Labeling of individual amino acid residues in the membrane-embedded F0 part of the F1 F0 ATP synthase from Neurospora crassa. Influence of oligomycin and dicyclohexylcarbodiimide

Reduction of all-trans retinal to all-trans retinol in the outer segments of frog and mouse rod photoreceptors

The first step in the Visual Cycle, the series of reactions that regenerate the vertebrate visual pigment rhodopsin, is the reduction of all-trans retinal to all-trans retinol, a reaction that requires NADPH. We have used the fluorescence of all-trans retinol to study this reduction in living rod photoreceptors. After the bleaching of rhodopsin, fluorescence (excitation, 360 nm; emission, 457 or 540 nm) appears in frog and wild-type mouse rod outer segments reaching a maximum in 30-60 min at room temperature. With this excitation and emission, the mitochondrial-rich ellipsoid region of the cells shows strong fluorescence as well. Fluorescence measurements at different emission wavelengths establish that the outer segment and ellipsoid signals originate from all-trans retinol and reduced pyridine nucleotides, respectively. Using outer segment fluorescence as a measure of all-trans retinol formation, we find that in frog rod photoreceptors the NADPH necessary for the reduction of all-trans retinal can be supplied by both cytoplasmic and mitochondrial metabolic pathways. Inhibition of the reduction reaction, either by retinoic acid or through suppression of metabolic activity, reduced the formation of retinol. Finally, there are no significant fluorescence changes after bleaching in the rod outer segments of Rpe65(-/-) mice, which lack 11-cis retinal.

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.

F1 and F0 connections in the bovine mitochondrial ATP synthase: the role of the of alpha subunit N-terminus, oligomycin-sensitivity conferring protein (OCSP) and subunit d

We have studied the functional effect of limited proteolysis by trypsin of the constituent subunits in the native and reconstituted F1F0 complex and isolated F1 of the bovine heart mitochondrial ATP synthase (EC 3.6.1.34). Chemical cross-linking of oligomycin-sensitivity conferring protein (OSCP) with other subunits of the ATP synthase and the consequent functional effects were also investigated. The results obtained show that the alpha subunit N-terminus is essential for the correct, functional connection of F1 to F0. The alpha-subunit N-terminus contacts OSCP which, in turn, contacts the F0I-PVP(b) and the F0-d subunits. The N-terminus of subunit alpha, OSCP, a segment of subunit d and the C-terminal and central region of F0I-PVP(b) subunits are peripherally located with respect to subunits gamma and delta which are completely shielded in the F1F0 complex against trypsin digestion. This qualifies the N-terminus of subunit alpha, OSCP, subunit d and F0I-PVP(b) as components of the lateral element of the stalk. These subunits, rather than being confined at one side of the complex which would leave most of the central part of the gamma subunit uncovered, surround the gamma and the delta subunits located in the central stalk.

Structural interpretations of F(0) rotary function in the Escherichia coli F(1)F(0) ATP synthase

F(1)F(0) ATP synthases are known to synthesize ATP by rotary catalysis in the F(1) sector of the enzyme. Proton translocation through the F(0) membrane sector is now proposed to drive rotation of an oligomer of c subunits, which in turn drives rotation of subunit gamma in F(1). The primary emphasis of this review will be on recent work from our laboratory on the structural organization of F(0), which proves to be consistent with the concept of a c(12) oligomeric rotor. From the NMR structure of subunit c and cross-linking studies, we can now suggest a detailed model for the organization of the c(12) oligomer in F(0) and some of the transmembrane interactions with subunits a and b. The structural model indicates that the H(+)-carrying carboxyl of subunit c is located between subunits of the c(12) oligomer and that two c subunits pack in a front-to-back manner to form the proton (cation) binding site. The proton carrying Asp61 side chain is occluded between subunits and access to it, for protonation and deprotonation via alternate entrance and exit half-channels, requires a swiveled opening of the packed c subunits and stepwise association with different transmembrane helices of subunit a. We suggest how some of the structural information can be incorporated into models of rotary movement of the c(12) oligomer during coupled synthesis of ATP in the F(1) portion of the molecule.

