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

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.

New Perspective on the Reversibility of ATP Synthesis and Hydrolysis by Fo×F1-ATP Synthase (Hydrolase)

F_o×F₁-ATPases of mitochondria, chloroplasts, and microorganisms catalyze transformation of proton motive force (the difference between the electrochemical potentials of hydrogen ion across a coupling membrane) to the free energy of ATP phosphoryl potential. It is often stated that F_o×F₁-ATPases operate as reversible chemo-mechano-electrical molecular machines that provide either ATP synthesis or hydrolysis depending on particular physiological demands of an organism; the microreversibility principle of the enzyme catalysis is usually taken as a dogma. Since 1980, the author has upheld the view that the mechanisms of ATP synthesis and hydrolysis by the F_o×F₁ complex are different (Vinogradov, A. D. (2000) J. Exp. Biol., 203, 41-49). In this paper, the author proposes a new model considering the existence in coupling membranes of two non-equilibrium isoforms of F_o×F₁ unidirectionally catalyzing synthesis and/or hydrolysis of ATP.

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.

Photo-Powered Artificial Organelles for ATP Generation and Life-Sustainment

Adenosine triphosphate (ATP) is the most important immediate energy source for driving intracellular biochemical reactions in nearly all life forms. Controllable generation of ATP in life is still an unrealized goal. Here, thylakoid fragments are recombined with lipid molecules to synthesize a synthetic/biological hybrid proteoliposome, named highly efficient life-support intracellular opto-driven system (HELIOS) for the generation of ATP. With red light irradiation, HELIOS can improve the intracellular ATP concentration to 1.38-2.45 times in various cell lines. Moreover, it is noticed that HELIOS-mediated ATP generation can comprehensively promote cell functions such as protein synthesis and insulin secretion. At organ and individual levels, it is also proved that HELIOS can rescue a mouse heart from myocardial infarction and sustain life of fasting zebrafish Danio rerio models. The photo-powered artificial organelle can deepen our understanding of metabolism and enable the development of optical therapy that targets intracellular energy supply.

Paracoccus denitrificans Oxidative Phosphorylation: Retentions, Gains, Losses, and Lessons En Route to Mitochondria

There are many similarities between the oxidative phosphorylation apparatus of mitochondria and those found in the cytoplasmic membranes of alpha-proteobacteria, exemplified by Paracocus denitrificans. These similarities are reviewed here alongside consideration of the differences between mitochondrial and bacterial counterparts, as well as the loss from the modern mitochondria of many of the bacterial respiratory proteins. The assembly of c-type cytochromes is of particular evolutionary interest as the post-translational apparatus used in the alpha-proteobacteria is found in plants, and for example in eukyarotic species including algae of various kinds together with jakobids, but has been superseded by different systems in mitochondria of metazoans and trypanosomatids. All mitochondrial cytochromes c have the N-terminal sequence feature that is recognised by the metazoan system whereas the bacterial counterparts do not, suggesting that the loss of the bacterial system from eukaryotes occurred in the context of an already present recognition sequence in the eukaryotic cytochromes. Interestingly, in the case of cytochromes c₁ the putative recognition features for the metazoans appear to be substantially present in the bacterial proteins. The ability to prepare from P. denitrificans inverted membrane vesicles with classic respiratory control presents a valuable system from which to draw lessons concerning the long debated topic of what controls the rates of respiration and ATP synthesis in mitochondria. © 2018 IUBMB Life, 70(12):1214-1221, 2018.

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.

Deletion of a unique loop in the mycobacterial F-ATP synthase γ subunit sheds light on its inhibitory role in ATP hydrolysis-driven H(+) pumping

The F1 FO -ATP synthase is one of the enzymes that is essential to meet the energy requirement of both the proliferating aerobic and hypoxic dormant stages of the life cycle of mycobacteria. Most F-ATP synthases consume ATP in the α3 :β3 headpiece to drive the γ subunit, which couples ATP cleavage with proton pumping in the c ring of FO via the bottom of the γ subunit. ATPase-driven H(+) pumping is latent in mycobacteria. The presence of a unique 14 amino acid residue loop of the mycobacterial γ subunit has been described and aligned in close vicinity to the c-ring loop Priya R et al. (2013) J Bioenerg Biomembr 45, 121-129 Here, we used inverted membrane vesicles (IMVs) of fast-growing Mycobacterium smegmatis and a variety of covalent and non-covalent inhibitors to characterize the ATP hydrolysis activity of the F-ATP synthase inside IMVs. These vesicles formed a platform to investigate the function of the unique mycobaterial γ loop by deleting the respective loop-encoding sequence (γ166-179 ) in the genome of M. smegmatis. ATP hydrolysis-driven H(+) pumping was observed in IMVs containing the Δγ166-179 mutant protein but not for IMVs containing the wild-type F-ATP synthase. In addition, when compared to the wild-type enzyme, IMVs containing the Δγ166-179 mutant protein showed increased ATP cleavage and lower levels of ATP synthesis, demonstrating that the loop affects ATPase activity, ATPase-driven H(+) pumping and ATP synthesis. These results further indicate that the loop may affect coupling of ATP hydrolysis and synthesis in a different mode.