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Structure And Function Of Atp Synthase Pdf

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ATP Synthases from Archaea: Structure and Function

As for every enzyme, the laws of thermodynamics command it; however, it is privileged to have a dedicated molecular regulator that controls its rotation. Recent evidence has also demonstrated that IF 1 may control the alignment of the enzyme along the mitochondrial inner membrane, thus increasing the interest for the molecule.

We conceived this review to outline the fundamental knowledge of the F 1 F o -ATPsynthase and link it to the molecular mechanisms by which IF 1 regulates its way of function, with the ultimate goal to highlight this as an important and possibly unique means to control this indispensable enzyme in both physiological and pathological settings.

It is present in bacteria and intracellular organelles such as chloroplasts and mitochondria. The molecular structure, catalytic mechanism, and regulation of the mitochondrial F 1 F o -ATPsynthase were described by the seminal work of the Nobel Laureates Mitchell, Boyer and Walker, that revealed its complexity and the functional steps that drive the synthesis of ATP.

IF 1 is primarily responsible for inhibiting the hydrolysis of ATP by the ATP synthase [ 6 ], an event that occurs when the electrochemical proton gradient across the mitochondrial inner membrane is lost e.

The interest for this inhibitor, or regulator—as we like to consider it—stems from many reasons; among them, the evidence for a key role in pathologies is the most meaningful but the less explored. Here, we will explain why the interaction between IF 1 and F 1 F o -ATPsynthase is important, and why the quality of cellular bioenergetics depends on it.

The Inhibitory Factor 1 IF 1 is often regarded as the 16th subunit, although we will learn in this review that the protein is far more correctly defined as its endogenous regulator. The crystal structure of the mitochondrial F 1 -ATPsynthase, extracted from bovine heart mitochondria, was revealed at the beginning of the Nineties [ 19 , 20 ]. According to this model, the three catalytic sites can be in three different conformations at any given time. Unfortunately, there is less structural information on the F o domain of ATP synthase than the F 1 complex.

Mitochondria are the sites where cellular energy is most abundantly produced, due to the constant activity of the mitochondrial F 1 F o -ATPsynthase. Although publications have suggested that it may also be localized on the plasma membrane [ 32 , 33 ], we shall be exclusively discussing and referring to that embedded in the mitochondrial inner membrane.

The reversal of the F 1 F o -ATPsynthase is avoidable in eukaryotes and the enzyme must be controlled to prevent futile hydrolysis of ATP when the transmembrane proton electrochemical gradient collapses.

Only facultative anaerobic bacteria employ this method for generating a vital proton electrochemical gradient in the absence of oxygen [ 37 ]. When reversal of the F 1 F o -ATPsynthase does occur, the depletion of cellular ATP can be more or less severe depending on the energy requests of the tissue, but in organs with high ATP demand, like brain or skeletal muscle, or in case of augmented ATP request, cellular demise is tangibly accelerated.

Apart from pathological states, repression or upregulation of ATP synthesis normally occurs in physiological conditions when intracellular ATP levels are, respectively, sufficiently high or too low. Several are the mechanisms by which the activity of the F 1 F o -ATPsynthase is regulated: a transcriptional factors [ 39 , 40 ]; b translational control [ 41 — 43 ]; c modulation of the electron transport chain or the citric acid cycle [ 44 , 45 ]; d ADP inhibition [ 37 ] and e regulatory proteins , such as IF 1.

Although recent evidence has also suggested that the oncoprotein Bcl-XL interacts with the F 1 F o -ATPsynthase [ 46 , 47 ], IF 1 is the only molecular regulator of the enzyme characterized both biochemically and functionally.

IF 1 was discovered in by Pullman and Monroy [ 6 ] in mitochondria from bovine hearts a schematic representation of the structure of bovine IF 1 is reported in Figure 2 a. To date, IF 1 homologues have been isolated from other mammals e.

It is predominantly compartmentalized inside the mitochondrial matrix Figure 2 b , although studies have proposed that IF 1 is also present in the cytosol and on the plasma membrane [ 56 ], as well as secreted into the extracellular environment, where it is implicated in the modulation of the activity of endothelial cells [ 32 ].

Intriguingly, in this very extramitochondrial localization, a role for hepatic HDL-cholesterol and triglyceride metabolism was also proposed [ 32 , 57 ]. The regulatory protein is therefore an indispensable component to protect the cell from ATP depletion-driven damage and demise.

IF 1 completely inhibits, through a noncompetitive mechanism, the ATP-hydrolyzing activity of the F 1 F o -ATPsynthase without affecting the synthesis of ATP during oxidative phosphorylation, although a few studies argue differently on this [ 58 , 59 ]; nevertheless, IF 1 is reported to be largely active only at low pH [ 60 ], hence in conditions of ATP hydrolysis.

