Proton ATPase of rat liver mitochondria. Preparation and visualization of a functional complex using the novel zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate

Iron transport by proteoliposomes containing mitochondrial F(1)F(0) ATP synthase isolated from rat heart

In this work, we present evidence of Fe(2+) transport by rat heart mitochondrial F(1)F(0) ATP synthase. Iron uptake by the vesicles containing the enzyme was concentration- and temperature-dependent, with an optimum temperature of 37 degrees C. Both ATP and ADP stimulated iron uptake in a concentration-dependent manner, whereas AMP, AMPPCP, and mADP did not. Inhibitors of the enzyme, oligomycin, and resveratrol similarly blocked iron transport. The iron uptake was confirmed by inhibition using specific antibodies against the alpha, beta, and c subunits of the enzyme. Interestingly, slight transport of common divalent and trivalent metal ions such as Mg(+2), Ca(+2), Mn(+2), Zn(+2), Cu(+2), Fe(+3), and Al(+3) was observed. Moreover, Cu(+2), even in the nM range, inhibited iron uptake and attained maximum inhibition of approximately 56%. Inorganic phosphate (Pi) in the medium exerted an opposite effect depending on the type of adenosine nucleotide, which was suppressed with ATP, but enhanced with ADP. A similarly stimulating effect of ATP and ADP with an inverse effect of Pi suggests that the activity of ATPase and ATP synthase may be associated with iron uptake in a different manner, probably via antiport of H(+).

Cardiolipin is essential for higher proton translocation activity of reconstituted F(0)

The F(0) membrane domain of F(0)F(1)-ATPase complex had been purified from porcine heart mitochondria. SDS-PAGE with silver staining indicated that the purity of F(0) was about 85% and the sample contained no subunits of F(1)-ATPase. The purified F(0) was reconstituted into liposomes with different phospholipid composition, and the effect of CL (cardiolipin), PA (phosphatidic acid), PI (phosphatidylinositol) and PS (phosphatidylserine) on the H(+) translocation activity of F(0) was investigated. The results demonstrated that CL, PA and PI could promote the proton translocation of F(0) with the order of CLPA>PI, while PS inhibited it. Meanwhile ADM (adriamycin) severely impaired the proton translocation activity of F(0) vesicles containing CL, which suggested that CL's stimulation of the activity of reconstituted F(0) might correlate with its non-bilayer propensity. After F(0) was incorporated into the liposomes containing PE (phosphatidylethanolamine), DOPE (dioleoylphosphatidylethanolamine) as well as DEPE (dielaidoylphosphatidylethanolamine), it was found that the proton translocation activity of F(0) vesicles increased with the increasing content of PE or DOPE, which has high propensity of forming non-bilayer structure, but was independent of DEPE. The dynamic quenching of the intrinsic fluorescence of tryptophan by HB (hypocrellin B) as well as fluorescent spectrum of acrylodan labeling F(0) at cysteine indicated that CL could induce F(0) to a suitable conformation resulting in higher proton translocation activity.

Identification of mitochondrial F(1)F(0)-ATP synthase interacting with galectin-3 in colon cancer cells

To evaluate the effect of galectin-3 in cell cycle regulation of colon cancer cells, we looked for binding molecules interacting with galectin-3 and examined the changes in cell cycle by suppressing galectin-3 and the binding molecule. To identify target molecules interacting with galectin-3, we analyzed immunoprecipitate of the anti-galectin-3 antibody obtained from human colon cancer cell line, using matrix-assisted laser desorption ionization-mass spectrometry. We validated subcellular localization of galectin-3 and ATP synthase identified, and ATP synthase activity was determined in the presence of galectin-3. Cell cycle regulation was monitored after galectin-3 siRNA transfection. ATP synthase b-subunit was identified in immunoprecipitate of the anti-galectin-3 antibody. Galectin-3 and ATP synthase were co-isolated in the inner membrane vesicles of mitochondria. Galectin-3 has an inhibitory activity against ATP synthase, and intracellular ATP content showed increasing tendency after galectin-3 suppression. Suppression of galectin-3 resulted in G0/G1 progression of human colon cancer cells arrested at S, S/G2 and G2/M phase in the presence of doxorubicin, and etoposide or nocodazole, respectively. Compared to cells in which ATP synthase d-subunit was suppressed alone, sub-G1 fraction caused by etoposide or nocodazole was decreased in cells with galectin-3 suppression alone. In conclusion, galectin-3 co-localized with ATP synthase in the inner membrane of mitochondria and has an inhibitory effect on ATP synthase in human colon cancer cells. In the presence of cell cycle synchronizing drugs, doxorubicin, etoposide, or nocodazole, suppression of galectin-3 induced cell cycle progression to G0/G1 phase.

Rotary molecular motors

The F-, V-, and A-adenosine triphosphatases (ATPases) represent a family of evolutionarily related ion pumps found in every living cell. They either function to synthesize adenosine triphosphate (ATP) at the expense of an ion gradient or they act as primary ion pumps establishing transmembrane ion motive force at the expense of ATP hydrolysis. The A-, F-, and V-ATPases are rotary motor enzymes. Synthesis or hydrolysis of ATP taking place in the three catalytic sites of the membrane extrinsic domain is coupled to ion translocation across the single ion channel in the membrane-bound domain via rotation of a central part of the complex with respect to a static portion of the enzyme. This chapter reviews recent progress in the structure determination of several members of the family of F-, A-, and V-ATPases and our current understanding of the rotary mechanism of energy coupling.