Differential remodeling of the left and right heart after norepinephrine treatment in rats: studies on cytokines and collagen

Continuous intravenous infusion of norepinephrine norepinephrine (NE, 0.1 mg/kg/h) induced hypertrophy of the left ventricle (LV), but not of the right ventricle (RV) in rats, although RV systolic pressure (RVSP) was much more elevated than LVSP. After NE infusion, there was a time-dependent (20 min to 72 h) expression in the mRNA of interleukin (IL)-6 and IL-1 beta. The expression of IL-6 increased markedly and reached the maximum after 4 h with an 80-fold elevation. In the RV, the expression increased only 20-fold. The mRNA of IL-1 beta increased significantly after NE stimulation only in the LV and reached the maximum after 12 h with a 12-fold elevation. After 12 h of NE infusion, colligin mRNA was elevated for the first time with further progression until 72 h. The six-fold abundance of colligin mRNA seen after 72 h was significantly higher in the LV than in the RV. A similar increase was observed on the protein level (Western blotting). The expression of collagen I and III increased significantly after 24 h only in the LV. After 72 h, the mRNA expression of collagen I was increased 16-fold and that of collagen III 10-fold. This expression was significantly higher than that in the RV. Also the elevation in atrial natriuretic peptide (ANP) mRNA started earlier and was more pronounced in the LV than in the RV. The alpha- and beta-adrenergic receptor blocker carvedilol normalized all functional parameters after 6 h and 72 h and prevented the development of LV hypertrophy that occurred after 72 h. The NE-induced increased expression of the mRNAs studied was either prevented (IL-6, IL-1 beta ) or attenuated (colligin, collagen I and III, ANP) by combined alpha- and beta-receptor blockade. The elevation of afterload which was associated with the NE effect was normalized by the calcium-channel blocker nisoldipin, but NE-induced LV hypertrophy and the increase in ANP and collagen mRNA were not affected.

The F0F1-type ATP synthases of bacteria: structure and function of the F0 complex

Membrane-bound ATP synthases (F0F1-ATPases) of bacteria serve two important physiological functions. The enzyme catalyzes the synthesis of ATP from ADP and inorganic phosphate utilizing the energy of an electrochemical ion gradient. On the other hand, under conditions of low driving force, ATP synthases function as ATPases, thereby generating a transmembrane ion gradient at the expense of ATP hydrolysis. The enzyme complex consists of two structurally and functionally distinct parts: the membrane-integrated ion-translocating F0 complex and the peripheral F1 complex, which carries the catalytic sites for ATP synthesis and hydrolysis. The ATP synthase of Escherichia coli, which has been the most intensively studied one, is composed of eight different subunits, five of which belong to F1, subunits alpha, beta, gamma, delta, and epsilon (3:3:1:1:1), and three to F0, subunits a, b, and c (1:2:10 +/- 1). The similar overall structure and the high amino acid sequence homology indicate that the mechanism of ion translocation and catalysis and their mode of coupling is the same in all organisms.

Differential activation by platelet-derived growth factor-BB of mitogen activated protein kinases in starved or nonstarved AKR-2B fibroblasts

More than 90% of serum-deprived (starved) AKR-2B mouse fibroblasts are stimulated to divided by the addition of platelet-derived growth factor (PDGF)-BB. In density-arrested (nonstarved) cells, PDGF-BB affords protection from cell death without stimulation of cell division. In both cultivation conditions the cells express similar amounts of PDGF beta-receptors and the receptor kinase activity was identical as judged by its autophosphorylation capacity. Three signaling pathways were studied in detail: 1) Phospholipase C-gamma (PLC-gamma) and [Ca2+]i increase, 2) activation of the phosphatidylinositol-3 kinase (PI-3 kinase), and 3) activation of mitogen activated kinases I and II (MAP kinases I and II). There was no difference in starved or nonstarved cells regarding PLC-gamma activation, increase of [Ca2+]i, and stimulation of PI-3 kinase activity. But most remarkably the activation of MAP-I was largely suppressed in nonstarved cells. The implications of these signaling pathways in cell protection or cell division are discussed.

Platelet-derived growth factor isoforms prevent cell death during starvation of AKR-2B fibroblasts

Confluent AKR-2B fibroblasts rapidly desintegrate upon removal of serum until a final density of approximately 50% of the initial value was reached after 12 h. This density remained unchanged for at least 48 h. Platelet-derived growth factor (PDGF)-BB stimulated more than 95% of these cells to divide. PDGF-AB or -BB added immediately after serum removal caused complete survival of the cells, but did not stimulate cell division as demonstrated by two-dimensional DNA flow cytometry. PDGF-AA was less effective leading to approximately 75% of the initial cell density. This effect could be augmented by the addition of ocadaic acid, a potent phosphatase inhibitor, suggesting that protein phosphorylation plays a role in this process. By using tyrphostin AG807 it was demonstrated that the signaling mechanism for survival requires receptor tyrosine autophosphorylation.

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.