The mature polypeptide 81—84 aa in mammals is significantly conserved among various species. Interestingly, there is a strong correlation between the high sequence conservation and function, as IF 1 from one species is able to inhibit the F 1 F o -ATPsynthase from another, including yeast [ 51 , 62 , 63 ].

Conversely, yeast IF 1 is not able to inhibit the animal F 1 domain because its activity is stabilized by accessory proteins which have no homologues in animals [ 64 ]. Van Raaij and coworkers investigated this [ 65 ], by measuring the activity of several truncated forms of the protein. The intact and truncated forms assayed for inhibition of F 1 F o -ATPsynthase using IF 1 -depleted submitochondrial particles revealed that the minimal inhibitory sequence consists of residues 14— In , Ichikawa and colleagues [ 66 ] showed by amino acid replacement that in yeast five residues F17, R20, R22, E25 and F28 are essential for the inhibitory activity of the protein.

The molecular structure of IF 1 was initially characterized by Cabezon et al. When the pH is above neutrality 7. Every protomer of the dimer can participate in two coiled-coil units with two different helices, binding two dimers simultaneously. Dimers and oligomers are in equilibrium at pH 6. Mammalian IF 1 contains five highly conserved histidines at positions 48, 49, 55, 56 and 70 that, if chemically modified or replaced, lead to a complete loss of the pH-susceptible activity of the protein without affecting its inhibitory capacity [ 60 , 71 ].

This histidine-rich region residues 48—70 is involved in the pH sensing mechanism of bovine IF 1 , and undergoes conformational changes depending on acidity or alkalinity of the environment [ 61 ].

Critical for the pH-dependent interconversion between the two aggregation states of the polypeptide is the histidine 49 [ 70 , 71 ]. It was observed that replacement of this residue with a different amino acid induces full activation of IF 1 at pH 8, and abolishes the ability of the dimers to form oligomers [ 67 , 71 ]. The five histidines seem to be important for the pH-regulated decrease in activity between pH 6. In fact, a pH-dependent activity was also observed in the IF 1 22—46 peptide [ 72 ] and detected in a residue segment from 32 to 43 [ 70 ]; moreover, H49 is not conserved in yeast, suggesting a diverse pH-sensitivity of the protein [ 73 ].

Apart from controlling the oligomerization of the polypeptide and consequently the availability of its inhibitory site, the pH itself was proposed to represent the switch between inactive and active forms by controlling the helical content and the flexibility of the whole protein [ 74 ].

Recently, Ando and Ichikawa [ 73 ] discovered that pH could effectively change the conformation of the active site by acting on a highly conserved glutamate residue, E26 in bovine IF 1 or E21 in yeast IF 1 H49 is not conserved in yeast and, as a consequence, cannot represent the only pH sensor residue of the protein.

The mechanism of pH-dependency mediated by glutamate regulates only the inhibitory activity of the F 1 -binding site and not the aggregation state of the polypeptide. Residues 4—18, which are disordered in the dimer, are instead resolvable after binding. Although the inhibitory sequence is comprised of residues 14 to 47, this is not the only region that interacts with the F 1 F o -ATPsynthase.

In fact, as demonstrated by the time-dependent loss of inhibition seen by van Raaij and co-workers [ 65 ], residues 1—13 and 48—56 are important for stabilizing the structure the first peptide interacts directly with the F 1 domain, while the second probably contributes to stabilize only the IF 1 dimer.

With different approaches, Cabezon et al. Interestingly, one of the three residues, E26, is also implicated in the pH sensing mechanism of I F 1. In , Ando and Ichikawa [ 73 ] discovered the key role of the glutamate residue in the pH-dependent activity of the inhibitory protein. They proposed that it was the high pH, by inducing the dissociation of the carboxyl group of E26, to affect the conformation or direction of the side chain of the neighboring residue E30, thus destabilizing the interaction between IF 1 and the F 1 domain.

Garcia and colleagues provided the first compelling evidences for a role of IF 1 in promoting the dimerization of the F 1 F o -ATPsynthase, and for its involvement in the biogenesis of mitochondrial cristae [ 79 ].

The dimerization of the enzyme is essential for a correct biogenesis of mitochondrial cristae; in fact, it represents a prerequisite for the generation of larger oligomers with a ribbon-like structure that promotes curvature and growth of tubular cristae membranes [ 80 ]. In a recent study, we demonstrated the pivotal role of IF 1 in cell physiology through promotion of the F 1 F o -ATPsynthase dimerization.

