What kind of molecule is atp synthase

Basically, protons are pumped across the inner mitochondrial membrane as electrons pass through the electron transfer chain. This induces a proton gradient, with a decreased pH in the intermembrane space and an increased pH in the matrix of the mitochondria.

The proton gradient and membrane potential are the major forces involved in ATP synthesis. It is well established that the electrochemical potential of protons delivered by electron transfer chains across the mitochondrial, chloroplast or bacterial membrane provides the energy for ATP synthesis [ 14 ].

Cellular respiration in the mitochondria is a widely studied process that incorporates chemiosmosis for the production of ATP. Mitochondria, the chief organelles producing ATP, are absent in prokaryotic organisms. In the absence of mitochondria, archaea and bacteria maneuver chemiosmosis to produce ATP through photophosphorylation.

The electrochemical energy built through the difference in proton concentration and separation of charge across inner mitochondrial membrane translates to the proton motive force PMF. This also satisfies a main criterion stated by Mitchell for the chemiosmotic coupling to occur: the inner mitochondrial membrane must be impermeable to protons. Thus, protons are compelled to re-enter matrix through F 0 while F 1 catalyzes the synthesis of ATP [ 16 ].

The Electron transport chain composed of four different multi-subunit complexes transfer electrons e- in a sequential manner ultimately reducing O 2 to H 2 O. Electron transfer is coupled to a vectorial proton translocation outdoor into the matrix via three of the four complexes I, III and IV. Protons gather and create an electrochemical gradient throughout the inner mitochondrial membrane. This osmotic potential is used to power ATP synthesis when protons re-enter the mitochondrial matrix through ATP synthase [ 13 ].

The equation for reaction catalyzed is:. There are only slight variations in its structure in the chloroplast and in the mitochondria. The chloroplast ATPase has two isoforms and in the mitochondria it has additional subunits. Besides these differences, ATPases are structurally and functionally similar. The F 0 part, bound to inner mitochondrial membrane is involved in proton translocation, whereas the F 1 part found in the mitochondrial matrix is the water soluble catalytic domain.

F 1 is the first factor recognized and isolated from bovine heart mitochondria and is involved in oxidative phosphorylation. F 0 was named so as it is a factor that conferred oligomycin sensitivity to soluble F 1 [ 18 ].

Schematic subunit composition of ATP synthase. The structure of enzyme ATP synthase mimics an assembly of two motors with a shared common rotor shaft and stabilized by a peripheral stator stalk. Bacterial F 0 has the simplest subunit structure consisting a 1 , b 2 and c subunits.

Other additional subunits such as subunit e, f, g, and A6L extending over the membrane cohort with F 0 [ 5 , 10 , 20 ]. Paul Boyer proposed a simple catalytic scheme, commonly known as the binding change mechanism, which predicted that F-ATPase implements a rotational mechanism in the catalysis of ATP [ 21 ].

The movement of subunits within the ATP synthase complex plays essential roles in both transport and catalytic mechanisms. Another subsequent change in conformation brings about the release of ATP. These conformational changes are accomplished by rotating the inner core of the enzyme. The core itself is powered by the proton motive force conferred by protons crossing the mitochondrial membrane.

The binding-change mechanism as seen from the top of the F 1 complex. There are three catalytic sites in three different conformations: loose, open, and tight. As a result, ATP is released from the enzyme. In step 2, substrate again binds to the open site, and another ATP is synthesized at the tight site [ 25 ].

Masamitsu et. Conformational transitions that are significant in rotational catalysis are directed by the passage of protons through the F 0 assembly of ATP synthase. On the other hand, when the proton concentration is higher in the mitochondrial matrix, the F 1 motor reverses the F 0 motor bringing about the hydrolysis of ATP to power translocation of protons to the other side of membrane.

A team of Japanese scientists have succeeded in attaching magnetic beads to the stalks of F 1 -ATPase isolated in vitro , which rotated in presence of a rotating magnetic field.

