Peptide analogs of the beef heart mitochondrial F1-ATPase inhibitor protein

Differential Expression ESTs Associated with Fluorosis in Rats Liver

The fluoride has volcanic activity and abundantly exists in environment combining with other elements as fluoride compounds. Recent researches indicated that the molecular mechanisms of intracellular fluoride toxicity were very complex. However, the molecular mechanisms underlying the effects on gene expression of chronic fluoride-induced damage is unknown, especially the detailed regulatory process of mitochondria. In the present study, we screened the differential expression ESTs associated with fluorosis by DDRT-PCR in rat liver. We gained 8 genes, 3 new ESTs, and 1 unknown function sequence and firstly demonstrated that microsomal glutathione S-transferase 1 (MGST1), ATP synthase H⁺ transporting mitochondrial F₀ complex subunit C1, selenoprotein S, mitochondrial IF1 protein, and mitochondrial succinyl-CoA synthetase alpha subunit were participated in mitochondria metabolism, functional and structural damage process caused by chronic fluorosis. This information will be very helpful for understanding the molecular mechanisms of fluorosis.

How the N-terminal extremity of Saccharomyces cerevisiae IF1 interacts with ATP synthase: a kinetic approach

The N-terminal part of the inhibitory peptide IF1 interacts with the central γ subunit of mitochondrial isolated extrinsic part of ATP synthase in the inhibited complex (J.R. Gledhill, M.G. Montgomery, G.W. Leslie, J.E. Walker, 2007). To explore its role in the different steps of IF1 binding, kinetics of inhibition of the isolated and membrane-bound enzymes were investigated using Saccharomyces cerevisiae IF1 derivatives modified in N-terminal extremity. First, we studied peptides truncated in Nter up to the amino acid immediately preceding Phe17, a well-conserved residue thought to play a key role. These deletions did not affect or even improve the access of IF1 to its target. They decreased the stability of the inhibited complex but much less than previously proposed. We also mutated IF1-Phe17 and found this amino acid not mandatory for the inhibitory effect. The most striking finding came from experiments in which PsaE, a 8 kDa globular-like protein, was attached in Nter of IF1. Unexpectedly, such a modification did not appreciably affect the rate of IF1 binding. Taken together, these data show that IF1-Nter plays no role in the recognition step but contributes to stabilize the inhibited complex. Moreover, the data obtained using chimeric PsaE-IF1 suggest that before binding IF1 presents to the enzyme with its middle part facing a catalytic interface and its Nter extremity folded in the opposite direction.

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.

Cross-linking of the endogenous inhibitor protein (IF1) with rotor (gamma, epsilon) and stator (alpha) subunits of the mitochondrial ATP synthase

The location of the endogenous inhibitor protein (IF1) in the rotor/stator architecture of the bovine mitochondrial ATP synthase was studied by reversible cross-linking with dithiobis(succinimidylpropionate) in soluble F1I and intact F1F0I complexes of submitochondrial particles. Reducing two-dimensional electrophoresis, Western blotting, and fluorescent cysteine labeling showed formation of alpha-IF1, IF1-IF1, gamma-IF1, and epsilon-IF1 cross-linkages in soluble F1I and in native F1F0I complexes. Cross-linking blocked the release of IF1 from its inhibitory site and therefore the activation of F1I and F1F0I complexes in a dithiothreitol-sensitive process. These results show that the endogenous IF1 is at a distance < or = 12 angstroms to gamma and epsilon subunits of the central rotor of the native mitochondrial ATP synthase. This finding strongly suggests that, without excluding the classical assumption that IF1 inhibits conformational changes of the catalytic beta subunits, the inhibitory mechanism of IF1 may involve the interference with rotation of the central stalk.

Fluorescence resonance energy transfer between coumarin-derived mitochondrial F(1)-ATPase gamma subunit and pyrenylmaleimide-labelled fragments of IF(1) and c subunit

We introduced a reporting group into a critical position of the mitochondrial F(1)-ATPase in order to gain structural information about enzyme-ligand complexes. Incubation of 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM) with bovine heart mitochondrial F(1)-ATPase pretreated with 1 nM sodium arsenite modified the only cysteine residue in the gamma subunit (gamma-Cys(78)), resulting in an enzyme-CPM fluorescent complex (CPM-F(1)) with an ATPase activity similar to that of the native enzyme. Transferred fluorescence of F(1)-bound CPM occurred when different peptide fragments of naturally binding polypeptides carrying a pyrenylmaleimide (PM) moiety were bound to the enzyme. Fluorescence resonance energy transfer (RET) from PM bound to cysteine residues associated with Glu(40), Lys(47) and Lys(58) of fragments of the inhibitor protein (IF(1)) with CPM-F(1) occurred with an efficiency of approx. 20, 21 and 3% respectively. The distance at which the efficiency of energy transfer was 50%, R(0), for the CPM and PM donor/acceptor pair was 4.1 nm, indicating that the three IF(1) fragments must be within 6.7 nm of gamma-Cys(78). RET from the PM-bound hydrophilic fragment of c subunit (residues 37-42) of the F(1)F(0)-ATPase complex and CPM-bound gamma-Cys(78) occurred with an efficiency of approx. 30%, indicating a distance of 4.7 nm between the two fluorophores. Based on previous observations and on the present RET measurements, the hydrophilic loop of c subunit was located at the base of the F(1) foot, and the N-terminal region of IF(1) was located on the surface of F(1) in the lower part of the alpha(3)beta(3) hexamer ring.