Briefly, we showed that IF 1 overexpression efficiently increase the activity and the ratio of dimeric to monomeric forms of the F 1 F o -ATPsynthase, with augmented cristae number, mitochondrial membrane stability, and mitochondrial volume [ 81 ], thus ensuring a correct mitochondrial inner structure.

This is a phenomenon of secure relevance for apoptosis. This condition associates with ischaemia, in which the interruption of tissue blood flow causes a reduction of cell oxygenation hypoxia inhibiting mitochondrial respiration.

These cells will experience a reduced depletion of ATP compared to those bathed with the ETC inhibitor but without oligomycin. The negative effect of the reversal of the F 1 F o -ATPsynthase is coupled to the reversal of the adenosine nucleotide translocator ANT [ 82 ], an IMM transmembrane complex that, in physiological conditions, mediates the exchange of cytosolic ADP and mitochondrial matrix ATP utilizing the different gradients between the two compartments.

Early reperfusion minimizes the extent of cellular damage, salvaging cells within ischaemic regions from necrosis, but it can also causes lethal injury to cells with severe ischaemia-induced metabolic derangements reviewed in [ 83 ]. In the latter case, reperfusion alters the activity of plasma membrane transporters e. At the same time, resupply of oxygen to mitochondria restores ATP production but also induces a rise in reactive oxygen species ROS production.

Oligomycin-mediated inhibition slows down ATP depletion during ischaemia. Rouslin and colleagues [ 11 ] proved that the antibiotic has a very small and transient effect on mitochondrial function when used in fast heart-rate animals, like rats, if compared to slow heart-rate species, like larger mammals are.

The same authors have subsequently shown that this diversity depends on the different F 1 F o -ATPsynthase: IF 1 ratios, with a diverse ability to inhibit mitochondrial-driven consumption of ATP when needed [ 84 ]. Upon reperfusion, the binding of IF 1 to the F 1 F o -ATPsynthase is quickly reversed [ 86 ], so that sublethal ischaemic episodes could be followed by a relatively rapid recovery of intracellular ATP.

Although this model is challenged by later evidence showing that in rat heart, during ischaemic preconditioning, mitochondrial ATP hydrolysis is inhibited probably as a consequence of the binding of IF 1 [ 87 ], the variations in ratio between the enzyme and its controller among animal species are still a fascinating possibility.

Nonetheless, this ratio differs per se among organs and cell types of the same organ [ 12 ]. Thus, variations in IF 1 expression could influence cellular or tissue resistance to ischaemic injury in different species or cell types. Notably, IF 1 expression is elevated in highly oxidative cells, like neurons and kidney proximal tubules [ 12 ], which are highly susceptible to mitochondria deregulations. Thus, higher levels of IF 1 could be advantageous in cells highly depending on oxidative phosphorylation by preventing ATP depletion and quick cellular damage during ischaemia.

A final interesting aspect is the highly probable involvement of IF 1 in the ischaemic preconditioning mechanism. This phenomenon, which is characterized by the acquirement of a strong resistance to ischaemia in tissue undergoing brief, repeated periods of sublethal ischaemia, is commonly observed in heart, skeletal muscle and brain [ 61 ].

It is described as a slowing of energy metabolism with a decreased rate of ATP depletion during ischaemia [ 88 ]. IF 1 is proposed to take part in this process after the observation that rat heart preconditioning associates with the inhibition of mitochondrial ATP hydrolysis during ischaemia [ 87 ]. This was later confirmed by Penna et al. The importance of mitochondrial metabolism in cancer cells is underlined by the frequently observed, close interaction of glycolytic enzymes with mitochondria.

This creates a mutually sustaining relationship between glycolysis, which represents the primary metabolic pathway for tumours sustenance [ 90 ], and oxidative phosphorylation. Regarding the F 1 F o -ATPsynthase endogenous regulator, IF 1 , its overexpression has been observed in many human carcinomas including lung, colon, breast, and cervix carcinomas [ 10 ], Ehrlich ascites carcinoma [ 91 ], Zajdela hepatoma and Yoshida sarcoma [ 92 ] , but little is still known about the associated effects, and the few theories that have been put forward are highly controversial.

Increased expression of the protein is associated with a higher binding efficiency to the F 1 F o -ATPsynthase [ 93 ], suggesting a greater protection of cancer cells against energy dissipation upon F 1 F o -ATPsynthase reversal. This was theorized by Chernyak et al. The protein may therefore be involved in protecting tumour cells from cytosolic ATP depletion and excessive reactive oxygen species ROS production the majority of tumours have little or no vascularization, so that cancerous cells grow in a hypoxic environment.

