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

A New Real-Time Simple Method to Measure the Endogenous Nitrate Reductase Activity (Nar) in Paracoccus denitrificans and Other Denitrifying Bacteria

The transmembrane nitrate reductase (Nar) is the first enzyme in the dissimilatory alternate anaerobic nitrate respiratory chain in denitrifying bacteria. To date, there has been no real-time method to determine its specific activity embedded in its native membrane; here, we describe such a new method, which is useful with the inside-out membranes of Paracoccus denitrificans and other denitrifying bacteria. This new method takes advantage of the native coupling of the endogenous NADH dehydrogenase or Complex I with the reduction of nitrate by Nar through the quinone pool of the inner membranes of P. denitrificans. This is achieved under previously reached anaerobic conditions. Inner controls confirming the specific Nar activity determined by this new method were made by the total inhibition of the Nar enzyme by sodium azide and cyanide, well-known Nar inhibitors. The estimation of the Michaelis-Menten affinity of Nar for NO3- using this so-called Nar-JJ assay gave a Km of 70.4 μM, similar to previously determined values. This new Nar-JJ assay is a suitable, low-cost, and reproducible method to determine in real-time the endogenous Nar activity not only in P. denitrificans, but in other denitrifying bacteria such as Brucella canis, and potentially in other entero-pathogenic bacteria.

Inhibitory to non-inhibitory evolution of the ζ subunit of the F1FO-ATPase of Paracoccus denitrificans and α-proteobacteria as related to mitochondrial endosymbiosis

Introduction: The ζ subunit is a potent inhibitor of the F1FO-ATPase of Paracoccus denitrificans (PdF1FO-ATPase) and related α-proteobacteria different from the other two canonical inhibitors of bacterial (ε) and mitochondrial (IF1) F1FO-ATPases. ζ mimics mitochondrial IF1 in its inhibitory N-terminus, blocking the PdF1FO-ATPase activity as a unidirectional pawl-ratchet and allowing the PdF1FO-ATP synthase turnover. ζ is essential for the respiratory growth of P. denitrificans, as we showed by a Δζ knockout. Given the vital role of ζ in the physiology of P. denitrificans, here, we assessed the evolution of ζ across the α-proteobacteria class. Methods: Through bioinformatic, biochemical, molecular biology, functional, and structural analyses of several ζ subunits, we confirmed the conservation of the inhibitory N-terminus of ζ and its divergence toward its C-terminus. We reconstituted homologously or heterologously the recombinant ζ subunits from several α-proteobacteria into the respective F-ATPases, including free-living photosynthetic, facultative symbiont, and intracellular facultative or obligate parasitic α-proteobacteria. Results and discussion: The results show that ζ evolved, preserving its inhibitory function in free-living α-proteobacteria exposed to broad environmental changes that could compromise the cellular ATP pools. However, the ζ inhibitory function was diminished or lost in some symbiotic α-proteobacteria where ζ is non-essential given the possible exchange of nutrients and ATP from hosts. Accordingly, the ζ gene is absent in some strictly parasitic pathogenic Rickettsiales, which may obtain ATP from the parasitized hosts. We also resolved the NMR structure of the ζ subunit of Sinorhizobium meliloti (Sm-ζ) and compared it with its structure modeled in AlphaFold. We found a transition from a compact ordered non-inhibitory conformation into an extended α-helical inhibitory N-terminus conformation, thus explaining why the Sm-ζ cannot exert homologous inhibition. However, it is still able to inhibit the PdF1FO-ATPase heterologously. Together with the loss of the inhibitory function of α-proteobacterial ε, the data confirm that the primary inhibitory function of the α-proteobacterial F1FO-ATPase was transferred from ε to ζ and that ζ, ε, and IF1 evolved by convergent evolution. Some key evolutionary implications on the endosymbiotic origin of mitochondria, as most likely derived from α-proteobacteria, are also discussed.

Atomic insights of an up and down conformation of the Acinetobacter baumannii F1 -ATPase subunit ε and deciphering the residues critical for ATP hydrolysis inhibition and ATP synthesis

The Acinetobacter baumannii F1 FO -ATP synthase (α3 :β3 :γ:δ:ε:a:b2 :c10 ), which is essential for this strictly respiratory opportunistic human pathogen, is incapable of ATP-driven proton translocation due to its latent ATPase activity. Here, we generated and purified the first recombinant A. baumannii F1 -ATPase (AbF1 -ATPase) composed of subunits α3 :β3 :γ:ε, showing latent ATP hydrolysis. A 3.0 Å cryo-electron microscopy structure visualizes the architecture and regulatory element of this enzyme, in which the C-terminal domain of subunit ε (Abε) is present in an extended position. An ε-free AbF1 -ɑβγ complex generated showed a 21.5-fold ATP hydrolysis increase, demonstrating that Abε is the major regulator of AbF1 -ATPase's latent ATP hydrolysis. The recombinant system enabled mutational studies of single amino acid substitutions within Abε or its interacting subunits β and γ, respectively, as well as C-terminal truncated mutants of Abε, providing a detailed picture of Abε's main element for the self-inhibition mechanism of ATP hydrolysis. Using a heterologous expression system, the importance of Abε's C-terminus in ATP synthesis of inverted membrane vesicles, including AbF1 FO -ATP synthases, has been explored. In addition, we are presenting the first NMR solution structure of the compact form of Abε, revealing interaction of its N-terminal β-barrel and C-terminal ɑ-hairpin domain. A double mutant of Abε highlights critical residues for Abε's domain-domain formation which is important also for AbF1 -ATPase's stability. Abε does not bind MgATP, which is described to regulate the up and down movements in other bacterial counterparts. The data are compared to regulatory elements of F1 -ATPases in bacteria, chloroplasts, and mitochondria to prevent wasting of ATP.

Rotary properties of hybrid F1-ATPases consisting of subunits from different species

F₁-ATPase (F₁) is an ATP-driven rotary motor protein ubiquitously found in many species as the catalytic portion of F_oF₁-ATP synthase. Despite the highly conserved amino acid sequence of the catalytic core subunits: α and β, F₁ shows diversity in the maximum catalytic turnover rate V_max and the number of rotary steps per turn. To study the design principle of F₁, we prepared eight hybrid F₁s composed of subunits from two of three genuine F₁s: thermophilic Bacillus PS3 (TF₁), bovine mitochondria (bMF₁), and Paracoccus denitrificans (PdF₁), differing in the V_max and the number of rotary steps. The V_max of the hybrids can be well fitted by a quadratic model highlighting the dominant roles of β and the couplings between α-β. Although there exist no simple rules on which subunit dominantly determines the number of steps, our findings show that the stepping behavior is characterized by the combination of all subunits.

