Regulation of the F0F1-ATP synthase: the conformation of subunit epsilon might be determined by directionality of subunit gamma rotation

Directed proton transfer from Fo to F1 extends the multifaceted proton functions in ATP synthase

The role of protons in ATP synthase is typically considered to be energy storage in the form of an electrochemical potential, as well as an operating element proving rotation. However, this review emphasizes that protons also act as activators of conformational changes in F1 and as direct participants in phosphorylation reaction. The protons transferred through Fo do not immediately leave to the bulk aqueous phase, but instead provide for the formation of a pH gradient between acidifying Fo and alkalizing F1. It facilitates a directed inter-subunit proton transfer to F1, where they are used in the ATP synthesis reaction. This ensures that the enzyme activity is not limited by a lack of protons in the alkaline mitochondrial matrix or chloroplast stroma. Up to one hundred protons bind to the carboxyl groups of the F1 subunit, altering the electrical interactions between the amino acids of the enzyme. This removes the inhibition of ATP synthase caused by the electrostatic attraction of charged amino acids of the stator and rotor and also makes the enzyme more prone to conformational changes. Protonation occurs during ATP synthesis initiation and during phosphorylation, while deprotonation blocks the rotation inhibiting both synthesis and hydrolysis. Thus, protons participate in the functioning of all main components of ATP synthase molecular machine making it effectively a proton-driven electric machine. The review highlights the key role of protons as a coupling factor in ATP synthase with multifaceted functions, including charge and energy transport, torque generation, facilitation of conformational changes, and participation in the ATP synthesis reaction.

Transcriptomics reveals the effect of ammonia nitrogen concentration on Pseudomonas stutzeri F2 assimilation and the analysis of amtB function

The biological treatment of wastewater with high concentrations of ammonia nitrogen has become a hot research issue, but there are limited reports on the mechanism of ammonia nitrogen utilization by microorganisms. In this paper, a transcriptomic approach was used to investigate the differences in gene expression at 500.0 mg/L (Amo 500) and 100.0 mg/L (Amo 100) ammonium concentrations to reveal the mechanism of ammonia nitrogen removal from water by Pseudomonas stutzeri F2. The transcriptome data showed 1015 (459 up-regulated and 556 down-regulated) differentially expressed genes with functional gene annotation related to nitrogen source metabolism, glycolysis, tricarboxylic acid cycle, extracellular polysaccharide synthesis, energy conversion and transmembrane transport, revealing the metabolic process of ammonium nitrogen conversion to biological nitrogen in P. stutzeri F2 through assimilation. To verify the effect of ammonium transporter protein (AmtB) of cell membrane on assimilation, a P. stutzeri F2-ΔamtB mutant strain was obtained by constructing a knockout plasmid (pK18mobsacB-ΔamtB), and it was found that the growth characteristics and ammonium removal rate of the mutant strain were significantly reduced at high ammonium concentration. The carbon source components and dissolved oxygen conditions were optimized after analyzing the transcriptome data, and the ammonium removal rate was increased from 41.23% to 94.92% with 500.0 mg/L ammonium concentration. The study of P. stutzeri F2 transcript level reveals the mechanism of ammonia nitrogen influence on microbial assimilation process and improvement strategy, which provides a new strategy for the treatment of ammonia nitrogen wastewater.

The genome and antigen proteome analysis of Spiroplasma mirum

Spiroplasma mirum, small motile wall-less bacteria, was originally isolated from a rabbit tick and had the ability to infect newborn mice and caused cataracts. In this study, the whole genome and antigen proteins of S. mirum were comparative analyzed and investigated. Glycolysis, pentose phosphate pathway, arginine metabolism, nucleotide biosynthesis, and citrate fermentation were found in S. mirum, while trichloroacetic acid, fatty acids metabolism, phospholipid biosynthesis, terpenoid biosynthesis, lactose-specific PTS, and cofactors synthesis were completely absent. The Sec systems of S. mirum consist of SecA, SecE, SecDF, SecG, SecY, and YidC. Signal peptidase II was identified in S. mirum, but no signal peptidase I. The relative gene order in S. mirum is largely conserved. Genome analysis of available species in Mollicutes revealed that they shared only 84 proteins. S. mirum genome has 381 pseudogenes, accounting for 31.6% of total protein-coding genes. This is the evidence that spiroplasma genome is under an ongoing genome reduction. Immunoproteomics, a new scientific technique combining proteomics and immunological analytical methods, provided the direction of our research on S. mirum. We identified 49 proteins and 11 proteins (9 proteins in common) in S. mirum by anti-S. mirum serum and negative serum, respectively. Forty proteins in S. mirum were identified in relation to the virulence. All these proteins may play key roles in the pathogeny and can be used in the future for diagnoses and prevention.

