Resolution and reconstitution of complex V of the mitochondrial oxidative phosphorylation system: properties and composition of the membrane sector

Membrane topography and near-neighbor relationships of the mitochondrial ATP synthase subunits e, f, and g

The well characterized subunits of the bovine ATP synthase complex are the alpha, beta, gamma, delta, and epsilon subunits of the catalytic sector, F1; the ATPase inhibitor protein; and subunits a, b, c, and d, OSCP (oligomycin sensitivity-conferring protein), F6, and A6L, which are present in the membrane sector, F0, and the 45-A-long stalk that connects F1 to F0. It has been shown recently that bovine ATP synthase preparations also contain three small polypeptides, designated e, f, and g, with respective molecular masses of 8.2, 10. 2, and 11.3 kDa. To ascertain their involvement as bona fide subunits of the ATP synthase and to investigate their membrane topography and proximity to the above ATP synthase subunits, polyclonal antipeptide antibodies were raised in the rabbit to the COOH-terminal amino acid residues 57-70 of e, 75-86 of f, and 91-102 of g. It was shown that (i) e, f, and g could be immunoprecipitated with anti-OSCP IgG from a fraction of bovine submitochondrial particles enriched in oligomycin-sensitive ATPase; (ii) the NH2 termini of f and g are exposed on the matrix side of the mitochondrial inner membrane and can be curtailed by proteolysis; (iii) the COOH termini of all three polypeptides are exposed on the cytosolic side of the inner membrane; and (iv) f cross-links to A6L and to g, and e cross-links to g and appears to form an e-e dimer. Thus, the bovine ATP synthase complex appears to have 16 unlike subunits, twice as many as its counterpart in Escherichia coli.

ATP synthase complex. Proximities of subunits in bovine submitochondrial particles

The catalytic sector, F1, and the membrane sector, F0, of the mitochondrial ATP synthase complex are joined together by a 45-A-long stalk. Knowledge of the composition and structure of the stalk is crucial to investigating the mechanism of conformational energy transfer between F0 and F1. This paper reports on the near neighbor relationships of the stalk subunits with one another and with the subunits of F1 and F0, as revealed by cross-linking experiments. The preparations subjected to cross-linking were bovine heart submitochondrial particles (SMP) and F1-deficient SMP. The cross-linkers were three reagents of different chemical specificities and different lengths of cross-linking from zero to 10 A. Cross-linked products were identified after gel electrophoresis of the particles and immunoblotting with subunit-specific antibodies to the individual subunits alpha, beta, gamma, delta, OSCP, F6, A6L, a (subunit 6), b, c, and d. The results suggested that the two b subunits form the principal stem of the stalk to which OSCP, d, and F6 are bound independent of one another. Subunits b, OSCP, d, and F6 cross-linked to alpha and/or beta, but not to gamma or delta. The COOH-terminal half of A6L, which is extramembranous, cross-linked to d but not to any other stalk or F1 subunit. No cross-links of subunits a and c with any stalk or F1 subunits were detected. In F1-deficient SMP, cross-linked b+b and d+F6 dimers appeared, and the extent of cross-linking between b and OSCP diminished greatly. The addition of F1 to F1-deficient particles appeared to reverse these changes. Treatment of F1-deficient particles with trypsin rapidly hydrolyzed away OSCP and F6, fragmented b to membrane-bound 18-, 12-, and 8-9-kDa antigenic fragments, which cross-linked to d and/or with one another. Trypsin also removed the COOH-terminal part of A6L, but the remainder still cross-linked to subunit d. Models showing the near neighbor relationships of the stalk subunits with one another and with the alpha and beta subunits at a level near the proximal end (bottom) of F1 and at the membrane-matrix interface are presented.

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.

High-conductance pathways in mitochondrial membranes

The outer and inner membranes of mitochondria have recently been studied with the patch clamp technique. What has emerged is still an ill-defined picture for either membrane, primarily for the wide range of conductances found. Interestingly, however, a few conductances (in the range of 10-80 pS) seem to be ubiquitously distributed. Parallel studies in situ and in reconstituted systems have allowed the assignment to distinct membrane locations of some conductances, whose physiological role is, however, not yet elucidated.

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.

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.

Mechanism of local anesthetic effect. Involvement of F0 in the inhibition of mitochondrial ATP synthase by phenothiazines

The mechanism whereby tertiary amine local anesthetics affect the activity of membrane proteins was investigated by studying the interaction of phenothiazines with mitochondrial ATP synthase. These drugs caused inhibition of the activity of the membrane-bound enzyme at concentrations that do not perturb the phospholipid bilayer. The inhibitory effect appeared consequent to interaction with multiple sites located on both the F1 and the F0 components of the enzyme complex, since: (a) Dixon plots were parabolic; (b) the membrane-bound enzyme was more sensitive to the drug effect than the isolated F1 component; (c) conditions that decreased oligomycin sensitivity also decreased the sensitivity to phenothiazines; (d) irreversible binding of photochemically activated phenothiazines to the ATP synthase complex, followed by detachment of the F1 moiety and reconstitution with purified F1 resulted in an inhibited enzyme complex. These data are interpreted as indicating that tertiary amine local anesthetics affect the activity of membrane proteins by interacting with hydrophobic sites located on both their integral and peripheral domains.

