Structural and functional characterization of subunits of the F0 sector of the mitochondrial F0F1-ATP synthase

Role of copper in mitochondrial biogenesis via interaction with ATP synthase and cytochrome c oxidase

Animals that are copper deficient have cardiac hypertrophy where there is a dramatic increase in mitochondria. Mitochondrial biogenesis is enhanced in this model and there is an upregulation of mitochondrial transcription factor A (mtTFA) and nuclear respiratory factors 1 and 2 (NRF-1 and NRF-2). While the cuproenzyme, cytochrome c oxidase (CCO), is an attractive candidate to explain the connection between cardiac hypertrophy in copper deficiency and subsequent mitochondrial biogenesis, studies have revealed that ATP synthase may be impacted by copper depletion. NRF-1 and NRF-2 can bind to some of the subunits of both CCO and ATP synthase to regulate gene expression. Furthermore, oxidative phosphorylation appears to occur unaltered in the copper-deficient state. Copper-deficient mitochondria appear to be less sensitive to the inhibitory effect of oligomycin compared to controls. Decreases in the delta subunit protein and beta mRNA transcript have been reported for ATP synthase as a function of copper deficiency. The limited data available suggest that copper, either indirectly or directly, alters ATP synthase function.

The structural and functional connection between the catalytic and proton translocating sectors of the mitochondrial F1F0-ATP synthase

The structural and functional connection between the peripheral catalytic F1 sector and the proton-translocating membrane sector F0 of the mitochondrial ATP synthase is reviewed. The observations examined show that the N-terminus of subunit gamma, the carboxy-terminal and central region of F0I-PVP(b), OSCP, and part of subunit d constitute a continuous structure, the lateral stalk, which connects the peripheries of F1 to F0 and surrounds the central element of the stalk, constituted by subunits gamma and delta. The ATPase inhibitor protein (IF1) binds at one side of the F1F0 connection. The carboxy-terminal segment of IF1 apparently binds to OSCP. The 42L-58K segment of IF1, which is per se the most active domain of the protein, binds at the surface of one of the three alpha/beta pairs of F1, thus preventing the cyclic interconversion of the catalytic sites required for ATP hydrolysis.

Nutrient-gene interactions determine mitochondrial function: effect of dietary fat

The effect on mitochondrial respiration of feeding hydrogenated coconut oil, corn oil, or menhaden oil (MO) to diabetes-prone BHE/cdb rats and normal Sprague Dawley (SD) rats was studied. Both fat source and strain affected the temperature dependence of succinate-supported respiration. The transition temperature was greater in BHE/cdb rats than in the SD rats. The efficiency of ATP synthesis as reflected by the ADP:O ratio was decreased in the BHE/cdb rats compared to SD rats, with the exception of the comparison made at 37 degrees C with the MO-fed rats; at this temperature, the ADP:O ratios were similar. The diet and strain differences suggest a dietary lipid-gene interaction with respect to the mobility of subunit 6 of the F1F0ATPase. This subunit has two errors in its gene: one that affects the proton channel and another that likely affects its mobility within the inner mitochondrial membrane.

The effect of mild trypsin digestion of F1 on energy coupling in the mitochondrial ATP synthase

Mild trypsin digestion of isolated bovine-heart mitochondrial F1-ATPase removed the first 15 residues from the N-terminus of subunit alpha under conditions in which other F1 subunits were apparently untouched. When the trypsinized F1 (TF1) was reconstituted with the F0 sector in the mitochondrial membrane (USMP), the ATP hydrolase activity acquired oligomycin sensitivity but ATP hydrolysis was decoupled from proton pumping. TF1 added to USMP did not block the proton channel in F0 as the native F1 did. AMP-PNP inhibited proton conductivity in reconstituted F1-USMP but this effect was lost in reconstituted TF1-USMP. These results indicate that the N-terminus of the F1 alpha subunit plays a critical role in the conformational communication between F1 and F0.

DCCD-sensitive proton permeability of bacterial photosynthetic membranes. Cross-reconstitution studies with purified bovine heart Fo subunits

The DCCD-sensitive proton permeability of chromatophores, from a green strain of Rhodobacter Capsulatus is potentiometrically detected following the proton release induced by a transmembrane diffusion potential imposed by a valinomycin-mediated potassium influx with a procedure already used for bovine heart submitochondrial particles (ESMP) and vesicles from Escherichia coli (Zanotti et al. (1994) Eur. J. Biochem. 222, 733-741). In the photosynthetic system, addition of increasing amounts of DCCD inhibits, with a similar titre, both proton permeability and MgATP-dependent ATPase activity as detected in the dark. The titre for 50% inhibition coincides with that obtained measuring proton permeability and ATP hydrolysis in ESMP. Upon removal of F1, the passive proton permeability is much less sensitive to DCCD in chromatophores than in USMP, suggesting that in chromatophores the F1-Fo interaction shapes the DCCD-sensitive proton conducting pathway. Addition of the purified mitochondrial FoI-PVP and oligomycin sensitivity-conferring (OSCP) proteins to the F1 stripped chromatophores restored the sensitivity of proton permeability to DCCD detected in untreated chromatophores. Analysis of the binding of 14C[DCCD] on F1 stripped chromatophores shows that the increase of DCCD sensitivity of proton permeability, caused by addition of mitochondrial Fo proteins, is related to an increase of the binding of the inhibitor to subunit c of Fo sector of ATP synthase complex.