Factor B and the mitochondrial ATP synthase complex

Factor B is a subunit of the mammalian ATP synthase complex, whose existence has been controversial. This paper describes the molecular and functional properties of a recombinant human factor B, which when added to bovine submitochondrial particles depleted of their factor B restores the energy coupling activity of the ATP synthase complexes. The mature human factor B has 175 amino acids and a molecular mass of 20,341 Da. The preparation is water-soluble, monomeric, and is inactivated by monothiol- and especially dithiol-modifying reagents, probably reacting at its cysteine residues Cys-92 and Cys-94. A likely factor B gene composed of 5 exons has been identified on chromosome 14q21.3, and the functional role of factor B in the mammalian ATP synthase complex has been discussed.

Biochemical and anatomical evidence for specialized voltage-dependent calcium channel gamma isoform expression in the epileptic and ataxic mouse, stargazer

Inherited forms of ataxia and absence seizures in mice have been linked to defects in voltage-dependent calcium channel subunits. However, a correlation between the sites of neuronal dysfunction and the impact of the primary lesion upon calcium channel subunit expression or function has not been clearly established. For example, the mutation in stargazer mice has pleiotropic consequences including synaptic alterations in cerebellar granule cells, hippocampal CA3/mossy fibers, and cortical neurons in layer V that, presumably, lead to ataxia and seizures. Genetic analysis of stargazer mice determined that the defective gene encodes a protein expressed in brain (gamma2) with limited homology to the skeletal muscle L-type calcium channel gamma1 subunit. Although additional gamma isoforms have been subsequently identified primarily in neural tissue, little was known about the proteins they encode. Therefore, this study explored the distribution and biochemical properties of gamma2 and other gamma isoforms in wild-type and stargazer brain. We cloned human gamma2, gamma3, and gamma4 isoforms, produced specific anti-peptide antibodies to gamma isoforms and characterized both heterologously expressed and endogenous gamma. We identified regional specificity in the expression of gamma isoforms by western analysis and immunohistochemistry. We report for the first time that the mutation in the stargazer gene resulted in the loss of gamma2 protein. Furthermore, no compensatory changes in the expression of gamma3 or gamma4 protein were evident in stargazer brain. In contrast to other voltage-dependent calcium channel subunits, gamma immunostaining was striking in that it was primarily detected in regions highly enriched in excitatory glutamatergic synapses and faintly detected in cell bodies, suggesting a role for gamma in synaptic functions. Sites of known synaptic dysfunction in stargazer (the hippocampal CA3 region, dentate gyrus, and cerebellar molecular layer) were revealed as relying primarily upon gamma2, as total gamma isoform expression was dramatically decreased in these regions. Electron microscopy localized anti-gamma antibody immunostaining to dendritic structures of hippocampal mossy fiber synapses, with enrichment at postsynaptic densities. To assess the association of native gamma with voltage-dependent calcium channel or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor subunits, gamma isoforms (gamma2, gamma3 and gamma4) were detergent solubilized from mouse forebrain. Antibodies against a highly conserved C-terminal epitope present in gamma2, gamma3 and gamma4 immunoprecipitated voltage-dependent calcium channel subunits (alpha1B), providing the first in vivo evidence that gamma and voltage-dependent calcium channels form stable complexes. Furthermore, both anti-gamma2 antibodies and anti-alpha1B antibodies independently immunoprecipitated the AMPA receptor subunit, GluR1, from mouse forebrain homogenates. In summary, loss of gamma2 immunoreactivity in stargazer is precisely localized so as to contribute to previously characterized synaptic defects. The data in this paper provide compelling evidence that gamma isoforms form complexes in vivo with voltage-dependent calcium channels as well as AMPA receptors, are selectively and differentially expressed in neuronal processes, and localize primarily to dendritic structures in the hippocampal mossy fiber region.

Mitochondrial F(0)F(1) ATP synthase. Subunit regions on the F1 motor shielded by F(0), Functional significance, and evidence for an involvement of the unique F(0) subunit F(6)

Studies reported here were undertaken to gain greater molecular insight into the complex structure of mitochondrial ATP synthase (F(0)F(1)) and its relationship to the enzyme's function and motor-related properties. Significantly, these studies, which employed N-terminal sequence, mass spectral, proteolytic, immunological, and functional analyses, led to the following novel findings. First, at the top of F(1) within F(0)F(1), all six N-terminal regions derived from alpha + beta subunits are shielded, indicating that one or more F(0) subunits forms a "cap." Second, at the bottom of F(1) within F(0)F(1), the N-terminal region of the single delta subunit and the C-terminal regions of all three alpha subunits are shielded also by F(0). Third, and in contrast, part of the gamma subunit located at the bottom of F(1) is already shielded in F(1), indicating that there is a preferential propensity for interaction with other F(1) subunits, most likely delta and epsilon. Fourth, and consistent with the first two conclusions above that specific regions at the top and bottom of F(1) are shielded by F(0), further proteolytic shaving of alpha and beta subunits at these locations eliminates the capacity of F(1) to couple a proton gradient to ATP synthesis. Finally, evidence was obtained that the F(0) subunit called "F(6)," unique to animal ATP synthases, is involved in shielding F(1). The significance of the studies reported here, in relation to current views about ATP synthase structure and function in animal mitochondria, is discussed.

