Redox regulation of the rotation of F(1)-ATP synthase

Structure, Regulation, and Significance of Cyanobacterial and Chloroplast Adenosine Triphosphate Synthase in the Adaptability of Oxygenic Photosynthetic Organisms

In cyanobacteria and chloroplasts (in algae and plants), ATP synthase plays a pivotal role as a photosynthetic membrane complex responsible for producing ATP from adenosine diphosphate and inorganic phosphate, utilizing a proton motive force gradient induced by photosynthesis. These two ATP synthases exhibit similarities in gene organization, amino acid sequences of subunits, structure, and functional mechanisms, suggesting that cyanobacterial ATP synthase is probably the evolutionary precursor to chloroplast ATP synthase. In this review, we explore the precise synthesis and assembly of ATP synthase subunits to address the uneven stoichiometry within the complex during transcription, translation, and assembly processes. We also compare the regulatory strategies governing ATP synthase activity to meet varying energy demands in cyanobacteria and chloroplasts amid fluctuating natural environments. Furthermore, we delve into the role of ATP synthase in stress tolerance and photosynthetic carbon fixation efficiency in oxygenic photosynthetic organisms (OPsOs), along with the current researches on modifying ATP synthase to enhance carbon fixation efficiency under stress conditions. This review aims to offer theoretical insights and serve as a reference for understanding the functional mechanisms of ATP synthase, sparking innovative ideas for enhancing photosynthetic carbon fixation efficiency by utilizing ATP synthase as an effective module in OPsOs.

Temperature-dependent regulation of electron transport and ATP synthesis in chloroplasts in vitro and in silico

The significance of temperature-dependent regulation of photosynthetic apparatus (PSA) is determined by the fact that plant temperature changes with environmental temperature. In this work, we present a brief overview of temperature-dependent regulation of photosynthetic processes in class B chloroplasts (thylakoids) and analyze these processes using a computer model that takes into account the key stages of electron and proton transport coupled to ATP synthesis. The rate constants of partial reactions were parametrized on the basis of experimental temperature dependences of partial photosynthetic processes: (1) photosystem II (PSII) turnover and plastoquinone (PQ) reduction, (2) the plastoquinol (PQH₂) oxidation by the cytochrome (Cyt) b₆f complex, (3) the ATP synthase activity, and (4) the proton leak from the thylakoid lumen. We consider that PQH₂ oxidation is the rate-limiting step in the intersystem electron transport. The parametrization of the rate constants of these processes is based on earlier experimental data demonstrating strong correlations between the functional and structural properties of thylakoid membranes that were probed with the lipid-soluble spin labels embedded into the membranes. Within the framework of our model, we could adequately describe a number of experimental temperature dependences of photosynthetic reactions in thylakoids. Computer modeling of electron and proton transport coupled to ATP synthesis supports the notion that PQH₂ oxidation by the Cyt b₆f complex and proton pumping into the lumen are the basic temperature-dependent processes that determine the overall electron flux from PSII to molecular oxygen and the net ATP synthesis upon variations of temperature. The model describes two branches of the temperature dependence of the post-illumination reduction of [Formula: see text] characterized by different activation energies (about 60 and ≤ 3.5 kJ mol^-1). The model predicts the bell-like temperature dependence of ATP formation, which arises from the balance of several factors: (1) the thermo-induced acceleration of electron transport through the Cyt b₆f complex, (2) deactivation of PSII photochemistry at sufficiently high temperatures, and (3) acceleration of the passive proton outflow from the thylakoid lumen bypassing the ATP synthase complex. The model describes the temperature dependence of experimentally measured parameter P/2e, determined as the ratio between the rates of ATP synthesis and pseudocyclic electron transport (H₂O → PSII → PSI → O₂).

Structural basis of redox modulation on chloroplast ATP synthase

In higher plants, chloroplast ATP synthase has a unique redox switch on its γ subunit that modulates enzyme activity to limit ATP hydrolysis at night. To understand the molecular details of the redox modulation, we used single-particle cryo-EM to determine the structures of spinach chloroplast ATP synthase in both reduced and oxidized states. The disulfide linkage of the oxidized γ subunit introduces a torsional constraint to stabilize the two β hairpin structures. Once reduced, free cysteines alleviate this constraint, resulting in a concerted motion of the enzyme complex and a smooth transition between rotary states to facilitate the ATP synthesis. We added an uncompetitive inhibitor, tentoxin, in the reduced sample to limit the flexibility of the enzyme and obtained high-resolution details. Our cryo-EM structures provide mechanistic insight into the redox modulation of the energy regulation activity of chloroplast ATP synthase.

Jay-How Yang et al. use single-particle cryo-EM to determine the structures of spinach chloroplast ATP synthase in reduced and oxidized states. They report a torsional constraint in the oxidized γ subunit that is alleviated by free cysteines in the reduced state. Their work provides mechanistic insights into the redox modulation of the ATP synthesis by the chloroplast ATP synthase.

The interactome of 2-Cys peroxiredoxins in Plasmodium falciparum

Peroxiredoxins (Prxs) are crucially involved in maintaining intracellular H2O2homeostasis via their peroxidase activity. However, more recently, this class of proteins was found to also transmit oxidizing equivalents to selected downstream proteins, which suggests an important function of Prxs in the regulation of cellular protein redox relays. Using a pull-down assay based on mixed disulfide fishing, we characterized the thiol-dependent interactome of cytosolic Prx1a and mitochondrial Prx1m from the apicomplexan malaria parasitePlasmodium falciparum(Pf). Here, 127 cytosolic and 20 mitochondrial proteins that are components of essential cellular processes were found to interact withPfPrx1a andPfPrx1m, respectively. Notably, our data obtained with active-site mutants suggests that reducing equivalents might also be transferred from Prxs to target proteins. Initial functional analyses indicated that the interaction with Prx can strongly impact the activity of target proteins. The results provide initial insights into the interactome of Prxs at the level of a eukaryotic whole cell proteome. Furthermore, they contribute to our understanding of redox regulatory principles and thiol-dependent redox relays of Prxs in subcellular compartments.

