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Concept: ATP synthase

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Aging is a major driving force underlying dementia, such as that caused by Alzheimer’s disease (AD). While the idea of targeting aging as a therapeutic strategy is not new, it remains unclear how closely aging and age-associated diseases are coupled at the molecular level. Here, we discover a novel molecular link between aging and dementia through the identification of the molecular target for the AD drug candidate J147. J147 was developed using a series of phenotypic screening assays mimicking disease toxicities associated with the aging brain. We have previously demonstrated the therapeutic efficacy of J147 in several mouse models of AD. Here, we identify the mitochondrial α-F1 -ATP synthase (ATP5A) as a target for J147. By targeting ATP synthase, J147 causes an increase in intracellular calcium leading to sustained calcium/calmodulin-dependent protein kinase kinase β (CAMKK2)-dependent activation of the AMPK/mTOR pathway, a canonical longevity mechanism. Accordingly, modulation of mitochondrial processes by J147 prevents age-associated drift of the hippocampal transcriptome and plasma metabolome in mice and extends lifespan in drosophila. Our results link aging and age-associated dementia through ATP synthase, a molecular drug target that can potentially be exploited for the suppression of both. These findings demonstrate that novel screens for new AD drug candidates identify compounds that act on established aging pathways, suggesting an unexpectedly close molecular relationship between the two.

Concepts: Alzheimer's disease, Cancer, Molecular biology, Adenosine triphosphate, Mitochondrion, Aging, Aging-associated diseases, ATP synthase

29

The machinery that conducts the light-driven reactions of oxygenic photosynthesis is hosted within specialized paired membranes called thylakoids. In higher plants, the thylakoids are segregated into two morphological and functional domains called grana and stroma lamellae. A large fraction of the luminal volume of the granal thylakoids is occupied by the oxygen-evolving complex of photosystem II. Electron microscopy data we obtained on dark- and light-adapted Arabidopsis thylakoids indicate that the granal thylakoid lumen significantly expands in the light. Models generated for the organization of the oxygen-evolving complex within the granal lumen predict that the light-induced expansion greatly alleviates restrictions imposed on protein diffusion in this compartment in the dark. Experiments monitoring the redox kinetics of the luminal electron carrier plastocyanin support this prediction. The impact of the increase in protein mobility within the granal luminal compartment in the light on photosynthetic electron transport rates and processes associated with the repair of photodamaged photosystem II complexes is discussed.

Concepts: Cyanobacteria, Photosynthesis, Chloroplast, Plastocyanin, Chlorophyll, Thylakoid, Light-dependent reactions, ATP synthase

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Thylakoid membranes, the universal structure where photosynthesis takes place in all oxygenic photosynthetic organisms from cyanobacteria to higher plants, have a unique lipid composition. They contain a high fraction of 2 uncharged glycolipids, the galactoglycerolipids mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), and an anionic sulfolipid, sulfoquinovosediacylglycerol (SQDG). A remarkable feature of the evolution from cyanobacteria to higher plants is the conservation of MGDG, DGDG, SQDG, and phosphatidylglycerol (PG), the major phospholipid of thylakoids. Using neutron diffraction on reconstituted thylakoid lipid extracts, we observed that the thylakoid lipid mixture self-organizes as a regular stack of bilayers. This natural lipid mixture was shown to switch from hexagonal II toward lamellar phase on hydration. This transition and the observed phase coexistence are modulated by the fine-tuning of the lipid profile, in particular the MGDG/DGDG ratio, and by the hydration. Our analysis highlights the critical role of DGDG as a contributing component to the membrane stacking via hydrogen bonds between polar heads of adjacent bilayers. DGDG interactions balance the repulsive electrostatic contribution of the charged lipids PG and SQDG and allow the persistence of regularly stacked membranes at high hydration. In developmental contexts or in response to environmental variations, these properties can contribute to the highly dynamic flexibility of plastid structure.-Demé, B., Cataye, C., Block, M. A., Maréchal, E., Jouhet, J. Contribution of galactoglycerolipids to the 3-dimensional architecture of thylakoids.

Concepts: Cyanobacteria, Photosynthesis, Chloroplast, Plant, Lipids, Thylakoid, Light-dependent reactions, ATP synthase

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The neuronal ceroid-lipofuscinosis (NCL) are a heterogeneous group of neurodegenerative diseases characterized by the lysosomal accumulation of ceroid and lipofuscin with mitochondrial ATP synthase subunit C in various tissues. Clinical features include progressive mental and motor deterioration, myoclonus, seizure, visual failure and premature death. Ten CLN genes have been identified, among them CLN6 genes for which 55 disease-causing mutations have already been reported. The authors describe here a large consanguineous Moroccan family with three affected patients due to the p.I154del mutation that has been exclusively reported in Portuguese patients. This is the first published report of a genetic study in a Moroccan family with NCL. A relatively inexpensive CLN6 mutation screening should be considered first in Morocco as an initial diagnosis step when the disease course is consistent with late infantile neuronal ceroid-lipofuscinosis.