F1·Fo ATP Synthase/ATPase: Contemporary View on Unidirectional Catalysis

F1·Fo-ATP synthases/ATPases (F1·Fo) are molecular machines that couple either ATP synthesis from ADP and phosphate or ATP hydrolysis to the consumption or production of a transmembrane electrochemical gradient of protons. Currently, in view of the spread of drug-resistant disease-causing strains, there is an increasing interest in F1·Fo as new targets for antimicrobial drugs, in particular, anti-tuberculosis drugs, and inhibitors of these membrane proteins are being considered in this capacity. However, the specific drug search is hampered by the complex mechanism of regulation of F1·Fo in bacteria, in particular, in mycobacteria: the enzyme efficiently synthesizes ATP, but is not capable of ATP hydrolysis. In this review, we consider the current state of the problem of “unidirectional” F1·Fo catalysis found in a wide range of bacterial F1·Fo and enzymes from other organisms, the understanding of which will be useful for developing a strategy for the search for new drugs that selectively disrupt the energy production of bacterial cells.

ATP binding by an F1Fo ATP synthase ε subunit is pH dependent, suggesting a diversity of ε subunit functional regulation in bacteria

It is a conjecture that the ε subunit regulates ATP hydrolytic function of the F₁F_o ATP synthase in bacteria. This has been proposed by the ε subunit taking an extended conformation, with a terminal helix probing into the central architecture of the hexameric catalytic domain, preventing ATP hydrolysis. The ε subunit takes a contracted conformation when bound to ATP, thus would not interfere with catalysis. A recent crystallographic study has disputed this; the Caldalkalibacillus thermarum TA2.A1 F₁F_o ATP synthase cannot natively hydrolyse ATP, yet studies have demonstrated that the loss of the ε subunit terminal helix results in an ATP synthase capable of ATP hydrolysis, supporting ε subunit function. Analysis of sequence and crystallographic data of the C. thermarum F₁F_o ATP synthase revealed two unique histidine residues. Molecular dynamics simulations suggested that the protonation state of these residues may influence ATP binding site stability. Yet these residues lie outside the ATP/Mg²⁺ binding site of the ε subunit. We then probed the effect of pH on the ATP binding affinity of the ε subunit from the C. thermarum F₁F_o ATP synthase at various physiologically relevant pH values. We show that binding affinity changes 5.9 fold between pH 7.0, where binding is weakest, to pH 8.5 where it is strongest. Since the C. thermarum cytoplasm is pH 8.0 when it grows optimally, this correlates to the ε subunit being down due to ATP/Mg²⁺ affinity, and not being involved in blocking ATP hydrolysis. Here, we have experimentally correlated that the pH of the bacterial cytoplasm is of critical importance for ε subunit ATP affinity regulated by second-shell residues thus the function of the ε subunit changes with growth conditions.

Structural Elements Involved in ATP Hydrolysis Inhibition and ATP Synthesis of Tuberculosis and Nontuberculous Mycobacterial F-ATP Synthase Decipher New Targets for Inhibitors

The F₁F_O-ATP synthase is required for the viability of tuberculosis (TB) and nontuberculous mycobacteria (NTM) and has been validated as a drug target. Here, we present the cryo-EM structures of the Mycobacterium smegmatis F₁-ATPase and the F₁F_O-ATP synthase with different nucleotide occupation within the catalytic sites and visualize critical elements for latent ATP hydrolysis and efficient ATP synthesis. Mutational studies reveal that the extended C-terminal domain (αCTD) of subunit α is the main element for the self-inhibition mechanism of ATP hydrolysis for TB and NTM bacteria. Rotational studies indicate that the transition between the inhibition state by the αCTD and the active state is a rapid process. We demonstrate that the unique mycobacterial γ-loop and subunit δ are critical elements required for ATP formation. The data underline that these mycobacterium-specific elements of α, γ, and δ are attractive targets, providing a platform for the discovery of species-specific inhibitors.

Interaction of Venturicidin and Fo·F1-ATPase/ATP Synthase of Tightly Coupled Subbacterial Particles of Paracoccus denitrificans in Energized Membranes

Proton-translocating F_o×F₁-ATPase/synthase that catalyzes synthesis and hydrolysis of ATP is commonly considered to be a reversibly functioning complex. We have previously shown that venturicidin, a specific F_o-directed inhibitor, blocks the synthesis and hydrolysis of ATP with a significant difference in the affinity [Zharova, T. V. and Vinogradov, A. D. (2017) Biochim. Biophys. Acta, 1858, 939-944]. In this paper, we have studied in detail inhibition of F_o×F₁-ATPase/synthase by venturicidin in tightly coupled membranes of Paracoccus denitrificans under conditions of membrane potential generation. ATP hydrolysis was followed by the ATP-dependent succinate-supported NAD+ reduction (potential-dependent reverse electron transfer) catalyzed by the respiratory chain complex I. It has been demonstrated that membrane energization did not affect the affinity of F_o×F₁-ATPase/synthase for venturicidin. The dependence of the residual ATP synthase activity on the concentration of venturicidin approximated a linear function, whereas the dependence of ATP hydrolysis was sigmoidal: at low inhibitor concentrations venturicidin strongly inhibited ATP synthesis without decrease in the rate of ATP hydrolysis. A model is proposed suggesting that ATP synthesis and ATP hydrolysis are catalyzed by two different forms of F_o×F₁.

