ATP Synthesis by Oxidative Phosphorylation

Preharvest ABA treatment reduces browning of watercore apple fruit by regulating antioxidant and energy metabolism

Watercore is a physiological disorder that occurs before harvest and can result in internal browning of apple fruit during storage, ultimately reducing its economic value. Browning more easily occurred in the position of watercore and its surrounding area compared with healthy tissue. Preharvest Abscisic acid (ABA) treatment (200 mg∙L-1) affected respiratory metabolism, enhanced antioxidant capacity, reduced enzymatic browning, and alleviated energy deficits, thus decreasing browning and delaying quality deterioration. First, ABA was found to lower the respiration rate and reduce the depletion of soluble sugars and organic acids by down-regulating the expression of genes MdSDH2-2, MdCOX6A, MdPDH, and decreasing the activity of succinate dehydrogenase, cytochrome c oxidase, pyruvate dehydrogenase, and NAD-malic enzyme, while increasing the activity of NAD-malate dehydrogenase and phosphoenolpyruvate carboxylase. Second, ABA effectively decreased the accumulation of reactive oxygen species and maintained cell membrane integrity by enhancing the activity of catalase, superoxide dismutase, and peroxidase. In addition, ABA treatment maintained mitochondrial function, as indicated by increased ATP content, energy charge, NADH and NADPH concentrations, NADH/NAD and NADPH/NADP ratios, and expression levels of MdACC3 and MdUCPb. Furthermore, ABA treatment promoted the accumulation of phenolic compounds and flavonoid, which was associated with increased activity of phenylalanine ammonia-lyase and the inhibition of polyphenol oxidase activity, leading to increased antioxidant capacity and reduced browning. These results suggest that ABA treatment could display a better performance to retard browning in watercore apple fruit by modulating physicochemical metabolisms.

Molecular Signatures Integral to Natural Reprogramming in the Pigment Epithelium Cells after Retinal Detachment in Pleurodeles waltl

The reprogramming of retinal pigment epithelium (RPE) cells into retinal cells (transdifferentiation) lies in the bases of retinal regeneration in several Urodela. The identification of the key genes involved in this process helps with looking for approaches to the prevention and treatment of RPE-related degenerative diseases of the human retina. The purpose of our study was to examine the transcriptome changes at initial stages of RPE cell reprogramming in adult newt Pleurodeles waltl. RPE was isolated from the eye samples of day 0, 4, and 7 after experimental surgical detachment of the neural retina and was used for a de novo transcriptome assembly through the RNA-Seq method. A total of 1019 transcripts corresponding to the differently expressed genes have been revealed in silico: the 83 increased the expression at an early stage, and 168 increased the expression at a late stage of RPE reprogramming. We have identified up-regulation of classical early response genes, chaperones and co-chaperones, genes involved in the regulation of protein biosynthesis, suppressors of oncogenes, and EMT-related genes. We revealed the growth in the proportion of down-regulated ribosomal and translation-associated genes. Our findings contribute to revealing the molecular mechanism of RPE reprogramming in Urodela.

Complex and flexible catabolism in Aromatoleum aromaticum pCyN1

Large quantities of organic matter are continuously deposited, and (a)biotic gradients intersect in the soil-rhizosphere, where biodegradation contributes to the global cycles of elements. The betaproteobacterial genus Aromatoleum comprises cosmopolitan, facultative denitrifying degradation specialists. A. aromaticum pCyN1 stands out for anaerobically decomposing plant-derived monoterpenes in addition to monoaromatic hydrocarbons, polar aromatics and aliphatics. The catabolic network's structure and flexibility in A. aromaticum pCyN1 was studied across 34 growth conditions by superimposing proteome profiles onto the manually annotated 4.37 Mbp genome. Strain pCyN1 employs three fundamentally different enzymes for C-H-bond cleavage at the methyl groups of p-cymene/4-ethyltoluene, toluene and p-cresol, respectively. Regulation of degradation modules displayed substrate specificities ranging from narrow (toluene and cyclohexane carboxylate) via medium-wide (one module shared by p-cymene, 4-ethyltoluene, α-phellandrene, α-terpinene, γ-terpinene and limonene) to broad (central benzoyl-CoA pathway serving 16 aromatic substrates). Remarkably, three variants of ATP-dependent (class I) benzoyl-CoA reductase and four different β-oxidation routes establish a degradation hub that accommodates the substrate diversity. The respiratory system displayed several conspicuous profiles, e.g., the presence of nitrous oxide reductase under oxic and of low-affinity oxidase under anoxic conditions. Overall, nutritional versatility in conjunction with network regulation endow A. aromaticum pCyN1 with broad adaptability. This article is protected by copyright. All rights reserved.

