ADP-Inhibition of H+-FOF1-ATP Synthase

Association between Perfluorooctanoic Acid-Related Poor Embryo Quality and Metabolite Alterations in Human Follicular Fluid during IVF: A Cohort Study

BACKGROUND

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) have been shown to disrupt normal follicular development and ovulation. However, it is unknown which specific PFAS in follicular fluid negatively impact oocyte development and embryo quality or whether any of the metabolites present in the follicular fluid contribute to these adverse effects.

OBJECTIVES

We conducted a cross-sectional and cohort study to identify specific PFAS with significant adverse effects on embryo quality and their associated modes of action.

METHODS

We enrolled 378 women undergoing assisted reproductive technology (ART) and collected follicular fluid samples during oocyte retrieval. We performed PFAS detection and untargeted metabolomics on the follicular fluid. The associations of individual PFAS with high-quality embryo rates and clinical pregnancy outcomes were assessed using beta regression and logistic regression, respectively, and the potential joint effect of mixtures of PFAS was assessed using Bayesian kernel machine regression (BKMR) and quantile g-computation models. A causal mediation effect model was performed to estimate the average indirect impact of PFAS, mediated by high-quality embryo rates, on clinical pregnancy outcomes, as well as its direct impact representing all other causal effects. Spearman's rank correlation coefficient was used to identify the associations between the differentially expressed metabolites and the high-quality embryo rates.

RESULTS

The detection frequencies of 15 PFAS exceeded 85%, and perfluorooctanoic acid (PFOA) had the highest median concentration (6.54  ng / mL ). The PFAS mixture was negatively associated with the high-quality embryo rate, and PFOA was the major contributor (conditional posterior inclusion probability = 0.97295 ). PFAS was also negatively associated with clinical pregnancy outcome, and the causal mediation analysis revealed that the embryo quality potentially mediated the relationship between the clinical pregnancy outcome with PFOA [proportion mediated: 0.181; 95% confidence interval (CI): 0.024, 0.755], perfluoro-n-nonanoic acid (PFNA) (proportion mediated: 0.148; 95% CI: 0.022, 0.656), or perfluoro-n-tridecanoic acid (PFTrDA) (proportion mediated: 0.130; 95% CI: 0.005, 0.693). The decreased organonitrogens (Pro-Trp and lauryldimethylamine oxide) and sphingolipids metabolites (phytosphingosine, N-myristoylsphinganine, and N-lauroyl-d-erythro-sphinganine) in the follicular fluid were associated with PFOA-related poor embryo quality.

CONCLUSIONS

High exposure to follicular fluid PFAS was negatively correlated with embryo quality during ART, with PFOA likely to be the major contributor. PFOA-related poor embryo quality was associated with the reduction of organonitrogens and sphingolipids metabolites that are crucial for the maintenance of normal cell growth and metabolism. https://doi.org/10.1289/EHP15422.

Activation of Bacterial F-ATPase by LDAO: Deciphering the Molecular Mechanism

Proton FOF1 ATP synthase catalyzes the formation of ATP from ADP and inorganic phosphate coupled with transmembrane proton transfer using the energy of the protonmotive force (pmf). As pmf decreases, the direction of the reaction is reversed and the enzyme generates pmf, transferring protons across the membrane using the energy of ATP hydrolysis. ATPase activity of the enzyme can be suppressed by ADP in a non-competitive manner (ADP-inhibition), and in a number of bacteria, it can be inhibited by conformational changes in the regulatory C-terminal domain of the ε subunit. Lauryldimethylamine oxide (LDAO), a zwitterionic detergent, is known to attenuate both of these inhibitory mechanisms, significantly increasing the ATPase activity of the enzyme. For this reason, LDAO is sometimes used for semi-quantitative estimation of the enzyme's susceptibility to these regulatory mechanisms. However, the binding site of LDAO in ATP synthase remains unknown. The mechanism by which the detergent counteracts ADP-inhibition and the inhibition involving the ε subunit is also unclear. We performed molecular docking and predicted that LDAO binding might occur at the catalytic site of ATP synthase, whether empty or containing nucleotides. Molecular dynamics simulations showed that LDAO could affect the mobility of the loop in the β subunit (residues β404-415 in Escherichia coli ATP synthase) near the catalytic site. Mutagenesis of residue β409 in the E. coli enzyme and the corresponding β419 residue in the Bacillus subtilis ATP synthase revealed that the type of side chain of this residue indeed affects LDAO-dependent stimulation of ATPase activity. We also found that LDAO activates the enzyme more strongly in the presence of 100 mM sulfate compared to sulfate-free medium. This phenomenon is likely due to the enhancement of ADP-inhibition of the enzyme by sulfate.