F-ATP-ase of Escherichia coli membranes: The ubiquitous MgADP-inhibited state and the inhibited state induced by the ε-subunit's C-terminal domain are mutually exclusive

ATP synthases are important energy-coupling, rotary motor enzymes in all kingdoms of life. In all F-type ATP synthases, the central rotor of the catalytic F₁ complex is composed of the γ subunit and the N-terminal domain (NTD) of the ε subunit. In the enzymes of diverse bacteria, the C-terminal domain of ε (εCTD) can undergo a dramatic conformational change to trap the enzyme in a transiently inactive state. This inhibitory mechanism is absent in the mitochondrial enzyme, so the εCTD could provide a means to selectively target ATP synthases of pathogenic bacteria for antibiotic development. For Escherichia coli and other bacterial model systems, it has been difficult to dissect the relationship between ε inhibition and a MgADP-inhibited state that is ubiquitous for F_OF₁ from bacteria and eukaryotes. A prior study with the isolated catalytic complex from E. coli, EcF₁, showed that these two modes of inhibition are mutually exclusive, but it has long been known that interactions of F₁ with the membrane-embedded F_O complex modulate inhibition by the εCTD. Here, we study membranes containing EcF_OF₁ with wild-type ε, ε lacking the full εCTD, or ε with a small deletion at the C-terminus. By using compounds with distinct activating effects on F-ATP-ase activity, we confirm that εCTD inhibition and ubiquitous MgADP inhibition are mutually exclusive for membrane-bound E. coli F-ATP-ase. We determine that most of the enzyme complexes in wild-type membranes are in the ε-inhibited state (>50%) or in the MgADP-inhibited state (30%).

Cryo-EM reveals distinct conformations of E. coli ATP synthase on exposure to ATP

ATP synthase produces the majority of cellular energy in most cells. We have previously reported cryo-EM maps of autoinhibited E. coli ATP synthase imaged without addition of nucleotide (Sobti et al. 2016), indicating that the subunit ε engages the α, β and γ subunits to lock the enzyme and prevent functional rotation. Here we present multiple cryo-EM reconstructions of the enzyme frozen after the addition of MgATP to identify the changes that occur when this ε inhibition is removed. The maps generated show that, after exposure to MgATP, E. coli ATP synthase adopts a different conformation with a catalytic subunit changing conformation substantially and the ε C-terminal domain transitioning via an intermediate 'half-up' state to a condensed 'down' state. This work provides direct evidence for unique conformational states that occur in E. coli ATP synthase when ATP binding prevents the ε C-terminal domain from entering the inhibitory 'up' state.

ADP-Inhibition of H+-FOF1-ATP Synthase

H+-F_OF₁-ATP synthase (F-ATPase, F-type ATPase, F_OF₁ complex) catalyzes ATP synthesis from ADP and inorganic phosphate in eubacteria, mitochondria, chloroplasts, and some archaea. ATP synthesis is powered by the transmembrane proton transport driven by the proton motive force (PMF) generated by the respiratory or photosynthetic electron transport chains. When the PMF is decreased or absent, ATP synthase catalyzes the reverse reaction, working as an ATP-dependent proton pump. The ATPase activity of the enzyme is regulated by several mechanisms, of which the most conserved is the non-competitive inhibition by the MgADP complex (ADP-inhibition). When ADP binds to the catalytic site without phosphate, the enzyme may undergo conformational changes that lock bound ADP, resulting in enzyme inactivation. PMF can induce release of inhibitory ADP and reactivate ATP synthase; the threshold PMF value required for enzyme reactivation might exceed the PMF for ATP synthesis. Moreover, membrane energization increases the catalytic site affinity to phosphate, thereby reducing the probability of ADP binding without phosphate and preventing enzyme transition to the ADP-inhibited state. Besides phosphate, oxyanions (e.g., sulfite and bicarbonate), alcohols, lauryldimethylamine oxide, and a number of other detergents can weaken ADP-inhibition and increase ATPase activity of the enzyme. In this paper, we review the data on ADP-inhibition of ATP synthases from different organisms and discuss the in vivo role of this phenomenon and its relationship with other regulatory mechanisms, such as ATPase activity inhibition by subunit ε and nucleotide binding in the noncatalytic sites of the enzyme. It should be noted that in Escherichia coli enzyme, ADP-inhibition is relatively weak and rather enhanced than prevented by phosphate.

