The Assembly of Super-Complexes in the Plant Chloroplast

Increasing evidence has revealed that the enzymes of several biological pathways assemble into larger supramolecular structures called super-complexes. Indeed, those such as association of the mitochondrial respiratory chain complexes play an essential role in respiratory activity and promote metabolic fitness. Dynamically assembled super-complexes are able to alternate between participating in large complexes and existing in a free state. However, the functional significance of the super-complexes is not entirely clear. It has been proposed that the organization of respiratory enzymes into super-complexes could reduce oxidative damage and increase metabolism efficiency. There are several protein complexes that have been revealed in the plant chloroplast, yet little research has been focused on the formation of super-complexes in this organelle. The photosystem I and light-harvesting complex I super-complex’s structure suggests that energy absorbed by light-harvesting complex I could be efficiently transferred to the PSI core by avoiding concentration quenching. Here, we will discuss in detail core complexes of photosystem I and II, the chloroplast ATPase the chloroplast electron transport chain, the Calvin–Benson cycle and a plastid localized purinosome. In addition, we will also describe the methods to identify these complexes.

The subcompartmented oxphosomic model of the phosphorylating system organization in mitochondria

The oxidative phosphorylation (OXPHOS) system of mitochondria supports all the vitally important energyconsuming processes in eukaryotic cells, providing them with energy in the form of ATP. OXPHOS enzymes (complexes I–V) are located in the inner mitochondrial membrane, mainly in the cristae subcompartment. At present, there is a large body of data evidencing that the respiratory complexes I, III2 and IV under in vivo conditions can physically interact with each other in diverse stoichiometry, thereby forming supercomplexes. Despite active accumulation of knowledge about the structure of the main supercomplexes of the OXPHOS system, its physical and functional organization in vivo remains unclear. Contemporary models of the OXPHOS system’s organization in the inner membrane of mitochondria are contradictory and presume the existence of either highly organized respiratory strings, or, by contrast, a set of randomly dispersed respiratory supercomplexes and complexes. Furthermore, it is assumed that ATP-synthase (complex V) does not form associations with respiratory enzymes and operates autonomously. Our latest data obtained on mitochondria of etiolated shoots of pea evidence the possibility of physical association between the respiratory supercomplexes and dimeric ATP-synthase. These data have allowed us to reconsider the contemporary concept of the phosphorylation system organization and propose a new subcompartmented oxphosomic model. According to this model, a substantial number of the OXPHOS complexes form oxphosomes, which in a definite stoichiometry include complexes I–V and are located predominantly in the cristae subcompartment of mitochondria in the form of highly organized strings or patches. These suprastructures represent “mini-factories” for ATP production. It is assumed that such an organization (1) contributes to increasing the efficiency of the OXPHOS system operation, (2) involves new levels of activity regulation, and (3) may determine the inner membrane morphology to some extent. The review discusses the proposed model in detail. For a better understanding of the matter, the history of development of concepts concerning the OXPHOS organization with the emphasis on recent contemporary models is briefly considered. The principal experimental data accumulated over the past 40 years, which confirm the validity of the oxphosomic hypothesis, are also provided.

Hypothetical protein gene 1038 contributes to colistin resistance in Aeromonas hydrophila

Inhibition of vital respiratory enzymes, such as NADH: ubiquinone oxidoreductase (complex I), type II NADH-quinone oxidoreductases (NDH-2), and malate: quinone oxidoreductase, in the inner membrane, is a secondary antibacterial mechanism of colistin (1–3). However, colistin resistance mechanisms associated with this secondary mode of action of colistin have rarely been reported. Herein, we confirmed that the hypothetical protein gene 1038 was associated with colistin resistance in Aeromonas hydrophila by reducing antibiotic function in the inner membrane, providing novel knowledge on the generation of colistin resistance.

Lipopolysaccharide Transport System Links Physiological Roles of σ E and ArcA in the Cell Envelope Biogenesis in Shewanella oneidensis

Arc is a well-characterized global regulatory system that modulates cellular respiration by responding to changes in the redox status in bacterial cells. In addition to regulating expression of respiratory enzymes, Shewanella oneidensis Arc also plays a critical role in cell envelope integrity.

Comparative study on the influence of silicon and selenium to mitigate arsenic induced stress by modulating TCA cycle, GABA and polyamine synthesis in rice seedlings

Arsenic contamination of groundwater is a major concern for its use as drinking water and crop irrigation in many regions of the world. Arsenic is absorbed by rice plants from arsenic contaminated water during irrigation, hampers growth and agricultural productivity. The aim of the study was to mitigate the activity of TCA cycle, synthesis of γ-aminobutyric acid (GABA) and polyamines (PAs) in rice (Oryza sativa L. cv. MTU-1010) seedlings under arsenate (As-V) stress [25 µM, 50 µM and 75 µM] by silicon (Si) [2 mM] and selenium (Se) [5 µM] amendments, and to investigate which chemical was more potential to combat this threat. As(V) application decreased the activities of tested respiratory enzymes while the levels of organic acids (OAs) were increased in the test seedlings. Co-application of Si and As(V) increased the activities of respiratory enzymes, consequently further increased accumulation of OAs that were more than Se with As(V) application in the test seedlings. GABA accumulation along with the activities of its regulatory enzymes were enhanced under As(V) stress. During joint application of Si and As(V) and Se and As(V) said parameters were decreased showing defensive role of these chemicals to resist As(V) toxicity in rice but amendment of Si was more potential than Se amendment resulted reduction of stress induced damage in the test seedlings. PAs trigger tolerance mechanism against stress in plants. PAs viz., Putrescine, spermidine and spermine were synthesized more during Si and Se amendments in As(V) contaminated rice seedlings to combat the effect of stress. Si amendment substantially modulated the toxic effects caused by As(V) over Se amendment in As(V) challenged test seedlings. Thus in future application Si enriched fertilizer will be beneficial than application of Se enriched fertilizer to grow rice plants with normal vigor in arsenic contaminated soil.