Evolution of the Inhibitory and Non-Inhibitory ε, ζ, and IF1 Subunits of the F1FO-ATPase as Related to the Endosymbiotic Origin of Mitochondria

The F1FO-ATP synthase nanomotor synthesizes >90% of the cellular ATP of almost all living beings by rotating in the “forward” direction, but it can also consume the same ATP pools by rotating in “reverse.” To prevent futile F1FO-ATPase activity, several different inhibitory proteins or domains in bacteria (ε and ζ subunits), mitochondria (IF1), and chloroplasts (ε and γ disulfide) emerged to block the F1FO-ATPase activity selectively. In this study, we analyze how these F1FO-ATPase inhibitory proteins have evolved. The phylogeny of the α-proteobacterial ε showed that it diverged in its C-terminal side, thus losing both the inhibitory function and the ATP-binding/sensor motif that controls this inhibition. The losses of inhibitory function and the ATP-binding site correlate with an evolutionary divergence of non-inhibitory α-proteobacterial ε and mitochondrial δ subunits from inhibitory bacterial and chloroplastidic ε subunits. Here, we confirm the lack of inhibitory function of wild-type and C-terminal truncated ε subunits of P. denitrificans. Taken together, the data show that ζ evolved to replace ε as the primary inhibitor of the F1FO-ATPase of free-living α-proteobacteria. However, the ζ inhibitory function was also partially lost in some symbiotic α-proteobacteria and totally lost in some strictly parasitic α-proteobacteria such as the Rickettsiales order. Finally, we found that ζ and IF1 likely evolved independently via convergent evolution before and after the endosymbiotic origin mitochondria, respectively. This led us to propose the ε and ζ subunits as tracer genes of the pre-endosymbiont that evolved into the actual mitochondria.

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.

Discovery of Venturicidin Congeners and Identification of the Biosynthetic Gene Cluster from Streptomyces sp. NRRL S-4

Chemical screening of Streptomyces sp. NRRL S-4 with liquid chromatography-mass spectrometry (LC-MS) and the following chromatographic isolation led to the discovery of four 20-membered macrolides, venturicidin A (4) and three new congeners venturicidins D-F (1-3). Genome sequencing of strain S-4 revealed the presence of a biosynthetic gene cluster (BGC) encoding glycosylated type I polyketides (PKS). The BGC designated to venturicidin biosynthesis (ven) was supported by the proposed biosynthetic pathway and confirmed by inactivation of the core PKS gene of venK. Bioinformatic analyses on the conserved motifs and known stereospecificities in PKS modules are consistent with the structure and absolute configuration. This is the first report of venturicidin BGC since the discovery of the macrolide in 1961. In the biological assays, venturicidin A (4) and E (2) displayed a high selective cytotoxicity against acute monocytic leukemia MV-4-11 cells with IC₅₀ values of 0.09 and 0.94 μM, respectively. Venturicidin A (4) also showed a weak inhibitory activity on FMS-like-tyrosine kinase.

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.

The 3 × 120° rotary mechanism of Paracoccus denitrificans F1-ATPase is different from that of the bacterial and mitochondrial F1-ATPases

The rotation of Paracoccus denitrificans F₁-ATPase (PdF₁) was studied using single-molecule microscopy. At all concentrations of adenosine triphosphate (ATP) or a slowly hydrolyzable ATP analog (ATPγS), above or below K _m, PdF₁ showed three dwells per turn, each separated by 120°. Analysis of dwell time between steps showed that PdF₁ executes binding, hydrolysis, and probably product release at the same dwell. The comparison of ATP binding and catalytic pauses in single PdF₁ molecules suggested that PdF₁ executes both elementary events at the same rotary position. This point was confirmed in an inhibition experiment with a nonhydrolyzable ATP analog (AMP-PNP). Rotation assays in the presence of adenosine diphosphate (ADP) or inorganic phosphate at physiological concentrations did not reveal any obvious substeps. Although the possibility of the existence of substeps remains, all of the datasets show that PdF₁ is principally a three-stepping motor similar to bacterial vacuolar (V₁)-ATPase from Thermus thermophilus This contrasts with all other known F₁-ATPases that show six or nine dwells per turn, conducting ATP binding and hydrolysis at different dwells. Pauses by persistent Mg-ADP inhibition or the inhibitory ζ-subunit were also found at the same angular position of the rotation dwell, supporting the simplified chemomechanical scheme of PdF₁ Comprehensive analysis of rotary catalysis of F₁ from different species, including PdF₁, suggests a clear trend in the correlation between the numbers of rotary steps of F₁ and F_o domains of F-ATP synthase. F₁ motors with more distinctive steps are coupled with proton-conducting F_o rings with fewer proteolipid subunits, giving insight into the design principle the F₁F_o of ATP synthase.

Characterizing the Hydration Properties of Proton Binding Sites in the ATP Synthase c-Rings of Bacillus Species

The membrane-embedded domain of ATP synthases contains the c-ring, which translocates ions across the membrane, and its resultant rotation is coupled to ATP synthesis in the extramembranous domain. During rotation, the c-ring becomes accessible on both sides of the lipid bilayer to solvent via channels connected to the other membrane-embedded component, the a subunit, and thereby allows the ion to be released into the solvent environment. In recent times, many experimental structures of c-rings from different species have been solved. In some of these, a water molecule with a proposed "structural role" has been identified within the c-ring ion binding site, but in general, the requirement for high resolution to resolve specific water densities complicates their interpretation. In the present study, we use molecular dynamics (MD) simulations and rigorous free energy calculations to characterize the dynamics and energetics of a water molecule within the ion binding site of the c-ring from Bacillus pseudofirmus OF4, in its wild type (WT) and P51A mutant forms, along with the c-ring from thermophilic Bacillus PS3. Our data suggest that a water molecule stably binds to the P51A mutant, as well as helping to identify a bound water molecule in Bacillus PS3 whose presence was previously overlooked due to the limited resolution of the structural data. Sequence analysis further identifies a novel conserved sequence motif that is likely required to harbor a water molecule for stable ion coordination in the binding site of such proteins.

The Molecular Basis for Purine Binding Selectivity in the Bacterial ATP Synthase ϵ Subunit

The ϵ subunit of ATP synthases has been proposed to regulate ATP hydrolysis in bacteria. Prevailing evidence supports the notion that when the ATP concentration falls below a certain threshold, the ϵ subunit changes its conformation from a non-inhibitory down-state to an extended up-state that then inhibits enzymatic ATP hydrolysis by binding to the catalytic domain. It has been demonstrated that the ϵ subunit from Bacillus PS3 is selective for ATP over other nucleotides, including GTP. In this study, the purine triphosphate selectivity is rationalized by using results from MD simulations and free energy calculations for the R103A/R115A mutant of the ϵ subunit from Bacillus PS3, which binds ATP more strongly than the wild-type protein. Our results are in good agreement with experimental data, and the elucidated molecular basis for selectivity could help to guide the design of novel GTP sensors.