The N-terminal region of the ϵ subunit from cyanobacterial ATP synthase alone can inhibit ATPase activity

ATP hydrolysis activity catalyzed by chloroplast and proteobacterial ATP synthase is inhibited by their ϵ subunits. To clarify the function of the ϵ subunit from phototrophs, here we analyzed the ϵ subunit-mediated inhibition (ϵ-inhibition) of cyanobacterial F₁-ATPase, a subcomplex of ATP synthase obtained from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1. We generated three C-terminal α-helix null ϵ-mutants; one lacked the C-terminal α-helices, and in the other two, the C-terminal conformation could be locked by a disulfide bond formed between two α-helices or an α-helix and a β-sandwich structure. All of these ϵ-mutants maintained ATPase-inhibiting competency. We then used single-molecule observation techniques to analyze the rotary motion of F₁-ATPase in the presence of these ϵ-mutants. The stop angular position of the γ subunit in the presence of the ϵ-mutant was identical to that in the presence of the WT ϵ. Using magnetic tweezers, we examined recovery from the inhibited rotation and observed restoration of rotation by 80° forcing of the γ subunit in the case of the ADP-inhibited form, but not when the rotation was inhibited by the ϵ-mutants or by the WT ϵ subunit. These results imply that the C-terminal α-helix domain of the ϵ subunit of cyanobacterial enzyme does not directly inhibit ATP hydrolysis and that its N-terminal domain alone can inhibit the hydrolysis activity. Notably, this property differed from that of the proteobacterial ϵ, which could not tightly inhibit rotation. We conclude that phototrophs and heterotrophs differ in the ϵ subunit-mediated regulation of ATP synthase.

Mitochondrial-derived reactive oxygen species influence ADP sensitivity, but not CPT-I substrate sensitivity

The mechanisms regulating oxidative phosphorylation during exercise remain poorly defined; however, key mitochondrial proteins, including carnitine palmitoyltransferase-I (CPT-I) and adenine nucleotide translocase, have redox-sensitive sites. Interestingly, muscle contraction has recently been shown to increase mitochondrial membrane potential and reactive oxygen species (ROS) production; therefore, we aimed to determine if mitochondrial-derived ROS influences bioenergetic responses to exercise. Specifically, we examined the influence of acute exercise on mitochondrial bioenergetics in WT (wild type) and transgenic mice (MCAT, mitochondrial-targeted catalase transgenic) possessing attenuated mitochondrial ROS. We found that ablating mitochondrial ROS did not alter palmitoyl-CoA (P-CoA) respiratory kinetics or influence the exercise-mediated reductions in malonyl CoA sensitivity, suggesting that mitochondrial ROS does not regulate CPT-I. In contrast, while mitochondrial protein content, maximal coupled respiration, and ADP (adenosine diphosphate) sensitivity in resting muscle were unchanged in the absence of mitochondrial ROS, exercise increased the apparent ADP K _m (decreased ADP sensitivity) ∼30% only in WT mice. Moreover, while the presence of P-CoA decreased ADP sensitivity, it did not influence the basic response to exercise, as the apparent ADP K _m was increased only in the presence of mitochondrial ROS. This basic pattern was also mirrored in the ability of ADP to suppress mitochondrial H₂O₂ emission rates, as exercise decreased the suppression of H₂O₂ only in WT mice. Altogether, these data demonstrate that while exercise-induced mitochondrial-derived ROS does not influence CPT-I substrate sensitivity, it inhibits ADP sensitivity independent of P-CoA. These data implicate mitochondrial redox signaling as a regulator of oxidative phosphorylation.

Comparative effects of Ni(II) and Cu(II) ions and their combinations on redox potential and hydrogen photoproduction by Rhodobacter sphaeroides

The aim of the present work was the study of comparative effects of Cu(II) and Ni(II) and their mixture on growth, redox potential, hydrogen (H₂) yield and ATPase activity in phototrophic purple bacteria R. sphaeroides MDC6522 from Jermuk mineral spring in Armenia. It was ascertained, that Cu²⁺ and Ni²⁺ have different effects on bacterial specific growth rate: in the presence of 5μM Cu²⁺ growth rate was ~3.2-fold lower in comparison with control (no addition), and increased ~1.5-fold in medium with 5μM Ni²⁺. These changes may be resulted by action of the ions on redox potential (E_h). Low concentrations of Ni²⁺ had an enhancing effect on the E_h drop and H₂ production. The increase of concentration from 1 to 5μM enhanced the stimulatory effect of Ni²⁺. H₂ yield in R. sphaeroides (72h of growth) was enhanced ~3-fold with 5μM Ni²⁺, whereas in the presence of 5μM Cu²⁺ H₂ yield was ~1.2 fold lower in comparison with control. Cu²⁺+Ni²⁺ combinations effects were differed from the effect when ions used separately. When Cu²⁺ and Ni²⁺ were added together, the Ni²⁺ stimulatory effect disappeared, which indicated that heavy metal ions mixture may have different action mechanisms. Moreover, N,N'-dicyclohexylcarbodiimide-sensitive ATPase activity of R. sphaeroides membrane vesicles has been increased in the presence of both ions, but in the presence of Сu²⁺ the influence was feebly marked in comparison with Ni²⁺. The results suggest an interaction between these ions and the F_OF₁-ATPase. Thus, the results obtained point out discrimination between Cu²⁺ and Ni²⁺ and their combinations effects and reveal new regulatory pathways to enhance H₂ yield in R. sphaeroides.

Rotation of artificial rotor axles in rotary molecular motors

F₁- and V₁-ATPase are rotary molecular motors that convert chemical energy released upon ATP hydrolysis into torque to rotate a central rotor axle against the surrounding catalytic stator cylinder with high efficiency. How conformational change occurring in the stator is coupled to the rotary motion of the axle is the key unknown in the mechanism of rotary motors. Here, we generated chimeric motor proteins by inserting an exogenous rod protein, FliJ, into the stator ring of F₁ or of V₁ and tested the rotation properties of these chimeric motors. Both motors showed unidirectional and continuous rotation, despite no obvious homology in amino acid sequence between FliJ and the intrinsic rotor subunit of F₁ or V₁ These results showed that any residue-specific interactions between the stator and rotor are not a prerequisite for unidirectional rotation of both F₁ and V₁ The torque of chimeric motors estimated from viscous friction of the rotation probe against medium revealed that whereas the F₁-FliJ chimera generates only 10% of WT F₁, the V₁-FliJ chimera generates torque comparable to that of V₁ with the native axle protein that is structurally more similar to FliJ than the native rotor of F₁ This suggests that the gross structural mismatch hinders smooth rotation of FliJ accompanied with the stator ring of F₁.