The regulatory subunit ε in Escherichia coli FOF1-ATP synthase

F-type ATP synthases are extraordinary multisubunit proteins that operate as nanomotors. The Escherichia coli (E. coli) enzyme uses the proton motive force (pmf) across the bacterial plasma membrane to drive rotation of the central rotor subunits within a stator subunit complex. Through this mechanical rotation, the rotor coordinates three nucleotide binding sites that sequentially catalyze the synthesis of ATP. Moreover, the enzyme can hydrolyze ATP to turn the rotor in the opposite direction and generate pmf. The direction of net catalysis, i.e. synthesis or hydrolysis of ATP, depends on the cell's bioenergetic conditions. Different control mechanisms have been found for ATP synthases in mitochondria, chloroplasts and bacteria. This review discusses the auto-inhibitory behavior of subunit ε found in F_OF₁-ATP synthases of many bacteria. We focus on E. coli F_OF₁-ATP synthase, with insights into the regulatory mechanism of subunit ε arising from structural and biochemical studies complemented by single-molecule microscopy experiments.

Insights into the regulatory function of the ɛ subunit from bacterial F-type ATP synthases: a comparison of structural, biochemical and biophysical data

ATP synthases catalyse the formation of ATP, the most common chemical energy storage unit found in living cells. These enzymes are driven by an electrochemical ion gradient, which allows the catalytic evolution of ATP by a binding change mechanism. Most ATP synthases are capable of catalysing ATP hydrolysis to varying degrees, and to prevent wasteful ATP hydrolysis, bacteria and mitochondria have regulatory mechanisms such as ADP inhibition. Additionally, ɛ subunit inhibition has also been described in three bacterial systems, Escherichia coli, Bacillus PS3 and Caldalkalibacillus thermarum TA2.A1. Previous studies suggest that the ɛ subunit is capable of undergoing an ATP-dependent conformational change from the ATP hydrolytic inhibitory 'extended' conformation to the ATP-induced non-inhibitory 'hairpin' conformation. A recently published crystal structure of the F1 domain of the C. thermarum TA2.A1 F1Fo ATP synthase revealed a mutant ɛ subunit lacking the ability to bind ATP in a hairpin conformation. This is a surprising observation considering it is an organism that performs no ATP hydrolysis in vivo, and appears to challenge the current dogma on the regulatory role of the ɛ subunit. This has prompted a re-examination of present knowledge of the ɛ subunits role in different organisms. Here, we compare published biochemical, biophysical and structural data involving ɛ subunit-mediated ATP hydrolysis regulation in a variety of organisms, concluding that the ɛ subunit from the bacterial F-type ATP synthases is indeed capable of regulating ATP hydrolysis activity in a wide variety of bacteria, making it a potentially valuable drug target, but its exact role is still under debate.

Effects of rare earth and acid rain pollution on plant chloroplast ATP synthase and element contents at different growth stages

Combined rare earth and acid rain pollution has become a new environmental problem, seriously affecting plant survival. The effects of these two kinds of pollutants on plant photosynthesis have been reported, but the micro mechanisms are not very clear. In this research, we studied the effects of lanthanum [La(III), 0.08, 1.20 and 2.40 mM] and acid rain (pH value = 2.5, 3.5 and 4.5) on the ATPase activity and gene transcription level and the functional element contents in rice leaf chloroplasts. The results showed that the combined 0.08 mM La(III) and pH 4.5 acid rain increased the ATPase activity and gene transcription level as well as contents of some functional elements. But other combined treatments of acid rain and La(III) reduced the ATPase activity and gene transcription level as well as functional element contents. The change magnitude of the above indexes at rice booting stage was greater than that in seedling stage or grain filling stage. These results reveal that effects of La(III) and acid rain on ATPase activity and functional element contents in rice leaf chloroplasts are related to the combination of La(III) dose and acid rain intensity and the plant growth stage. In addition, the changes in the ATPase activity were related to ATPase gene transcription level. This study would provide a reference for understanding the microcosmic mechanism of rare earth and acid rain pollution on plant photosynthesis and contribute to evaluate the possible environmental risks associated with combined La(III) and acid rain pollution.