Bio-denitrification performance enhanced by graphene-facilitated iron acquisition

Bio-denitrification is widely used for remediation of nitrate contaminated site or removal of nitrate from wastewater, but its efficiency is not always satisfied and high nitrite accumulation and nitrous oxide emission occur frequently. Iron plays an important role in achieving efficient biological denitrification. Nevertheless, its concentration in cells is usually inadequate, and additional supply of iron to denitrification system has been adopted in the literature. In this study, a novel approach to increase the intracellular iron concentration of denitrifying microbes by using graphene to accelerate iron transport, which significantly enhanced bio-denitrification and decreased intermediates accumulations, was reported, and the underlying mechanisms were explored. The presence of 50 mg/L of graphene was observed to not only significantly promote nitrate removal efficiency by 67.3%, but also decrease nitrite and nitrous oxide generation by 49.0% and 63.9%, respectively. It was found that graphene promoted the generation, transfer and consumption of electrons, increased the activities or gene expressions of Fe-containing enzymes (such as complex I, complex III, various cytochromes, and most denitrification reductases), and enhanced the growth of denitrifiers due to iron acquisition by denitrifying bacteria being remarkably facilitated, leading to a significant increment of intracellular iron concentration. Meanwhile, the intracellular proton-motive force and ATP levels were promoted as well. This study provided a new approach to enhancing bio-denitrification and revealed a novel insight into biological iron acquisition.

Structure of F1-ATPase from the obligate anaerobe Fusobacterium nucleatum

The crystal structure of the F₁-catalytic domain of the adenosine triphosphate (ATP) synthase has been determined from the pathogenic anaerobic bacterium Fusobacterium nucleatum. The enzyme can hydrolyse ATP but is partially inhibited. The structure is similar to those of the F₁-ATPases from Caldalkalibacillus thermarum, which is more strongly inhibited in ATP hydrolysis, and in Mycobacterium smegmatis, which has a very low ATP hydrolytic activity. The β_E-subunits in all three enzymes are in the conventional ‘open’ state, and in the case of C. thermarum and M. smegmatis, they are occupied by an ADP and phosphate (or sulfate), but in F. nucleatum, the occupancy by ADP appears to be partial. It is likely that the hydrolytic activity of the F. nucleatum enzyme is regulated by the concentration of ADP, as in mitochondria.

The structure of the catalytic domain of the ATP synthase from Mycobacterium smegmatis is a target for developing antitubercular drugs

The crystal structure of the F₁-catalytic domain of the adenosine triphosphate (ATP) synthase has been determined from Mycobacterium smegmatis which hydrolyzes ATP very poorly. The structure of the α₃β₃-component of the catalytic domain is similar to those in active F₁-ATPases in Escherichia coli and Geobacillus stearothermophilus However, its ε-subunit differs from those in these two active bacterial F₁-ATPases as an ATP molecule is not bound to the two α-helices forming its C-terminal domain, probably because they are shorter than those in active enzymes and they lack an amino acid that contributes to the ATP binding site in active enzymes. In E. coli and G. stearothermophilus, the α-helices adopt an "up" state where the α-helices enter the α₃β₃-domain and prevent the rotor from turning. The mycobacterial F₁-ATPase is most similar to the F₁-ATPase from Caldalkalibacillus thermarum, which also hydrolyzes ATP poorly. The β_E-subunits in both enzymes are in the usual "open" conformation but appear to be occupied uniquely by the combination of an adenosine 5'-diphosphate molecule with no magnesium ion plus phosphate. This occupation is consistent with the finding that their rotors have been arrested at the same point in their rotary catalytic cycles. These bound hydrolytic products are probably the basis of the inhibition of ATP hydrolysis. It can be envisaged that specific as yet unidentified small molecules might bind to the F₁ domain in Mycobacterium tuberculosis, prevent ATP synthesis, and inhibit the growth of the pathogen.

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.

Single mutations in the ε subunit from thermophilic Bacillus PS3 generate a high binding affinity site for ATP

The ε subunit from ATP synthases acts as an ATP sensor in the bacterial cell to prevent ATP hydrolysis and thus the waste of ATP under conditions of low ATP concentration. However, the ATP binding affinities from various bacterial organisms differ markedly, over several orders of magnitude. For example, the ATP synthases from thermophilic Bacillus PS3 and Escherichia coli exhibit affinities of 4 µM and 22 mM, respectively. The recently reported R103A/R115A double mutant of Bacillus PS3 ATP synthase demonstrated an increased binding affinity by two orders of magnitude with respect to the wild type. Here, we used atomic-resolution molecular dynamics simulations to determine the role of the R103A and R115A single mutations. These lead us to predict that both single mutations also cause an increased ATP binding affinity. Evolutionary analysis reveals R103 and R115 substitutions in the ε subunit from other bacillic organisms, leading us to predict they likely have a higher ATP binding affinity than previously expected.

Unidirectional regulation of the F1FO-ATP synthase nanomotor by the ζ pawl-ratchet inhibitor protein of Paracoccus denitrificans and related α-proteobacteria

The ATP synthase is a reversible nanomotor that gyrates its central rotor clockwise (CW) to synthesize ATP and in counter clockwise (CCW) direction to hydrolyse it. In bacteria and mitochondria, two natural inhibitor proteins, namely the ε and IF1 subunits, prevent the wasteful CCW F1FO-ATPase activity by blocking γ rotation at the αDP/βDP/γ interface of the F1 portion. In Paracoccus denitrificans and related α-proteobacteria, we discovered a different natural F1-ATPase inhibitor named ζ. Here we revise the functional and structural data showing that this novel ζ subunit, although being different to ε and IF1, it also binds to the αDP/βDP/γ interface of the F1 of P. denitrificans. ζ shifts its N-terminal inhibitory domain from an intrinsically disordered protein region (IDPr) to an α-helix when inserted in the αDP/βDP/γ interface. We showed for the first time the key role of a natural ATP synthase inhibitor by the distinctive phenotype of a Δζ knockout mutant in P. denitrificans. ζ blocks exclusively the CCW F1FO-ATPase rotation without affecting the CW-F1FO-ATP synthase turnover, confirming that ζ is important for respiratory bacterial growth by working as a unidirectional pawl-ratchet PdF1FO-ATPase inhibitor, thus preventing the wasteful consumption of cellular ATP. In summary, ζ is a useful model that mimics mitochondrial IF1 but in α-proteobacteria. The structural, functional, and endosymbiotic evolutionary implications of this ζ inhibitor are discussed to shed light on the natural control mechanisms of the three natural inhibitor proteins (ε, ζ, and IF1) of this unique ATP synthase nanomotor, essential for life.

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.