Novel antibiotics against Staphylococcus aureus without detectable resistance by targeting proton motive force and FtsH

The increased prevalence of methicillin-resistant Staphylococcus aureus (MRSA) and its biofilms poses a great threat to human health. Especially, S. aureus-related osteomyelitis was hardly cured even by conventional antibiotics combined with surgical treatment. The development of novel structural antibiotics is urgently needed. By high-throughput screening and rational design, we identified a small molecule C218-0546 and its optimized analog STK848198 with great antimicrobial potential against MRSA avoiding resistance occurrence. And significant synergistical antimicrobial effects were found between the molecules and conventional antibiotics. Mechanisms studies by transcriptomics, fluorescent probes, molecule dynamics, and plasma surface resonance indicated that the proton motive force as well as FtsH are the main potential targets of these molecules. The compounds exhibited excellent in vivo pharmacokinetics, toxicity profiles, and antimicrobial activities in the abscess model as well as the peritonitis-sepsis model. In addition, STK848198 was found to be effective against MRSA biofilms by interacting with the quorum sensing system. STK848198 also showed in vivo efficacy in the periprosthetic joint infection model. In all, our study identified a class of antimicrobials with novel scaffolds that could be potential alternatives for the treatment of MRSA and its biofilm-related infections.

Fo·F1 ATP-synthase/ATPase of Paracoccus denitrificans: Mystery of Unidirectional Catalysis

Fo·F1 ATP synthases/ATPases (Fo·F1) catalyze ATP synthesis by consuming energy of electrochemical potential of hydrogen ions (pmf), or ATP hydrolysis resulting in the pmf formation. It is generally accepted to consider Fo·F1 as a reversible chemomechanical-electrical molecular machine, however: (i) the mechanism of energy-dependent ATP synthesis is based only on the data on hydrolytic activity of the enzyme, (ii) Fo·F1 from a number of organisms effectively synthesize, but is unable to hydrolyze ATP, which indicates non-observance of the principle of microreversibility and requires development of a new hypotheses concerning the enzyme mechanism. Since 1980, the group of A. D. Vinogradov has been developing a concept according to which the elementary catalysis stages of ATP hydrolysis and ATP synthesis do not coincide, and there are two independently operating forms of Fo·F1 in the coupled membranes - pmf-generating ATPase and pmf-consuming ATP synthase. Fo·F1 of P. denitrificans as a natural model of an irreversibly functioning enzyme is a convenient object for experimental verification of the hypothesis of unidirectional energy conversion. The review considers modern concepts of the molecular mechanisms of regulation of Fo·F1 ATP synthase/ATPase of P. denitrificans and development of the hypothesis of two forms of Fo·F1.

The chloroplast ATP synthase redox domain in Chlamydomonas reinhardtii eludes activity regulation for heterotrophic dark metabolism

