Purification and Reconstitution of Ilyobacter tartaricus ATP Synthase

F-type adenosine triphosphate (ATP) synthase is a membrane-bound macromolecular complex, which is responsible for the synthesis of ATP, the universal energy source in living cells. This enzyme uses the proton- or sodium-motive force to power ATP synthesis by a unique rotary mechanism and can also operate in reverse, ATP hydrolysis, to generate ion gradients across membranes. The F₁F_o-ATP synthases from bacteria consist of eight different structural subunits, forming a complex of ∼550 kDa in size. In the bacterium Ilyobacter tartaricus the ATP synthase has the stoichiometry α₃β₃γδεab₂c₁₁. This chapter describes a wet-lab working protocol for the purification of several tens of milligrams of pure, heterologously (E. coli-)produced I. tartaricus Na⁺-driven F₁F_o-ATP synthase and its subsequent efficient reconstitution into proteoliposomes. The methods are useful for a broad range of subsequent biochemical and biotechnological applications.

Direct real-time detection of single proteins using silicon nanowire-based electrical circuits

We present an efficient strategy through surface functionalization to build a single silicon nanowire field-effect transistor-based biosensor that is capable of directly detecting protein adsorption/desorption at the single-event level. The step-wise signals in real-time detection of His-tag F₁-ATPases demonstrate a promising electrical biosensing approach with single-molecule sensitivity, thus opening up new opportunities for studying single-molecule biophysics in broad biological systems.

The affinity purification and characterization of ATP synthase complexes from mitochondria

The mitochondrial F₁-ATPase inhibitor protein, IF₁, inhibits the hydrolytic, but not the synthetic activity of the F-ATP synthase, and requires the hydrolysis of ATP to form the inhibited complex. In this complex, the α-helical inhibitory region of the bound IF₁ occupies a deep cleft in one of the three catalytic interfaces of the enzyme. Its N-terminal region penetrates into the central aqueous cavity of the enzyme and interacts with the γ-subunit in the enzyme's rotor. The intricacy of forming this complex and the binding mode of the inhibitor endow IF₁ with high specificity. This property has been exploited in the development of a highly selective affinity procedure for purifying the intact F-ATP synthase complex from mitochondria in a single chromatographic step by using inhibitor proteins with a C-terminal affinity tag. The inhibited complex was recovered with residues 1-60 of bovine IF₁ with a C-terminal green fluorescent protein followed by a His-tag, and the active enzyme with the same inhibitor with a C-terminal glutathione-S-transferase domain. The wide applicability of the procedure has been demonstrated by purifying the enzyme complex from bovine, ovine, porcine and yeast mitochondria. The subunit compositions of these complexes have been characterized. The catalytic properties of the bovine enzyme have been studied in detail. Its hydrolytic activity is sensitive to inhibition by oligomycin, and the enzyme is capable of synthesizing ATP in vesicles in which the proton-motive force is generated from light by bacteriorhodopsin. The coupled enzyme has been compared by limited trypsinolysis with uncoupled enzyme prepared by affinity chromatography. In the uncoupled enzyme, subunits of the enzyme's stator are degraded more rapidly than in the coupled enzyme, indicating that uncoupling involves significant structural changes in the stator region.

Crystallization and preliminary X-ray analysis of the FliH-FliI complex responsible for bacterial flagellar type III protein export

The bacterial flagellar proteins are translocated into the central channel of the flagellum by a specific protein-export apparatus for self-assembly at the distal growing end. FliH and FliI are soluble components of the export apparatus and form an FliH2-FliI heterotrimer in the cytoplasm. FliI is an ATPase and the FliH2-FliI complex delivers export substrates from the cytoplasm to an export gate made up of six integral membrane proteins of the export apparatus. In this study, an FliHC fragment consisting of residues 99-235 was co-purified with FliI and the FliHC2-FliI complex was crystallized. Crystals were obtained using the hanging-drop vapour-diffusion technique with PEG 400 as a precipitant. The crystals belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a=133.7, b=147.3, c=164.2 Å, and diffracted to 3.0 Å resolution.

