The spore-forming bacterium and model prokaryotic genetic system, Bacillus subtilis, is extremely useful in the study of oxidative stress management through proteomic and genome-wide transcriptomic ...analyses, as well as through detailed structural studies of the regulatory factors that govern the oxidative stress response. The factors that sense oxidants and induce expression of protective activities include the PerR and OhrR proteins, which show acute discrimination for their peroxide stimuli, whereas the general stress control factor, the RNA polymerase sigma(B) subunit and the thiol-based sensor Spx, govern the protective response to oxidants under multiple stress conditions. Some specific and some redundant protective mechanisms are mobilized at different stages of the Bacillus developmental cycle to deal with vulnerable cells in stationary-phase conditions and during spore germination and outgrowth. An important unknown is the nature and influence of the low-molecular-weight thiols that mediate the buffering of the redox environment.
Summary
The global regulator, Spx, is under proteolytic control exerted by the adaptor YjbH and ATP‐dependent protease ClpXP in Bacillus subtilis. While YjbH is observed to bind the Spx C‐terminus, ...YjbH shows little affinity for ClpXP, indicating adaptor activity that does not operate by tethering. Chimeric proteins derived from B. subtilis AbrB and the Spx C‐terminus showed that a 28‐residue C‐terminal section of Spx (AbrB28), but not the last 12 or 16 residues (AbrB12, AbrB16), was required for YjbH interaction and for ClpXP proteolysis, although the rate of AbrB28 proteolysis was not affected by YjbH addition. The result suggested that the YjbH‐targeted 28 residue segment of the Spx C‐terminus bears a ClpXP‐recognition element(s) that is hidden in the intact Spx protein. Residue substitutions in the conserved helix α6 of the C‐terminal region generated Spx substrates that were degraded by ClpXP at accelerated rates compared to wild‐type Spx, and showed reduced dependency on the YjbH activity. The residue substitutions also weakened the interaction between Spx and YjbH. The results suggest a model in which YjbH, through interaction with residues of helix α6, exposes the C‐terminus of Spx for recognition and proteolysis by ClpXP.
It is widely acknowledged that the human-associated microbial community influences host physiology, systemic health, disease progression, and even behavior. There is currently an increased interest ...in the oral microbiome, which occupies the entryway to much of what the human initially encounters from the environment. In addition to the dental pathology that results from a dysbiotic microbiome, microbial activity within the oral cavity exerts significant systemic effects. The composition and activity of the oral microbiome is influenced by (1) host-microbial interactions, (2) the emergence of niche-specific microbial "ecotypes," and (3) numerous microbe-microbe interactions, shaping the underlying microbial metabolic landscape. The oral streptococci are central players in the microbial activity ongoing in the oral cavity, due to their abundance and prevalence in the oral environment and the many interspecies interactions in which they participate. Streptococci are major determinants of a healthy homeostatic oral environment. The metabolic activities of oral Streptococci, particularly the metabolism involved in energy generation and regeneration of oxidative resources vary among the species and are important factors in niche-specific adaptations and intra-microbiome interactions. Here we summarize key differences among streptococcal central metabolic networks and species-specific differences in how the key glycolytic intermediates are utilized.
Spx, a member of the ArsC protein family, is a regulatory factor that interacts with RNA polymerase (RNAP). It is highly conserved in Gram-positive bacteria and controls transcription on a ...genome-wide scale in response to oxidative stress. The structural requirements for RNAP interaction and promoter DNA recognition by Spx were examined through mutational analysis. Residues near the CxxC redox disulfide center of Spx functioned in RNAP α subunit interaction and in promoter DNA binding. R60E and C10A mutants were shown previously to confer defects in transcriptional activation, but both were able to interact with RNAP. R92, which is conserved in ArsC-family proteins, is likely involved in redox control of Spx, as the C10A mutation, which blocks disulfide formation, was epistatic to the R92A mutation. The R91A mutation reduced transcriptional activation and repression, suggesting a defect in RNAP interaction, which was confirmed by interaction assays using an epitope-tagged mutant protein. Protein-DNA cross-linking detected contact between RNAP-bound Spx and the AGCA element at −44 that is conserved in Spx-controlled genes. This interaction caused repositioning of the RNAP σA subunit from a −35-like element upstream of the trxB (thioredoxin reductase) promoter to positions −36 and −11 of the core promoter. The study shows that RNAP-bound Spx contacts a conserved upstream promoter sequence element when bound to RNAP.