Further investigation on the high-conductance ion channel of the inner membrane of mitochondria

By use of the patch-clamp technique, the inner membrane of mouse liver and heart mitochondria is shown to contain a highly conductive (around 100 pS in symmetrical 150 mM KCl) and voltage-dependent ion channel. This channel closely resembles that previously found in cuprizone-treated mouse liver inner mitochondrial membrane. The paper discusses the electrical properties of the channel and its possible physiological function. The reconstitution in giant liposomes of a partially purified ox heart inner membrane fraction containing the channel and the use of various inhibitors are also presented.

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.

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

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Proton translocation by the H+-ATPase of mitochondria. Effect of modification by monofunctional reagents of thiol residues in F0 polypeptides

A study is presented on the effect of chemical modification of thiol groups on proton conduction by the H+-ATPase complex in 'inside out' submitochondrial particles, before and after removal of the F1 moiety, and by F0 liposomes. The results obtained show that modification with monofunctional reagents [N-ethylmaleimide, 2,2'-dithiobispyridine, mersalyl and N-(7-dimethylamino-4-methyl-coumarinyl)-maleimide] of thiol residues in membrane integral proteins of F0 results in inhibition of proton conduction. Comparison of the inhibitory effects with the binding of [14C]N-ethylmaleimide to the various F0 polypeptides indicates that the inhibition of proton conduction by thiol reagents was correlated with modification of the 25-kDa, 11-kDa and 9-kDa (N,N'-dicyclohexylcarbodiimide-binding protein) proteins. Involvement of the last component is supported by the observation that modification by thiol reagents depressed the binding of N,N'-dicyclo[14C]hexylcarbodiimide to the 9-kDa protein.

Thiols in oxidative phosphorylation: thiols in the F0 of ATP synthase essential for ATPase activity

It was shown previously that the ATP synthase complex of bovine heart mitochondria contains an essential set of thiols or dithiols in its membrane sector (F0), whose modification by various reagents results in uncoupling [Yagi, T., and Hatefi, Y. (1984) Biochemistry 23, 2449-2455]. The sensitivity to modifiers was increased by membrane energization, and the uncoupling was reversed by membrane-permeable thiol compounds when modifiers other than alkylating agents were used to uncouple. The present paper demonstrates that there exists in the F0 of bovine ATP synthase another set of essential thiols, whose modification results in reversible inhibition of ATPase activity. These thiols are most susceptible to modification by mercurials (p-chloromercuribenzoate greater than p-chloromercuribenzene sulfonate) and do not appear to be modified by N-ethylmaleimide. The reversible modification of these thiols by mercurials protects the ATP synthase against irreversible inhibition in F0 by N,N-dicyclohexylcarbodiimide. The possible location of these two sets of thiols in the F0 of bovine ATP synthase is discussed.

Studies on polypeptide composition, hydrolytic activity and proton conduction of mitochondrial FoF1 H+ ATPase in regenerating rat liver

A study of the FoF1 ATPase complex of mitochondria isolated from regenerating rat liver following partial (70%) hepatectomy is presented. As we have previously reported, ATPase activity in submitochondrial particles prepared from regenerating rat liver 24 h following partial hepatectomy was depressed by 75% with respect to controls (submitochondrial particles from sham-operated animals). Polyacrylamide gel electrophoresis and immunodecoration using an antibody raised against isolated bovine heart F1 sector of the FoF1 ATPase indicated a substantial decrease in F1 content in the mitochondrial membrane from regenerating rat liver. Proton conduction by the FoF1 ATPase complex was studied by following the anaerobic relaxation of the transmembrane proton gradient (delta mu H+) generated by succinate-driven respiration. In control rat-liver submitochondrial particles containing the FoF1 moiety of the ATPase complex, anaerobic relaxation of delta mu H+ showed biphasic kinetics, whilst the same process in particles derived from regenerating rat liver exhibited monophasic kinetics and was significantly more rapid. Oligomycin and N,N-dicyclohexyl carbodiimide [(cHxN)2C] inhibited proton conductance by the F1-Fo ATPase complex in submitochondrial particles from both control and regenerating rat liver. Binding of [14C](cHxN)2C and immunodecoration using an antibody raised against bovine heart oligomycin-sensitivity-conferring protein (OSCP) indicated no difference in the content of either the (cHxN)2C binding protein or OSCP between control and regenerating rat-liver mitochondrial membranes. The results reported show that the structural and functional integrity of the Fo-F1 ATPase of rat liver is severely perturbed during regeneration.