To maintain CO2 fixation in the Calvin-Benson-Bassham cycle, multistep regulation of the chloroplast ATP synthase (CF1Fo) is crucial to balance the ATP output of photosynthesis with protection of the apparatus. A well-studied mechanism is thiol modulation; a light/dark regulation through reversible cleavage of a disulfide in the CF1Fo γ-subunit. The disulfide hampers ATP synthesis and hydrolysis reactions in dark-adapted CF1Fo from land plants by increasing the required transmembrane electrochemical proton gradient ([Formula: see text]). Here, we show in Chlamydomonas reinhardtii that algal CF1Fo is differently regulated in vivo. A specific hairpin structure in the γ-subunit redox domain disconnects activity regulation from disulfide formation in the dark. Electrochromic shift measurements suggested that the hairpin kept wild-type CF1Fo active, whereas the enzyme was switched off in algal mutant cells expressing a plant-like hairpin structure. The hairpin segment swap resulted in an elevated [Formula: see text] threshold to activate plant-like CF1Fo, increased by ~1.4 photosystem (PS) I charge separations. The resulting dark-equilibrated [Formula: see text] dropped in the mutants by ~2.7 PSI charge separation equivalents. Photobioreactor experiments showed no phenotypes in autotrophic aerated mutant cultures. In contrast, chlorophyll fluorescence measurements under heterotrophic dark conditions point to an altered dark metabolism in cells with the plant-like CF1Fo as the result of bioenergetic deviations from wild-type. Our results suggest that the lifestyle of C. reinhardtii requires a specific CF1Fo dark regulation that partakes in metabolic coupling between the chloroplast and acetate-fueled mitochondria.

Engineering of IF1 -susceptive bacterial F1 -ATPase

IF1 , an inhibitor protein of mitochondrial ATP synthase, suppresses ATP hydrolytic activity of F1 . One of the unique features of IF1 is the selective inhibition in mitochondrial F1 (MF1 ); it inhibits catalysis of MF1 but does not affect F1 with bacterial origin despite high sequence homology between MF1 and bacterial F1 . Here, we aimed to engineer thermophilic Bacillus F1 (TF1 ) to confer the susceptibility to IF1 for elucidating the molecular mechanism of selective inhibition of IF1 . We first examined the IF1 -susceptibility of hybrid F1 s, composed of each subunit originating from bovine MF1 (bMF1 ) or TF1 . It was clearly shown that only the hybrid with the β subunit of mitochondrial origin has the IF1 -susceptibility. Based on structural analysis and sequence alignment of bMF1 and TF1 , the five non-conserved residues on the C-terminus of the β subunit were identified as the candidate responsible for the IF1 -susceptibility. These residues in TF1 were substituted with the bMF1 residues. The resultant mutant TF1 showed evident IF1 -susceptibility. Reversely, we examined the bMF1 mutant with TF1 residues at the corresponding sites, which showed significant suppression of IF1 -susceptibility, confirming the critical role of these residues. We also tested additional three substitutions with bMF1 residues in α and γ subunits that further enhanced the IF1 -susceptibility, suggesting the additive role of these residues. We discuss the molecular mechanism by which IF1 specifically recognizes F1 with mitochondrial origin, based on the present result and the structure of F1 -IF1 complex. These findings would help the development of the inhibitors targeting bacterial F1 .

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.

Modulation of the H+/ATP coupling ratio by ADP and ATP as a possible regulatory feature in the F-type ATP synthases

F-type ATP synthases are transmembrane enzymes, which play a central role in the metabolism of all aerobic and photosynthetic cells and organisms, being the major source of their ATP synthesis. Catalysis occurs via a rotary mechanism, in which the free energy of a transmembrane electrochemical ion gradient is converted into the free energy of ATP phosphorylation from ADP and Pi, and vice versa. An ADP, tightly bound to one of the three catalytic sites on the stator head, is associated with catalysis inhibition, which is relieved by the transmembrane proton gradient and by ATP. By preventing wasteful ATP hydrolysis in times of low osmotic energy and low ATP/ADP ratio, such inhibition constitutes a classical regulatory feedback effect, likely to be an integral component of in vivo regulation. The present miniview focuses on an additional putative regulatory phenomenon, which has drawn so far little attention, consisting in a substrate-induced tuning of the H+/ATP coupling ratio during catalysis, which might represent an additional key to energy homeostasis in the cell. Experimental pieces of evidence in support of such a phenomenon are reviewed.