The Biological Role of the ζ Subunit as Unidirectional Inhibitor of the F1FO-ATPase of Paracoccus denitrificans

The biological roles of the three natural F₁F_O-ATPase inhibitors, ε, ζ, and IF₁, on cell physiology remain controversial. The ζ subunit is a useful model for deletion studies since it mimics mitochondrial IF₁, but in the F₁F_O-ATPase of Paracoccus denitrificans (PdF₁F_O), it is a monogenic and supernumerary subunit. Here, we constructed a P. denitrificans 1222 derivative (PdΔζ) with a deleted ζ gene to determine its role in cell growth and bioenergetics. The results show that the lack of ζ in vivo strongly restricts respiratory P. denitrificans growth, and this is restored by complementation in trans with an exogenous ζ gene. Removal of ζ increased the coupled PdF₁F_O-ATPase activity without affecting the PdF₁F_O-ATP synthase turnover, and the latter was not affected at all by ζ reconstitution in vitro. Therefore, ζ works as a unidirectional pawl-ratchet inhibitor of the PdF₁F_O-ATPase nanomotor favoring the ATP synthase turnover to improve respiratory cell growth and bioenergetics.

Deleting the IF1-like ζ subunit from Paracoccus denitrificans ATP synthase is not sufficient to activate ATP hydrolysis

In oxidative phosphorylation, ATP synthases interconvert two forms of free energy: they are driven by the proton-motive force across an energy-transducing membrane to synthesize ATP and displace the ADP/ATP ratio from equilibrium. For thermodynamically efficient energy conversion they must be reversible catalysts. However, in many species ATP synthases are unidirectional catalysts (their rates of ATP hydrolysis are negligible), and in others mechanisms have evolved to regulate or minimize hydrolysis. Unidirectional catalysis by Paracoccus denitrificans ATP synthase has been attributed to its unique ζ subunit, which is structurally analogous to the mammalian inhibitor protein IF1 Here, we used homologous recombination to delete the ζ subunit from the P. denitrificans genome, and compared ATP synthesis and hydrolysis by the wild-type and knockout enzymes in inverted membrane vesicles and the F1-ATPase subcomplex. ATP synthesis was not affected by loss of the ζ subunit, and the rate of ATP hydrolysis increased by less than twofold, remaining negligible in comparison with the rates of the Escherichia coli and mammalian enzymes. Therefore, deleting the P. denitrificans ζ subunit is not sufficient to activate ATP hydrolysis. We close by considering our conclusions in the light of reversible catalysis and regulation in ATP synthase enzymes.

Functional heterogeneity of Fo·F1H+-ATPase/synthase in coupled Paracoccus denitrificans plasma membranes

F_o·F₁H⁺-ATPase/synthase in coupled plasma membrane vesicles of Paracoccus denitrificans catalyzes ATP hydrolysis and/or ATP synthesis with comparable enzyme turnover. Significant difference in pH-profile of these alternative activities is seen: decreasing pH from 8.0 to 7.0 results in reversible inhibition of hydrolytic activity, whereas ATP synthesis activity is not changed. The inhibition of ATPase activity upon acidification results from neither change in ADP(Mg²⁺)-induced deactivation nor the energy-dependent enzyme activation. V_max, not apparent Km^ATP is affected by lowering the pH. Venturicidin noncompetitively inhibits ATP synthesis and coupled ATP hydrolysis, showing significant difference in the affinity to its inhibitory site depending on the direction of the catalysis. This difference cannot be attributed to variations of the substrate-enzyme intermediates for steady-state forward and back reactions or to possible equilibrium between ATP hydrolase and ATP synthase F_o·F₁ modes of the opposite directions of catalysis. The data are interpreted as to suggest that distinct non-equilibrated molecular isoforms of F_o·F₁ ATP synthase and ATP hydrolase exist in coupled energy-transducing membranes.

Regulation of the thermoalkaliphilic F1-ATPase from Caldalkalibacillus thermarum

The crystal structure has been determined of the F1-catalytic domain of the F-ATPase from Caldalkalibacillus thermarum, which hydrolyzes adenosine triphosphate (ATP) poorly. It is very similar to those of active mitochondrial and bacterial F1-ATPases. In the F-ATPase from Geobacillus stearothermophilus, conformational changes in the ε-subunit are influenced by intracellular ATP concentration and membrane potential. When ATP is plentiful, the ε-subunit assumes a "down" state, with an ATP molecule bound to its two C-terminal α-helices; when ATP is scarce, the α-helices are proposed to inhibit ATP hydrolysis by assuming an "up" state, where the α-helices, devoid of ATP, enter the α3β3-catalytic region. However, in the Escherichia coli enzyme, there is no evidence that such ATP binding to the ε-subunit is mechanistically important for modulating the enzyme's hydrolytic activity. In the structure of the F1-ATPase from C. thermarum, ATP and a magnesium ion are bound to the α-helices in the down state. In a form with a mutated ε-subunit unable to bind ATP, the enzyme remains inactive and the ε-subunit is down. Therefore, neither the γ-subunit nor the regulatory ATP bound to the ε-subunit is involved in the inhibitory mechanism of this particular enzyme. The structure of the α3β3-catalytic domain is likewise closely similar to those of active F1-ATPases. However, although the βE-catalytic site is in the usual "open" conformation, it is occupied by the unique combination of an ADP molecule with no magnesium ion and a phosphate ion. These bound hydrolytic products are likely to be the basis of inhibition of ATP hydrolysis.

On the ATP binding site of the ε subunit from bacterial F-type ATP synthases

F-type ATP synthases are reversible machinery that not only synthesize adenosine triphosphate (ATP) using an electrochemical gradient across the membrane, but also can hydrolyze ATP to pump ions under certain conditions. To prevent wasteful ATP hydrolysis, subunit ε in bacterial ATP synthases changes its conformation from the non-inhibitory down- to the inhibitory up-state at a low cellular ATP concentration. Recently, a crystal structure of the ε subunit in complex with ATP was solved in a non-biologically relevant dimeric form. Here, to derive the functional ATP binding site motif, we carried out molecular dynamics simulations and free energy calculations. Our results suggest that the ATP binding site markedly differs from the experimental resolved one; we observe a reorientation of several residues, which bind to ATP in the crystal structure. In addition we find that an Mg(2+) ion is coordinated by ATP, replacing interactions of the second chain in the crystal structure. Thus we demonstrate more generally the influence of crystallization effects on ligand binding sites and their respective binding modes. Furthermore, we propose a role for two highly conserved residues to control the ATP binding/unbinding event, which have not been considered before. Additionally our results provide the basis for the rational development of new biosensors based on subunit ε, as shown previously for novel sensors measuring the ATP concentration in cells.