The effect of medium viscosity on kinetics of ATP hydrolysis by the chloroplast coupling factor CF1

The coupling factor CF1 is a catalytic part of chloroplast ATP synthase which is exposed to stroma whose viscosity is many-fold higher than that of reaction mixtures commonly used to measure kinetics of CF1-catalyzed ATP hydrolysis. This study is focused on the effect of medium viscosity modulated by sucrose or bovine serum albumin (BSA) on kinetics of Ca(2+)- and Mg(2+)-dependent ATP hydrolysis by CF1. These agents were shown to reduce the maximal rate of Ca(2+)-dependent ATPase without changing the apparent Michaelis constant (К m), thus supporting the hypothesis on viscosity dependence of CF1 activity. For the sulfite- and ethanol-stimulated Mg(2+)-dependent reaction, the presence of sucrose increased К m without changing the maximal rate that is many-fold as high as that of Ca(2+)-dependent hydrolysis. The hydrolysis reaction was shown to be stimulated by low concentrations of BSA and inhibited by its higher concentrations, with the increasing maximal reaction rate estimated by extrapolation. Sucrose- or BSA-induced inhibition of the Mg(2+)-dependent ATPase reaction is believed to result from diffusion-caused deceleration, while its BSA-induced stimulation is probably caused by optimization of the enzyme structure. Molecular mechanisms of the inhibitory effect of viscosity are discussed. Taking into account high protein concentrations in the chloroplast stroma, it was suggested that kinetic parameters of ATP hydrolysis, and probably those of ATP synthesis in vivo as well, must be quite different from measurements taken at a viscosity level close to that of water.

Induction events and short-term regulation of electron transport in chloroplasts: an overview

Regulation of photosynthetic electron transport at different levels of structural and functional organization of photosynthetic apparatus provides efficient performance of oxygenic photosynthesis in plants. This review begins with a brief overview of the chloroplast electron transport chain. Then two noninvasive biophysical methods (measurements of slow induction of chlorophyll a fluorescence and EPR signals of oxidized P700 centers) are exemplified to illustrate the possibility of monitoring induction events in chloroplasts in vivo and in situ. Induction events in chloroplasts are considered and briefly discussed in the context of short-term mechanisms of the following regulatory processes: (i) pH-dependent control of the intersystem electron transport; (ii) the light-induced activation of the Calvin-Benson cycle; (iii) optimization of electron transport due to fitting alternative pathways of electron flow and partitioning light energy between photosystems I and II; and (iv) the light-induced remodeling of photosynthetic apparatus and thylakoid membranes.

ATP synthase

Oxygenic photosynthesis is the principal converter of sunlight into chemical energy. Cyanobacteria and plants provide aerobic life with oxygen, food, fuel, fibers, and platform chemicals. Four multisubunit membrane proteins are involved: photosystem I (PSI), photosystem II (PSII), cytochrome b6f (cyt b6f), and ATP synthase (FOF1). ATP synthase is likewise a key enzyme of cell respiration. Over three billion years, the basic machinery of oxygenic photosynthesis and respiration has been perfected to minimize wasteful reactions. The proton-driven ATP synthase is embedded in a proton tight-coupling membrane. It is composed of two rotary motors/generators, FO and F1, which do not slip against each other. The proton-driven FO and the ATP-synthesizing F1 are coupled via elastic torque transmission. Elastic transmission decouples the two motors in kinetic detail but keeps them perfectly coupled in thermodynamic equilibrium and (time-averaged) under steady turnover. Elastic transmission enables operation with different gear ratios in different organisms.

Redox regulation of CF1-ATPase involves interplay between the γ-subunit neck region and the turn region of the βDELSEED-loop

The soluble F1 complex of ATP synthase (FoF1) is capable of ATP hydrolysis, accomplished by the minimum catalytic core subunits α3β3γ. A special feature of cyanobacterial F1 and chloroplast F1 (CF1) is an amino acid sequence inserted in the γ-subunit. The insertion is extended slightly into the CF1 enzyme containing two additional cysteines for regulation of ATPase activity via thiol modulation. This molecular switch was transferred to a chimeric F1 by inserting the cysteine-containing fragment from spinach CF1 into a cyanobacterial γ-subunit [Y. Kim et al., redox regulation of rotation of the cyanobacterial F1-ATPase containing thiol regulation switch, J Biol Chem, 286 (2011) 9071-9078]. Under oxidizing conditions, the obtained F1 tends to lapse into an ADP-inhibited state, a common regulation mechanism to prevent wasteful ATP hydrolysis under unfavorable circumstances. However, the information flow between thiol modulation sites on the γ-subunit and catalytic sites on the β-subunits remains unclear. Here, we clarified a possible interplay for the CF1-ATPase redox regulation between structural elements of the βDELSEED-loop and the γ-subunit neck region, i.e., the most convex part of the α-helical γ-termini. Critical residues were assigned on the β-subunit, which received the conformation change signal produced by disulfide/dithiol formation on the γ-subunit. Mutant response to the ATPase redox regulation ranged from lost to hypersensitive. Furthermore, mutant cross-link experiments and inversion of redox regulation indicated that the γ-redox state might modulate the subunit interface via reorientation of the βDELSEED motif region.

Cu(II), Fe(III) and Mn(II) combinations as environmental stress factors have distinguishing effects on Enterococcus hirae

Pollution by various heavy metals as environmental stress factors might affect bacteria. It was established that iron (Fe(III)), manganese (Mn(II)) and copper (Cu(II)) ion combinations caused effects on Enterococcus hirae that differed from the sum of the effects when the metals were added separately. It was shown that the Cu2+-Fe3+ combination decreased the growth and ATPase activity of membrane vesicles of wild-type E. hirae ATCC9790 and atpD mutant (with defective FoF1-ATPase) MS116. Addition of Mn2+-Fe3+ combinations within the same concentration range had no effects on growth compared to control (without heavy metals). ATPase activity was increased in the presence of Mn2+-Fe3+, while together with 0.2 mmol/L N,N'-dicyclohexylcarbodiimide (DCCD), ATPase activity was decreased compared to control (when only 0.2 mmol/L DCCD was present). These results indicate that heavy metals ion combinations probably affect the FOF1-ATPase, leading to conformational changes. Moreover the action may be direct or be mediated by environment redox potential. The effects observed when Fe3+ was added separately disappeared in both cases, which might be a result of competing processes between Fe3+ and other heavy metals. These findings are novel and improve the understanding of heavy metals ions effects on bacteria, and could be applied for regulation of stress response patterns in the environment.

A review on emerging diagnostic assay for viral detection: the case of avian influenza virus

Biotechnology-based detection systems and sensors are in use for a wide range of applications in biomedicine, including the diagnostics of viral pathogens. In this review, emerging detection systems and their applicability for diagnostics of viruses, exemplified by the case of avian influenza virus, are discussed. In particular, nano-diagnostic assays presently under development or available as prototype and their potentials for sensitive and rapid virus detection are highlighted.