ONE SENTENCE SUMMARY

The effects of La(III) and acid rain on activity and gene transcription level of rice chloroplast ATPase and contents of functional elements were different at different growth stages.

Aerobic Growth of Escherichia coli Is Reduced, and ATP Synthesis Is Selectively Inhibited when Five C-terminal Residues Are Deleted from the ϵ Subunit of ATP Synthase

F-type ATP synthases are rotary nanomotor enzymes involved in cellular energy metabolism in eukaryotes and eubacteria. The ATP synthase from Gram-positive and -negative model bacteria can be autoinhibited by the C-terminal domain of its ϵ subunit (ϵCTD), but the importance of ϵ inhibition in vivo is unclear. Functional rotation is thought to be blocked by insertion of the latter half of the ϵCTD into the central cavity of the catalytic complex (F1). In the inhibited state of the Escherichia coli enzyme, the final segment of ϵCTD is deeply buried but has few specific interactions with other subunits. This region of the ϵCTD is variable or absent in other bacteria that exhibit strong ϵ-inhibition in vitro. Here, genetically deleting the last five residues of the ϵCTD (ϵΔ5) caused a greater defect in respiratory growth than did the complete absence of the ϵCTD. Isolated membranes with ϵΔ5 generated proton-motive force by respiration as effectively as with wild-type ϵ but showed a nearly 3-fold decrease in ATP synthesis rate. In contrast, the ϵΔ5 truncation did not change the intrinsic rate of ATP hydrolysis with membranes. Further, the ϵΔ5 subunit retained high affinity for isolated F1 but reduced the maximal inhibition of F1-ATPase by ϵ from >90% to ∼20%. The results suggest that the ϵCTD has distinct regulatory interactions with F1 when rotary catalysis operates in opposite directions for the hydrolysis or synthesis of ATP.

A mechano-chemiosmotic model for the coupling of electron and proton transfer to ATP synthesis in energy-transforming membranes: a personal perspective

ATP is synthesized using ATP synthase by utilizing energy either from the oxidation of organic compounds, or from light, via redox reactions (oxidative- or photo phosphorylation), in energy-transforming membranes of mitochondria, chloroplasts, and bacteria. ATP synthase undergoes several changes during its functioning. The generally accepted model for ATP synthesis is the well-known rotatory model (see e.g., Junge et al., Nature 459:364-370, 2009; Junge and Müller, Science 333:704-705, 2011). Here, we present an alternative modified model for the coupling of electron and proton transfer to ATP synthesis, which was initially developed by Albert Lester Lehninger (1917-1986). Details of the molecular mechanism of ATP synthesis are described here that involves cyclic low-amplitude shrinkage and swelling of mitochondria. A comparison of the well-known current model and the mechano-chemiosmotic model is also presented. Based on structural, and other data, we suggest that ATP synthase is a Ca(2+)/H(+)-K(+) Cl(-)-pump-pore-enzyme complex, in which γ-subunit rotates 360° in steps of 30°, and 90° due to the binding of phosphate ions to positively charged amino acid residues in the N-terminal γ-subunit, while in the electric field. The coiled coil b 2-subunits are suggested to act as ropes that are shortened by binding of phosphate ions to positively charged lysines or arginines; this process is suggested to pull the α 3 β 3-hexamer to the membrane during the energization process. ATP is then synthesized during the reverse rotation of the γ-subunit by destabilizing the phosphated N-terminal γ-subunit and b 2-subunits under the influence of Ca(2+) ions, which are pumped over from storage-intermembrane space into the matrix, during swelling of intermembrane space. In the process of ATP synthesis, energy is first, predominantly, used in the delivery of phosphate ions and protons to the α 3 β 3-hexamer against the energy barrier with the help of C-terminal alpha-helix of γ-subunit that acts as a lift; then, in the formation of phosphoryl group; and lastly, in the release of ATP molecules from the active center of the enzyme and the loading of ADP. We are aware that our model is not an accepted model for ATP synthesis, but it is presented here for further examination and test.