Additionally, ATP was hydrolyzed when the stalks were rotated in the counterclockwise direction or when they were not rotated at all [ 26 ]. Defects or mutations in this enzyme are known to cause many diseases in humans. The first defect in ATP synthase was reported by Houstek et. It was postulated that mutations in some factors explicitly involved in the assembly of ATP synthase could have caused the defect [ 27 ].

Kucharczyk et. A mutation in one or many of the subunits in ATPase synthase can cause these diseases [ 28 ]. These diseases also result decrement in intermediary metabolism and functioning of the kidneys in removing acid from the body due to increased production of free oxygen radicals.

Dysfunction of F 1 specific nuclear encoded assembly factors causes selective ATPase deficiency [ 31 ]. Similar inborn defects in the mitochondrial F-ATP synthase, termed ATP synthase deficiency, have been noted where newborns die within few months or a year. Current research on ATP synthase as a potential molecular target for the treatment for some human diseases have produced positive consequences.

Recently, ATPase has emerged as appealing molecular target for the development of new treatment options for several diseases. ATP synthase is regarded as one of the oldest and most conserved enzymes in the molecular world and it has a complex structure with the possibility of inhibition by a number of inhibitors.

In addition, structure elucidation has opened new horizons for development of novel ATP synthase-directed agents with plausible therapeutic effects. More than natural and synthetic inhibitors have been classified to date, with reports of their known or proposed inhibitory sites and modes of action [ 30 ]. We look to explore a few important inhibitors of ATP synthase in this paper.

A drug, diarylquinoline also known as TMC developed against tuberculosis is known to block the synthesis of ATP by targeting subunit c of ATP synthase of tuberculosis bacteria. Another such diarylquinone, Bedaquiline, is used for the treatment of multidrug resistant tuberculosis. Among other ATP synthase inhibitors, Bz is proapoptotic and 1,4-benzodiazepine binds the oligomycin sensitivity conferring protein OSCP component resulting in the generation of superoxide and subsequent apoptosis [ 32 , 33 , 34 ].

Melittin, a cationic, amphiphilic polypeptide is yet another ATP synthase inhibitor with documented inhibition of catalytic activities in mitochondrial and chloroplast ATP synthases [ 35 ]. IF1 and oligomycin are two other important classes of ATPase inhibitors. Oligomycin, an antibiotic, blocks protein channel F 0 subunit and this inhibition eventually inhibits the electron transport chain. This further prevents protons from passing back into mitochondria, eventually ceasing the operations of the proton pump, as the gradients become too high for them to operate.

Several polyphenolic phytochemicals, such as quercetin and resveratrol, have been known to affect the activity ATPase. At decreased concentrations, it inhibits both soluble and insoluble mitochondrial ATPase. However, it does not impact oxidative phosphorylation occurring in other mitochondrial entities [ 39 , 40 , 41 ]. This scheme is based on the binding change mechanism of ATP hydrolysis [ 36 ].

IF1 is a naturally occurring 9. Several other plant products also serve as ATPase inhibitors. Polyphenols and flavones has been found effective in the inhibition of bovine and porcine heart F 0 F 1 -ATPase [ 41 , 42 ]. There have been few randomized controlled trials for the treatment of mitochondrial disease Chinnery et al. To date, there is no clear evidence supporting the use of pharmacological agents, non-pharmacological treatments vitamins and food supplements , and physical training in patients with mitochondrial disorders Chinnery et al.

Although very promising, all genetic techniques are still in an experimental phase and different technical, ethical and safety issues still have to be solved DiMauro et al. Nevertheless, they do allow cautious optimism for the future.

Since current therapeutic options for mitochondrial diseases are insufficient, the possibility of prenatal diagnosis for fetuses at risk is a valuable alternative.