On the structure of platelet-derived growth factor AA: C-terminal processing, epitopes, and characterization of cysteine residues

The complete amino acid sequence analysis of the "short" form of rPDGF-AA expressed in baby hamster kidney cells revealed the absence of posttranslationally modified amino acid. Approximately 50% of the proteins were shortened by two to three amino acid residues at the C-terminus. Trypsin treatment of BHK rPDGF-AA lead to the identification of two internal epitopes that correspond to the two previously described domains in rPDGF-BB [Vogel, S., & Hoppe, J. (1989) Biochemistry 28, 2961-2966]. Cysteine residues at positions 37, 46, 47, and 93, respectively, were converted by site-directed mutagenesis into serine residues, and the monomeric proteins were prepared through expression in Escherichia coli. None of the mutant proteins was able to dimerize, but all of them exhibited to various extents a reversible conformational change which may reflect an intermediate prefolded monomer. An intramolecular disulfide bridge between Cys-10 and Cys-91/93 was identified in these monomers. From a mixture of the mutant proteins 37 and 46, an active dimer was reconstituted, suggesting an intermolecular cysteine bridge between these two residues.

Preparation of biologically active platelet-derived growth factor isoforms AA and AB. Preferential formation of AB heterodimers

We have expressed the mature platelet-derived growth factor (PDGF) A chain within a fusion protein of the cro repressor and beta-galactosidase in Escherichia coli. Monomeric PDGF-A was excised from this fusion protein by CNBr cleavage. After protection of thiols by S-sulfonation, this fragment was purified by gel permeation chromatography and reversed-phase high-performance liquid chromatography. The monomeric protein was dimerized in the presence of a mixture of reduced and oxidized glutathione to yield biologically active recombinant AA dimer (rPDGF-AA) with an overall yield of about 0.2 mg/l culture. When monomeric rPDGF-A and rPDGF-B were reacted at stoichiometric concentrations in the presence of glutathione, almost exclusively hetero-dimers of type AB were formed. Heterodimers AB stimulated [3H]thymidine incorporation into AKR-2B fibroblasts half-maximally at about 2 ng/ml. AA homodimers were fivefold less active. About 60,000 binding sites were found for rPDGF-AB, 30,000 for rPDGF-AA and 45,000 for rPDGF-BB on AKR-2B fibroblasts.

Large-scale preparation of recombinant platelet-derived growth factor AA secreted from recombinant baby hamster kidney cells

The short isoform of platelet-derived growth factor A (PDGF-A) was expressed in a mammalian host (BHK-21 cell). A cell line was obtained that secreted up to 0.3 micrograms/10(6) cells recombinant PDGF-A chain homodimer/day into the medium. For large-scale production of supernatant, cells were grown either in roller bottles or in 2.5-1 stirred tank fermenters. A simple two-step procedure was developed to purify recombinant PDGF-AA (rPDGF-AA). The first step was adsorption onto porous glass and the final step was reversed-phase high-performance liquid chromatography. The yield was 0.2 mg/l supernatant. A total amount of 20-30 mg pure rPDGF-AA may be obtained from a single fermenter run. Sequence analysis showed the correct amino terminus and no internal proteolytic cleavages. The specific activity was 5 ng/ml for mouse AKR-2B cells. [125I]rPDGF-AA had an affinity constant of approximately 0.5 nM to these cells and 25,000 binding sites were estimated/cell.

Role of the carboxyl-terminal region of the PVP protein (F0I subunit) in the H+ conduction of F0F1 H+-ATP synthase of bovine heart mitochondria

By means of protein sequencing, labelling with thiol reagents and reconstitution studies it is shown that the carboxyl-terminal region of the PVP protein (F0I subunit, nuclear-encoded protein of Mr 25,000) of mitochondrial F0 promotes transmembrane proton conduction by F0 and the sensitivity of this process to oligomycin.

Photolabeling of the phosphate binding site of mitochondrial F1-ATPase by [32P]azidonitrophenyl phosphate. Identification of the photolabeled amino acid residues

[32P]Azidonitrophenyl phosphate [( 32P]ANPP) is a photoactivatable analogue of Pi. It competes efficiently with Pi for binding to the F1 sector of beef heart mitochondrial ATPase and photolabels the Pi binding site located in the beta subunit of F1 [Lauquin, G. J. M., Pougeois, R., & Vignais, P. V. (1980) Biochemistry 19, 4620-4626]. By cleavage of the photolabeled beta subunit of F1 with cyanogen bromide, trypsin, and chymotrypsin, bound [32P]ANPP was localized in a fragment spanning Thr 299-Phe 326. By Edman degradation of the radiolabeled tryptic peptide spanning Ile 296-Arg 337, [32P]ANPP was found to be attached covalently by its photoreactive group to Ile 304, Gln 308, and Tyr 311. These results are discussed in terms of a model in which the phosphate group of [32P]ANPP interacts with a glycine-rich sequence of the beta subunit, spanning Gly 156-Lys 162, which is spatially close to the photolabeled Ile 304-Tyr 311 segment of the same subunit.

