Cation-dependent reassembly of F0F1-ATPase in submitochondrial particles: evidence for a binding site for F1 on F0 in the absence of F6 and oligomycin sensitivity-conferring protein

Potential protein markers for nutritional health effects on colorectal cancer in the mouse as revealed by proteomics analysis

It is suggested that colorectal cancer might be prevented by changes in diet, and vegetable consumption has been demonstrated to have a protective effect. Until now, little is known about the effects of vegetable consumption at the proteome level. Therefore, the effect of increased vegetable intake on the protein expression in the colonic mucosa of healthy mice was studied. Aim was to identify the proteins that are differentially expressed by increased vegetable consumption and to discriminate their possible role in the protection against colorectal cancer. Mice were fed four different vegetable diets, which was followed by analysis of total cellular protein from colonic mucosal cells by a combination of 2-DE and MS. We found 30 proteins that were differentially expressed in one or more diets as compared to the control diet. Six could be identified by MALDI-TOF MS: myosin regulatory light chain 2, carbonic anhydrase I, high-mobility group protein 1, pancreatitis-associated protein 3, glyceraldehyde-3-phosphate dehydrogenase and ATP synthase oligomycin sensitivity conferral protein. Alterations in the levels of these proteins agree with a role in the protection against colon cancer. We conclude that these proteins are suitable markers for the health effect of food on cancer. The observed altered protein levels therefore provide support for the protective effects of vegetables against colorectal cancer.

Bovine coupling factor 6, with just 14.5% shared identity, replaces subunit h in the yeast ATP synthase

The mammalian mitochondrial ATP synthase is composed of at least 16 polypeptides. With the exception of coupling factor F(6), there are likely yeast homologs for each of these polypeptides. There are no obvious yeast homologs of F(6), as predicted from primary sequence comparison of the putative peptides encoded by the open reading frames in the yeast genome. In this manuscript, we demonstrate that expression of bovine F(6) complements a null mutant in ATP14 gene in yeast Saccharomyces cerevisiae. Subunit h of the yeast ATP synthase is encoded by ATP14 and is just 14.5% identical to bovine F(6). Expression of bovine F(6) in an atp14 null mutant strain recovers oxidative phosphorylation, and the ATP synthase is active, although functioning with a lower efficiency than the wild type enzyme. Like subunit h, bovine F(6) is shown to interact mainly with subunit 4 (subunit b), a component of the second stalk of the enzyme. These data indicated the subunit h is the yeast homolog of mammalian coupling factor F(6).

Quantitation and origin of the mitochondrial membrane potential in human cells lacking mitochondrial DNA

Mammalian mitochondrial DNA (mtDNA) encodes 13 polypeptide components of oxidative phosphorylation complexes. Consequently, cells that lack mtDNA (termed rho degrees cells) cannot maintain a membrane potential by proton pumping. However, most mitochondrial proteins are encoded by nuclear DNA and are still imported into mitochondria in rho degrees cells by a mechanism that requires a membrane potential. This membrane potential is thought to arise from the electrogenic exchange of ATP4- for ADP3- by the adenine nucleotide carrier. An intramitochondrial ATPase, probably an incomplete FoF1-ATP synthase lacking the two subunits encoded by mtDNA, is also essential to ensure sufficient charge flux to maintain the potential. However, there are considerable uncertainties about the magnitude of this membrane potential, the nature of the intramitochondrial ATPase and the ATP flux required to maintain the potential. Here we have investigated these factors in intact and digitonin-permeabilized mammalian rho degrees cells. The adenine nucleotide carrier and ATP were essential, but not sufficient to generate a membrane potential in rho degrees cells and an incomplete FoF1-ATP synthase was also required. The maximum value of this potential was approximately 110 mV in permeabilized cells and approximately 67 mV in intact cells. The membrane potential was eliminated by inhibitors of the adenine nucleotide carrier and by azide, an inhibitor of the incomplete FoF1-ATP synthase, but not by oligomycin. This potential is sufficient to import nuclear-encoded proteins but approximately 65 mV lower than that in 143B cells containing fully functional mitochondria. Subfractionation of rho degrees mitochondria showed that the azide-sensitive ATPase activity was membrane associated. Further analysis by blue native polyacrylamide gel electrophoresis (BN/PAGE) followed by activity staining or immunoblotting, showed that this ATPase activity was an incomplete FoF1-ATPase loosely associated with the membrane. Maintenance of this membrane potential consumed about 13% of the ATP produced by glycolysis. This work has clarified the role of the adenine nucleotide carrier and an incomplete FoF1-ATP synthase in maintaining the mitochondrial membrane potential in rho degrees cells.

