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

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(+).

Activity and NMR structure of synthetic peptides of the bovine ATPase inhibitor protein, IF1

The protein IF(1) is a natural inhibitor of the mitochondrial F(o)F(1)-ATPase. Many investigators have been prompted to identify the shortest segment of IF(1), retaining its native activity, for use in biomedical applications. Here, the activity of the synthetic peptides IF(1)-(42-58) and IF(1)-(22-46) is correlated to their structure and conformational plasticity determined by CD and [1H]-NMR spectroscopy. Among all the IF(1) segments tested, IF(1)-(42-58) exerts the most potent, pH and temperature dependent activity on the F(o)F(1) complex. The results suggest that, due to its flexible structure, it can fold in helical and/or beta-spiral arrangements that favor the binding to the F(o)F(1) complex, where the native IF(1) binds. IF(1)-(22-46), instead, as it adopts a rigid alpha-helical conformation, it inhibits ATP hydrolysis only in the soluble F(1) moiety.

The role of the stalk in the coupling mechanism of F1F0-ATPases

The extrinsic and intrinsic membrane sectors of F1F0-ATPases are linked by a slender stalk 40-50 A in length. The stalk transmits the energy produced by oxidative or photosynthetic phosphorylation from the intrinsic sector, F0, to the catalytic sites in the extrinsic F1 sector. How this is achieved is unknown, but long-range conformational changes linked to transmembrane proton transport may be involved. In bacterial and chloroplast F1F0-ATPases, the stalk is probably a composite of subunits delta and epsilon, part of the gamma-subunit, and the extrinsic membrane domains of 2 subunits (identical or non-identical according to the species) that are bound to the membrane by their N-terminal regions. The stalk in the bovine mitochondrial enzyme appears to be more complex, and the gamma, delta, epsilon, OSCP, F6, b and d subunits all contribute to it. A bovine stalk complex has been assembled in vitro from bacterially expressed OSCP, F6, b and d, both in the presence and in the absence of F1-ATPase. One molecule of each of these subunits is present in the assembled complex, as there is also in each native F1F0-ATPase assembly. Providing that suitable crystals can be obtained, the stalk complex and the F1.stalk complex may permit the high resolution structure of bovine F1-ATPase to be extended into the stalk domain.

The F0 subunits of bovine mitochondrial ATP synthase complex: purification, antibody production, and interspecies cross-immunoreactivity

The known subunits of the membrane sector F0 of the bovine mitochondrial ATP synthase complex are subunits b, d, 6, F6, OSCP (oligomycin sensitivity-conferring protein), the DCCD (dicyclohexylcarbodiimide) binding proteolipid, and A6L. The first six subunits were purified from SMP or preparations of the ATP synthase complex, and monospecific antibodies were raised against each. The antisera were shown to be competent for immuno-blotting, and each antiserum recognized a single polypeptide of the expected Mr in preparations of the ATP synthase complex. Immunoblots utilizing antibodies to OSCP and subunits d and 6, which exhibit the same Mr on dodecyl sulfate-polyacrylamide gels, showed clearly that these polypeptides are immunologically distinct. Immunological cross-reactivity was demonstrated between bovine, human, rat, Saccharomyces cerevisiae, Paracoccus denitrificans, and Escherichia coli for subunit 6; between bovine, human, and rat for subunits b, d, OSCP, and F6; and between bovine and rat for the DCCD binding proteolipid. Anti-subunit 6 antiserum, before or after immunopurification against the ATP synthase complex, recognized a single polypeptide in the bovine ATP synthase complex and S. cerevisiae mitochondria, but two polypeptides of different Mr in bovine SMP, human, and rat mitochondria, and Paracoccus and E. coli membranes.

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

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

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.

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.