Assembly of mitochondrial ATP synthase in cultured human cells: implications for mitochondrial diseases

To study the assembly of mitochondrial F1F0 ATP synthase, cultured human cells were labeled with [35S]methionine in pulse-chase experiments. Next, two-dimensional electrophoresis and fluorography were used to analyze the assembly pattern. Two assembly intermediates could be demonstrated. First the F1 part appeared to be assembled, and next an intermediate product that contained F1 and subunit c. This product probably also contained subunits b, F6 and OSCP, but not the mitochondrially encoded subunits a and A6L. Both intermediate complexes accumulated when mitochondrial protein synthesis was inhibited, suggesting that mitochondrially encoded subunits are indispensable for the formation of a fully assembled ATP synthase complex, but not for the formation of the intermediate complexes. The results and methods described in this study offer an approach to study the effects of mutations in subunits of mitochondrial ATP synthase on the assembly of this complex. This might be of value for a better understanding of deficiencies of ATP synthase activity in mitochrondrial diseases.

Characterization of the oligomycin-sensitivity properties of the F1F0-ATPase in mitochondria from rats infected with the liver fluke Fasciola hepatica

The F1F0-ATPase activity of liver mitochondria isolated from rats infected with Fasciola hepatica at 3 and 4 weeks post-infection showed a marked loss of sensitivity to oligomycin and to N,N'-dicyclohexylcarbodiimide. A loss of sensitivity to diethylstilbestrol was also demonstrated at 4 weeks post-infection. Recovery was apparent in most cases by 6 weeks post-infection. No significant difference in latent ATPase activity was observed between mitochondria from control and infected livers at any stage of the infection. The mitochondria from infected livers were therefore considered to have a full complement of the F1 moiety of the F1F0-ATPase complex. Purification of the mitochondrial ATPase from 4-week infected livers resulted in a very low yield of an oligomycin-insensitive complex. This was due to a failure to enrich specific activity during purification. The evidence presented indicates that infection with Fasciola hepatica gives rise to alterations in the function of the host liver mitochondrial ATPase, namely loss of inhibitor sensitivity and apparent structural alterations of the ATPase complex.

Cross-reconstitution studies with polypeptides of Escherichia coli and bovine heart mitochondrial F0F1 ATP synthase

To characterize the role of supernumerary subunits of the mammalian F0F1 ATP synthase, cross-reconstitution of mitochondrial and bacterial F0F1 complexes has been carried out. Escherichia coli F1 (EcF1) can be reconstituted with F1-stripped everted membranes of E. coli (UPEc) and of bovine heart mitochondria (USMP). Bovine heart mitochondrial F1 (BHF1) can also be reconstituted with both membranes. Both EcF1 and BHF1, when reconstituted with UPEc, exhibited oligomycin-insensitive ATP-hydrolase activity. Subunits of the mammalian F0, in particular F0I-PVP protein, F6 and oligomycin-sensitivity-conferring protein (OSCP) conferred oligomycin sensitivity to the catalytic activity of EcF1 or BHF1 reconstituted with UPEc. Reaction of N,N'-dicyclohexylcarbodiimide and development of inhibition of passive H+ conduction was, in UPEc, considerably slower and exhibited a lower apparent affinity than in USMP. The ATP hydrolase activity of UPEc+EcF1 or UPEc+BHF1 was, also, less sensitive to inhibition by N,N'-dicyclohexylcarbodiimide than USMP+EcF1 or USMP+BHF1. Addition of mitochondrial F0I-PVP to UPEc enhanced the sensitivity of H+ conduction to oligomycin. F0I-PVP and OSCP added to UPEc, promoted inhibition by N,N'-dicyclohexylcarbodiimide of passive H+ conduction and increased its binding affinity to subunit c of E. coli F0. The presence of F0I-PVP and OSCP also promoted inhibition by N,N'-dicyclohexylcarbodiimide of the ATP-hydrolase activity of EcF1 or BHF1 reconstituted with UPEc.

Electron microscopy of the F1F0 ATP synthase: from structure to function

The F1F0 ATP synthase is the large multisubunit complex which uses the proton gradient of energetically active membranes to synthesize ATP. While biochemical and genetic approaches have characterized the composition of the enzyme and elucidated many details of its mechanism and assembly, electron microscopy has been the tool of primary importance in determining the arrangement of the many subunits which comprise the F1F0. The highly cooperative catalytic mechanism is tightly coupled to transmembrane proton translocation in a separate and rather distant sector of the complex. An understanding of this intricate process and its control requires an appreciation of subunit interactions, starting with their locations relative to one another. Electron microscopy has provided most of the available structural information on the F1F0, and recent applications of cryo-electron microscopy have captured different functionally relevant configurations which may finally address longstanding questions about subunit rearrangements during the catalytic cycle.