If it concerns a known nuclear genetic defect, the mutation can directly be searched for in fetal tissue. Second, the heteroplasmy level differs between tissues and in one tissue through time Poulton and Marchington In this context, the m. Finally, it is suggested that the heteroplasmy level remains stable after 10 weeks of gestation Steffann et al.

Hitherto termination of pregnancy has been preferred in case of intermediate mutant loads Steffann et al. Remarkably, the intermediate mutant loads question the observation that the m. Post-zygotic drift might explain this discrepancy Steffann et al. The interpretation of PGD results nevertheless demands a known correlation between mutation load and clinical phenotype.

In addition, caution is warranted since some pathogenic mutations could exhibit different segregation behavior Dean et al. In case the genetic examination of an index case has revealed no mutations in both mtDNA and nDNA, prenatal diagnosis could still be possible.

In Nijmegen, complex V activity can be measured spectrophotometrically in native chorionic villi, cultured chorionic cells or cultured amniotic cells if there is a clear isolated complex V deficiency in fibroblasts and muscle tissue or other tissue of the index patient Niers et al.

As mentioned briefly, most of the structure of the bovine mitochondrial enzyme has been resolved. The structure of the membrane extrinsic part of bovine ATP synthase is complete Rees et al. The structure of the c-ring has been resolved recently Watt et al. The structures of the membrane domain of subunit b, subunit a, and the accessory subunits e, f, g, and A6L remain to be determined Rees et al.

Still, understanding the enzyme fully at a molecular level will require further efforts, both experimental and theoretical for a review, see Junge et al.

Next to structure and function of the monocomplex, also the role of di- and oligomerization of complex V, shaping the inner mitochondrial membrane, has been addressed in many studies both in yeast and in mammalian mitochondria Paumard et al.

The role of IF 1 in this process has been shown to be important Campanella et al. Despite this huge progress, lots of questions remain to be answered. As mentioned, the assembly of the different subunits into the holocomplex continues to be puzzling. Most of the research has been done in yeast. However, the yeast assembly process probably differs from the one in mammalian mitochondria, since there are substantial differences between higher and lower eukaryotes such as the number of F o subunit c-genes, ATP synthase-specific assembly factors, and factors regulating transcription of ATP synthase genes Houstek et al.

To gain further insight into the assembly of complex V, techniques like blue native and clear native PAGE, combined with incorporation and knock-down experiments of different subunits as described in Wagner et al. They both have a role in F 1 assembly. TMEM70 maintains normal expression levels of complex V, and has been suggested to have a role in complex V biogenesis Cizkova et al.

The exact mechanism however still remains to be elucidated. Moreover, the existence of specific factors involved in mammalian F o formation is probable Houstek et al. A possible approach could be to study the evolution of complex V subunits and complex V chaperones by comparative genomics.

For example, the yeast F o assembly factor Atp23p has a human homolog for which, however, no involvement in ATP synthase assembly could be demonstrated Kucharczyk et al. Also a homology of complex V chaperones with other human proteins could be of interest in the search of specific assembly factors. Another intriguing fact is that to date, only one mutation has been found in a nuclear structural complex V gene Mayr et al.

It could be possible that mutations in some of the structural subunits are incompatible with life. On the other hand, given the lower frequency of complex V deficiency compared to the other OXPHOS deficiencies, routine screening of all nuclear structural genes is rarely implemented in a diagnostic setting.

Whole genome or whole exome screening could counter this problem and possibly solve some of the hitherto unknown genetic defects causing complex V deficiency. Finally, the biggest challenge will be to find a tailored curative therapy for this patient group. Large-scale and high-throughput compound screening is needed to find a possible pharmacological approach.

For mtDNA defects, gene-shifting and germline techniques are promising, but much more and thorough experimental research is needed before this can be implemented in the patient setting. In conclusion, mitochondrial ATP synthase has been and still is a popular research topic.

Thanks to sustained effort, many aspects of this intriguing protein have been elucidated. This knowledge will guide further physio patho logical studies, paving the way for future therapeutic interventions. The authors confirm independence from the sponsors; the content of the article has not been influenced by the sponsors.