Inhibition of mitochondrial proton F0F1-ATPase/ATP synthase by polyphenolic phytochemicals

Mitochondrial proton F0F1-ATPase/ATP synthase synthesizes ATP during oxidative phosphorylation. In this study, we examined the effects of several groups of polyphenolic phytochemicals on the activity of the enzyme. Resveratrol, a stilbene phytoalexin that is present in grapes and red wine, concentration-dependently inhibited the enzymatic activity of both rat brain and liver F0F1-ATPase/ATP synthase (IC(50) of 12 - 28 microM). Screening of other polyphenolic phytochemicals using rat brain F0F1-ATPase activity resulted in the following ranking potency (IC(50) in parenthesis): piceatannol (8 microM)>resveratrol (19 microM)=(-)epigallocatechin gallate (17 microM)>(-)epicatechin gallate, curcumin (45 microM)>genistein=biochanin A=quercetin=kaempferol=morin (55 - 65 microM)>phloretin=apigenin=daidzein (approx. 100 microM). Genistin, quercitrin, phloridzin, (+)catechin, (+)epicatechin, (-)epicatechin and (-)epigallocatechin had little effect at similar concentrations. Tannic acid, theaflavins (tea extract) and grape seed proanthocyanidin extract (GSPE) had IC(50) values of 5, 20 and 30 microg ml(-1), respectively. Several monophenolic antioxidants and non-phenolic compounds were ineffective at concentrations of 210 microM or higher. The inhibition of F0F1-ATPase by resveratrol and genistein was non-competitive in nature. The effects of polyphenolic phytochemicals were additive. Both resveratrol and genistein had little effect on the Na(+)/K(+)-ATPase activity of porcine cerebral cortex, whereas quercetin had similar inhibitory potency as for F0F1-ATPase. In conclusion, the ATP synthase is a target for dietary phytochemicals. This pharmacological property of these phytochemicals should be included in the examination of their health benefits as well as potential cytotoxicity.

Preparative electrophoretic method for the purification of a hydrophobic membrane protein: subunit c of the mitochondrial ATP synthase from rat liver

A method is described for the purification of subunit c of ATP synthase from rat liver mitochondria. After sample preparation and solvent extraction, the protein was purified to homogeneity by a single-step preparative electrophoretic procedure, using aqueous buffer and containing lithium dodecyl sulfate. The subunit is an extremely hydrophobic and insoluble protein and all solubilization attempts, using a variety of detergents, were unsuccessful except for lithium dodecyl sulfate. Buffer exchange and FPLC gel filtration removed the detergent from the purified sample, leaving the protein in a soluble form. The mammalian protein is composed of 75 amino acid residues, with a molecular mass of 7602 Da and is classified as a proteolipid. Subunit c accounts for 25 and 85% of the intralysosomal accumulation, within neurons, of storage material in juvenile and late-infantile forms of Batten's disease, respectively. This purification procedure allows access to a continuous supply of pure subunit c from a conventional source such as rat liver and preserves precious autopsy materials. The protein could be used as substrate in future proteolytic studies involving pepstatin-insensitive lysosomal proteases and for raising of more specific antibodies. The procedure could also be adapted/modified and used as a model for purifying other extremely insoluble proteins.

Rapid inhibition of rat brain mitochondrial proton F0F1-ATPase activity by estrogens: comparison with Na+, K+ -ATPase of porcine cortex

Our earlier studies have identified oligomycin sensitivity-conferring protein (OSCP), a subunit of proton F0F1-ATPase/ATP synthase in the mitochondrial inner membranes, as a new estradiol binding protein. This finding suggests that mitochondrial ATPase/ATP synthase could be a potential target for estradiol or compounds with similar structures. Here, we report that estradiol and several other compounds inhibited F0F1-ATPase activity of detergent-solubilized rat brain mitochondrial preparations in a following decreasing order: diethylstilbestrol (half-inhibition concentration, IC50 of 10-25 microM) > alpha-zearalenol, 4-hydroxyestradiol (1C50 of 55 microM) >2-hydroxyestradiol (IC50 of 110 microM), 17beta-estradiol, 17alpha-estradiol > beta-zearalanol > estriol, testosterone, 16alpha-hydroxyestrone > corticosterone, progesterone, dehydroepiandrosterone, dehydroepiandrosterone 3-sulfate, cholesterol (less than 10% inhibition at 140 microM). On the other hand, Na+, K+ -ATPase of porcine cortex showed different sensitivity to the compounds tested above. At 70 microM, the rank of inhibitory potency in decreasing order was as follows: 2-hydroxyestradiol (IC50 of 70 microM) > diethylstilbestrol> 4-hydroxyestradiol > progesterone > alpha-zearalenol, while other compounds had little effect (less than 5%). The data indicate that the ubiquitous mitochondrial F0F1-ATPase is a specific target site for estradiol and related estrogenic compounds; however, under this in vitro condition, the effect seems to require pharmacological concentrations.