The chloroplast ATP synthase features the characteristic redox regulation machinery

SIGNIFICANCE

Regulation of the activity of the chloroplast ATP synthase is largely accomplished by the chloroplast thioredoxin system, the main redox regulation system in chloroplasts, which is directly coupled to the photosynthetic reaction. We review the current understanding of the redox regulation system of the chloroplast ATP synthase.

RECENT ADVANCES

The thioredoxin-targeted portion of the ATP synthase consists of two cysteines located on the central axis subunit γ. The redox state of these two cysteines is under the influence of chloroplast thioredoxin, which directly controls rotation during catalysis by inducing a conformational change in this subunit. The molecular mechanism of redox regulation of the chloroplast ATP synthase has recently been determined.

CRITICAL ISSUES

Regulation of the activity of the chloroplast ATP synthase is critical in driving efficiency into the ATP synthesis reaction in chloroplasts.

FUTURE DIRECTIONS

The molecular architecture of the chloroplast ATP synthase, which confers redox regulatory properties requires further investigation, in light of the molecular structure of the enzyme complex as well as the physiological significance of the regulation system.

pH-dependent regulation of electron transport and ATP synthesis in chloroplasts

This review is focused on pH-dependent mechanisms of regulation of photosynthetic electron transport and ATP synthesis in chloroplasts. The light-induced acidification of the thylakoid lumen is known to decelerate the plastoquinol oxidation by the cytochrome b 6 f complex, thus impeding the electron flow between photosystem II and photosystem I. Acidification of the lumen also triggers the dissipation of excess energy in the light-harvesting antenna of photosystem II, thereby protecting the photosynthetic apparatus against a solar stress. After brief description of structural and functional organization of the chloroplast electron transport chain, our attention is focused on the nature of the rate-limiting step of electron transfer between photosystem II and photosystem I. In the context of pH-dependent mechanism of photosynthetic control in chloroplasts, the mechanisms of plastoquinol oxidation by the cytochrome b 6 f complex have been considered. The light-induced alkalization of stroma is another factor of pH-dependent regulation of electron transport in chloroplasts. Alkalization of stroma induces activation of the Bassham-Benson-Calvin cycle reactions, thereby promoting efflux of electrons from photosystem I to NADP(+). The mechanisms of the light-induced activation of ATP synthase are briefly considered.

Redox regulation of mitochondrial ATP synthase

Reversible cysteine oxidative post-translational modifications (Ox-PTMs) represent an important mechanism to regulate protein structure and function. In mitochondria, redox reactions can modulate components of the electron transport chain (ETC), the F(1)F(0)-ATP synthase complex, and other matrix proteins/enzymes. Emerging evidence has linked Ox-PTMs to mitochondrial dysfunction and heart failure, highlighting some potential therapeutic avenues. Ox-PTMs can modify a variety of amino acid residues, including cysteine, and have the potential to modulate the function of a large number of proteins. Among this group, there is a selected subset of amino acid residues that can function as redox switches. These unique sites are proposed to monitor the cell's oxidative balance through their response to the various Ox-PTMs. In this review, the role of Ox-PTMs in the regulation of the F(1)F(0)-ATP synthase complex is discussed in the context of heart failure and its possible clinical treatment.

Thiol modulation of the chloroplast ATP synthase is dependent on the energization of thylakoid membranes

Thiol modulation of the chloroplast ATP synthase γ subunit has been recognized as an important regulatory system for the activation of ATP hydrolysis activity, although the physiological significance of this regulation system remains poorly characterized. Since the membrane potential required by this enzyme to initiate ATP synthesis for the reduced enzyme is lower than that needed for the oxidized form, reduction of this enzyme was interpreted as effective regulation for efficient photophosphorylation. However, no concrete evidence has been obtained to date relating to the timing and mode of chloroplast ATP synthase reduction and oxidation in green plants. In this study, thorough analysis of the redox state of regulatory cysteines of the chloroplast ATP synthase γ subunit in intact chloroplasts and leaves shows that thiol modulation of this enzyme is pivotal in prohibiting futile ATP hydrolysis activity in the dark. However, the physiological importance of efficient ATP synthesis driven by the reduced enzyme in the light could not be demonstrated. In addition, we investigated the significance of the electrochemical proton gradient in reducing the γ subunit by the reduced form of thioredoxin in chloroplasts, providing strong insights into the molecular mechanisms underlying the formation and reduction of the disulfide bond on the γ subunit in vivo.

Fe(III) and Fe(II) ions different effects on Enterococcus hirae cell growth and membrane-associated ATPase activity

Enterococcus hirae is able to grow under anaerobic conditions during glucose fermentation (pH 8.0) which is accompanied by acidification of the medium and drop in its oxidation-reduction potential (E(h)) from positive values to negative ones (down to ∼-200 mV). In this study, iron (III) ions (Fe(3+)) have been shown to affect bacterial growth in a concentration-dependent manner (within the range of 0.05-2 mM) by decreasing lag phase duration and increasing specific growth rate. While iron(II) ions (Fe(2+)) had opposite effects which were reflected by suppressing bacterial growth. These ions also affected the changes in E(h) values during bacterial growth. It was revealed that ATPase activity with and without N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of the F(0)F(1)-ATPase, increased in the presence of even low Fe(3+) concentration (0.05 mM) but decreased in the presence of Fe(2+). It was established that Fe(3+) and Fe(2+) both significantly inhibited the proton-potassium exchange of bacteria, but stronger effects were in the case of Fe(2+) with DCCD. Such results were observed with both wild-type ATCC9790 and atpD mutant (with defective F(0)F(1)) MS116 strains but they were different with Fe(3+) and Fe(2+). It is suggested that the effects of Fe(3+) might be due to interaction of these ions with F(0)F(1) or there might be a Fe(3+)-dependent ATPase different from F(0)F(1) in these bacteria that is active even in the presence of DCCD. Fe(2+) inhibits E. hirae cell growth probably by strong effect on E(h) leading to changes in F(0)F(1) and decreasing its activity.