Attenuated ADP-inhibition of FOF1 ATPase mitigates manifestations of mitochondrial dysfunction in yeast

Proton-translocating F_OF₁ ATP synthase (F-ATPase) couples ATP synthesis or hydrolysis to transmembrane proton transport in bacteria, chloroplasts, and mitochondria. The primary function of the mitochondrial F_OF₁ is ATP synthesis driven by protonmotive force (pmf) generated by the respiratory chain. However, when pmf is low or absent (e.g. during anoxia), F_OF₁ consumes ATP and functions as a proton-pumping ATPase. Several regulatory mechanisms suppress the ATPase activity of F_OF₁ at low pmf. In yeast mitochondria they include special inhibitory proteins Inh1p and Stf1p, and non-competitive inhibition of ATP hydrolysis by MgADP (ADP-inhibition). Presumably, these mechanisms help the cell to preserve the ATP pool upon membrane de-energization. However, no direct evidence was presented to support this hypothesis so far. Here we report that a point mutation Q263L in subunit beta of Saccharomyces cerevisiae ATP synthase significantly attenuated ADP-inhibition of the enzyme without major effect on the rate of ATP production by mitochondria. The mutation also decreased the sensitivity of the enzyme ATPase activity to azide. Similar effects of the corresponding mutations were observed in earlier studies in bacterial enzymes. This observation indicates that the molecular mechanism of ADP-inhibition is probably the same in mitochondrial and in bacterial F_OF₁. The mutant yeast strain had lower growth rate and had a longer lag period preceding exponential growth phase when starved cells were transferred to fresh growth medium. However, upon the loss of mitochondrial DNA (ρ⁰) the βQ263L mutation effect was reversed: the βQ263L ρ⁰ mutant grew faster than the wild-type ρ⁰ yeast. The results suggest that ADP-inhibition might play a role in prevention of wasteful ATP hydrolysis in the mitochondrial matrix.

Heterogeneity of Starved Yeast Cells in IF1 Levels Suggests the Role of This Protein in vivo

In mitochondria, a small protein IF1 suppresses the hydrolytic activity of ATP synthase and presumably prevents excessive ATP hydrolysis under conditions of energy deprivation. In yeast Saccharomyces cerevisiae, IF1 homologs are encoded by two paralogous genes: INH1 and STF1. INH1 expression is known to aggravate the deleterious effects of mitochondrial DNA (mtDNA) depletion. Surprisingly, no beneficial effects of INH1 and STF1 were documented for yeast so far, and the functions of INH1 and STF1 in wild type cells are unclear. Here, we put forward a hypothesis that INH1 and STF1 bring advantage during the fast start of proliferation after reentry into exponential growth from post-diauxic or stationary phases. We found that yeast cells increase the concentration of both proteins in the post-diauxic phase. Post-diauxic phase yeast cells formed two subpopulations distinct in Inh1p and Stf1p concentrations. Upon exit from the post-diauxic phase cells with high level of Inh1-GFP started growing earlier than cells devoid of Inh1-GFP. However, double deletion of INH1 and STF1 did not increase the lag period necessary for stationary phase yeast cells to start growing after reinoculation into the fresh medium. These results point to a redundancy of the mechanisms preventing uncontrolled ATP hydrolysis during energy deprivation.

AtpΘ is an inhibitor of F0F1 ATP synthase to arrest ATP hydrolysis during low-energy conditions in cyanobacteria