Delta subunit of rat liver mitochondrial ATP synthase: molecular description and novel insights into the nature of its association with the F1-moiety

The F1 moiety of ATP synthase complexes consists of five subunit types in the stoichiometric ratio alpha 3, beta 3, gamma, delta epsilon. Of these, the delta subunit has received very little attention in the study of F1 preparations from eukaryotic cells. Although recently shown to associate tightly with the beta subunit [Pedersen, P. L., Hullihen, J., Bianchet, M., Amzel, L. M., and Lebowitz, M. S. (1995) J. Biol. Chem. 270, 1775-1784], the delta subunit is not resolved in the X-ray structure of either the rat liver or bovine heart enzyme. For these reasons, the novel studies reported here were designed both to provide a molecular description of the rat liver delta subunit and to gain insight into the nature of its interaction with F1. The rat liver delta subunit was cloned from a lambda gt11 library, sequenced, overexpressed in Escherichia coli (E. coli) in fusion with the maltose binding protein, and, after cleavage of the latter protein, purified to homogeneity. The purified delta subunit (MW = 14.7 kDa) was shown by circular dichroism spectroscopy to be highly structured and to exhibit about 25% sequence identity to the chloroplast and E. coli epsilon subunits, frequently regarded as homologues of higher eukaryotic delta subunits. Significantly, and in contrast to the chloroplast and E. coli epsilon subunits, which are readily removed from their parent F1 moieties after treatment respectively with ethanol and lauryldimethylamine oxide, the rat liver delta subunit remained tightly bound to F1 under these relatively mild conditions. For the above reasons, four types of experiments were carried out on rat liver F1 in order to (1) determine the accessibility of the delta subunit to both specific antibodies and to proteases, (2) establish the effect of nucleotides on this subunit's accessibility, (3) identify in cross-linking studies with disuccinimidyl glutarate this subunit's most reactive neighbor, and (4) determine whether this subunit can be dissociated from F1 by using ionic detergents while leaving the remaining complex intact. The data derived from this detailed set of studies (a) supports the view that the rat liver F1-delta subunit is in very close proximity to the gamma subunit near the bottom of the F1 molecule but does not penetrate deeply into the central core, (b) shows that within F1 the delta subunit's N-terminus is exposed while its C-terminus is masked, (c) indicates that access to the delta subunit is shielded in part by the alpha, beta, and gamma subunits and changes during the catalytic cycle of F1, and (d) implicates the delta subunit as important for the structural stability of the F1 unit. These novel findings on a higher eukaryotic F1-delta subunit are discussed in relationship to earlier studies on the related epsilon subunits from both chloroplasts and E. coli.

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.

Plant mitochondrial F0F1 ATP synthase. Identification of the individual subunits and properties of the purified spinach leaf mitochondrial ATP synthase

Spinach leaf mitochondrial F0F1 ATPase has been purified and is shown to consist of twelve polypeptides. Five of the polypeptides constitute the F1 part of the enzyme. The remaining polypeptides, with molecular masses of 28 kDa, 23 kDa, 18.5 kDa, 15 kDa, 10.5 kDa, 9.5 kDa and 8.5 kDa, belong to the F0 part of the enzyme. This is the first report concerning identification of the subunits of the plant mitochondrial F0. The identification of the components is achieved on the basis of the N-terminal amino acid sequence analysis and Western blot technique using monospecific antibodies against proteins characterized in other sources. The 28-kDa protein crossreacts with antibodies against the subunit of bovine heart ATPase with N-terminal Pro-Val-Pro- which corresponds to subunit F0b of Escherichia coli F0F1. Sequence analysis of the N-terminal 32 amino acids of the 23-kDa protein reveals that this protein is similar to mammalian oligomycin-sensitivity-conferring protein and corresponds to the F1 delta subunit of the chloroplast and E. coli ATPases. The 18.5-kDa protein crossreacts with antibodies against subunit 6 of the beef heart F0 and its N-terminal sequence of 14 amino acids shows a high degree of sequence similarity to the conserved regions at N-terminus of the ATPase subunits 6 from different sources. ATPase subunit 6 corresponds to subunit F0a of the E. coli enzyme. The 15-kDa protein and the 10.5-kDa protein crossreact with antibodies against F6 and the endogenous ATPase inhibitor protein of beef heart F0F1-ATPase, respectively. The 9.5-kDa protein is an N,N'-dicyclohexylcarbodiimide-binding protein corresponding to subunit F0c of the E. coli enzyme. The 8.5-kDa protein is of unknown identity. The isolated spinach mitochondrial F0F1 ATPase catalyzes oligomycin-sensitive ATPase activity of 3.5 mumol.mg-1.min-1. The enzyme catalyzes also hydrolysis of GTP (7.5 mumol.mg-1.min-1) and ITP (4.4 mumol.mg-1.min-1). Hydrolysis of ATP was stimulated fivefold in the presence of amphiphilic detergents, however the hydrolysis of other nucleotides could not be stimulated by these agents. These results show that the plant mitochondrial F0F1 ATPase complex differs in composition from the other mitochondrial, chloroplast and bacterial ATPases. The enzyme is, however, more closely related to the yeast mitochondrial ATPase and to the animal mitochondrial ATPase than to the chloroplast enzyme. The plant mitochondrial enzyme, however, exhibits catalytic properties which are characteristic for the chloroplast enzyme.