Evidence from immunological studies of structure-mechanism relationship of F1 and F1F0

Monoclonal and polyclonal antibodies directed against peptides of F1-ATPase of F1F0-ATPase synthase provide new and efficient tools to study structure-function relationships and mechanisms of such complex membrane enzymes. This review summarizes the main results obtained using this approach. Antibodies have permitted the determination of the nature of subunits involved in the complex, their stoichiometry, their organization, neighboring interactions, and vectorial distribution within or on either face of the membrane. Moreover, in a few cases, amino acid sequences exposed on a face of the membrane or buried inside the complex have been identified. Antibodies are very useful for detecting the role of each subunit, especially for those subunits which appear to have no direct involvement in the catalytic mechanism. Concerning the mechanisms, the availability of monoclonal antibodies which inhibit (or activate) ATP hydrolysis or ATP synthesis, which modify nucleotide binding or regulation of activities, which detect specific conformations, etc. brings many new ways of understanding the precise functions. The specific recognition by monoclonal antibodies on the beta subunit of epitopes in the proximity of, or in the catalytic site, gives information on this site. The use of anti-alpha monoclonal antibodies has shown asymmetry of alpha in the complex as already shown for beta. In addition, the involvement of alpha with respect to nucleotide site cooperativity has been detected. Finally, the formation of F1F0-antibody complexes of various masses, seems to exclude the functional rotation of F1 around F0 during catalysis.

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.

The definition of mitochondrial H+ ATPase assembly defects in mit- mutants of Saccharomyces cerevisiae with a monoclonal antibody to the enzyme complex as an assembly probe

mit- mutants with genetically defined mutations in the mitochondrial structural genes of the H+-ATPase membrane subunits 6, 8 and 9 were analysed to determine the H+-ATPase assembly defects that resulted as a consequence of the mutations. These include mutants which do not synthesize one of the membrane subunits and mutants which can synthesize these subunits, but in an altered form. Protein subunits which can still be assembled to the defective H+-ATPase in these mutants were determined by immunoprecipitation using a monoclonal antibody to the beta-subunit of the enzyme complex. The results suggest that the assembly pathway of the mitochondrially synthesized H+-ATPase subunits involves the sequential addition of subunits 9, 8 and 6 to a membrane-bound F1-sector. In addition to subunits of the F0- and F1-sectors, two other polypeptides (Mr = 18,000 and Mr = 25,000) are associated with the yeast H+-ATPase. These polypeptides were not observed in the immunoprecipitates obtained from mutants in which the F0-sector is not properly assembled.

ATP4, the structural gene for yeast F0F1 ATPase subunit 4

A plasmid containing the gene coding for the Saccharomyces cerevisiae F0F1 ATPase subunit 4 was isolated from a yeast genomic DNA library using the oligonucleotide probe procedure. The gene and the surrounding regions were cloned into M13 tg 130 and M13 tg 131 phage vectors. A 732-base-pair open reading frame encoding a 244-amino-acid polypeptide is described. The nucleotide sequence predicts that subunit 4 is probably derived from a precursor protein with a hydrophilic and basic 35-amino-acid leader sequence. Mature subunit 4 contains 209 amino acid residues and the predicted molecular mass is 23250 Da. This subunit presents amphiphilic behaviour with two distinct domains. A high alpha-helix content of 77% was predicted from the sequence. Subunit 4 shows homology with the b subunit of Escherichia coli ATP synthase.

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

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Subunit 4 of ATP synthase (F0F1) from yeast mitochondria. Purification, amino-acid composition and partial N-terminal sequence

One subunit of the membrane portion of yeast ATP synthase was purified. Structural data are reported. This subunit (subunit 4) is the fourth polypeptide of the complex when classifying subunits in order of decreasing molecular mass. Its apparent relative molecular mass is about 25,000. The polypeptide was extracted from the complex with a mixture of chloroform/methanol (1/1) and 0.5 M pyridinium acetate pH 6.0. Purification was performed with a combination of gel permeation chromatography on Sephadex G-75 and high-performance gel permeation chromatography with aqueous solvents containing 5% sodium dodecyl sulfate. The amino acid composition is reported here. The following sequence of the NH2-terminal ten residues was determined: Met-Ser-Ser-Thr-Pro-Glu-Lys-Gln-Thr-Asp.