Biological processes in all living cells are powered by ATP, a nearly universal molecule of energy transfer. ATP synthases produce ATP utilizing proton gradients that are usually generated by either respiration or photosynthesis. However, cyanobacteria are unique in combining photosynthetic and respiratory electron transport chains in the same membrane system, the thylakoids. How cyanobacteria prevent the futile reverse operation of ATP synthase under unfavorable conditions pumping protons while hydrolyzing ATP is mostly unclear. Here, we provide evidence that the small protein AtpΘ, which is widely conserved in cyanobacteria, is mainly fulfilling this task. The expression of AtpΘ becomes induced under conditions such as darkness or heat shock, which can lead to a weakening of the proton gradient. Translational fusions of AtpΘ to the green fluorescent protein revealed targeting to the thylakoid membrane. Immunoprecipitation assays followed by mass spectrometry and far western blots identified subunits of ATP synthase as interacting partners of AtpΘ. ATP hydrolysis assays with isolated membrane fractions, as well as purified ATP synthase complexes, demonstrated that AtpΘ inhibits ATPase activity in a dose-dependent manner similar to the F₀F₁-ATP synthase inhibitor N,N-dicyclohexylcarbodimide. The results show that, even in a well-investigated process, crucial new players can be discovered if small proteins are taken into consideration and indicate that ATP synthase activity can be controlled in surprisingly different ways.

Fast ATP-Dependent Subunit Rotation in Reconstituted FoF1-ATP Synthase Trapped in Solution

F_oF₁-ATP synthases are ubiquitous membrane-bound, rotary motor enzymes that can catalyze ATP synthesis and hydrolysis. Their enzyme kinetics are controlled by internal subunit rotation, by substrate and product concentrations, and by mechanical inhibitory mechanisms but also by the electrochemical potential of protons across the membrane. Single-molecule Förster resonance energy transfer (smFRET) has been used to detect subunit rotation within F_oF₁-ATP synthases embedded in freely diffusing liposomes. We now report that kinetic monitoring of functional rotation can be prolonged from milliseconds to seconds by utilizing an anti-Brownian electrokinetic trap (ABEL trap). These extended observation times allowed us to observe fluctuating rates of functional rotation for individual F_oF₁-liposomes in solution. Broad distributions of ATP-dependent catalytic rates were revealed. The buildup of an electrochemical potential of protons was confirmed to limit the maximum rate of ATP hydrolysis. In the presence of ionophores or uncouplers, the fastest subunit rotation speeds measured in single reconstituted F_oF₁-ATP synthases were 180 full rounds per second. This was much faster than measured by biochemical ensemble averaging, but not as fast as the maximum rotational speed reported previously for isolated single F₁ complexes uncoupled from the membrane-embedded F_o complex. Further application of ABEL trap measurements should help resolve the mechanistic causes of such fluctuating rates of subunit rotation.

Rotary Ion-Translocating ATPases/ATP Synthases: Diversity, Similarities, and Differences

Ion-translocating ATPases and ATP synthases (F-, V-, A-type ATPases, and several P-type ATPases and ABC-transporters) catalyze ATP hydrolysis or ATP synthesis coupled with the ion transport across the membrane. F-, V-, and A-ATPases are protein nanomachines that combine transmembrane transport of protons or sodium ions with ATP synthesis/hydrolysis by means of a rotary mechanism. These enzymes are composed of two multisubunit subcomplexes that rotate relative to each other during catalysis. Rotary ATPases phosphorylate/dephosphorylate nucleotides directly, without the generation of phosphorylated protein intermediates. F-type ATPases are found in chloroplasts, mitochondria, most eubacteria, and in few archaea. V-type ATPases are eukaryotic enzymes present in a variety of cellular membranes, including the plasma membrane, vacuoles, late endosomes, and trans-Golgi cisternae. A-type ATPases are found in archaea and some eubacteria. F- and A-ATPases have two main functions: ATP synthesis powered by the proton motive force (pmf) or, in some prokaryotes, sodium-motive force (smf) and generation of the pmf or smf at the expense of ATP hydrolysis. In prokaryotes, both functions may be vitally important, depending on the environment and the presence of other enzymes capable of pmf or smf generation. In eukaryotes, the primary and the most crucial function of F-ATPases is ATP synthesis. Eukaryotic V-ATPases function exclusively as ATP-dependent proton pumps that generate pmf necessary for the transmembrane transport of ions and metabolites and are vitally important for pH regulation. This review describes the diversity of rotary ion-translocating ATPases from different organisms and compares the structural, functional, and regulatory features of these enzymes.