ATP-induced dimerization of the F0F1 ε subunit from Bacillus PS3: a hydrogen exchange-mass spectrometry study

F0F1 ATP synthase harnesses a transmembrane electrochemical gradient for the production of ATP. When operated in reverse, this multiprotein complex catalyzes ATP hydrolysis. In bacteria, the ε subunit is involved in regulating this ATPase activity. Also, ε is essential for coupling ATP hydrolysis (or synthesis) to proton translocation. The ε subunit consists of a β sandwich and two C-terminal helices, α1 and α2. The protein can switch from a compact fold to an alternate conformation where α1 and α2 are separated, resulting in an extended structure. ε from the thermophile Bacillus PS3 (Tε) binds ATP with high affinity such that this protein may function as an intracellular ATP level sensor. ATP binding to isolated Tε triggers a major conformational transition. Earlier data were interpreted in terms of an ATP + Tεextended → ATP·Tεcompact transition that may mimic aspects of the regulatory switching within F0F1 (Yagi et al. (2007) Proc. Natl. Acad. Sci. U.S.A., 104, 11233–11238). In this work, we employ complementary biophysical techniques for examining the ATP-induced conformational switching of isolated Tε. CD spectroscopy confirmed the occurrence of a large-scale conformational transition upon ATP binding, consistent with the formation of stable helical structure. Hydrogen/deuterium exchange (HDX) mass spectrometry revealed that this transition is accompanied by a pronounced stabilization in the vicinity of the ATP-binding pocket. Surprisingly, dramatic stabilization is also seen in the β8−β9 region, which is remote from the site of ATP interaction. Analytical ultracentrifugation uncovered a previously unrecognized feature of Tε: a high propensity to undergo dimerization in the presence of ATP. Comparison with existing crystallography data strongly suggests that the unexpected β8−β9 HDX protection is due to newly formed protein–protein contacts. Hence, ATP binding to isolated Tε proceeds according to 2ATP + 2Tεextended → (ATP·Tεcompact)2. Implications of this dimerization propensity for the possible role of Tε as an antibiotic target are discussed.

Astrocyte-dependent protective effect of quetiapine on GABAergic neuron is associated with the prevention of anxiety-like behaviors in aging mice after long-term treatment

Previous studies have demonstrated that quetiapine (QTP) may have neuroprotective properties; however, the underlying mechanisms have not been fully elucidated. In this study, we identified a novel mechanism by which QTP increased the synthesis of ATP in astrocytes and protected GABAergic neurons from aging-induced death. In 12-month-old mice, QTP significantly improved cell number of GABAegic neurons in the cortex and ameliorated anxiety-like behaviors compared to control group. Complimentary in vitro studies showed that QTP had no direct effect on the survival of aging GABAergic neurons in culture. Astrocyte-conditioned medium (ACM) pretreated with QTP (ACMQTP) for 24 h effectively protected GABAergic neurons against aging-induced spontaneous cell death. It was also found that QTP boosted the synthesis of ATP from cultured astrocytes after 24 h of treatment, which might be responsible for the protective effects on neurons. Consistent with the above findings, a Rhodamine 123 test showed that ACMQTP, not QTP itself, was able to prevent the decrease in mitochondrial membrane potential in the aging neurons. For the first time, our study has provided evidence that astrocytes may be the conduit through which QTP is able to exert its neuroprotective effects on GABAergic neurons. The neuroprotective properties of quetiapine (QTP) have not been fully understood. Here, we identify a novel mechanism by which QTP increases the synthesis of ATP in astrocytes and protects GABAergic neurons from aging-induced death in a primary cell culture model. In 12-month-old mice, QTP significantly improves cell number of GABAegic neurons and ameliorates anxiety-like behaviors. Our study indicates that astrocytes may be the conduit through which QTP exerts its neuroprotective effects on GABAergic neurons.

Cytadherence of Mycoplasma pneumoniae induces inflammatory responses through autophagy and toll-like receptor 4