Mitochondrial sulfhydryl groups under oligomycin-inhibited, aging, and uncoupling conditions: beneficial influence of cardioprotective drugs

Uncoupling, oligomycin-inhibited, and aging/swelling conditions comprise three models for mitochondrial dysfunction. In these models, the effects of cardioprotective agents on rat heart mitochondrial membrane -SH reactivity have been studied. For -SH detection two different chromophores were used: dithionitrobenzoate (NbS2) and monobromobimane (MB). The objective of this study is to reveal the influence of three cardioprotective substances against the loss of membrane -SH reactivity: (i) The thiol reagent 2-mercaptopropionylglycine (MPG) prevents the decrease of thiols caused by carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP), aging, and oligomycin measured with MB and NbS2, and the diminution by oleate detected with MB. The small amount of MPG (6 nmol/mg protein), necessary for the protection, agrees with oligomycin sensitivity of the -SH groups concerned. (ii) The active metabolite of molsidomine, 3-morpholinosydnonimine (SIN-1), protects against the decrease of thiols by FCCP, oleate, and aging monitored with MB. In the case of oligomycin -SH groups accessible to NbS2 are protected. (iii) Another antianginal drug, isosorbidedinitrate (ISDN) does not protect membrane thiol groups. In contrast to SIN-1, ISDN probably requires enzymatic activation. It is suggested that MPG as well as SIN-1 may help to restitute the original -SH status of the mitochondrial membrane.

Reactivity of mitochondrial sulfhydryl groups toward dithionitrobenzoic acid and bromobimanes under oligomycin-inhibited and uncoupling conditions

Thiol reactivity was determined in rat heart mitochondria using chromophores of differing polarities: monobromobimane (MB), dithionitrobenzoate (NbS2), and bromobimane-q (MQ). The purpose of this study is to correlate reaction rates of protein thiols in the mitochondrial membrane with the oligomycin-inhibited and uncoupled states: In all cases investigated the reactivity of -SH groups toward MB decreases under the above conditions. In parallel with an increase of their uncoupling activities the uncouplers reduce the reaction rate of thiol groups toward NbS2 and, progressively, toward MQ, indicating differences in sensitivity of thiol groups to uncouplers depending on the polarity of the environment. The pattern of -SH reactivity under inhibition by oligomycin resembles that of carbonylcyanide-p-trifluoromethoxyphenylhydrazone. Functional changes of the mitochondrial membrane probably correlate with reactivity/polarity changes of membrane -SH groups. Masking of membrane thiol groups thus is not specific for uncouplers but is also observed under inhibition with oligomycin.

F0 part of the ATP synthase from Escherichia coli. Influence of subunits a, and b, on the structure of subunit c

Four different sets of proteoliposomes were prepared from F0, subunit c, a complex of subunits a and c (ac complex) and an ac complex supplemented with subunit b. Only liposomes containing intact F0 or all subunits of F0 were active in proton translocation and F1 binding [Schneider, E. and Altendorf, K. (1985) EMBO J. 4, 515-518]. The conformation of subunit c in the different preparations was analyzed by labelling the proteoliposomes with the hydrophobic photoactivatable reagent 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]TID). Subsequent isolation and Edman degradation of this polypeptide revealed distinct radioactive labelling patterns over the entire amino acid sequence. In the F0 complex and in the ac complex subunit c retains a labelling pattern which is related to that found in TID-labelled membrane vesicles of Escherichia coli [Hoppe et al. (1984) Biochemistry 23, 5610-5616]. In the absence of subunit a, considerably more and different amino acid residues of subunit c are modified. The labelling data are discussed in relation to structural aspects of F0 and functional properties of proteoliposomes reconstituted with F0 or individual subunits.

Complete amino-acid sequence of the natural ATPase inhibitor from the mitochondria of the yeast Candida utilis

The complete alignment of the 63 residues of the mitochondrial ATPase inhibitor from the yeast Candida utilis has been determined. The sequence study was carried out mainly by automatic (liquid and solid-phase) methods. Peptides were obtained by enzymatic digestion with clostripain and purified by reverse-phase high-performance liquid chromatography. The ATPase inhibitor contains three sets of repetitive sequences and eight clusters of charged residues, as also found in the inhibitor of Saccharomyces cerevisiae, with which it shares 58.7% homology of conserved residues. When the two yeast ATPase inhibitor sequences were compared to that of beef heart, 20 residues remained common to the three alignments, although the latter protein contained a long histidine-rich insertion, only found in this inhibitor. Most of the homologous residues were clustered near the center of the protein, which by partial proteolytic digestion of the beef heart ATPase inhibitor [Dianoux, A.C. et al. (1982) FEBS Lett. 140, 223-228] has already been shown to be involved in the biological function.