Deletion of the natural inhibitory protein Inh1 in Ustilago maydis has no effect on the dimeric state of the F1FO-ATP synthase but increases the ATPase activity and reduces the stability

Transduction of electrochemical proton gradient into ATP synthesis is performed by F₁F_O-ATP synthase. The reverse reaction is prevented by the regulatory subunit Inh1. Knockout of the inh1 gene in the basidiomycete Ustilago maydis was generated in order to study the function of this protein in the mitochondrial metabolism and cristae architecture. Deletion of inh1 gen did not affect cell growth, glucose consumption, and biomass production. Ultrastructure and fluorescence analyzes showed that size, cristae shape, network, and distribution of mitochondria was similar to wild strain. Membrane potential, ATP synthesis, and oxygen consumption in wild type and mutant strains had similar values. Kinetic analysis of ATPase activity of complex V in permeabilized mitochondria showed similar values of V_max and K_M for both strains, and no effect of pH was observed. Interestingly, the dimeric state of complex V occurs in the mutant strain, indicating that this subunit is not essential for dimerization. ATPase activity of the isolated monomeric and dimeric forms of complex V indicated V_max values 4-times higher for the mutant strain than for the WT strain, suggesting that the absence of Inh1 subunit increased ATPase activity, and supporting a regulatory role for this protein; however, no effect of pH was observed. ATPase activity of WT oligomers was stimulated several times by dodecyl-maltoside (DDM), probably by removal of ADP from F₁ sector, while DDM induced an inactive form of the mutant oligomers.

The Physiological Functionality of PGR5/PGRL1-Dependent Cyclic Electron Transport in Sustaining Photosynthesis

The cyclic electron transport (CET), after the linear electron transport (LET), is another important electron transport pathway during the light reactions of photosynthesis. The proton gradient regulation 5 (PGR5)/PRG5-like photosynthetic phenotype 1 (PGRL1) and the NADH dehydrogenase-like complex pathways are linked to the CET. Recently, the regulation of CET around photosystem I (PSI) has been recognized as crucial for photosynthesis and plant growth. Here, we summarized the main biochemical processes of the PGR5/PGRL1-dependent CET pathway and its physiological significance in protecting the photosystem II and PSI, ATP/NADPH ratio maintenance, and regulating the transitions between LET and CET in order to optimize photosynthesis when encountering unfavorable conditions. A better understanding of the PGR5/PGRL1-mediated CET during photosynthesis might provide novel strategies for improving crop yield in a world facing more extreme weather events with multiple stresses affecting the plants.

Regulation of ATP hydrolysis by the ε subunit, ζ subunit and Mg-ADP in the ATP synthase of Paracoccus denitrificans

F₁F_O-ATP synthase is a crucial metabolic enzyme that uses the proton motive force from respiration to regenerate ATP. For maximum thermodynamic efficiency ATP synthesis should be fully reversible, but the enzyme from Paracoccus denitrificans catalyzes ATP hydrolysis at far lower rates than it catalyzes ATP synthesis, an effect often attributed to its unique ζ subunit. Recently, we showed that deleting ζ increases hydrolysis only marginally, indicating that other common inhibitory mechanisms such as inhibition by the C-terminal domain of the ε subunit (ε-CTD) or Mg-ADP may be more important. Here, we created mutants lacking the ε-CTD, and double mutants lacking both the ε-CTD and ζ subunit. No substantial activation of ATP hydrolysis was observed in any of these strains. Instead, hydrolysis in even the double mutant strains could only be activated by oxyanions, the detergent lauryldimethylamine oxide, or a proton motive force, which are all considered to release Mg-ADP inhibition. Our results establish that P. denitrificans ATP synthase is regulated by a combination of the ε and ζ subunits and Mg-ADP inhibition.