Mycoplasma pneumoniae causes pneumonia, tracheobronchitis, pharyngitis, and asthma in humans. The pathogenesis of M. pneumoniae infection is attributed to excessive immune responses. We previously demonstrated that M. pneumoniae lipoproteins induced inflammatory responses through Toll-like receptor 2 (TLR2). In the present study, we demonstrated that M. pneumoniae induced strong inflammatory responses in macrophages derived from TLR2 knockout (KO) mice. Cytokine production in TLR2 KO macrophages was increased compared with that in the macrophages of wild-type (WT) mice. Heat-killed, antibiotic-treated, and overgrown M. pneumoniae failed to induce inflammatory responses in TLR2 KO macrophages. 3-Methyladenine and chloroquine, inhibitors of autophagy, decreased the induction of inflammatory responses in TLR2 KO macrophages. These inflammatory responses were also inhibited in macrophages treated with the TLR4 inhibitor VIPER and those obtained from TLR2 and TLR4 (TLR2/4) double-KO mice. Two mutants that lacked the ability to induce inflammatory responses in TLR2 KO macrophages were obtained by transposon mutagenesis. The transposons were inserted in atpC encoding an ATP synthase F0F1 ε subunit and F10_orf750 encoding hypothetical protein MPN333. These mutants showed deficiencies in cytadherence. These results suggest that cytadherence of M. pneumoniae induces inflammatory responses through TLR4 and autophagy.

Efflux pumps of Gram-negative bacteria: what they do, how they do it, with what and how to deal with them

This review discusses the relationship of the efflux pump (EP) system of Gram-negative bacteria to other antibiotic resistance mechanisms of the bacterium such as quorum sensing, biofilms, two component regulons, etc. The genetic responses of a Gram-negative to an antibiotic that render it immune to an antibiotic are also discussed. Lastly, the methods that have been developed for the identification of bacteria that over-express their EP system are presented in detail. Phenothiazines are well-known antipsychotic drugs with reported activity against bacterial EPs and other ancillary antibiotic mechanisms of the organism. Therefore these compounds will also be discussed.

Structure of the ATP synthase catalytic complex (F(1)) from Escherichia coli in an autoinhibited conformation

ATP synthase is a membrane-bound rotary motor enzyme that is critical for cellular energy metabolism in all kingdoms of life. Despite conservation of its basic structure and function, autoinhibition by one of its rotary stalk subunits occurs in bacteria and chloroplasts but not in mitochondria. The crystal structure of the ATP synthase catalytic complex (F(1)) from Escherichia coli described here reveals the structural basis for this inhibition. The C-terminal domain of subunit ɛ adopts a heretofore unknown, highly extended conformation that inserts deeply into the central cavity of the enzyme and engages both rotor and stator subunits in extensive contacts that are incompatible with functional rotation. As a result, the three catalytic subunits are stabilized in a set of conformations and rotational positions distinct from previous F(1) structures.

Conformational transitions of subunit epsilon in ATP synthase from thermophilic Bacillus PS3

Subunit epsilon of bacterial and chloroplast F(O)F(1)-ATP synthase is responsible for inhibition of ATPase activity. In Bacillus PS3 enzyme, subunit epsilon can adopt two conformations. In the "extended", inhibitory conformation, its two C-terminal alpha-helices are stretched along subunit gamma. In the "contracted", noninhibitory conformation, these helices form a hairpin. The transition of subunit epsilon from an extended to a contracted state was studied in ATP synthase incorporated in Bacillus PS3 membranes at 59 degrees C. Fluorescence energy resonance transfer between fluorophores introduced in the C-terminus of subunit epsilon and in the N-terminus of subunit gamma was used to follow the conformational transition in real time. It was found that ATP induced the conformational transition from the extended to the contracted state (half-maximum transition extent at 140 microM ATP). ADP could neither prevent nor reverse the ATP-induced conformational change, but it did slow it down. Acid residues in the DELSEED region of subunit beta were found to stabilize the extended conformation of epsilon. Binding of ATP directly to epsilon was not essential for the ATP-induced conformational change. The ATP concentration necessary for the half-maximal transition (140 microM) suggests that subunit epsilon probably adopts the extended state and strongly inhibits ATP hydrolysis only when the intracellular ATP level drops significantly below the normal value.

Effect of epsilon subunit on the rotation of thermophilic Bacillus F1-ATPase

F(1)-ATPase is an ATP-driven motor in which gammaepsilon rotates in the alpha(3)beta(3)-cylinder. It is attenuated by MgADP inhibition and by the epsilon subunit in an inhibitory form. The non-inhibitory form of epsilon subunit of thermophilic Bacillus PS3 F(1)-ATPase is stabilized by ATP-binding with micromolar K(d) at 25 degrees C. Here, we show that at [ATP]>2 microM, epsilon does not affect rotation of PS3 F(1)-ATPase but, at 200 nM ATP, epsilon prolongs the pause of rotation caused by MgADP inhibition while the frequency of the pause is unchanged. It appears that epsilon undergoes reversible transition to the inhibitory form at [ATP] below K(d).