Concepts: DNA, Genetics, Cell, Neuronal ceroid lipofuscinosis, Batten disease, Lipofuscin, ATP synthase subunit C, ATP synthase

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We report the high-resolution (1.9 Å) crystal structure of oligomycin bound to the subunit c(10) ring of the yeast mitochondrial ATP synthase. Oligomycin binds to the surface of the c(10) ring making contact with two neighboring molecules at a position that explains the inhibitory effect on ATP synthesis. The carboxyl side chain of Glu59, which is essential for proton translocation, forms an H-bond with oligomycin via a bridging water molecule but is otherwise shielded from the aqueous environment. The remaining contacts between oligomycin and subunit c are primarily hydrophobic. The amino acid residues that form the oligomycin-binding site are 100% conserved between human and yeast but are widely different from those in bacterial homologs, thus explaining the differential sensitivity to oligomycin. Prior genetics studies suggest that the oligomycin-binding site overlaps with the binding site of other antibiotics, including those effective against Mycobacterium tuberculosis, and thereby frames a common “drug-binding site.” We anticipate that this drug-binding site will serve as an effective target for new antibiotics developed by rational design.

Concepts: DNA, Bacteria, Amino acid, Adenosine triphosphate, Oxidative phosphorylation, Chemistry, Atom, ATP synthase

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In addition to ∆pH formed across the thylakoid membrane, membrane potential contributes to proton motive force (pmf) in chloroplasts. However, the regulation of photosynthetic electron transport is mediated solely by ∆pH. To assess the contribution of two cyclic electron transport pathways around photosystem I (one depending on PGR5/PGRL1 and one on NDH) to pmf formation, electrochromic shift (ECS) was analyzed in the Arabidopsis pgr5 mutant, NDH-defective mutants (ndhs and crr4-2), and their double mutants (ndhs pgr5 and crr4-2 pgr5). In pgr5, the size of the pmf, as represented by ECSt, was reduced by 30% to 47% compared with that in the wild type (WT). A gH(+) parameter, which is considered to represent the activity of ATP synthase, was enhanced at high light intensities. However, gH(+) recovered to its low-light levels after 20min in the dark, implying that the elevation in gH(+) is due to the disturbed regulation of ATP synthase rather than to photodamage. After long dark adaptation more than 2h, gH(+) was higher in pgr5 than in the WT. During induction of photosynthesis, gH(+) was more rapidly elevated in pgr5 than that in the WT. Both results suggest that ATP synthase is not fully inactivated in the dark in pgr5. In the NDH-deficient mutants, ECSt was slightly but significantly lower than in the WT, whereas gH(+) was not affected. In the double mutants, ECSt was even lower than in pgr5. These results suggest that both PGR5/PGRL1- and NDH-dependent pathways contribute to pmf formation, although to different extents. This article is part of a Special Issue entitled: Chloroplast Biogenesis.

Concepts: Cyanobacteria, Photosynthesis, Adenosine triphosphate, Organelle, Chloroplast, Cellular respiration, Thylakoid, ATP synthase

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Plants are sessile organisms and need to acclimate to ever-changing light conditions in order to survive. These changes trigger a dynamic reorganization of the membrane protein complexes in the thylakoid membranes. Photosystem II (PSII) and its light harvesting system (LHCII) are the major target of this acclimation response, and accumulating evidences indicate that the amount and composition of PSII-LHCII supercomplexes in thylakoids are dynamically adjusted in response to changes in light intensity and quality. In this study, we characterized the PSII-LHCII supercomplexes in thylakoid membranes of pea plants in response to long-term acclimation to different light intensities. We provide evidence of a reorganization of the PSII-LHCII supercomplexes showing distinct changes in their antenna moiety. Mass spectrometry analysis revealed a specific reduction of Lhcb3, Lhcb6 and M-LHCII trimers bound to the PSII cores, while the Lhcb4.3 isoform increased in response to high light intensities. The modulation of Lhcb protein content correlates with the reduction of the functional PSII antenna size. These results suggest that the Lhcb3, Lhcb4.3 and Lhcb6 antenna subunits are major players in modulation of the PSII antenna size upon long-term acclimation to increased light levels. PsbS was not detected in the isolated PSII-LHCII supercomplexes at any light condition, despite an increased accumulation in thylakoids of high light acclimated plants, suggesting that PsbS is not a constitutive component of PSII-LHCII supercomplexes.