Effect of diamide on proton translocation by the mitochondrial H+-ATPase

Treatment of sonic submitochondrial particles with the bifunctional thiol reagent, diamide, results in an enhancement of proton conductivity and ATPase activity, which is reversed by the reducing agent dithiothreitol, is suppressed by Fo inhibitors like oligomycin and is absent in particles that are deprived of peripheral Fo polypeptides. The effect of diamide is apparently due to oxidation of dithiols to disulfides in peripheral polypeptide(s) of Fo.

Resolution and reconstitution of H+ -ATPase complex from beef heart mitochondria

Mitochondrial H+ -ATPase complex, purified by the lysolecithin extraction procedure, has been resolved into a "membrane" (NaBr-F0) and a "soluble" fraction by treatment with 3.5 M sodium bromide. The NaBr-F0 fraction is completely devoid of beta, delta, and epsilon subunits of the F, ATPase and largely devoid of alpha and gamma subunits of F1, where F0 is used to denote the membrane fraction and F1, coupling factor 1. This is confirmed by complete loss of ATPase and Pi-ATP exchange activities. The addition of F1 (400 micrograms X mg-1 F0) results in complete restoration of oligomycin sensitivity without any reduction in the F1-ATPase activity. Presumably, this is due to release of ATPase inhibitor protein from the F1-F0 complex consequent to sodium bromide extraction. Restoration of Pi-ATP exchange and H+ -pumping activities require coupling factor B in addition to F1-ATPase. The oligomycin-sensitive ATPase and 32Pi-ATP exchange activities in reconstituted F1-F0 have the same sensitivity to uncouplers and energy transfer inhibitors as in starting submitochondrial particles from the heavy layer of mitochondria and F1-F0 complex. The data suggest that the altered properties of NaBr-F0 observed in other laboratories are probably inherent to their F1-F0 preparations rather than to sodium bromide treatment itself. The H+ -ATPase (F1-F0) complex of all known prokaryotic (3, 8, 9, 10, 21, 32, 34) and eukaryotic (11, 26, 30, 33, 35-37) phosphorylating membranes contain two functionally and structurally distinct entities. The hydrophilic component F1, composed of five unlike subunits, shows ATPase activity that is cold labile as well as uncoupler- and oligomycin-insensitive. The membrane-bound hydrophobic component F0, having no energy-linked catalytic activity of its own, is indirectly assayed by its ability to regain oligomycin sensitive ATPase and Pi-ATP exchange activities on binding to F1-ATPase (33). The purest preparations of bovine heart mitochondrial F0 show seven or eight major components in polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate or SDS-PAGE (1, 2, 12, 14), ranging from 6 to 54 ku in molecular weight (12). The precise structure and polypeptide composition of mitochondrial F0 is not known. The F0 preparations from bovine heart reported so far have been derived from H+ -ATPase preparations isolated in the presence of cholate and deoxycholate (11, 33, 36, 37).(ABSTRACT TRUNCATED AT 400 WORDS)

On the mechanism of H+ translocation by mitochondrial H+ -ATPase. Studies with chemical modifier of tyrosine residues

In this paper a detailed study of the effect of nitration of tyrosine residues by tetranitromethane on H+ conduction and other reactions catalyzed by the H+ -ATPase complex in phosphorylating submitochondrial particles, uncoupled particles, and the purified complex is presented. Tetranitromethane treatment of submitochondrial particles results in marked inhibition of ATP hydrolysis, ATP-33Pi exchange, and proton conduction by the H+ -ATPase complex. These effects are caused by nitration of tyrosine residues of H+ -ATPase complex as shown by the appearance of the absorption peak at 360 nm (specific for nitrotyrosine formation) and inhibition of ATP hydrolysis and ATP-33Pi exchange in the complex purified from tetranitromethane-treated particles. H+ conduction in phospholipid vesicles inlaid with F0 is also inhibited by tetranitromethane treatment. These observations indicate that tyrosine residue(s) of F0 are critically involved in energy-linked proton translocation in the ATP-ase complex.

Membrane topology of ATP synthase from bovine heart mitochondria and Escherichia coli

The polypeptides exposed to lipids in the membranous F0 sector of the mitochondrial and Escherichia coli ATP synthases were labelled with radioactive photoreactive lipids. Highly resolving gel electrophoretic conditions were used in order to separate all the eighteen components forming the bovine heart mitochondrial enzyme. The hydrophobic labelling was performed on fully active and inhibitor-sensitive ATP synthases. In the mitochondrial enzyme prepared according to Serrano et al. (1976) [J. Biol. Chem. 251, 2453-2461] seven polypeptides of Mr 30500; 11500; 10500; 10000; 9500; 8500 and 4500 were labelled. The major amount of radioactivity was associated with the 30500-Mr component, which is thought to be the adenine nucleotide carrier. In the preparation of Galante et al., (1979) which almost completely lacks this component [J. Biol. Chem. 254, 12372-12378] nine polypeptides of Mr 25000; 21000; 11500; 10500; 10000; 9500; 9200; 8500 and 4500 were labelled. In the ATPase synthase from E. coli the major amount of labelling was associated with subunit b and only a minor portion with subunit c.