Spx, an ArsC (arsenate reductase) family member, is a global transcriptional regulator of the microbial stress response and is highly conserved amongst Gram-positive bacteria. Bacillus subtilis Spx ...protein exerts positive and negative control of transcription through its interaction with the C-terminal domain of the RNA polymerase (RNAP) alpha subunit (alphaCTD). Spx activates trxA (thioredoxin) and trxB (thioredoxin reductase) in response to thiol stress, and bears an N-terminal C10XXC13 redox disulfide center that is oxidized in active Spx.
The structure of mutant Spx(C10S) showed a change in the conformation of helix alpha4. Amino acid substitutions R60E and K62E within and adjacent to helix alpha4 conferred defects in Spx-activated transcription but not Spx-dependent repression. Electrophoretic mobility-shift assays showed alphaCTD interaction with trxB promoter DNA, but addition of Spx generated a supershifted complex that was disrupted in the presence of reductant (DTT). Interaction of alphaCTD/Spx complex with promoter DNA required the cis-acting elements -45AGCA-42 and -34AGCG-31 of the trxB promoter. The Spx(G52R) mutant, defective in alphaCTD binding, did not interact with the alphaCTD-trxB complex. Spx(R60E) not only failed to complex with alphaCTD-trxB, but also disrupted alphaCTD-trxB DNA interaction.
The results show that Spx and alphaCTD form a complex that recognizes the promoter DNA of an Spx-controlled gene. A conformational change during oxidation of Spx to the disulfide form likely alters the structure of Spx alpha helix alpha4, which contains residues that function in transcriptional activation and alphaCTD/Spx-promoter interaction. The results suggest that one of these residues, R60 of the alpha4 region of oxidized Spx, functions in alphaCTD/Spx-promoter contact but not in alphaCTD interaction.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Spx protein of Bacillus subtilis represses activator-stimulated transcription by interacting with the C-terminal domain of RNA polymerase (RNAP) α subunit. Its concentration increases in cells ...lacking the ATP-dependent protease, ClpXP, resulting in severe effects on growth and developmental processes. Microarray analysis was undertaken to identify genes that are induced or repressed when Spx interacts with RNAP. The induced genes included those encoding products known to function in maintaining thiol homeostasis. Two genes, thioredoxin (trxA) and thioredoxin reductase (trxB), are transcriptionally induced under conditions of thiol-specific oxidative (disulfide) stress by a mechanism involving Spx-RNAP interaction. Disulfide stress also results in an increase in Spx-dependent transcriptional repression. The increase in Spx activity in cells encountering disulfide stress is due in part to a posttranscriptional mechanism of spx control resulting in an increase in Spx concentration. An spx null mutant and a strain bearing an allele of rpoA that prevents Spx-RNAP interaction show hypersensitivity to disulfide stress. From these results, it is proposed that Spx is an activator that mobilizes the operations necessary to reverse the effects of oxidative damage, but it also serves as a negative regulator that causes the postponement of developmental programs and energy-consuming growth-related functions while the cell copes with the period of stress.
Spx activates transcription initiation in Bacillus subtilis by directly interacting with the C-terminal domain of the RNA polymerase (RNAP) holoenzyme α subunit, which generates a complex that ...recognizes the promoter regions of genes within the Spx regulon. Many Gram-positive species possess multiple paralogs of Spx, suggesting that two paralogous forms of Spx could simultaneously contact RNAP. The composition of Spx/RNAP was examined in vitro using an Spx variant (SpxΔCHA) bearing a 12-amino-acid deletion of the C terminus (SpxΔC) and a hemagglutinin (HA) epitope tag and Spxc-Myc, a full-length Spx with a C-terminal myelocytomatosis oncoprotein (c-Myc) epitope tag. All Spx/RNAP complexes bearing deletion or C-terminal-tagged variants were transcriptionally active in vivo and in vitro. Reaction mixtures containing SpxΔCHA and Spxc-Myc combined with RNAP were applied to either anti-HA or anti-c-Myc affinity columns. Eluted fractions contained RNAP with only one of the epitope-tagged Spx derivatives. The resin-bound RNAP complex bearing a single epitope-tagged Spx derivative was transcriptionally active. In vivo production of SpxΔC and SpxΔCHA followed by anti-HA affinity column chromatography of a cleared lysate resulted in retrieval of Spx/RNAP with only the SpxΔCHA derivative. Binding reactions that combined active Spxc-Myc, inactive Spx(R60E)ΔCHA, and RNAP, when applied to the anti-HA affinity column, yielded only inactive Spx(R60E)ΔCHA/RNAP complexes. The results strongly argue for a model in which a single Spx monomer engages RNAP to generate an active transcriptional complex.
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