This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author s and source are credited. Competing interest: None declared.

National Center for Biotechnology Information , U. Journal of Inherited Metabolic Disease. J Inherit Metab Dis. Published online Aug Jonckheere , Jan A. Smeitink , and Richard J. Jan A. Richard J. Author information Article notes Copyright and License information Disclaimer. Corresponding author. This article has been cited by other articles in PMC. Abstract Human mitochondrial mt ATP synthase, or complex V consists of two functional domains: F 1 , situated in the mitochondrial matrix, and F o , located in the inner mitochondrial membrane.

ATP synthase: architecture Fig. Open in a separate window. Table 1 Subunit composition of human, yeast and E. Stoichiometry Bacteria Mitochondria E.

Complex V assembly Current knowledge about the assembly of ATP synthase is mainly based on research performed on assembly-deficient yeast mutants Kucharczyk et al. Complex V di- and oligomerization An important role of subunits a and A6L is the stabilization of holocomplex V Wittig et al. Complex V and mitochondrial morphology The association of ATP synthase dimers as generating the tubular cristae has been hypothesized by Allen Allen Biochemical diagnosis Measurement of the mitochondrial energy-generating system MEGS capacity in fresh muscle tissue is a powerful tool to assess mitochondrial function and to detect deficiencies of complex V and other OXPHOS complexes.

Modifiers Phenotypical variations between patients harboring the same mtDNA mutation have classically been attributed to mtDNA heteroplasmy. Therapy Current available treatment options for patients with mitochondrial diseases are mainly supportive. Antioxidants As mentioned above, complex V mutations can increase ROS production which is deleterious for the cell.

Affecting heteroplasmy of the mtDNA gene-shifting This genetic approach aims to force a shift in heteroplasmy, reducing the ratio of mutant to wild-type genomes also called gene-shifting DiMauro et al. Allotopic expression Here, a normal version of a mutant mtDNA-encoded protein is imported into the nucleus.

Xenotopic expression The correction here implies the transfection of mammalian cells with either mitochondrial or nuclear genes from other organisms encoding the protein of interest DiMauro et al. Oligomycin It has been shown that culturing heteroplasmic m. Germline therapy It has been proposed that nuclear transfer techniques may be an approach for the prevention of transmission of human mtDNA disease Sato et al.

Metaphase II spindle transfer between unfertilized metaphase II oocytes It has been demonstrated in mature non-human primate oocytes Macaca mulatta that the mitochondrial genome can be efficiently replaced by spindle-chromosomal complex transfer from one egg to an enucleated, mitochondrial-replete egg Tachibana et al.

Pronuclear transfer between zygotes This is essentially the same procedure, except that the nuclear material, both the male and female pronucleus, is removed after fertilization Tachibana et al. Prenatal and preimplantation diagnosis Since current therapeutic options for mitochondrial diseases are insufficient, the possibility of prenatal diagnosis for fetuses at risk is a valuable alternative.

Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author s and source are credited. Footnotes Competing interest: None declared.

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Comparison with the enzyme in Rho 0 cells completely lacking mtdna. The structure of the central stalk in bovine F 1 -ATPase at 2. Knockdown of F1 epsilon subunit decreases mitochondrial content of ATP synthase and leads to accumulation of subunit c. Expression and processing of the TMEM70 protein.

A new mitochondrial disease associated with mitochondrial DNA heteroplasmy. Mitochondrial encephalocardio-myopathy with early neonatal onset due to TMEM70 mutation. Arch Dis Child. Mitochondrial diseases and genetic defects of ATP synthase. John E. Walker; The ATP synthase: the understood, the uncertain and the unknown. Biochem Soc Trans 1 February ; 41 1 : 1— The ATP synthases are multiprotein complexes found in the energy-transducing membranes of bacteria, chloroplasts and mitochondria.

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.

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.

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