Antibacterial and ATP Synthesis Modulating Compounds from Salvia tingitana

A surface extract of the aerial parts of Salvia tingitana afforded a nor-sesterterpenoid (1) and eight new sesterterpenoids (2-̵9), along with five known sesterterpenoids, five labdane and one abietane diterpenoid, one sesquiterpenoid, and four flavonoids. The structures of the new compounds were established by 1D and 2D NMR spectroscopy, HRESIMS, and VCD data and Mosher's esters analysis. The antimicrobial activity of compounds was evaluated against 30 human pathogens including 27 clinical strains and three isolates of marine origin for their possible implications on human health. The methyl ester of salvileucolide (10), salvileucolide-6,23-lactone (11), sclareol (15), and manool (17) were the most active against Gram-positive bacteria. The compounds were also tested for the inhibition of ATP production in purified mammalian rod outer segments. Terpenoids 10, 11, 15, and 17 inhibited ATP production, while only 17 inhibited also ATP hydrolysis. Molecular modeling studies confirmed the capacity of 17 to interact with mammalian ATP synthase. A significant reduction of ATP production in the presence of 17 was observed in Enterococcus faecalis and E. faecium isolates.

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%).

Amino Acid Residues β139, β189, and β319 Modulate ADP-Inhibition in Escherichia coli H+-FOF1-ATP Synthase

Proton-translocating F_OF₁-ATP synthase (F-type ATPase, F-ATPase or F_OF₁) performs ATP synthesis/hydrolysis coupled to proton transport across the membrane in mitochondria, chloroplasts, and most eubacteria. The ATPase activity of the enzyme is suppressed in the absence of protonmotive force by several regulatory mechanisms. The most conserved of these mechanisms is noncompetitive inhibition of ATP hydrolysis by the MgADP complex (ADP-inhibition) which has been found in all the enzymes studied. When MgADP binds without phosphate in the catalytic site, the enzyme enters an inactive state, and MgADP gets locked in the catalytic site and does not exchange with the medium. The degree of ADP-inhibition varies in F_OF₁ enzymes from different organisms. In the Escherichia coli enzyme, ADP-inhibition is relatively weak and, in contrast to other organisms, is enhanced rather than suppressed by phosphate. In this study, we used site-directed mutagenesis to investigate the role of amino acid residues β139, β158, β189, and β319 of E. coli F_OF₁-ATP synthase in the mechanism of ADP-inhibition and its modulation by the protonmotive force. The amino acid residues in these positions differ in the enzymes from beta- and gammaproteobacteria (including E. coli) and F_OF₁-ATP synthases from other eubacteria, mitochondria, and chloroplasts. The βN158L substitution produced no effect on the enzyme activity, while substitutions βF139Y, βF189L, and βV319T only slightly affected ATP (1 mM) hydrolysis. However, in a mixture of ATP and ADP, the activity of the mutants was less suppressed than that of the wild-type enzyme. In addition, mutations βF189L and βV319T weakened the ATPase activity inhibition by phosphate in the presence of ADP. We suggest that residues β139, β189, and β319 are involved in the mechanism of ADP-inhibition and its modulation by phosphate.

Cryo-EM structure of the mammalian ATP synthase tetramer bound with inhibitory protein IF1

The mitochondrial adenosine triphosphate (ATP) synthase produces most of the ATP required by mammalian cells. We isolated porcine tetrameric ATP synthase and solved its structure at 6.2-angstrom resolution using a single-particle cryo-electron microscopy method. Two classical V-shaped ATP synthase dimers lie antiparallel to each other to form an H-shaped ATP synthase tetramer, as viewed from the matrix. ATP synthase inhibitory factor subunit 1 (IF1) is a well-known in vivo inhibitor of mammalian ATP synthase at low pH. Two IF1 dimers link two ATP synthase dimers, which is consistent with the ATP synthase tetramer adopting an inhibited state. Within the tetramer, we refined structures of intact ATP synthase in two different rotational conformations at 3.34- and 3.45-Å resolution.