Over and above that, to guarantee cell viability, mitochondria should not become ATP consumers. Numerous studies have also demonstrated that transient hyperpolarization of the mitochondrial membrane can lead to cell apoptosis [ 38 , 95 ]. Our previous studies seem to support these hypotheses [ 81 ], and, future and focused studies will shed light on this Tan et al. Moreover, an original recent work by Cuezva and co-workers has elegantly demonstrated that IF 1 is protective against chemotherapy and supports cell proliferation of cancerous cells via the NfkB pathway [ 96 ].

Although this work focuses principally on the postmitochondrial effects of IF 1 , it is anyway a compelling evidence for a contribution to neoplastic degeneration and resistance to apoptosis. A starting point to unravel how mitochondrial structure and function are primed by IF 1 overexpression, and to understand to what extent this dictates cellular transformation.

Basal ATPase activity in one of the two patients was seven times higher than normal [ 13 ], and no IF 1 activity was detected in fibroblasts cultured from the skeletal muscle [ 14 ]; however, no mutations in the ATPIF1 gene were identified, and the genetic cause of the disease remains obscure. Despite what discussed above, we have very recently collected evidences for a deficiency in the ATPIF1 gene associated with a form of hypochromic anaemia Shah et al. Anyway, we found that the increase in mitochondrial matrix pH, which is observed in zebrafish models and murine cells carrying the mutated form of the ATPIF1 gene, is causally linked to a decrease in ferrochelatase activity, which leads to defects in the incorporation of 59 Fe into protoporphyrin IX to generate the hemoglobin prosthetic group heme.

Such a remarkable finding puts IF 1 amongst the regulators of heme biosynthesis, not only describing a new mechanism for sideroblastic anaemia, but also confirming the involvement of the inhibitory protein in human pathologies related to mitochondrial disorders.

The F 1 F o -ATPsynthase is a wonderful machinery, with the unique capacity of producing and consuming energy, if necessary, to preserve the integrity of the organelle to which it belongs. A precise and sustainable way to regulate its activity is therefore paramount, and the Inhibitory Factor 1, a protein encoded by the nuclear DNA, represents the molecule deputed to do so.

In the face of a well-defined biochemistry, its role in cell physiology and mitochondrial anatomy has been only recently discovered, posing the protein at the cross-road between dynamics and energy balance.

This, together with growing evidence for a contribution to cell and tissue pathology, leads to novel ways to investigate and thoroughly address IF 1 functional biology. The research activities led by M. The authors would like to thank Dr.

Mitochondrial ATP synthase: architecture, function and pathology

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structure and function of atp synthase pdf

A multi subunit structure that works like a pump functions along the proton gradient across the membranes which not only results in ATP synthesis and.


Mitochondrial ATP synthase: architecture, function and pathology

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Bacterial ATP synthases have been studied extensively because they are the simplest form of the enzyme and because of the relative ease of genetic manipulation of these complexes. We expressed the Bacillus PS3 ATP synthase in Eschericia coli , purified it, and imaged it by cryo-EM, allowing us to build atomic models of the complex in three rotational states. The architecture of the membrane region shows how the simple bacterial ATP synthase is able to perform the same core functions as the equivalent, but more complicated, mitochondrial complex. The structures reveal the path of transmembrane proton translocation and provide a model for understanding decades of biochemical analysis interrogating the roles of specific residues in the enzyme.

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. This review covers the architecture, function and assembly of complex V. The role of complex V di-and oligomerization and its relation with mitochondrial morphology is discussed. Finally, pathology related to complex V deficiency and current therapeutic strategies are highlighted.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. However, important details of proton driven energy conversion are still unknown.

J Gen Physiol 1 December ; 6 : — The nature of this turbine-like energy conversion mechanism has been elusive for decades, owing to the lack of definitive structural information on subunit a or its c -ring interface. In a recent breakthrough, several structures of this complex were resolved by cryo—electron microscopy cryo-EM , but the modest resolution of the data has led to divergent interpretations. Moreover, the unexpected architecture of the complex has cast doubts on a wealth of earlier biochemical analyses conducted to probe this structure. Here, we use quantitative molecular-modeling methods to derive a structure of the a — c complex that is not only objectively consistent with the cryo-EM data, but also with correlated mutation analyses of both subunits and with prior cross-linking and cysteine accessibility measurements.

Understanding structure, function, and mutations in the mitochondrial ATP synthase

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    23.04.2021 at 14:43
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    A multi subunit structure that works like a pump functions along the proton gradient across the membranes which not only results in ATP synthesis and breakdown, but also facilitates electron transport. The Mitochondrial Electron transport chain and ATP synthase.

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