Concepts: Photosynthesis, Mass spectrometry, Photosystem, Chlorophyll, Plastoquinone, Thylakoid, Light-dependent reactions, ATP synthase

24

Diclofenac is a widely prescribed NSAID, which by itself and its reactive metabolites (Phase-I and Phase-II) may be involved in serious idiosyncratic hepatotoxicity. Mitochondrial injury is the one of the mechanism of drug induced liver injury (DILI). In the present work, an investigation of the inhibitory effects of diclofenac (Dic) and its phase I [4-hydroxy diclofenac (4'-OH-Dic) and 5-hydroxy diclofenac (5-OH-dic)] and Phase-II [diclofenac acyl glucuronide (DicGluA) and diclofenac glutathione thioester (DicSG)] metabolites, on ATP synthesis in rat liver mitochondria were carried out. A mechanism based inhibition of ATP synthesis is excerted by diclofenac and its metabolites. Phase-I metabolite (4'-OH-Dic) and Phase-II metabolites (DicGluA and DicSG) showed potent inhibition (2-5 fold) of ATP synthesis, where as 5-OH-Dic, one of the Phase-I metabolite, was a less potent inhibitor as compared to Dic. The calculated kinetic constants of mechanism based inhibition of ATP synthesis by Dic showed maximal rate of inactivation (Kinact) of 2.64±0.15min(-1) and half maximal rate of inactivation (KI) of 7.69±2.48μM with Kinact/KI ratio of 0.343min(-1)μM(-1). Co-incubation of mitochondria with Dic and reduced GSH exhibited a protective effect on Dic mediated inhibition of ATP synthesis. Our data from this study strongly indicate that Dic as well as its metabolites could be involved in the hepato-toxic action through inhibition of ATP synthesis.

Concepts: Photosynthesis, Metabolism, Adenosine triphosphate, Mitochondrion, Oxidative phosphorylation, Cellular respiration, Reactive oxygen species, ATP synthase

21

ATP synthase, H+transporting, mitochondrial F1 complex, δ subunit (ATP5F1D; formerly ATP5D) is a subunit of mitochondrial ATP synthase and plays an important role in coupling proton translocation and ATP production. Here, we describe two individuals, each with homozygous missense variants in ATP5F1D, who presented with episodic lethargy, metabolic acidosis, 3-methylglutaconic aciduria, and hyperammonemia. Subject 1, homozygous for c.245C>T (p.Pro82Leu), presented with recurrent metabolic decompensation starting in the neonatal period, and subject 2, homozygous for c.317T>G (p.Val106Gly), presented with acute encephalopathy in childhood. Cultured skin fibroblasts from these individuals exhibited impaired assembly of F1FOATP synthase and subsequent reduced complex V activity. Cells from subject 1 also exhibited a significant decrease in mitochondrial cristae. Knockdown of Drosophila ATPsynδ, the ATP5F1D homolog, in developing eyes and brains caused a near complete loss of the fly head, a phenotype that was fully rescued by wild-type human ATP5F1D. In contrast, expression of the ATP5F1D c.245C>T and c.317T>G variants rescued the head-size phenotype but recapitulated the eye and antennae defects seen in other genetic models of mitochondrial oxidative phosphorylation deficiency. Our data establish c.245C>T (p.Pro82Leu) and c.317T>G (p.Val106Gly) in ATP5F1D as pathogenic variants leading to a Mendelian mitochondrial disease featuring episodic metabolic decompensation.

Concepts: Photosynthesis, Gene, Metabolism, Adenosine triphosphate, Mitochondrion, Oxidative phosphorylation, Cellular respiration, ATP synthase

15

Adenosine triphosphate (ATP), the chemical energy currency of biology, is synthesized in eukaryotic cells primarily by the mitochondrial ATP synthase. ATP synthases operate by a rotary catalytic mechanism where proton translocation through the membrane-inserted F0 region is coupled to ATP synthesis in the catalytic F1 region via rotation of a central rotor subcomplex. We report here single particle electron cryomicroscopy (cryo-EM) analysis of the bovine mitochondrial ATP synthase. Combining cryo-EM data with bioinformatic analysis allowed us to determine the fold of the a subunit, suggesting a proton translocation path through the F0 region that involves both the a and b subunits. 3D classification of images revealed seven distinct states of the enzyme that show different modes of bending and twisting in the intact ATP synthase. Rotational fluctuations of the c8-ring within the F0 region support a Brownian ratchet mechanism for proton-translocation driven rotation in ATP synthases.

Concepts: DNA, Photosynthesis, Cell, Adenosine triphosphate, Mitochondrion, Cellular respiration, Protein subunit, ATP synthase