Two-dimensional diffusion of F1F0-ATP synthase and ADP/ATP translocator. Testing a hypothesis for ATP synthesis in the mitochondrial inner membrane

We report here the first experimentally determined lateral diffusion coefficients of the F1F0-ATP synthase and the ADP/ATP translocator in isolated inner membranes of rat liver mitochondria. Rabbit IgG developed against the F1F0-ATP synthase isolated from rat liver mitochondria was determined to be immunospecific for the synthase subunits, notably the alpha-beta doublet, gamma and delta subunits of F1 and subunits two, three and four of F0. This IgG, conjugated with lissamine-rhodamine, was used as a fluorescent probe to monitor the diffusion of the synthase in the membrane. IgG to cytochrome bc1 complex, prepared and labeled similarly, was used as a fluorescent probe for diffusion of this redox component. Eosin maleimide was determined to specifically label the ADP/ATP translocator in the isolated inner membrane and was used as a specific probe for the diffusion of the translocator. Using fluorescence recovery after photobleaching, the experimental average lateral diffusion coefficient of the F1F0-ATP synthase was determined to be 8.4 x 10(-10) cm2/s or twice that of cytochrome bc1 complex while the diffusion coefficient of the ADP/ATP translocator was 1.7 x 10(-9) cm2/s or four times that of cytochrome bc1 complex suggesting that all three components are independent two-dimensional diffusants. Using these diffusion coefficients and applying a number of basic assumptions, we calculated the theoretical two-dimensional diffusion-controlled collision frequencies and derived collision efficiencies (protons transferred per collision) between each of the three proton-transferring redox complexes and both the F1F0-ATP synthase and ADP/ATP translocator by treating the redox components as proton donors and the synthase and translocator as proton acceptors. These collision efficiencies support the physical possibility of a diffusion-based, random collision process of proton transfer and ATP synthesis in the mitochondrial inner membrane.

H(+)-ATP synthase from rat liver mitochondria. A simple, rapid purification method of the functional complex and its characterization

A novel, simple, and rapid preparative method for purification of rat liver H(+)-ATP synthase by anion-exchange HPLC was developed. The H(+)-ATP synthase purified had higher ATPase activity in the absence of added phospholipids than any preparation reported previously, and this activity was completely inhibited by oligomycin. When reconstituted into proteoliposomes, the H(+)-ATP synthase showed an ATP-dependent 8-anilinonaphthalene-1-sulfonate response and ATP-Pi exchange activity, both of which were also completely inhibited by oligomycin and an uncoupler, indicating the intactness of the H(+)-ATP synthase. An immunochemical study and a labeling experiment with N,N'-[14C]dicyclohexylcarbodiimide ([14C]DCCD) demonstrated the presence of chargerin II ( a product of mitochondrial A6L DNA) and DCCD-binding protein (subunit c) in the complex. The subunits of the complex were separated into 11 main fractions by reverse-phase HPLC, and 3 of them and the delta subunit in F1 were partially sequenced. A search for sequence homologies indicated that these components were subunit b, coupling factor 6, subunit delta, and subunit epsilon. This is the first report of the existence of subunit b, factor 6, and chargerin II in H(+)-ATP synthase purified from rat liver mitochondria.

Identification of F0 subunits in the rat liver mitochondrial F0F1-ATP synthase

In order to identify the subunits constituting the rat liver F0F1-ATP synthase, the complex prepared by selective extraction from the mitochondrial membranes with a detergent followed by purification on a sucrose gradient has been compared to that obtained by immunoprecipitation with an anti-F1 serum. The subunits present in both preparations that are assumed to be authentic components of the complex have been identified. The results show that the total rat liver F0F1-ATP synthase contains at least 13 different proteins, seven of which can be attributed to F0. The following F0 subunits have been identified: the subunit b (migrating as a 24 kDa band in SDS-PAGE), the oligomycin-sensitivity-conferring protein (20 kDa), and F6 (9 kDa) that have N-terminal sequences homologous to the beef-heart ones; the mtDNA encoded subunits 6 (20 kDa) and 8 (less than 7 kDa) that can be synthesized in isolated mitochondria; an additional 20 kDa protein that could be equivalent to the beef heart subunit d.

cDNA cloning and sequencing for the import precursor of coupling factor 6 in H(+)-ATP synthase from rat liver mitochondria

The nucleotide sequence of the import precursor of coupling factor 6 (factor 6) of rat liver H(+)-ATP synthase has been determined from a recombinant cDNA clone isolated by screening a rat liver cDNA library with a probe DNA. The sequence was composed of 458 nucleotides including a coding region for the import precursor of factor 6 and noncoding regions of both the 5'- and 3'-sides. The import precursor of factor 6 and its mature polypeptide deduced from the open reading frame consisted of 108 and 76 amino acid residues with a molecular weight of 12,494 and 8,927, respectively. The presequence of 32 amino acids could be the import signal peptide which serves to direct the protein into the mitochondrial matrix.