Regulatory mechanisms of proton-translocating F(O)F (1)-ATP synthase

H(+)-F(O)F(1)-ATP synthase catalyzes synthesis of ATP from ADP and inorganic phosphate using the energy of transmembrane electrochemical potential difference of proton (deltamu(H)(+). The enzyme can also generate this potential difference by working as an ATP-driven proton pump. Several regulatory mechanisms are known to suppress the ATPase activity of F(O)F(1): 1. Non-competitive inhibition by MgADP, a feature shared by F(O)F(1) from bacteria, chloroplasts and mitochondria 2. Inhibition by subunit epsilon in chloroplast and bacterial enzyme 3. Inhibition upon oxidation of two cysteines in subunit gamma in chloroplast F(O)F(1) 4. Inhibition by an additional regulatory protein (IF(1)) in mitochondrial enzyme In this review we summarize the information available on these regulatory mechanisms and discuss possible interplay between them.

Inhibition of spinach chloroplast F0F1 by an Fe2+/ascorbate/H2O2 system

Plant chloroplasts are particularly threatened by free radical attack. We incubated purified soluble spinach chloroplast F(0)F(1) (CF(0)F(1), EC 3.6.3.34) with an Fe(2+)/H(2)O(2)/ascorbate system, and about 60% inactivation of the ATPase activity was reached after 60 min. Inactivation was not prevented by omission of H(2)O(2), by addition of catalase or superoxide dismutase, nor by the scavengers mannitol, DMSO, or BHT. No evidence for enzyme fragmentation or oligomerization was detected by SDS-PAGE. The chloroplast ATP synthase is resistant to attack by the reactive oxygen species commonly found at the chloroplast level. DTT in the medium completely prevented the inhibition, and its addition after the inhibition partially recovered the activity of the enzyme. CF(0)F(1) thiol residues were lost upon oxidation. The rate of thiol modification was faster than the rate of enzyme inactivation, suggesting that the thiol residues accounting for the inhibition may be hindered. Enzyme previously oxidized by iodobenzoate was not further inhibited by the oxidative system. The production of ascorbyl radical was identified by EPR and is possibly related to CF(0)F(1) inactivation. It is thus suggested that the ascorbyl radical, which accumulates under plant stress, might regulate CF(0)F(1).

Interactions of rotor subunits in the chloroplast ATP synthase modulated by nucleotides and by Mg2+

ATP synthases - rotary nano machines - consist of two major parts, F(O) and F(1), connected by two stalks: the central and the peripheral stalk. In spinach chloroplasts, the central stalk (subunits gamma, epsilon) forms with the cylinder of subunits III the rotor and transmits proton motive force from F(O) to F(1), inducing conformational changes of the catalytic centers in F(1). The epsilon subunit is an important regulator affecting adjacent subunits as well as the activity of the whole protein complex. Using a combination of chemical cross-linking and mass spectrometry, we monitored interactions of subunit epsilon in spinach chloroplast ATP synthase with III and gamma. Onto identification of interacting residues in subunits epsilon and III, one cross-link defined the distance between epsilon-Cys6 and III-Lys48 to be 9.4 A at minimum. epsilon-Cys6 was competitively cross-linked with subunit gamma. Altered cross-linking yields revealed the impact of nucleotides and Mg(2+) on cross-linking of subunit epsilon. The presence of nucleotides apparently induced a displacement of the N-terminus of subunit epsilon, which separated epsilon-Cys6 from both, III-Lys48 and subunit gamma, and thus decreasing the yield of the cross-linked subunits epsilon and gamma as well as epsilon and III. However, increasing concentrations of the cofactor Mg(2+) favoured cross-linking of epsilon-Cys6 with subunit gamma instead of III-Lys48 indicating an approximation of subunits gamma and epsilon and a separation from III-Lys48.

Regulatory interplay between proton motive force, ADP, phosphate, and subunit epsilon in bacterial ATP synthase

ATP synthase couples transmembrane proton transport, driven by the proton motive force (pmf), to the synthesis of ATP from ADP and inorganic phosphate (P(i)). In certain bacteria, the reaction is reversed and the enzyme generates pmf, working as a proton-pumping ATPase. The ATPase activity of bacterial enzymes is prone to inhibition by both ADP and the C-terminal domain of subunit epsilon. We studied the effects of ADP, P(i), pmf, and the C-terminal domain of subunit epsilon on the ATPase activity of thermophilic Bacillus PS3 and Escherichia coli ATP synthases. We found that pmf relieved ADP inhibition during steady-state ATP hydrolysis, but only in the presence of P(i). The C-terminal domain of subunit epsilon in the Bacillus PS3 enzyme enhanced ADP inhibition by counteracting the effects of pmf. It appears that these features allow the enzyme to promptly respond to changes in the ATP:ADP ratio and in pmf levels in order to avoid potentially wasteful ATP hydrolysis in vivo.