The Inhibitory Mechanism of the ζ Subunit of the F1FO-ATPase Nanomotor of Paracoccus denitrificans and Related α-Proteobacteria

The ζ subunit is a novel inhibitor of the F1FO-ATPase of Paracoccus denitrificans and related α-proteobacteria. It is different from the bacterial (ϵ) and mitochondrial (IF1) inhibitors. The N terminus of ζ blocks rotation of the γ subunit of the F1-ATPase of P. denitrificans (Zarco-Zavala, M., Morales-Ríos, E., Mendoza-Hernández, G., Ramírez-Silva, L., Pérez-Hernández, G., and García-Trejo, J. J. (2014) FASEB J. 24, 599-608) by a hitherto unknown quaternary structure that was first modeled here by structural homology and protein docking. The F1-ATPase and F1-ζ models of P. denitrificans were supported by cross-linking, limited proteolysis, mass spectrometry, and functional data. The final models show that ζ enters into F1-ATPase at the open catalytic αE/βE interface, and two partial γ rotations lock the N terminus of ζ in an "inhibition-general core region," blocking further γ rotation, while the ζ globular domain anchors it to the closed αDP/βDP interface. Heterologous inhibition of the F1-ATPase of P. denitrificans by the mitochondrial IF1 supported both the modeled ζ binding site at the αDP/βDP/γ interface and the endosymbiotic α-proteobacterial origin of mitochondria. In summary, the ζ subunit blocks the intrinsic rotation of the nanomotor by inserting its N-terminal inhibitory domain at the same rotor/stator interface where the mitochondrial IF1 or the bacterial ϵ binds. The proposed pawl mechanism is coupled to the rotation of the central γ subunit working as a ratchet but with structural differences that make it a unique control mechanism of the nanomotor to favor the ATP synthase activity over the ATPase turnover in the α-proteobacteria.

Structure of a catalytic dimer of the α- and β-subunits of the F-ATPase from Paracoccus denitrificans at 2.3 Å resolution

The structures of F-ATPases have predominantly been determined from mitochondrial enzymes, and those of the enzymes in eubacteria have been less studied. Paracoccus denitrificans is a member of the α-proteobacteria and is related to the extinct protomitochondrion that became engulfed by the ancestor of eukaryotic cells. The P. denitrificans F-ATPase is an example of a eubacterial F-ATPase that can carry out ATP synthesis only, whereas many others can catalyse both the synthesis and the hydrolysis of ATP. Inhibition of the ATP hydrolytic activity of the P. denitrificans F-ATPase involves the ζ inhibitor protein, an α-helical protein that binds to the catalytic F1 domain of the enzyme. This domain is a complex of three α-subunits and three β-subunits, and one copy of each of the γ-, δ- and ℇ-subunits. Attempts to crystallize the F1-ζ inhibitor complex yielded crystals of a subcomplex of the catalytic domain containing the α- and β-subunits only. Its structure was determined to 2.3 Å resolution and consists of a heterodimer of one α-subunit and one β-subunit. It has no bound nucleotides, and it corresponds to the `open' or `empty' catalytic interface found in other F-ATPases. The main significance of this structure is that it aids in the determination of the structure of the intact membrane-bound F-ATPase, which has been crystallized.

Purification, characterization and crystallization of the F-ATPase from Paracoccus denitrificans

The structures of F-ATPases have been determined predominantly with mitochondrial enzymes, but hitherto no F-ATPase has been crystallized intact. A high-resolution model of the bovine enzyme built up from separate sub-structures determined by X-ray crystallography contains about 85% of the entire complex, but it lacks a crucial region that provides a transmembrane proton pathway involved in the generation of the rotary mechanism that drives the synthesis of ATP. Here the isolation, characterization and crystallization of an integral F-ATPase complex from the α-proteobacterium Paracoccus denitrificans are described. Unlike many eubacterial F-ATPases, which can both synthesize and hydrolyse ATP, the P. denitrificans enzyme can only carry out the synthetic reaction. The mechanism of inhibition of its ATP hydrolytic activity involves a ζ inhibitor protein, which binds to the catalytic F₁-domain of the enzyme. The complex that has been crystallized, and the crystals themselves, contain the nine core proteins of the complete F-ATPase complex plus the ζ inhibitor protein. The formation of crystals depends upon the presence of bound bacterial cardiolipin and phospholipid molecules; when they were removed, the complex failed to crystallize. The experiments open the way to an atomic structure of an F-ATPase complex.

Oxidative phosphorylation and respiratory control phenomenon in Paracoccus denitrificans plasma membrane

Changes in respiratory activity, transmembrane electric potential, and ATP synthesis as induced by additions of limited amounts of ADP and P(i) to tightly coupled inverted (inside-out) Paracoccus denitrificans plasma membrane vesicles were traced. The pattern of the changes was qualitatively the same as those observed for coupled mitochondria during the classical State 4-State 3-State 4 transition. Bacterial vesicles devoid of energy-dependent permeability barriers for the substrates of oxidation and phosphorylation were used as a simple experimental model to investigate two possible mechanisms of respiratory control: (i) in State 4 phosphoryl transfer potential (ATP/ADP × P(i)) is equilibrated with proton-motive force by reversibly operating F(1)·F(o)-ATPase (thermodynamic control); (ii) in State 4 apparent "equilibrium" is reached by unidirectional operation of proton motive force-activated F(1)·F(o)-ATP synthase. The data support the kinetic mechanism of the respiratory control phenomenon.

NMR structures of α-proteobacterial ATPase-regulating ζ-subunits

NMR structures of ζ-subunits, which are recently discovered α-proteobacterial F1F0-ATPase-regulatory proteins representing a Pfam protein family of 246 sequences from 219 species (PF07345), exhibit a four-helix bundle, which is different from all other known F1F0-ATPase inhibitors. Chemical shift mapping reveals a conserved ADP/ATP binding site in ζ-subunit, which mediates long-range conformational changes related to function, as revealed by the structure of the Paracoccus denitrificans ζ-subunit in complex with ADP. These structural data suggest a new mechanism of F1F0-ATPase regulation in α-proteobacteria.