F0F1-ATPase of plant mitochondria: isolation and polypeptide composition

A simple and high yield purification procedure for the isolation of F0F1-ATPase from spinach leaf mitochondria has been developed. This is the first report concerning purification and composition of the plant mitochondrial F0F1-ATPase. The enzyme is selectively extracted from inner membrane vesicles with the zwitterionic detergent, 3-[(3-cholamidopropyl) dimethyl ammonio]-1- propane sulfonate (CHAPS). The purified enzyme exhibits a high oligomycin-sensitive ATPase activity (3,6 mumol.min-1.mg-1). SDS-PAGE of the purified F0F1-ATPase complex reveals protein bands of molecular masses of 54 kDa (F1 alpha,beta), 33 kDa (F1 gamma), 28 kDa, 23 kDa, 21 kDa (F1 delta), 18.5 kDa, 15 kDa, 10.5 kDa, 9.5 kDa (F1 epsilon) and 8.5 kDa. All polypeptides migrate as one complex in a polyacrylamide gradient gel under non-denaturing conditions in the presence of 0.1% Triton X-100. Five polypeptides could be identified as subunits of F1. Polypeptides of molecular masses 28 kDa, 23 kDa, 18.5 kDa, 15 kDa, 10.5 kDa, 9.5 kDa and 8.5 kDa constitute the F0 part of the complex. Our results show that polypeptide composition of the plant mitochondrial F0 differs from other eukaryotic F0 of yeast, mammals and chloroplasts.

Mitochondrial F0F1 H+-ATP synthase. Characterization of F0 components involved in H+ translocation

The membrane F0 sector of mitochondrial ATP synthase complex was rapidly isolated by direct extraction with CHAPS from F1-depleted submitochondrial particles. The preparation thus obtained is stable and can be reconstituted in artificial phospholipid membranes to result in oligomycin-sensitive proton conduction, or recombined with purified F1 to give the oligomycin-sensitive F0F1-ATPase complex. The F0 preparation and constituent polypeptides were characterized by SDS-polyacrylamide gel electrophoresis and immunoblot analysis. The functional role of F0 polypeptides was examined by means of trypsin digestion and reconstitution studies. It is shown that, in addition to the 8 kDa DCCD-binding protein, the nuclear encoded protein [(1987) J. Mol. Biol. 197, 89-100], characterized as an intrinsic component of F0 (F0I, PVP protein [(1988) FEBS Lett. 237,9-14]) [corrected] is involved in H+ translocation and the sensitivity of this process to the F0 inhibitors, DCCD and oligomycin.

Identification of nucleus-encoded F0I protein of bovine heart mitochondrial H+-ATPase as a functional part of the F0 moiety

The F0I protein of apparent Mr 27,000, previously characterized [(1988) Eur. J. Biochem. 173, 1-8] as a genuine component of bovine heart F0, has been sequenced and shown to be identical with the nucleus encoded 24,668 Da protein characterized earlier [(1987) J. Mol. Biol. 197, 89-100]. It is directly shown by proteolytic cleavage and reconstitution experiments that this protein, denoted here as PVP from the single-letter codes of the last three residues of the N-terminus, is involved in proton conduction by F0 and in its sensitivity to oligomycin.

Topological and functional characterization of the F0I subunit of the membrane moiety of the mitochondrial H+-ATP synthase

Using isolated polypeptides of the F0 sector of bovine heart mitochondrial H+-ATPase, antisera were developed detecting specifically two components of F0. These two components were identified as F0I and oligomycin-sensitivity-conferring protein (OSCP) respectively. Both F0I and OSCP were digested by mild trypsin treatment of submitochondrial particles depleted of the catalytic part of H+-ATPase (USMP). Proteolysis was largely prevented by binding of F1 to F0. Proteolysis of F0I resulted in the formation of three immunoreactive, membrane-bound fragments of apparently 26 kDa, 25.5 kDa and 18 kDa, respectively, indicating that F0I contains trypsin-accessible Arg or Lys residues located close to the end and the middle part of the protein, respectively, which are in intimate contact with F1. Digestion of USMP with trypsin resulted in depression of passive H+ conduction through F0 which could be ascribed to proteolysis of F0I.

Subunit composition of the H+-ATPase complex from anaerobic bacterium Lactobacillus casei

The H+-ATPase complex has been isolated from the membranes of the anaerobic bacterium Lactobacillus casei by two independent methods. 1. The crossed-immunoelectrophoresis of the 14C-labelled ATPase complex against antibodies to a highly purified soluble ATPase has been used. The subunit composition of the complex has been established by autoradiography. The soluble part of L. casei ATPase, in contrast to coupling factor F1-ATPases of aerobic bacteria, chloroplasts and mitochondria which include two kinds of large subunit (alpha and beta), consists of one kind of large subunit with a molecular mass of 43 kDa. Moreover, a minor polypeptide of 25 kDa has been found in the soluble ATPase. Factor F0 of L. casei ATPase complex consists of a 16-kDa subunit and two subunits with molecular masses less than 14 kDa. 2. A dicyclohexylcarbodiimide-sensitive ATPase complex has been isolated from L. casei membranes by treating them with a mixture of octyl glucoside and sodium cholate. The complex, purified by centrifugation on a sucrose density gradient, contains the main subunits with molecular masses of 43 kDa, 25 kDa and 16 kDa and a dicyclohexylcarbodiimide-binding subunit with a molecular mass less than 14 kDa.