The structure of bovine IF(1), the regulatory subunit of mitochondrial F-ATPase

In mitochondria, the hydrolytic activity of ATP synthase is regulated by an inhibitor protein, IF(1). Its binding to ATP synthase depends on pH, and below neutrality, IF(1) is dimeric and forms a stable complex with the enzyme. At higher pH values, IF(1) forms tetramers and is inactive. In the 2.2 A structure of the bovine IF(1) described here, the four monomers in the asymmetric unit are arranged as a dimer of dimers. Monomers form dimers via an antiparallel alpha-helical coiled coil in the C-terminal region. Dimers are associated into oligomers and form long fibres in the crystal lattice, via coiled-coil interactions in the N-terminal and inhibitory regions (residues 14-47). Therefore, tetramer formation masks the inhibitory region, preventing IF(1) binding to ATP synthase.

Functional domains of the ATPase inhibitor protein from bovine heart mitochondria

A study is presented of the activity and temperature dependence of the ATPase inhibitor protein (IF(1)) from bovine heart mitochondria and of synthetic partial IF(1) peptides. The results show that the IF(1)-(42-58) peptide is the most potent inhibitory domain of IF(1).

The structural and functional connection between the catalytic and proton translocating sectors of the mitochondrial F1F0-ATP synthase

The structural and functional connection between the peripheral catalytic F1 sector and the proton-translocating membrane sector F0 of the mitochondrial ATP synthase is reviewed. The observations examined show that the N-terminus of subunit gamma, the carboxy-terminal and central region of F0I-PVP(b), OSCP, and part of subunit d constitute a continuous structure, the lateral stalk, which connects the peripheries of F1 to F0 and surrounds the central element of the stalk, constituted by subunits gamma and delta. The ATPase inhibitor protein (IF1) binds at one side of the F1F0 connection. The carboxy-terminal segment of IF1 apparently binds to OSCP. The 42L-58K segment of IF1, which is per se the most active domain of the protein, binds at the surface of one of the three alpha/beta pairs of F1, thus preventing the cyclic interconversion of the catalytic sites required for ATP hydrolysis.

The IF(1) inhibitor protein of the mitochondrial F(1)F(0)-ATPase

Recent studies on the IF(1) inhibitor protein of the mitochondrial F(1)F(0)-ATPase from molecular biochemistry to possible pathophysiological roles are reviewed. The apparent mechanism of IF(1) inhibition of F(1)F(0)-ATPase activity and the biophysical conditions that influence IF(1) activity are summarized. The amino acid sequences of human, bovine, rat and murine IF(1) are compared and domains and residues implicated in IF(1) function examined. Defining the minimal inhibitory sequence of IF(1) and the role of conserved histidines and conformational changes using peptides or recombinant IF(1) is reviewed. Luft's disease, a mitochondrial myopathy where IF(1) is absent, is described with respect to IF(1) relevance to mitochondrial bioenergetics and clinical observations. The possible pathophysiological role of IF(1) in conserving ATP under conditions where cells experience oxygen deprivation (tumor growth, myocardial ischemia) is evaluated. Finally, studies attempting to correlate IF(1) activity to ATP conservation in myocardial ischemic preconditioning are compared.

Functional regions of the H(+)-ATPase inhibitory protein from ox heart mitochondria

Derivatives of the inhibitor protein (IF1) of the mitochondrial H(+)-ATP synthase, bearing deletions at the N- or C-terminal ends, were tested for their abilities (a) to bind to the synthase, (b) to inhibit its ATPase activity and (c) to respond to energisation of the mitochondrial membrane. Deletion of nine residues from its N-terminus, or ten from its C-terminus had little effect on any of these three properties of IF1. Further deletions from the N-terminus (up to residue 17) led to an increase in binding affinity but a reduced ability to inhibit ATPase activity and to form a stable ATPase-IF1 complex. Removal of five more residues from the N-terminus (up to residue 22) reduced these abilities further, but also decreased binding affinity by an order of magnitude. It was concluded that residues 10-17 of IF1 interact with F1 in a way which modulates the stability and function of the interaction between F1 and IF1.