Regulation and Functional Complexity of the Chlorophyll-Binding Protein IsiA

As the oldest known lineage of oxygen-releasing photosynthetic organisms, cyanobacteria play the key roles in helping shaping the ecology of Earth. Iron is an ideal transition metal for redox reactions in biological systems. Cyanobacteria frequently encounter iron deficiency due to the environmental oxidation of ferrous ions to ferric ions, which are highly insoluble at physiological pH. A series of responses, including architectural changes to the photosynthetic membranes, allow cyanobacteria to withstand this condition and maintain photosynthesis. Iron-stress-induced protein A (IsiA) is homologous to the cyanobacterial chlorophyll (Chl)-binding protein, photosystem II core antenna protein CP43. IsiA is the major Chl-containing protein in iron-starved cyanobacteria, binding up to 50% of the Chl in these cells, and this Chl can be released from IsiA for the reconstruction of photosystems during the recovery from iron limitation. The pigment–protein complex (CPVI-4) encoded by isiA was identified and found to be expressed under iron-deficient conditions nearly 30years ago. However, its precise function is unknown, partially due to its complex regulation; isiA expression is induced by various types of stresses and abnormal physiological states besides iron deficiency. Furthermore, IsiA forms a range of complexes that perform different functions. In this article, we describe progress in understanding the regulation and functions of IsiA based on laboratory research using model cyanobacteria.

Interactions between subunits a and b in the rotary ATP synthase as determined by cross-linking

The interaction of the membrane traversing stator subunits a and b of the rotary ATP synthase was probed by substitution of a single Cys into each subunit with subsequent Cu(2+) catalyzed cross-linking. Extensive interaction between the transmembrane (TM) region of one b subunit and TM2 of subunit a was indicated by cross-linking with 6 Cys pairs introduced into these regions. Additional disulfide cross-linking was observed between the N-terminus of subunit b and the periplasmic loop connecting TM4 and TM5 of subunit a. Finally, benzophenone-4-maleimide derivatized Cys in the 2-3 periplasmic loop of subunit a were shown to cross-link with the periplasmic N-terminal region of subunit b. These experiments help to define the juxtaposition of subunits b and a in the ATP synthase.

Conformational changes in the Escherichia coli ATP synthase b-dimer upon binding to F(1)-ATPase

Conformational changes within the subunit b-dimer of the E. coli ATP synthase occur upon binding to the F(1) sector. ESR spectra of spin-labeled b at room temperature indicated a pivotal point in the b-structure at residue 62. Spectra of frozen b +/- F(1) and calculated interspin distances suggested that where contact between b (2) and F(1) occurs (above about residue 80), the structure of the dimer changes minimally. Between b-residues 33 and 64 inter-subunit distances in the F(1)-bound b-dimer were found to be too large to accommodate tightly coiled coil packing and therefore suggest a dissociation and disengagement of the dimer upon F(1)-binding. Mechanistic implications of this "bubble" formation in the tether domain of ATP synthase b ( 2 ) are discussed.

Subunit b-dimer of the Escherichia coli ATP synthase can form left-handed coiled-coils

One remaining challenge to our understanding of the ATP synthase concerns the dimeric coiled-coil stator subunit b of bacterial synthases. The subunit b-dimer has been implicated in important protein interactions that appear necessary for energy conservation and that may be instrumental in energy conservation during rotary catalysis by the synthase. Understanding the stator structure and its interactions with the rest of the enzyme is crucial to the understanding of the overall catalytic mechanism. Controversy exists on whether subunit b adopts a classic left-handed or a presumed right-handed dimeric coiled-coil and whether or not staggered pairing between nonhomologous residues in the homodimer is required for intersubunit packing. In this study we generated molecular models of the Escherichia coli subunit b-dimer that were based on the well-established heptad-repeat packing exhibited by left-handed, dimeric coiled-coils by employing simulated annealing protocols with structural restraints collected from known structures. In addition, we attempted to create hypothetical right-handed coiled-coil models and left- and right-handed models with staggered packing in the coiled-coil domains. Our analyses suggest that the available structural and biochemical evidence for subunit b can be accommodated by classic left-handed, dimeric coiled-coil quaternary structures.