Redox regulation of rotation of the cyanobacterial F1-ATPase containing thiol regulation switch

F(1)-ATP synthase (F(1)-ATPase) is equipped with a special mechanism that prevents the wasteful reverse reaction, ATP hydrolysis, when there is insufficient proton motive force to drive ATP synthesis. Chloroplast F(1)-ATPase is subject to redox regulation, whereby ATP hydrolysis activity is regulated by formation and reduction of the disulfide bond located on the γ subunit. To understand the molecular mechanism of this redox regulation, we constructed a chimeric F(1) complex (α(3)β(3)γ(redox)) using cyanobacterial F(1), which mimics the regulatory properties of the chloroplast F(1)-ATPase, allowing the study of its regulation at the single molecule level. The redox state of the γ subunit did not affect the ATP binding rate to the catalytic site(s) and the torque for rotation. However, the long pauses caused by ADP inhibition were frequently observed in the oxidized state. In addition, the duration of continuous rotation was relatively shorter in the oxidized α(3)β(3)γ(redox) complex. These findings lead us to conclude that redox regulation of CF(1)-ATPase is achieved by controlling the probability of ADP inhibition via the γ subunit inserted region, a sequence feature observed in both cyanobacterial and chloroplast ATPase γ subunits, which is important for ADP inhibition (Sunamura, E., Konno, H., Imashimizu-Kobayashi, M., Sugano, Y., and Hisabori, T. (2010) Plant Cell Physiol. 51, 855-865).

The effects of copper (II) ions on Enterococcus hirae cell growth and the proton-translocating FoF1 ATPase activity

Enterococcus hirae grow well under anaerobic conditions at alkaline pH (pH 8.0) producing acids by glucose fermentation. Bacterial growth was shown to be accompanied by decrease of redox potential from positive values (approximately +35 mV) to negative ones (approximately -220 mV). An oxidizer copper (II) ions (Cu(2+)) affected bacterial growth in a concentration-dependent manner (within the range of 0.05 mM to 1 mM) increasing lag phase duration and decreasing specific growth rate. These effects were observed with the wild-type strain ATCC9790 and the atpD mutant strain MS116 (with absent beta subunit of F(1) of the F(o)F(1) ATPase) both. Also ATPase activity and proton-potassium ions exchange were assessed with and without N,N'-dicyclohexylcarbodiimide (DCCD), inhibitor of the F(o)F(1) ATPase. In both cases (DCCD +/-), even low Cu(2+) concentrations had noticeable effect on ATPase activity, but with less visible concentration-dependent manner. Changes in the number of accessible SH-groups were observed with E. hirae ATCC9790 and MS116 membrane vesicles. In both strains Cu(2+) markedly decreased the number of SH-groups in the presence of K(+) ions. The addition of ATP increased the amount of accessible SH-groups in ATCC9790 and decreased this number in MS116; Cu(2+) blocked ATP-installed increase in SH-groups number in ATCC9790. H(+)-K(+)-exchange of bacteria was markedly inhibited by Cu(2+), but stronger effects were detected together with DCCD. Moreover, discrimination between Cu(2+) and other bivalent cation--Ni(2+) was shown. It is suggested that Cu(2+) ions inhibit E. hirae cell growth by direct affect on the F(o)F(1) ATPase leading to conformational changes in this protein complex and decrease in its activity.

Subunit movements in single membrane-bound H+-ATP synthases from chloroplasts during ATP synthesis

Subunit movements within the H(+)-ATP synthase from chloroplasts (CF(0)F(1)) are investigated during ATP synthesis. The gamma-subunit (gammaCys-322) is covalently labeled with a fluorescence donor (ATTO532). A fluorescence acceptor (adenosine 5'-(beta,gamma-imino)triphosphate (AMPPNP)-ATTO665) is noncovalently bound to a noncatalytic site at one alpha-subunit. The labeled CF(0)F(1) is integrated into liposomes, and a transmembrane pH difference is generated by an acid base transition. Single-pair fluorescence resonance energy transfer is measured in freely diffusing proteoliposomes with a confocal two-channel microscope. The fluorescence time traces reveal a repetitive three-step rotation of the gamma-subunit relative to the alpha-subunit during ATP synthesis. Some traces show splitting into sublevels with fluctuations between the sublevels. During catalysis the central stalk interacts, with equal probability, with each alphabeta-pair. Without catalysis the central stalk interacts with only one specific alphabeta-pair, and no stepping between FRET levels is observed. Two inactive states of the enzyme are identified: one in the presence of AMPPNP and one in the presence of ADP.

Structural and functional analysis of the intrinsic inhibitor subunit epsilon of F1-ATPase from photosynthetic organisms

The epsilon subunit, a small subunit located in the F1 domain of ATP synthase and comprising two distinct domains, an N-terminal beta-sandwich structure and a C-terminal alpha-helical region, serves as an intrinsic inhibitor of ATP hydrolysis activity. This inhibitory function is especially important in photosynthetic organisms as the enzyme cannot synthesize ATP in the dark, but may catalyse futile ATP hydrolysis reactions. To understand the structure-function relationship of this subunit in F1 from photosynthetic organisms, we solved the NMR structure of the epsilon subunit of ATP synthase obtained from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1, and examined the flexibility of the C-terminal domains using molecular dynamics simulations. In addition, we revealed the significance of the C-terminal alpha-helical region of the epsilon subunit in determining the binding affinity to the complex based on the assessment of the inhibition of ATPase activity by the cyanobacterial epsilon subunit and the chimaeric subunits composed of the N-terminal domain from the cyanobacterium and the C-terminal domain from spinach. The differences observed in the structural and biochemical properties of chloroplast and bacterial epsilon subunits explains the distinctive characteristics of the epsilon subunits in the ATPase complex of the photosynthetic organism.

A novel 11-kDa inhibitory subunit in the F1FO ATP synthase of Paracoccus denitrificans and related alpha-proteobacteria

The F(1)F(O) and F(1)-ATPase complexes of Paracoccus denitrificans were isolated for the first time by ion exchange, gel filtration, and density gradient centrifugation into functional native preparations. The liposome-reconstituted holoenzyme preserves its tight coupling between F(1) and F(O) sectors, as evidenced by its high sensitivity to the F(O) inhibitors venturicidin and diciclohexylcarbodiimide. Comparison and N-terminal sequencing of the band profile in SDS-PAGE of the F(1) and F(1)F(O) preparations showed a novel 11-kDa protein in addition to the 5 canonical alpha, beta, gamma, delta, and epsilon subunits present in all known F(1)-ATPase complexes. BN-PAGE followed by 2D-SDS-PAGE confirmed the presence of this 11-kDa protein bound to the native F(1)F(O)-ATP synthase of P. denitrificans, as it was observed after being isolated. The recombinant 11 kDa and epsilon subunits of P. denitrificans were cloned, overexpressed, isolated, and reconstituted in particulate F(1)F(O) and soluble F(1)-ATPase complexes. The 11-kDa protein, but not the epsilon subunit, inhibited the F(1)F(O) and F(1)-ATPase activities of P. denitrificans. The 11-kDa protein was also found in Rhodobacter sphaeroides associated to its native F(1)F(O)-ATPase. Taken together, the data unveil a novel inhibitory mechanism exerted by this 11-kDa protein on the F(1)F(O)-ATPase nanomotor of P. denitrificans and closely related alpha-proteobacteria.