ATPase/synthase activity of Paracoccus denitrificans Fo·F1 as related to the respiratory control phenomenon

The time course of ATP synthesis, oxygen consumption, and change in the membrane potential in Paracoccus denitrificans inside-out plasma membrane vesicles was traced. ATP synthesis initiated by the addition of a limited amount of either ADP or inorganic phosphate proceeded up to very low residual concentrations of the limiting substrate. Accumulated ATP did not decrease the rate of its synthesis initiated by the addition of ADP. The amount of residual ADP determined at State 4 respiration was independent of ten-fold variation of Pi or the presence of ATP. The pH-dependence of Km for Pi could not be fitted to a simple phosphoric acid dissociation curve. Partial inhibition of respiration resulted in a decrease in the rate of ATP synthesis without affecting the ATP/ADP reached at State 4. At pH8.0, hydrolysis of ATP accumulated at State 4 was induced by a low concentration of an uncoupler, whereas complete uncoupling results in rapid inactivation of ATPase. At pH7.0, no reversal of the ATP synthase reaction by the uncoupler was seen. The data show that ATP/ADP×Pi ratio maintained at State 4 is not in equilibrium with respiratory-generated driving force. Possible mechanisms of kinetic control and unidirectional operation of the Fo·F1-ATP synthase are discussed.

The ζ subunit of the F1FO-ATP synthase of α-proteobacteria controls rotation of the nanomotor with a different structure

The ζ subunit is a novel natural inhibitor of the α-proteobacterial F1FO-ATPase described originally in Paracoccus denitrificans. To characterize the mechanism by which this subunit inhibits the F1FO nanomotor, the ζ subunit of Paracoccus denitrificans (Pd-ζ) was analyzed by the combination of kinetic, biochemical, bioinformatic, proteomic, and structural approaches. The ζ subunit causes full inhibition of the sulfite-activated PdF1-ATPase with an apparent IC50 of 270 nM by a mechanism independent of the ε subunit. The inhibitory region of the ζ subunit resides in the first 14 N-terminal residues of the protein, which protrude from the 4-α-helix bundle structure of the isolated ζ subunit, as resolved by NMR. Cross-linking experiments show that the ζ subunit interacts with rotor (γ) and stator (α, β) subunits of the F1-ATPase, indicating that the ζ subunit hinders rotation of the central stalk. In addition, a putatively regulatory nucleotide-binding site was found in the ζ subunit by isothermal titration calorimetry. Together, the data show that the ζ subunit controls the rotation of F1FO-ATPase by a mechanism reminiscent of, but different from, those described for mitochondrial IF1 and bacterial ε subunits where the 4-α-helix bundle of ζ seems to work as an anchoring domain that orients the N-terminal inhibitory domain to hinder rotation of the central stalk.

ATP synthase in mycobacteria: special features and implications for a function as drug target

ATP synthase is a ubiquitous enzyme that is largely conserved across the kingdoms of life. This conservation is in accordance with its central role in chemiosmotic energy conversion, a pathway utilized by far by most living cells. On the other hand, in particular pathogenic bacteria whilst employing ATP synthase have to deal with energetically unfavorable conditions such as low oxygen tensions in the human host, e.g. Mycobacterium tuberculosis can survive in human macrophages for an extended time. It is well conceivable that such ATP synthases may carry idiosyncratic features that contribute to efficient ATP production. In this review genetic and biochemical data on mycobacterial ATP synthase are discussed in terms of rotary catalysis, stator composition, and regulation of activity. ATP synthase in mycobacteria is of particular interest as this enzyme has been validated as a target for promising new antibacterial drugs. A deeper understanding of the working of mycobacterial ATP synthase and its atypical features can provide insight in adaptations of bacterial energy metabolism. Moreover, pinpointing and understanding critical differences as compared with human ATP synthase may provide input for the design and development of selective ATP synthase inhibitors as antibacterials. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.

Venturicidin C, a new 20-membered macrolide produced by Streptomyces sp. TS-2-2

Venturicidin C (1), a new 20-membered macrolide along with the known venturicidins A (2) and B (3) were isolated from the crude extract of the Appalachian bacterial strain Streptomyces sp. TS-2-2. Additionally, nine other known compounds namely nocardamine, dehydroxynocardamine, desmethylenylnocardamine, ferrioxamine E, adenosine, riboflavin, cyclo(D)-trans-4-OH-Pro-(D)-Phe, cyclo(D)-Pro-(D)-Phe and N-(2-phenylethyl)-acetamide were also isolated and identified. The structure of the new macrolide 1 was elucidated by the cumulative analyses of NMR spectroscopy and HR-MS data. Complete NMR assignments for the known venturicidins A (2) and B (3) are also provided, for the first time, in this report. Venturicidins A-C did not inhibit the proliferation of A549 lung cancer cell line but all displayed potent antifungal activity.

Dissecting a complex chemical stress: chemogenomic profiling of plant hydrolysates

Complex chemical stress arises during the production of biofuels. Large-scale mutant fitness profiling was used to identify bacterial and yeast tolerance genes and to model fitness in a complex hydrolysate mixture. The resulting model can be used to engineer more tolerant strains.

Genome-wide fitness profiling was used to identify plant hydrolysate tolerance genes in Zymomonas mobilis and Saccharomyces cerevisiae.

We modeled fitness in hydrolysate as a mixture of fitness in its components.

Outliers in our model led to the identification of a previously unknown component of hydrolysate.

Overexpression of a Z. mobilis tolerance gene of unknown function improved ethanol productivity in plant hydrolysate.

The efficient production of biofuels from cellulosic feedstocks will require the efficient fermentation of the sugars in hydrolyzed plant material. Unfortunately, plant hydrolysates also contain many compounds that inhibit microbial growth and fermentation. We used DNA-barcoded mutant libraries to identify genes that are important for hydrolysate tolerance in both Zymomonas mobilis (44 genes) and Saccharomyces cerevisiae (99 genes). Overexpression of a Z. mobilis tolerance gene of unknown function (ZMO1875) improved its specific ethanol productivity 2.4-fold in the presence of miscanthus hydrolysate. However, a mixture of 37 hydrolysate-derived inhibitors was not sufficient to explain the fitness profile of plant hydrolysate. To deconstruct the fitness profile of hydrolysate, we profiled the 37 inhibitors against a library of Z. mobilis mutants and we modeled fitness in hydrolysate as a mixture of fitness in its components. By examining outliers in this model, we identified methylglyoxal as a previously unknown component of hydrolysate. Our work provides a general strategy to dissect how microbes respond to a complex chemical stress and should enable further engineering of hydrolysate tolerance.