The energy transmission in ATP synthase: from the gamma-c rotor to the alpha 3 beta 3 oligomer fixed by OSCP-b stator via the beta DELSEED sequence

ATP synthase (F0F1) is driven by an electrochemical potential of H+ (delta microH+). F0F1 is composed of an ion-conducting portion (F0) and a catalytic portion (F1). The subunit composition of F1 is a alpha 3 beta 3 gamma delta epsilon. The active alpha 3 beta 3 oligomer, characterized by X-ray crystallography, has been obtained only from thermophilic F1 (TF1). We proposed in 1984 that ATP is released from the catalytic site (C site) by a conformational change induced by the beta DELSEED sequence via gamma delta epsilon-F0. In fact, cross-linking of beta DELSEED to gamma stopped the ATP-driven rotation of gamma in the center of alpha 3 beta 3. The torque of the rotation is estimated to be 420 pN x A from the delta microH+ and H(+)-current through F0F1. The angular velocity (omega) of gamma is the rate-limiting step, because delta microH+ increased the Vmax of H+ current through F0, but not the Km(ATP). The rotational unit of F0 (= ab2c10) is pi/5, while that in alpha 3 beta 3 is 2 pi/3. This difference is overcome by an analog-digital conversion via elasticity around beta DELSEED with a threshold to release ATP. The alpha beta distance at the C site is about 9.6 A (2,8-diN3-ATP), and tight Mg-ATP binding in alpha 3 beta 3 gamma was shown by ESR. The rotational relaxation of TF1 is too rapid (phi = 100 nsec), but the rate of AT(D)P-induced conformational change of alpha 3 beta 3 measured with a synchrotron is close to omega. The ATP bound between the P-loop and beta E188 is released by the shift of beta DELSEED from gamma RGL. Considering the viscosity resistance and inertia of the free rotor (gamma-c), there may be a stator containing OSCP (= delta of TF1) and F0-d to hold free rotation of alpha 3 beta 3.

Identification of functional domains and critical residues in the adenosinetriphosphatase inhibitor protein of mitochondrial F0F1 ATP synthase

Peptide segments of the inhibitor protein (IF1) of the F0F1 ATP synthase complex from bovine-heart mitochondria have been constructed by chemical synthesis. The IF1-(42-58)-peptide was equally effective as IF1 in inhibiting the ATPase activity of both the F0F1 complex in the mitochondrial membrane deprived of IF1 (SMP) and soluble F1. The IF1-(22-46)-peptide inhibited the ATPase activity in the soluble F1 but had no effect on either the ATPase activity or H+ conduction in SMP. Substitution of the His or Lys residues with Ala in the IF1-(42-58)-peptide decreased the inhibition of ATP hydrolysis. The inhibition exerted by the IF1-(42-58)-peptide on ATP hydrolysis in SMP exhibited a pH dependence, similar to that observed with IF1, which was lost upon replacement of His or Lys with Ala. In soluble F1, inhibition of ATP hydrolysis by IF1, the IF1-(42-58)-peptide and the IF1-(22-46)-peptide was pH dependent when F1 was first incubated with ATP. The IF1-(42-58)-peptide also caused inhibition of passive H+ conduction in SMP. This activity of the synthetic peptide was weaker, as compared to that of IF1, and practically unaffected by substitution of His or Lys with Ala. An antibody against the IF1-(42-58)-synthetic peptide stimulated ATP hydrolysis in the membrane-bound F0F1 complex with associated IF1 but was without effect on H+ conduction. An antibody against IF1 stimulated both processes.

Histidine-49 is necessary for the pH-dependent transition between active and inactive states of the bovine F1-ATPase inhibitor protein

The role of the histidyl residue at position 49 (H49) of the bovine mitochondrial F1-ATPase inhibitor protein (F1I) was examined by site-directed mutagenesis. Six amino acids (Q, E, K, V, L, and I) were substituted for H49 and the activities of the resulting inhibitor proteins were characterized with respect to pH. Each of the six mutations abolished the pH sensitivity which is characteristic of wild-type F1I. At pH 8.0 each of the mutations caused an increase in apparent maximum inhibition and a decrease in apparent Ki relative to wild type. At pH 6.7 the hydrophilic substitutions had little effect on apparent Ki, while the hydrophobic substitutions caused increases of 3.5- to 8.5-fold relative to wild type. The ratios of apparent Ki at pH 8.0 to apparent Ki at pH 6.7 were in the range of 0.5 to 1.6 for the mutants, whereas the wild-type value is 15.0. The mutations appear to shift the equilibrium between active and inactive conformations of F1I toward the active state. We find that H49 is required by F1I for sensitivity to pH and that it may facilitate the transition between active and inactive states of F1I. A possible role for H49 in the stabilization of the inactive state through participation in a multivalent complex with Zn2+ is also discussed.

The regulation of catalysis in ATP synthase

ATP synthase is regulated so as to prevent futile hydrolysis of ATP when the transmembrane proton electrochemical gradient, delta mu H+, falls. Mitochondria and chloroplasts have different mechanisms for inhibition of ATP synthase: by binding an inhibitor protein, and by stabilization of the ADP-inhibited state by making an intramolecular disulphide bond, respectively. The recently determined structure of bovine F1-ATPase is locked in a conformation that probably represents the ADP-inhibited state of the enzyme.