Regulation of translation by the redox state of elongation factor G in the cyanobacterium Synechocystis sp. PCC 6803

Elongation factor G (EF-G), a key protein in translational elongation, was identified as a primary target of inactivation by reactive oxygen species within the translational machinery of the cyanobacterium Synechocystis sp. PCC 6803 (Kojima, K., Oshita, M., Nanjo, Y., Kasai, K., Tozawa, Y., Hayashi, H., and Nishiyama, Y. (2007) Mol. Microbiol. 65, 936-947). In the present study, we found that inactivation of EF-G (Slr1463) by H(2)O(2) was attributable to the oxidation of two specific cysteine residues and formation of a disulfide bond. Substitution of these cysteine residues by serine residues protected EF-G from inactivation by H(2)O(2) and allowed the EF-G to mediate translation in a translation system in vitro that had been prepared from Synechocystis. The disulfide bond in oxidized EF-G was reduced by thioredoxin, and the resultant reduced form of EF-G regained the activity to mediate translation in vitro. Western blotting analysis showed that levels of the oxidized form of EF-G increased under strong light in a mutant that lacked NADPH-thioredoxin reductase, indicating that EF-G is reduced by thioredoxin in vivo. These observations suggest that the translational machinery is regulated by the redox state of EF-G, which is oxidized by reactive oxygen species and reduced by thioredoxin, a transmitter of reducing signals generated by the photosynthetic transport of electrons.

Two-stimuli manipulation of a biological motor

F1-ATPase is an enzyme acting as a rotary nano-motor. During catalysis subunits of this enzyme complex rotate relative to other parts of the enzyme. Here we demonstrate that the combination of two input stimuli causes stop of motor rotation. Application of either individual stimulus did not significantly influence motor motion. These findings may contribute to the development of logic gates using single biological motor molecules.

Diarylquinolines are bactericidal for dormant mycobacteria as a result of disturbed ATP homeostasis

An estimated one-third of the world population is latently infected with Mycobacterium tuberculosis. These nonreplicating, dormant bacilli are tolerant to conventional anti-tuberculosis drugs, such as isoniazid. We recently identified diarylquinoline R207910 (also called TMC207) as an inhibitor of ATP synthase with a remarkable activity against replicating mycobacteria. In the present study, we show that R207910 kills dormant bacilli as effectively as aerobically grown bacilli with the same target specificity. Despite a transcriptional down-regulation of the ATP synthase operon and significantly lower cellular ATP levels, we show that dormant mycobacteria do possess residual ATP synthase enzymatic activity. This activity is blocked by nanomolar concentrations of R207910, thereby further reducing ATP levels and causing a pronounced bactericidal effect. We conclude that this residual ATP synthase activity is indispensable for the survival of dormant mycobacteria, making it a promising drug target to tackle dormant infections. The unique dual bactericidal activity of diarylquinolines on dormant as well as replicating bacterial subpopulations distinguishes them entirely from the current anti-tuberculosis drugs and underlines the potential of R207910 to shorten tuberculosis treatment.

The ferredoxin/thioredoxin system of oxygenic photosynthesis

Forty years ago, ferredoxin (Fdx) was shown to activate fructose 1,6-bisphosphatase in illuminated chloroplast preparations, thereby laying the foundation for the field now known as "redox biology." Enzyme activation was later shown to require the ubiquitous protein thioredoxin (Trx), reduced photosynthetically by Fdx via an enzyme then unknown-ferredoxin:thioredoxin reductase (FTR). These proteins, Fdx, FTR, and Trx, constitute a regulatory ensemble, the "Fdx/Trx system." The redox biology field has since grown beyond all expectations and now embraces a spectrum of processes throughout biology. Progress has been notable with plants that possess not only the plastid Fdx/Trx system, but also the earlier known NADP/Trx system in the cytosol, endoplasmic reticulum, and mitochondria. Plants contain at least 19 types of Trx (nine in chloroplasts). In this review, we focus on the structure and mechanism of action of members of the photosynthetic Fdx/Trx system and on biochemical processes linked to Trx. We also summarize recent evidence that extends the Fdx/Trx system to amyloplasts-heterotrophic plastids functional in the biosynthesis of starch and other cell components. The review highlights the plant as a model system to uncover principles of redox biology that apply to other organisms.

Copper (II) ions affect Escherichia coli membrane vesicles' SH-groups and a disulfide-dithiol interchange between membrane proteins

The SH-groups in Escherichia coli membrane vesicles, prepared from cells grown in fermentation conditions on glucose at slightly alkaline pH, have a role in the F0F1-ATPase operation. The changes in the number of these groups by ATP are observed under certain conditions. In this study, copper ions (Cu2+) in concentration of 0.1 mM were shown to increase the number of SH-groups in 1.5- to 1.6-fold independent from K+ ions, and the suppression of the increased level of SH-groups by ATP was determined for Cu2+ in the presence of K+. Moreover, the increase in the number of SH-groups by Cu2+ was absent as well as the inhibition in ATP-dependent increasing SH-groups number by Cu2+ lacked when vesicles were treated with N-ethylmaleimide (NEM), specific thiol-reagent. Such an effect was not observed with zinc (Zn2+), cobalt (Co2+), or Cu+ ions. The increased level of SH-groups was observed in the hycE or hyfR mutants with defects in hydrogenases 3 or 4, whereas the ATP-dependent increase in the number of these groups was determined in hycE not in hyfR mutants. Both changes in SH-groups number disappeared in the atp or hyc mutants deleted for the F0F1-ATPase or hydrogenase 3 (no activity of hydrogenase 4 was detected in the hyc mutant used). A direct effect of Cu2+ but not Cu+ on the F0F1-ATPase is suggested to lead to conformational changes or damaging consequences, increasing accessible SH-groups number and disturbing disulfide-dithiol interchange within a protein-protein complex, where this ATPase works with K+ uptake system or hydrogenase 4 (Hyd-4); breaks in disulfides are not ruled out.