Functional F1-ATPase essential in maintaining growth and membrane potential of human mitochondrial DNA-depleted rho degrees cells

F1-ATPase assembly has been studied in human rho degrees cells devoid of mitochondrial DNA (mtDNA). Since, in these cells, oxidative phosphorylation cannot provide ATP, their growth relies on glycolysis. Despite the absence of the mtDNA-coded F0 subunits 6 and 8, rho degrees cells possessed normal levels of F1-ATPase alpha and beta subunits. This F1-ATPase was functional and azide- or aurovertin-sensitive but oligomycin-insensitive. In addition, aurovertin decreased cell growth in rho degrees cells and also reduced their mitochondrial membrane potential, as measured by rhodamine 123 fluorescence. Therefore, a functional F1-ATPase was important to maintain the mitochondrial membrane potential and the growth of these rho degrees cells. Bongkrekic acid, a specific adenine nucleotide translocator (ANT) inhibitor, also reduced rho degrees cell growth and mitochondrial membrane potential. In conclusion, rho degrees cells need both a functional F1-ATPase and a functional ANT to maintain their mitochondrial membrane potential, which is necessary for their growth. ATP hydrolysis catalyzed by F1 must provide ADP3- at a sufficient rate to maintain a rapid exchange with the glycolytic ATP4- by ANT, this electrogenic exchange inducing a mitochondrial membrane potential efficient enough to sustain cell growth. However, since the effects of bongkrekic acid and of aurovertin were additive, other electrogenic pumps should cooperate with this pathway.

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.

Molecular cloning of cDNA for the import precursor of human coupling factor 6 of H(+)-ATP synthase in mitochondria

The nucleotide sequence of the import precursor of coupling factor 6 (factor 6) of human H(+)-ATP synthase has been determined from a recombinant cDNA clone isolated by screening a human kidney cDNA library with a cDNA for rat factor 6 as a probe. The sequence was composed of 466 nucleotides including a coding region for the import precursor of factor 6 and noncoding regions on the 5'- and 3'-sides. The import precursor of factor 6 and its mature polypeptide deduced from the open reading frame were found to consist of 108 and 76 amino acid residues with molecular weights of 12,596 and 8,969, respectively. The presequence of 32 amino acids could be the import signal peptide for directing the protein into the mitochondrial matrix.

Subunit delta of H(+)-ATPases: at the interface between proton flow and ATP synthesis

The ATP synthases in photophosphorylation and respiration are of the F-type with a membrane-bound proton channel, F0, and an extrinsic catalytic portion, F1. The properties of one particular subunit, delta (in chloroplasts and Escherichia coli) and OSCP (in mitochondria), are reviewed and the role of this subunit at the interface between F0 and F1 is discussed. Delta and OSCP from the three sources have in common the molecular mass (approximately 20 kDa), an elongated shape (axial ratio in solution about 3:1), one high-affinity binding site to F1 (Kd approximately 100 nM) plus probably one or two further low-affinity sites. When isolated delta is added to CF1-depleted thylakoid membranes, it can block proton flow through exposed CF0 channels, as do CF1 or CF1(-delta)+ delta. This identifies delta as part of the proton conductor or, alternatively, conformational energy transducer between F0 (proton flow) and F1 (ATP). Hybrid constructs as CF1(-delta)+ E. coli delta and EF1(-delta)+ chloroplast delta diminish proton flow through CF0.CF1(-delta) + E. coli delta does the same on EF0. Impairment of proton leaks either through CF0 or through EF0 causes "structural reconstitution' of ATP synthesis by remaining intact F0F1. Functional reconstitution (ATP synthesis by fully reconstructed F0F1), however, is absolutely dependent on the presence of subunit delta and is therefore observed only with CF1 or CF1(-delta) + chloroplast delta on CF0 and EF1 or EF1(-delta) + E. coli delta on EF0. The effect of hybrid constructs on F0 channels is surprising in view of the limited sequence homology between chloroplast and E. coli delta (36% conserved residues including conservative replacements). An analysis of the distribution of the conserved residues at present does not allow us to discriminate between the postulated conformational or proton-conductive roles of subunit delta.

Bacterial adenosine 5'-triphosphate synthase (F1F0): purification and reconstitution of F0 complexes and biochemical and functional characterization of their subunits

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Efficient reconstitution of mitochondrial energy-transfer reactions from depleted membranes and F1-ATPase as a function of the amount of bound oligomycin sensitivity-conferring protein (OSCP)

Pig heart mitochondrial membranes depleted of F1 and OSCP by various treatments were analyzed for their content in alpha and beta subunits of F1 and in OSCP using monoclonal antibodies. Membrane treatments and conditions of rebinding of F1 and OSCP were optimized to reconstitute efficient NADH- and ATP-dependent proton fluxes, ATP synthesis and oligomycin-sensitive ATPase activity. F1 and OSCP can be rebound independently to depleted membranes but to avoid unspecific binding of F1 to depleted membranes (ASUA) which is not efficient for ATP synthesis, F1 must be rebound before the addition of OSCP. The rebinding of OSCP to depleted membranes reconstituted with F1 inhibits the ATPase activity of rebound F1, while it restores the ATP-driven proton flux measured by the quenching of ACMA fluorescence. The rebinding of OSCP also renders the ATPase activity of bound F1 sensitive to uncouplers. The rebinding of OSCP alone or F1 alone, does not modify the NADH-dependent proton flux, while the rebinding of both F1 and OSCP controls this flux, inducing an inhibition of the rate of NADH oxidation. Similarly, oligomycin, which seals the F0 channel even in the absence of F1 and OSCP, inhibits the rate of NADH oxidation. OSCP is required to adjust the fitting of F1 to F0 for a correct channelling of protons efficient for ATP synthesis. All reconstituted energy-transfer reactions reach their optimal value for the same amount of OSCP. This amount is consistent with a stoichiometry of two OSCP per F1 in the F0-F1 complex.