A novel A3 group aconitase tolerates oxidation and nitric oxide

The Metabolic Regulation of Amino Acid Synthesis Counteracts Reactive Nitrogen Stress via Aspergillus nidulans Cross-Pathway Control

Nitric oxide (NO) is a natural reactive nitrogen species (RNS) that alters proteins, DNA, and lipids and damages biological activities. Although microorganisms respond to and detoxify NO, the regulation of the cellular metabolic mechanisms that cause cells to tolerate RNS toxicity is not completely understood. We found that the proline and arginine auxotrophic proA5 and argB2 mutants of the fungus Aspergillus nidulans require more arginine and proline for normal growth under RNS stress that starves cells by accumulating fewer amino acids. Fungal transcriptomes indicated that RNS stress upregulates the expression of the biosynthetic genes required for global amino acids, including proline and arginine. A mutant of the gene disruptant, cpcA, which encodes the transcriptional regulation of the cross-pathway control of general amino acid synthesis, did not induce these genes, and cells accumulated fewer amino acids under RNS stress. These results indicated a novel function of CpcA in the cellular response to RNS stress, which is mediated through amino acid starvation and induces the transcription of genes for general amino acid synthesis. Since CpcA also controls organic acid biosynthesis, impaired intermediates of such biosynthesis might starve cells of amino acids. These findings revealed the importance of the mechanism regulating amino acid homeostasis for fungal responses to and survival under RNS stress.

Physiological Roles of Nitrite and Nitric Oxide in Bacteria: Similar Consequences from Distinct Cell Targets, Protection, and Sensing Systems

Nitrite and nitric oxide (NO) are two active nitrogen oxides that display similar biochemical properties, especially when interacting with redox-sensitive proteins (i.e., hemoproteins), an observation serving as the foundation of the notion that the antibacterial effect of nitrite is largely attributed to NO formation. However, a growing body of evidence suggests that they are largely treated as distinct molecules by bacterial cells. Although both nitrite and NO are formed and decomposed by enzymes participating in the transformation of these nitrogen species, NO can also be generated via amino acid metabolism by bacterial NO synthetase and scavenged by flavohemoglobin. NO seemingly interacts with all hemoproteins indiscriminately, whereas nitrite shows high specificity to heme-copper oxidases. Consequently, the homeostasis of redox-sensitive proteins may be responsible for the substantial difference in NO-targets identified to date among different bacteria. In addition, most protective systems against NO damage have no significant role in alleviating inhibitory effects of nitrite. Furthermore, when functioning as signal molecules, nitrite and NO are perceived by completely different sensing systems, through which they are linked to different biological processes.

Arabidopsis thaliana exudates induce growth and proteomic changes in Gluconacetobacter diazotrophicus

Background

Plants interact with a variety of microorganisms during their life cycle, among which beneficial bacteria deserve special attention. Gluconacetobacter diazotrophicus is a beneficial bacterium able to fix nitrogen and promote plant growth. Despite its biotechnological potential, the mechanisms regulating the interaction between G. diazotrophicus and host plants remain unclear.

Methods

We analyzed the response of G. diazotrophicus to cocultivation with Arabidopsis thaliana seedlings. Bacterial growth in response to cocultivation and plant exudates was analyzed. Through comparative proteomic analysis, G. diazotrophicus proteins regulated during cocultivation were investigated. Finally, the role of some up-accumulated proteins in the response G. diazotrophicus to cocultivation was analyzed by reverse genetics, using insertion mutants.

Results

Our results revealed the induction of bacterial growth in response to cocultivation. Comparative proteomic analysis identified 450 bacterial proteins, with 39 up-accumulated, and 12 down-accumulated in response to cocultivation. Among the up-accumulated pathways, the metabolism of pentoses and protein synthesis were highlighted. Proteins potentially relevant to bacterial growth response such as ABC-F-Etta, ClpX, Zwf, MetE, AcnA, IlvC, and AccC were also increased. Reverse genetics analysis, using insertion mutants, revealed that the lack of ABC-F-Etta and AccC proteins severely affects G. diazotrophicus response to cocultivation. Our data demonstrated that specific mechanisms are activated in the bacterial response to plant exudates, indicating the essential role of “ribosomal activity” and “fatty acid biosynthesis” in such a process. This is the first study to demonstrate the participation of EttA and AccC proteins in plant-bacteria interactions, and open new perspectives for understanding the initial steps of such associations.