ATP-dependent modulation and autophosphorylation of rapeseed 2-Cys peroxiredoxin

2-Cys peroxiredoxins (2-Cys Prx) are ubiquitous thiol-containing peroxidases that have been implicated in antioxidant defense and signal transduction. Although their biochemical features have been extensively studied, little is known about the mechanisms that link the redox activity and non-redox processes. Here we report that the concerted action of a nucleoside triphosphate and Mg(2+) on rapeseed 2-Cys Prx reversibly impairs the peroxidase activity and promotes the formation of high molecular mass species. Using protein intrinsic fluorescence in the analysis of site-directed mutants, we demonstrate that ATP quenches the emission intensity of Trp179, a residue close to the conserved Cys175. More importantly, we found that ATP facilitates the autophosphorylation of 2-Cys Prx when the protein is successively reduced with thiol-bearing compounds and oxidized with hydroperoxides or quinones. MS analyses reveal that 2-Cys Prx incorporates the phosphoryl group into the Cys175 residue yielding the sulfinic-phosphoryl [Prx-(Cys175)-SO(2)PO(3)(2-)] and the sulfonic-phosphoryl [Prx-(Cys175)-SO(3)PO(3)(2-)] anhydrides. Hence, the functional coupling between ATP and 2-Cys Prx gives novel insights into not only the removal of reactive oxygen species, but also mechanisms that link the energy status of the cell and the oxidation of cysteine residues.

Redox sensing by Escherichia coli: Effects of copper ions as oxidizers on proton-coupled membrane transport

Escherichia coli is able to grow under anaerobic fermentation conditions upon a decrease in redox potential (E(h)). Indeed, upon a transition of E. coli MC4100 wild-type culture to stationary growth phase a decrease in E(h) from the positive values ( approximately +100 mV) to the negative ones ( approximately -520 mV) was observed, the acidification of the medium and the H(2) production were obtained. An oxidizer, copper ions (Cu(2+)) affected a bacterial growth in a concentration-dependent manner (of 0.1 mM to 10 mM) increasing latent (lag) growth phase duration, delaying logarithmic (log) growth phase and decreasing specific growth rate. Acidification of the medium and the N,N'-dicyclohexylcarbodiimide (DCCD)- and azide-sensitive proton-potassium exchange by bacteria were inhibited, H(2) production upon growth and under assays disappeared with Cu(2+) (0.1 mM). These effects were observed with hycE but not hyfR and hyc(A-H) mutants and under aerobic conditions. Cu(2+) also increased membrane proton conductance. Copper ions are suggested to affect directly the F(0)F(1)-ATPase associated with potassium uptake transport system and/or formate hydrogenlyase composed with hydrogenase 4. A role of the F(0)F(1)-ATPase in redox sensing under fermentation is proposed.

Biochemical characteristics of Escherichia coli ATP synthase with insulin peptide A fused to the globular part of the gamma-subunit

The codon 5383-5385 (CCG) in the atpC gene of the unc operon of Escherichia coli cells was replaced with the sequence encoding peptide A of human insulin. The foreign protein fused to the middle part of the gamma-subunit of ATP synthase affects neither biosynthesis of the chimeric polypeptide nor the integration of the EF(0) x F(1) enzyme into the membranes of the E. coli cells. The inserted peptide A does not inhibit the process of oxidative phosphorylation. The ATPase activity of the mutant EF(0) x F(1) enzyme was equal to that of the wild-type enzyme and was regulated by modifiers in the similar way, suggesting that the space in the stalk area of F(0)/F(1) interaction is enough for the introduction of an additional oligopeptide without changing catalytic properties of the ATP synthase.

The increase in the number of accessible SH-groups in the enterococcal membrane vesicles by ATP and nicotinamide adenine dinucleotides

The number of accessible SH groups was determined in membrane vesicles prepared from Enterococcus hirae grown under anaerobic conditions at alkaline pH (pH 8.0). Addition of ATP or nicotinamide adenine dinucleotides (NAD(+) +NADH) to the vesicles caused a approximately 4-fold or approximately 1.9-fold increase in the number of SH-groups, respectively. This was inhibited by treatment with N-ethylmaleimide. The increase was significant when ATP and NAD(+) +NADH both were added. The change was lacking in the presence of the F0F1-ATPase inhibitors N,N'-diclohexylcarbodiimide or sodium azide. This was also absent in atp mutant with defect in the F0F1-ATPase and, in addition, it was less in potassium ion-free medium. These results are correlated with data about K+-dependent F0F1-ATPase activity, suggesting a relationship between the F0F1-ATPase and K+ uptake Trk-like system. The latter may be regulated by NAD or NADH mediating conformational changes.

Nature's design of nanomotors

The need for movement is an essential concept of all living organisms. On a macroscopic scale, animals and microbes have to be able to move towards food and away from poison and predators. Plants turn their leaves toward their energy source, the sunlight. But even on a molecular scale, movement is essential for life. It has been known for a long time that enzymes and proteins undergo large conformational changes while performing their biological tasks. The catalytically active regions of enzymes need to sequentially open to bind their respective substrates and close to allow the specific chemical reaction to occur in a defined chemical environment. The active sites finally open up again up to allow the product to be released. Molecular motors are proteins and protein complexes that have evolved in living cells to carry out a variety of functions essential for survival, reproduction and differentiation of the cells and organisms. They use chemical, electrochemical or potential energy and transduce that energy into physical, chemical or mechanical force. In this paper we review some of the molecular motors that were designed by nature to either perform physical work or that contain motor-like movements as part of their catalytic mechanism.

Thioredoxin affinity chromatography: a useful method for further understanding the thioredoxin network

Thioredoxin affinity chromatography can be used to recognize the target proteins of thioredoxin or thioredoxin-related proteins in whole cells or certain cellular compartments. In the last couple of years, many potential target proteins have been identified from various organelles and organisms by this method. Based on the information on the target proteins provided by these studies, the complete thioredoxin-related redox networks can now be efficiently described.

Observation of calcium-dependent unidirectional rotational motion in recombinant photosynthetic F1-ATPase molecules

ATP hydrolysis and synthesis by the F(0)F(1)-ATP synthase are coupled to proton translocation across the membrane in the presence of magnesium. Calcium is known, however, to disrupt this coupling in the photosynthetic enzyme in a unique way: it does not support ATP synthesis, and CaATP hydrolysis is decoupled from any proton translocation, but the membrane does not become leaky to protons. Understanding the molecular basis of these calcium-dependent effects can shed light on the as yet unclear mechanism of coupling between proton transport and rotational catalysis. We show here, using an actin filament gamma-rotation assay, that CaATP is capable of sustaining rotational motion in a highly active hybrid photosynthetic F(1)-ATPase consisting of alpha and beta subunits from Rhodospirillum rubrum and gamma subunit from spinach chloroplasts (alpha(R)(3)beta(R)(3)gamma(C)). The rotation was found to be similar to that induced by MgATP in Escherichia coli F(1)-ATPase molecules. Our results suggest a possible long range pathway that enables the bound CaATP to induce full rotational motion of gamma but might block transmission of this rotational motion into proton translocation by the F(0) part of the ATP synthase.