ATP synthesis at physiological nucleotide concentrations

Synthesis of ATP by the F₁F₀ ATP synthase in mitochondria and most bacteria is energized by the proton motive force (pmf) established and maintained by respiratory chain enzymes. Conversely, in the presence of ATP and in the absence of a pmf, the enzyme works as an ATP-driven proton pump. Here, we investigate how high concentrations of ATP affect the enzymatic activity of the F₁F₀ ATP synthase under high pmf conditions, which is the typical situation in mitochondria or growing bacteria. Using the ATP analogue adenosine 5′-O-(1-thiotriphosphate) (ATPαS), we have developed a modified luminescence-based assay to measure ATP synthesis in the presence of millimolar ATP concentrations, replacing an assay using radioactive nucleotides. In inverted membrane vesicles of E. coli, we found that under saturating pmf conditions, ATP synthesis was reduced to ~10% at 5 mM ATPαS. This reduction was reversed by ADP, but not P_i, indicating that the ATP/ADP ratio controls the ATP synthesis rate. Our data suggests that the ATP/ADP ratio ~30 in growing E. coli limits the ATP synthesis rate to ~20% of the maximal rate possible at the applied pmf and that the rate reduction occurs via product inhibition rather than an increased ATP hydrolysis rate.

Mutation Q259L in subunit beta in Bacillus subtilis ATP synthase attenuates ADP-inhibition and decreases fitness in mixed cultures

The ATPase activity of H⁺-F_OF₁-ATP synthase (F_OF₁) is down-regulated by several mechanisms. The most universal of them found in bacterial, chloroplast and mitochondrial enzymes is non-competitive inhibition by MgADP (ADP-inhibition). When MgADP binds in a catalytic site in the absence of phosphate, the nucleotide might be trapped instead of being released and replaced by new MgATP. In this case the enzyme becomes inactivated, and MgADP release is required for re-activation. The degree of ADP-inhibition varies between different organisms: it is strong in mitochondrial and chloroplast F_OF₁ and in enzymes of some bacteria (including Bacillus PS3 sp., and Bacillus subtilis), but in F_OF₁ of Escherichia coli it is much weaker. It was shown that mutation betaGln259Leu in Bacillus PS3 F_OF₁ noticeably relieves its strong ADP-inhibition. In this work, we introduced the same mutation in F_OF₁ from B. subtilis. ADP-inhibition in the mutant F_OF₁ was also attenuated in comparison to the wild-type enzyme. The ATPase activity in membrane preparations was 3 fold higher in the mutant. Mutant enzyme was capable of ATP-driven proton pumping, and its ATPase activity was stimulated by dissipation of the protonmotive force, implying that the coupling efficiency between ATP hydrolysis and proton transport was not impaired by the mutation. We observed no effect of mutation on the growth rate of B. subtilis in pure cultures. However, in competition growth experiments when the wild type and the mutant strains were cultivated together in mixed cultures, the wild type strain always crowded out the mutant. To our knowledge, this is the first demonstration of the negative effect of F_OF₁ ADP-inhibition attenuation in vivo.

Residue 249 in subunit beta regulates ADP inhibition and its phosphate modulation in Escherichia coli ATP synthase

ATPase activity of proton-translocating F_OF₁-ATP synthase (F-type ATPase or F-ATPase) is suppressed in the absence of protonmotive force by several regulatory mechanisms. The most conservative of these mechanisms found in all enzymes studied so far is allosteric inhibition of ATP hydrolysis by MgADP (ADP-inhibition). When MgADP is bound without phosphate in the catalytic site, the enzyme lapses into an inactive state with MgADP trapped. In chloroplasts and mitochondria, as well as in most bacteria, phosphate prevents MgADP inhibition. However, in Escherichia coli ATP synthase ADP-inhibition is relatively weak and phosphate does not prevent it but seems to enhance it. We found that a single amino acid residue in subunit β is responsible for these features of E. coli enzyme. Mutation βL249Q significantly enhanced ADP-inhibition in E. coli ATP synthase, increased the extent of ATP hydrolysis stimulation by sulfite, and rendered the ADP-inhibition sensitive to phosphate in the same manner as observed in F_OF₁ from mitochondria, chloroplasts, and most aerobic\photosynthetic bacteria.