The ATP synthase: the understood, the uncertain and the unknown

The ATP synthases are multiprotein complexes found in the energy-transducing membranes of bacteria, chloroplasts and mitochondria. They employ a transmembrane protonmotive force, Δp, as a source of energy to drive a mechanical rotary mechanism that leads to the chemical synthesis of ATP from ADP and Pi. Their overall architecture, organization and mechanistic principles are mostly well established, but other features are less well understood. For example, ATP synthases from bacteria, mitochondria and chloroplasts differ in the mechanisms of regulation of their activity, and the molecular bases of these different mechanisms and their physiological roles are only just beginning to emerge. Another crucial feature lacking a molecular description is how rotation driven by Δp is generated, and how rotation transmits energy into the catalytic sites of the enzyme to produce the stepping action during rotation. One surprising and incompletely explained deduction based on the symmetries of c-rings in the rotor of the enzyme is that the amount of energy required by the ATP synthase to make an ATP molecule does not have a universal value. ATP synthases from multicellular organisms require the least energy, whereas the energy required to make an ATP molecule in unicellular organisms and chloroplasts is higher, and a range of values has been calculated. Finally, evidence is growing for other roles of ATP synthases in the inner membranes of mitochondria. Here the enzymes form supermolecular complexes, possibly with specific lipids, and these complexes probably contribute to, or even determine, the formation of the cristae.

Variations of subunit {varepsilon} of the Mycobacterium tuberculosis F1Fo ATP synthase and a novel model for mechanism of action of the tuberculosis drug TMC207

The subunit ε of bacterial F(1)F(O) ATP synthases plays an important regulatory role in coupling and catalysis via conformational transitions of its C-terminal domain. Here we present the first low-resolution solution structure of ε of Mycobacterium tuberculosis (Mtε) F(1)F(O) ATP synthase and the nuclear magnetic resonance (NMR) structure of its C-terminal segment (Mtε(103-120)). Mtε is significantly shorter (61.6 Å) than forms of the subunit in other bacteria, reflecting a shorter C-terminal sequence, proposed to be important in coupling processes via the catalytic β subunit. The C-terminal segment displays an α-helical structure and a highly positive surface charge due to the presence of arginine residues. Using NMR spectroscopy, fluorescence spectroscopy, and mutagenesis, we demonstrate that the new tuberculosis (TB) drug candidate TMC207, proposed to bind to the proton translocating c-ring, also binds to Mtε. A model for the interaction of TMC207 with both ε and the c-ring is presented, suggesting that TMC207 forms a wedge between the two rotating subunits by interacting with the residues W15 and F50 of ε and the c-ring, respectively. T19 and R37 of ε provide the necessary polar interactions with the drug molecule. This new model of the mechanism of TMC207 provides the basis for the design of new drugs targeting the F(1)F(O) ATP synthase in M. tuberculosis.

Atypical cristae morphology of human syncytiotrophoblast mitochondria: role for complex V

Mitochondrial complexes I, III(2), and IV from human cytotrophoblast and syncytiotrophoblast associate to form supercomplexes or respirasomes, with the following stoichiometries: I(1):(III(2))(1) and I(1):(III(2))(1-2):IV(1-4). The content of respirasomes was similar in both cell types after isolating mitochondria. However, syncytiotrophoblast mitochondria possess low levels of dimeric complex V and do not have orthodox cristae morphology. In contrast, cytotrophoblast mitochondria show normal cristae morphology and a higher content of ATP synthase dimer. Consistent with the dimerizing role of the ATPase inhibitory protein (IF(1)) (García, J. J., Morales-Ríos, E., Cortés-Hernandez, P., and Rodríguez-Zavala, J. S. (2006) Biochemistry 45, 12695-12703), higher relative amounts of IF(1) were observed in cytotrophoblast when compared with syncytiotrophoblast mitochondria. Therefore, there is a correlation between dimerization of complex V, IF(1) expression, and the morphology of mitochondrial cristae in human placental mitochondria. The possible relationship between cristae architecture and the physiological function of the syncytiotrophoblast mitochondria is discussed.

ATP synthase in slow- and fast-growing mycobacteria is active in ATP synthesis and blocked in ATP hydrolysis direction

ATP synthase is a validated drug target for the treatment of tuberculosis, and ATP synthase inhibitors are promising candidate drugs for the treatment of infections caused by other slow-growing mycobacteria, such as Mycobacterium leprae and Mycobacterium ulcerans. ATP synthase is an essential enzyme in the energy metabolism of Mycobacterium tuberculosis; however, no biochemical data are available to characterize the role of ATP synthase in slow-growing mycobacterial strains. Here, we show that inverted membrane vesicles from the slow-growing model strain Mycobacterium bovis BCG are active in ATP synthesis, but ATP synthase displays no detectable ATP hydrolysis activity and does not set up a proton-motive force (PMF) using ATP as a substrate. Treatment with methanol as well as PMF activation unmasked the ATP hydrolysis activity, indicating that the intrinsic subunit ɛ and inhibitory ADP are responsible for the suppression of hydrolytic activity. These results suggest that the enzyme is needed for the synthesis of ATP, not for the maintenance of the PMF. For the development of new antimycobacterial drugs acting on ATP synthase, screening for ATP synthesis inhibitors, but not for ATP hydrolysis blockers, can be regarded as a promising strategy.

Structure of dimeric F1F0-ATP synthase

The structure of the dimeric ATP synthase from yeast mitochondria was analyzed by transmission electron microscopy and single particle image analysis. In addition to the previously reported side views of the dimer, top view and intermediate projections served to resolve the arrangement of the rotary c(10) ring and the other stator subunits at the F(0)-F(0) dimeric interface. A three-dimensional reconstruction of the complex was calculated from a data set of 9960 molecular images at a resolution of 27 Å. The structural model of the dimeric ATP synthase shows the two monomers arranged at an angle of ∼45°, consistent with our earlier analysis of the ATP synthase from bovine heart mitochondria (Minauro-Sanmiguel, F., Wilkens, S., and Garcia, J. J. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 12356-12358). In the ATP synthase dimer, the two peripheral stalks are located near the F(1)-F(1) interface but are turned away from each other so that they are not in contact. Based on the three-dimensional reconstruction, a model of how dimeric ATP synthase assembles to form the higher order oligomeric structures that are required for mitochondrial cristae biogenesis is discussed.