ATP synthase from bovine mitochondria. The characterization and sequence analysis of two membrane-associated sub-units and of the corresponding cDNAs

ATP synthase from bovine mitochondria is a complex of 13 different polypeptides, whereas the Escherichia coli enzyme is simpler and contains eight subunits only. Two of the bovine subunits, b and d, which had not been characterized, have been isolated from the purified enzyme. Subunits with sizes corresponding to bovine subunits b and d are evident in preparations of the enzyme from mitochondria of other species. Partial protein sequences have been determined by direct methods. On the basis of some of this information, two oligonucleotide mixtures, 17 and 18 bases in length, have been synthesized and used as hybridization probes in the isolation of clones of the cognate cDNAs. The sequences of the two proteins have been deduced from their DNA sequences. Subunit b is 214 amino acid residues in length and has a free N terminus. Subunit d is 160 amino acid residues long. Its N-terminal alanine is blocked by an N-acetyl group, as demonstrated by fast atom bombardment mass spectrometry of N-terminal peptides. The sequence near the N terminus of the b subunit is made predominantly of hydrophobic residues, whereas the remainder of the protein is mainly hydrophilic. This N-terminal hydrophobic region may be folded into an alpha-helical structure spanning the lipid bilayer. In its distribution of hydrophobic residues, this protein resembles the b subunits of ATP synthase complexes in bacteria and chloroplasts. The b subunit in E. coli forms an important structural link between the extramembrane sector of the enzyme F1, and the intrinsic membrane domain, FO. It is proposed that the bovine mitochondrial subunit b serves a similar function. If this is so, the mitochondrial enzyme, as the chloroplast ATP synthase, contains equivalent subunits to all eight of those that constitute the E. coli enzyme. Subunit d has no extensive hydrophobic sequences, and is not apparently related to any subunit described in the simpler ATP synthases in bacteria and chloroplasts.

The plasma membrane ATPase of the thermoacidophilic archaebacterium Sulfolobus acidocaldarius. Purification and immunological relationships to F1-ATPases

The plasma-membrane-associated ATPase of the thermoacidophilic archaebacterium Sulfolobus acidocaldarius characterized in a previous work [M. Lübben & G. Schäfer (1987) Eur. J. Biochem. 164, 533-540] has been solubilized. It can be easily removed from the membrane by mild treatment with zwitterionic detergents, therefore it appears to be a peripheral membrane protein analogous to the soluble F1-ATPase of eubacteria and eukaryotes. Further purification has been achieved by subsequent gel permeation and ion-exchange chromatography. The final purity is greater than 70% as judged by staining intensities after SDS/polyacrylamide gel electrophoresis. The ATPase consists of two major polypeptides of 65 kDa (alpha) and 51 kDa (beta) in comparable quantities; a minor band (20 kDa) is assumed to be a contaminant or a constitutive part of the enzyme, possibly copurified in substoichiometric amount. The native molecular mass of the solubilized ATPase determined by gel permeation is 430 kDa. Considering the precision of these methods, it remains open whether a 3:3 stoichiometry reflects the contribution of alpha and beta subunits to the quaternary structure, in analogy to known F1-ATPases. The catalytic properties resemble those of the membrane-bound state. There are two pH optima at 5.3 and 8.0 in the absence and only one optimum at 6.5 in the presence of the activating anion sulfite. Activity is strictly dependent on the divalent cations Mg2+ or Mn2+. ATP and dATP are hydrolyzed with highest rates; also other purine and pyrimidine nucleotides are cleaved significantly, but not ADP, pyrophosphate and p-nitrophenyl phosphate. The ATPase is insensitive to azide or vanadate but is inhibited by relatively low concentrations of nitrate. Polyclonal antisera have been raised against the beta subunit of the Sulfolobus ATPase. Cross-reactivities with cellular or membrane extracts of a number of archaebacteria, eubacteria and chloroplasts have been analyzed by means of Western blotting and immunodecoration. A strong cross-reactivity with other genera of the Sulfolobales is observed, also with Methanobacterium, Methanosarcina, Methanolobus and Halobacterium. Even membranes of the eubacterium Escherichia coli and of eukaryotic chloroplast react with the antibodies. With one exception, in all cases the molecular mass of the cross-reacting polypeptide falls in the range of 51-56 kDa. Only in Halobacterium halobium, bands at 66 and 68 kDa have been detected. In order to identify the cross-reacting polypeptides, the purified F1-ATPases of E. coli, chloroplasts and beef heart mitochondria have been tested.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure and function of the ATPase-ATP synthase complex of mitochondria as compared to chloroplasts and bacteria

An overview of the structure and function of the mitochondrial ATPase-ATP synthase complex is presented. Attempts are made to identify the analogies and differences between mitochondrial, chloroplastic and bacterial complexes. The relatively more precise information available on the structure of the E. coli enzyme is used to try and understand the apparently more complex structure of the mitochondrial enzyme. Recent ideas on the mechanism of ATP hydrolysis and ATP synthesis will be summarized.