Role of F0 and F1 subunits in the gating and coupling function of mitochondrial H(+)-ATP synthase. The effect of dithiol reagents

A study is presented on the role of F0 and F1 subunits in oligomycin-sensitive H+ conduction and energy transfer reactions of bovine heart mitochondrial F0F1 H(+)-ATP synthase. Mild treatment with azodicarboxylic acid bis(dimethylamide) (diamide) enhanced oligomycin-sensitive H+ conduction in submitochondrial particles containing F1 attached to F0. This effect was associated with stimulation of the ATPase activity, with no effect on its inhibition by oligomycin, and depression of the 32Pi-ATP exchange. The stimulatory effect of diamide on H+ conduction decreased in particles from which F1 subunits were partially removed by urea. The stimulatory effect exerted by diamide in the submitochondrial particles with F1 attached to F0 was directly correlated with a decrease of the original electrophoretic bands of a subunit of F0 (F0I-PVP protein) and the gamma subunit of F1, with corresponding formation of their cross-linking product. In F0 liposomes, devoid of gamma subunit, diamide failed to stimulate H+ conduction and to cause disappearance of F0I-PVP protein, unless purified gamma subunit was added back. The addition to F0 liposomes of gamma subunit, but not that of alpha and beta subunits, caused per se inhibition of H+ conduction. It is concluded that F0I-PVP and gamma subunits are directly involved in the gate of the F0F1 H(+)-ATP synthase. Data are also presented indicating contribution to the gate of oligomycin-sensitivity conferral protein and of another protein subunit of F0, F6.

Age-dependent changes in the mitochondrial F0F1 ATP synthase

The age dependence of ATP hydrolase activity and oligomycin sensitive passive proton conduction in sonicated submitochondrial particles of rat brain and rat heart has been investigated. The results show an increase of Vmax of the ATP hydrolase activity and decrease of oligomycin sensitive passive proton conduction with increase of the age of rats from 3 to 6 months. Decrease of ATPase activity and increase of oligomycin sensitive proton conduction occur with further aging to 24 months. Immunoblot analysis shows that both the F(1) and F(0) contents of mitochondria vary with the age of rats, the former exhibiting relatively larger changes.

Cardiolipins and biomembrane function

Evidence is discussed for roles of cardiolipins in oxidative phosphorylation mechanisms that regulate State 4 respiration by returning ejected protons across and over bacterial and mitochondrial membrane phospholipids, and that regulate State 3 respiration through the relative contributions of proteins that transport protons, electrons and/or metabolites. The barrier properties of phospholipid bilayers support and regulate the slow proton leak that is the basis for State 4 respiration. Proton permeability is in the range 10(-3)-10(-4) cm s-1 in mitochondria and in protein-free membranes formed from extracted mitochondrial phospholipids or from stable synthetic phosphatidylcholines or phosphatidylethanolamines. The roles of cardiolipins in proton conductance in model phospholipid membrane systems need to be assessed in view of new findings by Hübner et al. [313]: saturated cardiolipins form bilayers whilst natural highly unsaturated cardiolipins form nonlamellar phases. Mitochondrial cardiolipins apparently participate in bilayers formed by phosphatidylcholines and phosphatidylethanolamines. It is not yet clear if cardiolipins themselves conduct protons back across the membrane according to their degree of fatty acyl saturation, and/or modulate proton conductance by phosphatidylcholines and phosphatidylethanolamines. Mitochondrial cardiolipins, especially those with high 18:2 acyl contents, strongly bind many carrier and enzyme proteins that are involved in oxidative phosphorylation, some of which contribute to regulation of State 3 respiration. The role of cardiolipins in biomembrane protein function has been examined by measuring retained phospholipids and phospholipid binding in purified proteins, and by reconstituting delipidated proteins. The reconstitution criterion for the significance of cardiolipin-protein interactions has been catalytical activity; proton-pumping and multiprotein interactions have yet to be correlated. Some proteins, e.g., cytochrome c oxidase are catalytically active when dimyristoylphosphatidylcholine replaces retained cardiolipins. Cardiolipin-protein interactions orient membrane proteins, matrix proteins, and on the outerface receptors, enzymes, and some leader peptides for import; activate enzymes or keep them inactive unless the inner membrane is disrupted; and modulate formation of nonbilayer HII-phases. The capacity of the proton-exchanging uncoupling protein to accelerate thermogenic respiration in brown adipose tissue mitochondria of cold-adapted animals is not apparently affected by the increased cardiolipin unsaturation; this protein seems to take over the protonophoric role of cardiolipins in other mitochondria. Many in vivo influences that affect proton leakage and carrier rates selectively alter cardiolipins in amount per mitochondrial phospholipids, in fatty acyl composition and perhaps in sidedness; other mitochondrial membrane phospholipids respond less or not at all.(ABSTRACT TRUNCATED AT 400 WORDS)