in ordered structures and the sites were situated near the negatively charged glutamic acid residues. In addition, 59 of 103 acetylations were located within considerable distance that can disrupt electrostatic interactions and hydrogen bonding networks on protein surface, demonstrating the physiological significances of the acetylations. Finally, we further summarized 22 critical acetylation sites related to Schiff-base formation, ligand binding, protein-RNA and protein-protein interaction. The structural information of 113 acetylation sites provides new molecular insight into the role of lysine acetylation in the proteins. Data processing, bioinformatics: MS and MS/MS spectral data were processed by DataAnalysis 4.0 software (Bruker Daltonics). The peak lists containing m/z of precursor ions with that of their product ions were generated by the Compound-Auto MS(n) option of the DataAnalysis 4.0 software. Fifty non-deconvoluted peaks over the intensity threshold 150 and charge deconvoluted peaks in each MS/MS spectrum were exported into peak list files. The spectra were searched against our in-house T. thermophilus HB8 database, containing 2,238 protein sequence entries from the complete genome sequence using Mascot search engine (version 2.3; Matrix Science, London, UK). The acetylated peptides were identified using a mass tolerance of ±0.05 Da for precursor and product ions and allowed a maximum of 6 mis-cleavage sites for trypsin. The carbamidomethylation of cysteine was selected as a fixed modification. The oxidation of methionine, deamidation of asparagine and glutamine, acetylation of lysine and acetylation of protein N-terminus were selected as variable modifications. Only peptides in the confidence range of 99% probability (P value < 0.01) in Mascot ion score were assumed to be identified.
Project description:Ribosomal protein L11 and its associated binding site on 23S rRNA together comprise one of the principle components that mediate interactions of translation factors with the ribosome. This site is also the target of the antibiotic thiostrepton, which has been proposed to act by preventing important structural transitions that occur in this region of the ribosome during protein synthesis. Here, we describe the isolation and characterization of spontaneous thiostrepton-resistant mutants of the extreme thermophile, Thermus thermophilus. All mutations were found at conserved positions in the flexible N-terminal domain of L11 or at conserved positions in the L11-binding site of 23S rRNA. A number of the mutant ribosomes were affected in in vitro EF-G-dependent GTP hydrolysis but all showed resistance to thiostrepton at levels ranging from high to moderate. Structure probing revealed that some of the mutations in L11 result in enhanced reactivity of adjacent rRNA bases to chemical probes, suggesting a more open conformation of this region. These data suggest that increased flexibility of the factor binding site results in resistance to thiostrepton by counteracting the conformation-stabilizing effect of the antibiotic.
Project description:Laboratory-adapted strains of Thermus spp. have been shown to require oxygen for growth, including the model strains T. thermophilus HB27 and HB8. In contrast, many isolates of this species that have not been intensively grown under laboratory conditions keep the capability to grow anaerobically with one or more electron acceptors. The use of nitrogen oxides, especially nitrate, as electron acceptors is one of the most widespread capabilities among these facultative strains. In this process, nitrate is reduced to nitrite by a reductase (Nar) that also functions as electron transporter toward nitrite and nitric oxide reductases when nitrate is scarce, effectively replacing respiratory complex III. In many T. thermophilus denitrificant strains, most electrons for Nar are provided by a new class of NADH dehydrogenase (Nrc). The ability to reduce nitrite to NO and subsequently to N2O by the corresponding Nir and Nor reductases is also strain specific. The genes encoding the capabilities for nitrate (nar) and nitrite (nir and nor) respiration are easily transferred between T. thermophilus strains by natural competence or by a conjugation-like process and may be easily lost upon continuous growth under aerobic conditions. The reason for this instability is apparently related to the fact that these metabolic capabilities are encoded in gene cluster islands, which are delimited by insertion sequences and integrated within highly variable regions of easily transferable extrachromosomal elements. Together with the chromosomal genes, these plasmid-associated genetic islands constitute the extended pangenome of T. thermophilus that provides this species with an enhanced capability to adapt to changing environments.
Project description:In order to observe the heat-shock response of extremely thermohilic bacterium T. thermophilus HB8 strain, we analyzed the altered expression profile of the total mRNA in T. thermophilus HB8 wild-type strain after the growth temperature was shifted from 70°C to 80°C for 30 min.
Project description:The evolutionary potential of a thermostable alpha-galactosidase, with regard to improved catalytic activity at high temperatures, was investigated by employing an in vivo selection system based on thermophilic bacteria. For this purpose, hybrid alpha-galactosidase genes of agaA and agaB from Bacillus stearothermophilus KVE39, designated agaA1 and agaB1, were cloned into an autonomously replicating Thermus vector and introduced into Thermus thermophilus OF1053GD (DeltaagaT) by transformation. This selector strain is unable to metabolize melibiose (alpha-galactoside) without recombinant alpha-galactosidases, because the native alpha-galactosidase gene, agaT, has been deleted. Growth conditions were established under which the strain was able to utilize melibiose as a single carbohydrate source when harboring a plasmid-encoded agaA1 gene but unable when harboring a plasmid-encoded agaB1 gene. With incubation of the agaB1 plasmid-harboring strain under selective pressure at a restrictive temperature (67 degrees C) in a minimal melibiose medium, spontaneous mutants as well as N-methyl-N'-nitro-N-nitrosoguanidine-induced mutants able to grow on the selective medium were isolated. The mutant alpha-galactosidase genes were amplified by PCR, cloned in Escherichia coli, and sequenced. A single-base substitution that replaces glutamic acid residue 355 with glycine or valine was found in the mutant agaB1 genes. The mutant enzymes displayed the optimum hydrolyzing activity at higher temperatures together with improved catalytic capacity compared to the wild-type enzyme and furthermore showed an enhanced thermal stability. To our knowledge, this is the first report of an in vivo evolution of glycoside-hydrolyzing enzyme and selection within a thermophilic host cell.
Project description:The Thermus thermophilus succinate:quinone reductase (SQR), serving as the respiratory complex II, has been homologously produced under the control of a constitutive promoter and subsequently purified. The detailed biochemical characterization of the resulting wild type (wt-rcII) and His-tagged (rcII-His(8)-SdhB and rcII-SdhB-His(6)) complex II variants showed the same properties as the native enzyme with respect to the subunit composition, redox cofactor content and sensitivity to the inhibitors malonate, oxaloacetate, 3-nitropropionic acid and nonyl-4-hydroxyquinoline-N-oxide (NQNO). The position of the His-tag determined whether the enzyme retained its native trimeric conformation or whether it was present in a monomeric form. Only the trimer exhibited positive cooperativity at high temperatures. The EPR signal of the [2Fe-2S] cluster was sensitive to the presence of substrate and showed an increased rhombicity in the presence of succinate in the native and in all recombinant forms of the enzyme. The detailed analysis of the shape of this signal as a function of pH, substrate concentration and in the presence of various inhibitors and quinones is presented, leading to a model for the molecular mechanism that underlies the influence of succinate on the rhombicity of the EPR signal of the proximal iron-sulfur cluster.