Reactive nitrogen species (RNS)-resistant microbes: adaptation and medical implications

Nitrosative stress results from an increase in reactive nitrogen species (RNS) within the cell. Though the RNS - nitric oxide (·NO) and peroxynitrite (ONOO-) - play pivotal physiological roles, at elevated concentrations, these moieties can be poisonous to both prokaryotic and eukaryotic cells alike due to their capacity to disrupt a variety of essential biological processes. Numerous microbes are known to adapt to nitrosative stress by elaborating intricate strategies aimed at neutralizing RNS. In this review, we will discuss both the enzymatic systems dedicated to the elimination of RNS as well as the metabolic networks that are tailored to generate RNS-detoxifying metabolites - α-keto-acids. The latter has been demonstrated to nullify RNS via non-enzymatic decarboxylation resulting in the production of a carboxylic acid, many of which are potent signaling molecules. Furthermore, as aerobic energy production is severely impeded during nitrosative stress, alternative ATP-generating modules will be explored. To that end, a holistic understanding of the molecular adaptation to nitrosative stress, reinforces the notion that neutralization of toxicants necessitates significant metabolic reconfiguration to facilitate cell survival. As the alarming rise in antimicrobial resistant pathogens continues unabated, this review will also discuss the potential for developing therapies that target the alternative ATP-generating machinery of bacteria.

Functional characterization of aconitase X as a cis-3-hydroxy-L-proline dehydratase

In the aconitase superfamily, which includes the archetypical aconitase, homoaconitase, and isopropylmalate isomerase, only aconitase X is not functionally annotated. The corresponding gene (LhpI) was often located within the bacterial gene cluster involved in L-hydroxyproline metabolism. Screening of a library of (hydroxy)proline analogues revealed that this protein catalyzes the dehydration of cis-3-hydroxy-L-proline to Δ¹-pyrroline-2-carboxylate. Furthermore, electron paramagnetic resonance and site-directed mutagenic analyses suggests the presence of a mononuclear Fe(III) center, which may be coordinated with one glutamate and two cysteine residues. These properties were significantly different from those of other aconitase members, which catalyze the isomerization of α- to β-hydroxy acids, and have a [4Fe-4S] cluster-binding site composed of three cysteine residues. Bacteria with the LhpI gene could degrade cis-3-hydroxy-L-proline as the sole carbon source, and LhpI transcription was up-regulated not only by cis-3-hydroxy-L-proline, but also by several isomeric 3- and 4-hydroxyprolines.

SILAC-based proteomic analysis reveals that salidroside antagonizes cobalt chloride-induced hypoxic effects by restoring the tricarboxylic acid cycle in cardiomyocytes

Hypoxic status alters the energy metabolism and induces cell injury in cardiomyocytes, and it further triggers the occurrence and development of cardiovascular diseases. Our previous studies have shown that salidroside (SAL) exhibits anti-hypoxic activity. However, the mechanisms remain obscure. In the present study, we successfully screened 92 different expression proteins in CoCl2-induced hypoxic conditions, 106 different expression proteins in the SAL-mediated anti-hypoxic group were compared with the hypoxic group using quantitative proteomics strategy, respectively. We confirmed that SAL showed a positive protective function involving the acetyl-CoA metabolic, tricarboxylic acid (TCA) cycle using bioinformatics analysis. We also demonstrated that SAL plays a critical role in restoring the TCA cycle and in protecting cardiomyocytes from oxidative injury via up-regulation expressions of PDHE1-B, ACO2, SUCLG1, SUCLG2 and down-regulation of MDH2. SAL also inhibited H9c2 cell apoptosis by inhibiting the activation of pro-apoptotic molecules caspase 3 and caspase 9 as well as activation of the anti-apoptotic molecular Bcl-2. Additionally, SAL also improved mitochondrial membrane potential (ΔΨm), reduced reactive oxygen species (ROS) and intercellular Ca(2+) concentration ([Ca(2+)]i) accumulation and inhibited the excessive consumption of ATP in H9c2 cells.