Bacterial Hsp90 Facilitates the Degradation of Aggregation-Prone Hsp70–Hsp40 Substrates

In eukaryotes, the 90-kDa heat shock proteins (Hsp90s) are profusely studied chaperones that, together with 70-kDa heat shock proteins (Hsp70s), control protein homeostasis. In bacteria, however, the function of Hsp90 (HtpG) and its collaboration with Hsp70 (DnaK) remains poorly characterized. To uncover physiological processes that depend on HtpG and DnaK, we performed comparative quantitative proteomic analyses of insoluble and total protein fractions from unstressed wild-type (WT) Escherichia coli and from knockout mutants ΔdnaKdnaJ (ΔKJ), ΔhtpG (ΔG), and ΔdnaKdnaJΔhtpG (ΔKJG). Whereas the ΔG mutant showed no detectable proteomic differences with wild-type, ΔKJ expressed more chaperones, proteases and ribosomes and expressed dramatically less metabolic and respiratory enzymes. Unexpectedly, we found that the triple mutant ΔKJG showed higher levels of metabolic and respiratory enzymes than ΔKJ, suggesting that bacterial Hsp90 mediates the degradation of aggregation-prone Hsp70–Hsp40 substrates. Further in vivo experiments suggest that such Hsp90-mediated degradation possibly occurs through the HslUV protease.

Effect of Ozonation Process on the Energy Metabolism in Raspberry Fruit During Storage at Room Temperature

The major aim of this research was to investigate the effect of ozone treatment on the energy metabolism in raspberry fruit during storage at room temperature. Raspberries were ozonated with an ozone concentration of 8–10 mg L−1, for 30 min, every 12 h of storage at room temperature for 72 h. The results indicated that ozone treatment significantly enhanced the activities of mitochondrial respiratory enzymes, such as succinate dehydrogenase, cytochrome C oxidase, and H+-ATPase, which contributed to maintain the high level of ATP and energy charge in fruit during storage. Moreover, the energy metabolism in mitochondria was closely correlated with the antioxidant potential of raspberry fruit. This study has given an experimental evidence that ozonation procedure in proposed process conditions significantly affects the mitochondrial respiratory system leading to maintain the high quality of the fruit over a long period of storage at room temperature.

Protection of Eggplant Seed Germination from the Inhibitory Effect of o-Cresol by Bioaugmentation of Soil with Pseudomonas monteilii Strain

Bulk production and widespread end use of cresol isomers in various industrial processes result in their ubiquitous presence in the environment. Cresols are highly toxic to both fauna and flora and are included in the list of priority pollutants. This study presents the effect of o-cresol on germination of 10 different vegetable crop seeds as tested by the standard Filter Paper Method. The seeds of eggplant and long-podded cowpea were found to be highly sensitive. The most sensitive eggplant seeds were subjected to further studies in soil. Germination percentage and the seedling vigor were drastically reduced in the presence of o-cresol even at a concentration as low as 50 mg kg−1 soil. A number of abnormalities in the seedlings such as stunted root and shoot growth, non-emergence of primary leaves, and negative geotropic growth were observed. Standard 2, 3, 5-tetrazoliumtrichloride test showed marked reduction in the viability of eggplant seeds proportionate to the concentration of o-cresol (0 through 200 mg L−1) they were exposed to, which reached zero at 175 mg o-cresol L−1, indicating the inhibition of the respiratory enzymes of the seeds. Contrary to earlier reports on the effect of phenolics on the hydrolytic enzymes of germinating seeds, in the present case an enhanced activity of amylase was observed in the presence of o-cresol (50 and 150 mg kg−1 soil), whereas the protease activity was partially inhibited at higher concentration. The inhibition of seed germination by o-cresol was revoked by bioaugmentation of the soil with the cresol-degrading Pseudomonas monteilii S-CSR-0014 (2.3 x 108 CFU g−1 wet soil) enabling normal seed germination and seedling growth. The inoculated bacterium degraded 50 and 150 mg o-cresol kg−1 soil efficiently, with concomitant growth. It can be concluded that by bacterial bioaugmentation of o-cresol-contaminated soils the inhibition of germination of crop seeds could be eliminated effectively enabling healthy seedling growth.

Reversal effect of Solanum dasyphyllum against rotenone-induced neurotoxicity

We earlier reported the protective effect of Solanum dasyphyllum against cyanide neurotoxicity. In furtherance to this, we investigated the protective effect of S. dasyphyllum against rotenone, a chemical toxin that causes brain-related diseases. Mitochondria fraction obtained from the brain of male Wistar rats was incubated with various solvents (hexane, dichloromethane, ethylacetate, and methanol) extracts of S. dasyphyllum before rotenone exposure. Mitochondria respiratory enzymes (MRE) were evaluated along with markers of oxidative stress. The inhibition of MRE by rotenone was reversed by treatment with various fractions of S. dasyphyllum. The oxidative stress induced by rotenone was also reversed by fractions of S. dasyphyllum. In addition, the ethylacetate fraction of S. dasyphyllum was most potent against rotenone-induced neurotoxicity. In conclusion, S. dasyphyllum is rich in active phytochemicals that can prevent some neurotoxic effects of rotenone exposure. Further study can be done in an in vivo model to substantiate our results.