The regulator of the F1 motor: inhibition of rotation of cyanobacterial F1-ATPase by the epsilon subunit

The chloroplast-type F(1) ATPase is the key enzyme of energy conversion in chloroplasts, and is regulated by the endogenous inhibitor epsilon, tightly bound ADP, the membrane potential and the redox state of the gamma subunit. In order to understand the molecular mechanism of epsilon inhibition, we constructed an expression system for the alpha(3)beta(3)gamma subcomplex in thermophilic cyanobacteria allowing thorough investigation of epsilon inhibition. epsilon Inhibition was found to be ATP-independent, and different to that observed for bacterial F(1)-ATPase. The role of the additional region on the gamma subunit of chloroplast-type F(1)-ATPase in epsilon inhibition was also determined. By single molecule rotation analysis, we succeeded in assigning the pausing angular position of gamma in epsilon inhibition, which was found to be identical to that observed for ATP hydrolysis, product release and ADP inhibition, but distinctly different from the waiting position for ATP binding. These results suggest that the epsilon subunit of chloroplast-type ATP synthase plays an important regulator for the rotary motor enzyme, thus preventing wasteful ATP hydrolysis.

Modulation of proton pumping efficiency in bacterial ATP synthases

The ATP synthase in chromatophores of Rhodobacter caspulatus can effectively generate a transmembrane pH difference coupled to the hydrolysis of ATP. The rate of hydrolysis was rather insensitive to the depletion of ADP in the assay medium by an ATP regenerating system (phospho-enol-pyruvate (PEP) and pyruvate kinase (PK)). The steady state values of DeltapH were however drastically reduced as a consequence of ADP depletion. The clamped concentrations of ADP obtained using different PK activities in the assay medium could be calculated and an apparent Kd approximately 0.5 microM was estimated. The extent of proton uptake was also strongly dependent on the addition of phosphate to the assay medium. The Kd for this effect was about 70 microM. Analogous experiments were performed in membrane fragment from Escherichia coli. In this case, however, the hydrolysis rate was strongly inhibited by Pi, added up to 3 mM. Inhibition by Pi was nearly completely suppressed following depletion of ADP. The Kd's for the ADP and Pi were in the micromolar range and submillimolar range, respectively, and were mutually dependent from the concentration of the other ligand. Contrary to hydrolysis, the pumping of protons was rather insensitive to changes in the concentrations of the two ligands. At intermediate concentrations, proton pumping was actually stimulated, while the hydrolysis was inhibited. It is concluded that, in these two bacterial organisms, ADP and phosphate induce a functional state of the ATP synthase competent for a tightly coupled proton pumping, while the depletion of either one of these two ligands favors an inefficient (slipping) functional state. The switch between these states can probably be related to a structural change in the C-terminal alpha-helical hairpin of the epsilon-subunit, from an extended conformation, in which ATP hydrolysis is tightly coupled to proton pumping, to a retracted one, in which ATP hydrolysis and proton pumping are loosely coupled.

The role of subunit epsilon in the catalysis and regulation of FOF1-ATP synthase

The regulation of ATP synthase activity is complex and involves several distinct mechanisms. In bacteria and chloroplasts, subunit epsilon plays an important role in this regulation, (i) affecting the efficiency of coupling, (ii) influencing the catalytic pathway, and (iii) selectively inhibiting ATP hydrolysis activity. Several experimental studies indicate that the regulation is achieved through large conformational transitions of the alpha-helical C-terminal domain of subunit epsilon that occur in response to membrane energization, change in ATP/ADP ratio or addition of inhibitors. This review summarizes the experimental data obtained on different organisms that clarify some basic features as well as some molecular details of this regulatory mechanism. Multiple functions of subunit epsilon, its role in the difference between the catalytic pathways of ATP synthesis and hydrolysis and its influence on the inhibition of ATP hydrolysis by ADP are also discussed.