Significance of the epsilon subunit in the thiol modulation of chloroplast ATP synthase

To understand the regulatory function of the gamma and epsilon subunits of chloroplast ATP synthase in the membrane integrated complex, we constructed a chimeric FoF1 complex of thermophilic bacteria. When a part of the chloroplast F1 gamma subunit was introduced into the bacterial FoF1 complex, the inverted membrane vesicles with this chimeric FoF1 did not exhibit the redox sensitive ATP hydrolysis activity, which is a common property of the chloroplast ATP synthase. However, when the whole part or the C-terminal alpha-helices region of the epsilon subunit was substituted with the corresponding region from CF1-epsilon together with the mutation of gamma, the redox regulation property emerged. In contrast, ATP synthesis activity did not become redox sensitive even if both the regulatory region of CF1-gamma and the entire epsilon subunit from CF1 were introduced. These results provide important features for the regulation of FoF1 by these subunits: (1) the interaction between gamma and epsilon is important for the redox regulation of FoF1 complex by the gamma subunit, and (2) a certain structural matching between these regulatory subunits and the catalytic core of the enzyme must be required to confer the complete redox regulation mechanism to the bacterial FoF1. In addition, a structural requirement for the redox regulation of ATP hydrolysis activity might be different from that for the ATP synthesis activity.

Inverse regulation of rotation of F1-ATPase by the mutation at the regulatory region on the gamma subunit of chloroplast ATP synthase

In F1-ATPase, the rotation of the central axis subunit gamma relative to the surrounding alpha3beta3 subunits is coupled to ATP hydrolysis. We previously reported that the introduced regulatory region of the gamma subunit of chloroplast F1-ATPase can modulate rotation of the gamma subunit of the thermophilic bacterial F1-ATPase (Bald, D., Noji, H., Yoshida, M., Hirono-Hara, Y., and Hisabori, T. (2001) J. Biol. Chem. 276, 39505-39507). The attenuated enzyme activity of this chimeric enzyme under oxidizing conditions was characterized by frequent and long pauses of rotation of gamma. In this study, we report an inverse regulation of the gamma subunit rotation in the newly engineered F1-chimeric complex whose three negatively charged residues Glu210-Asp211-Glu212 adjacent to two cysteine residues of the regulatory region derived from chloroplast F1-ATPase gamma were deleted. ATP hydrolysis activity of the mutant complex was stimulated up to 2-fold by the formation of the disulfide bond at the regulatory region by oxidation. We successfully observed inverse redox switching of rotation of gamma using this mutant complex. The complex exhibited long and frequent pauses in its gamma rotation when reduced, but the rotation rates between pauses remained unaltered. Hence, the suppression or activation of the redox-sensitive F1-ATPase can be explained in terms of the change in the rotation behavior at a single molecule level. These results obtained by the single molecule analysis of the redox regulation provide further insights into the regulation mechanism of the rotary enzyme.

Complete inhibition and partial Re-activation of single F1-ATPase molecules by tentoxin: new properties of the re-activated enzyme

During hydrolysis of ATP, the gamma subunit of the rotary motor protein F(1)-ATPase rotates within a ring of alpha(3)beta(3) subunits. Tentoxin is a phyto-pathogenic cyclic tetrapeptide, which influences F(1)-ATPase activity of sensitive species. At low concentrations, tentoxin inhibits ATP hydrolysis of ensembles of F(1) molecules in solution. At higher concentrations, however, ATP hydrolysis recovers. Here we have examined how tentoxin acts on individual molecules of engineered F(1)-ATPase from the thermophilic Bacillus PS3 (Groth, G., Hisabori, T., Lill, H., and Bald, D. (2002) J. Biol. Chem. 277, 20117-20119). We found that inhibition by tentoxin caused a virtually complete stop of rotation, which was partially relieved at higher tentoxin concentrations. Re-activation, however, was not simply a reversal of inhibition; while the torque appears unaffected as compared with the situation without tentoxin, F(1) under re-activating conditions was less susceptible to inhibitory ADP binding but displayed a large number of short pauses, indicating infringed energy conversion.

Inactivation of the chloroplast ATP synthase gamma subunit results in high non-photochemical fluorescence quenching and altered nuclear gene expression in Arabidopsis thaliana

The nuclear atpC1 gene encoding the gamma subunit of the plastid ATP synthase has been inactivated by T-DNA insertion mutagenesis in Arabidopsis thaliana. In the seedling-lethal dpa1 (deficiency of plastid ATP synthase 1) mutant, the absence of detectable amounts of the gamma subunit destabilizes the entire ATP synthase complex. The expression of a second gene copy, atpC2, is unaltered in dpa1 and is not sufficient to compensate for the lack of atpC1 expression. However, in vivo protein labeling analysis suggests that assembly of the ATP synthase alpha and beta subunits into the thylakoid membrane still occurs in dpa1. As a consequence of the destabilized ATP synthase complex, photophosphorylation is abolished even under reducing conditions. Further effects of the mutation include an increased light sensitivity of the plant and an altered photosystem II activity. At low light intensity, chlorophyll fluorescence induction kinetics is close to those found in wild type, but non-photochemical quenching strongly increases with increasing actinic light intensity resulting in steady state fluorescence levels of about 60% of the minimal dark fluorescence. Most fluorescence quenching relaxed within 3 min after dark incubation. Spectroscopic and biochemical studies have shown that a high proton gradient is responsible for most quenching. Thylakoids of illuminated dpa1 plants were swollen due to an increased proton accumulation in the lumen. Expression profiling of 3292 nuclear genes encoding mainly chloroplast proteins demonstrates that most organelle functions are down-regulated. On the contrary, the mRNA expression of some photosynthesis genes is significantly up-regulated, probably to compensate for the defect in dpa1.

Molecular evolution of the modulator of chloroplast ATP synthase: origin of the conformational change dependent regulation

Chloroplast ATP synthase synthesizes ATP by utilizing a proton gradient as an energy supply, which is generated by photosynthetic electron transport. The activity of the chloroplast ATP synthase is regulated in several specific ways to avoid futile hydrolysis of ATP under various physiological conditions. Several regulatory signals such as Delta mu H(+), tight binding of ADP and its release, thiol modulation, and inhibition by the intrinsic inhibitory subunit epsilon are sensed by this complex. In this review, we describe the function of two regulatory subunits, gamma and epsilon, of ATP synthase based on their possible conformational changes and discuss the evolutionary origin of these regulation systems.