Cross-linking of bovine mitochondrial H+-ATPase by copper--o-phenanthroline. Interaction of the oligomycin-sensitivity-conferring protein with a 24-kDa protein

The nearest neighbor relationships between the Fo subunits of bovine mitochondrial H+-ATPase were studied by using copper-o-phenanthroline, an SH-oxidizing cross-linking reagent. The cross-linked samples of purified H+-ATPase, F1-ATPase or Fo were analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) and the disulfide cross-linked polypeptides were identified by enzyme-linked immunosorbent assay and immunoblot transfer using subunit specific antisera. SDS-PAGE of H+-ATPase showed several cross-links, although none involved subunits of Fo sector linked to those of F1. Both H+-ATPase and Fo showed formation of a 45-kDa product. Upon reduction, the 45-kDa component gave rise to a 21-kDa band, identified as oligomycin-sensitivity-conferring protein (OSCP), and a 24-kDa band. These two proteins thus appear to be near neighbors with their cysteine residues in close proximity with each other. Under the conditions of cross-linking, there was a concentration-dependent decrease in the Pi-ATP exchange activity of the intact H+-ATPase as well as of H+-ATPase reconstituted with copper-o-phenanthroline-treated Fo and untreated F1. The site of inhibition appeared to residue in the Fo sector. Loss of Pi-ATP exchange occurred at the same time as formation of the 45-kDa product. Our present data showing copper-o-phenanthroline-induced interactions of the 24-kDa protein with the OSCP and simultaneous inactivation of Pi-ATP exchange activity of the complex strengthen earlier suggestions [Hadikusumo, R.G., Hertzog, P.J. & Marzuki, S. (1984) Biochim. Biophys. Acta 765,258-267] that the 24-kDa protein may be a bona fide subunit of Fo.

The stokes radius of the CHAPS-solubilized benzodiazepine receptor complex

The Stokes radii and the apparent molecular weights of the CHAPS or Triton X-100 solubilized benzodiazepine receptors are calculated by gel exclusion chromatography. The results suggest that the molecular receptor complex solubilized by CHAPS is much larger than the complex solubilized by Triton X-100.

Subcellular localization and further characterization of a new elastase inhibitor from pneumococci

Streptococcus pneumoniae contains an inhibitor of human neutrophil elastase. The agent does not inhibit other proteases, including neutrophil cathepsin G and pancreatic elastase. It is active in the presence of insoluble elastin as well as synthetic elastase substrates. The inhibitor is present in the pneumococcal cell membrane. [125I]elastase binding studies and inhibition experiments with intact bacterial autoplasts suggest that this agent has its elastase-binding site(s) exposed on the outside of the bacterial cell membrane. Native and randomized membrane vesicles also show equal inhibitory activity. Active inhibitor can be solubilized from pneumococcal membranes by treatment with a dipolar ionic detergent and can then be reconstituted, in active form, within artificial liposomes. Complex formation between the neutrophil elastase inhibitor and neutrophil elastase may involve noncovalent associations. Although elastase containing a covalently bound substrate analog no longer binds the pneumococcal inhibitor, the present study shows that complex formation is nevertheless independent of neutrophil elastase catalytic activity. Specific inhibitor activity and inhibitor release during bile salt-stimulated autolysis are greater in a nonnecrotizing pneumococcal strain (type I) than they are in a necrotizing strain (type III) or in Klebsiella pneumoniae. These results may help explain the frequent resolution of some pneumococcal pneumonias, despite the presence in the early pneumonic exudate of many neutrophils containing an elastolytic protease capable of injuring lung connective tissue.

Properties of brain dolichol kinase activity solubilized with a zwitterionic detergent

Dolichol kinase activity is effectively solubilized by extracting calf brain microsomes with 2% 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS), a zwitterionic detergent. The solubilized kinase catalyzes the enzymatic phosphorylation of dolichols with either CTP or dCTP serving as phosphoryl donor in the presence of Ca2+. Similar Km values were calculated for CTP (7.7 microM) and dCTP (9.1 microM). Dolichol phosphorylation was inhibited by CDP and dCDP, but not CMP, ADP, GDP, or UDP. A kinetic analysis of the inhibitory effect of CDP revealed a pattern characteristic of competitive inhibition. Dolichol kinase activity was markedly stimulated by the addition of R-dolichol (C95) or S-dolichol(C95). The apparent Km value for R-dolichol(C95) and S-dolichol(C95) was 9 microM, but the Vmax for the phosphorylation reaction was 40% higher with S-dolichol(C95). Incubation of the CHAPS extract with [gamma-32P]CTP and exogenous undecaprenol(C55) resulted in the enzymatic synthesis of a radiolabeled product that was mild acid-labile and chromatographically identical to undecaprenyl monophosphate. An enzymatic comparison with a variety of polyprenol substrates indicates that the solubilized kinase prefers long-chain (C90-95) polyprenols with saturated alpha-isoprene units. The effect of exogenous phosphoglycerides on the kinase activity in the dialyzed CHAPS extracts has also been evaluated. These studies describe the properties and polyprenol specificity of stable, solubilized preparations of dolichol kinase that should be useful for further purification of the enzyme.

Proton ATPase of rat liver mitochondria: a rapid procedure for purification of a stable, reconstitutively active F1 preparation using a modified chloroform method

A method is described for the purification of rat liver F1-ATPase by a modification of the chloroform extraction procedure originally described by Beechey et al. (Biochem. J. (1975) 148, 533). Purified liver membrane vesicles are extracted with chloroform in the presence of ATP and EDTA. The procedure yields pure F1 in only 2-3 h without the necessity of ion-exchange chromatography. The enzyme exhibits the alpha, beta, gamma, delta, and epsilon bands characteristic of F1-ATPase. It has a high ATPase specific activity, and is reconstitutively active, catalyzing high rates of ATP synthesis. Significantly, it can be readily crystallized. If desired, the enzyme can be passed over a gel filtration column to place it in a stabilizing phosphate-EDTA buffer, lyophilized and stored indefinitely at -20 degrees C.