The ectopic F(O)F(1) ATP synthase of rat liver is modulated in acute cholestasis by the inhibitor protein IF1

Rat liver plasma membranes contain F(O)F(1) complexes (ecto-F(O)F(1)) displaying a similar molecular weight to the mitochondrial F(O)F(1) ATP synthase, as evidenced by Blue Native PAGE. Their ATPase activity was stably reduced in short-term extra-hepatic cholestasis. Immunoblotting and immunoprecipitation analyses demonstrated that the reduction in activity was not due to a decreased expression of ecto-F(O)F(1) complexes, but to an increased level of an inhibitory protein, ecto-IF(1), bound to ecto-F(O)F(1). Since cholestasis down regulates the hepatic uptake of HDL-cholesterol, and ecto-F(O)F(1) has been shown to mediate SR-BI-independent hepatic uptake of HDL-cholesterol, these findings provide support to the hypothesis that ecto-F(O)F(1) contributes to the fine control of reverse cholesterol transport, in parallel with SR-BI. No activity change of the mitochondrial F(O)F(1) ATP synthase (m-F(O)F(1)), or any variation of its association with m-IF(1) was observed in cholestasis, indicating that ecto-IF(1) expression level is modulated independently from that of ecto-F(O)F(1), m-IF(1) and m-F(O)F(1).

Structure of the c14 rotor ring of the proton translocating chloroplast ATP synthase

The structure of the membrane integral rotor ring of the proton translocating F(1)F(0) ATP synthase from spinach chloroplasts was determined to 3.8 A resolution by x-ray crystallography. The rotor ring consists of 14 identical protomers that are symmetrically arranged around a central pore. Comparisons with the c(11) rotor ring of the sodium translocating ATPase from Ilyobacter tartaricus show that the conserved carboxylates involved in proton or sodium transport, respectively, are 10.6-10.8 A apart in both c ring rotors. This finding suggests that both ATPases have the same gear distance despite their different stoichiometries. The putative proton-binding site at the conserved carboxylate Glu(61) in the chloroplast ATP synthase differs from the sodium-binding site in Ilyobacter. Residues adjacent to the conserved carboxylate show increased hydrophobicity and reduced hydrogen bonding. The crystal structure reflects the protonated form of the chloroplast c ring rotor. We propose that upon deprotonation, the conformation of Glu(61) is changed to another rotamer and becomes fully exposed to the periphery of the ring. Reprotonation of Glu(61) by a conserved arginine in the adjacent a subunit returns the carboxylate to its initial conformation.

Characterization of oligomeric forms from mammalian F0F1ATP synthase by BN-PAGE: the role of detergents

It is now widely accepted that F0F1ATPsynthase is present in membrane, beside as monomers, in homo-dimeric and higher homo-oligomeric forms, which probably play critical roles in determining mitochondrial morphology. One-step mild detergent extraction followed by blue native electrophoresis (BN-PAGE) is a very interesting tool for studying the native membrane protein assemblies which can be associated with second/third-dimensional SDS-PAGE, immunoblotting, in-gel enzyme activity staining and mass spectrometry analyses. By combining these techniques, we resolved monomers and higher oligomeric forms of ATPsynthase from bovine heart mitochondria. However, a critical point is the choice of the detergents, which strongly influence the protein pattern of BN-PAGE. By using Triton X-100 we obtained that, in spite of the same subunit composition, monomers have a much lower specific activity than dimers and the two forms have a different pattern of tyrosine phosphorylation, suggesting that monomers and dimers are functionally distinct in membrane. In addition, enzyme self-association appeared to occur independently from the binding to ATPsynthase of the inhibitor protein IF1. Dodecylmaltoside was optimal to extract the enzyme from single biopsy samples, allowing us to demonstrate that IF1 plays a central role in regulating the enzyme activity in heart in vivo. Only low concentration of digitonin maintained significant amounts of ATPsynthase oligomers, which seemed to retain intact their native catalytic properties.

Structural properties of the proton translocating complex of the clathrin-coated vesicle

The clathrin-coated vesicle proton pump is a representative member of the new class of endomembrane proton ATPases that share an inhibitor profile which distinguishes them from classic F1F0 and E1E2-type proton pumps. The coated vesicle proton pump is a large (530 kDa) heteroligomer composed of eight polypeptides with molecular masses of 116, 70, 58, 40, 38, 34, 33 and 17 kDa. The 200-fold purified enzyme catalyses ATP-generated proton pumping when reconstituted in liposomes composed of pure lipids. Subunit function has been determined by partial reaction analysis of subunit and subcomplex activities. The isolated 17 kDa subunit, when co-reconstituted with bacteriorhodopsin, forms a dicyclohexylcarbodiimide-inhibitable proton channel. Selective removal of the 116 kDa subunit transforms the proton ATPase from a Mg2+-activatable to a Ca2+-activatable ATPase. Subsequent dissociation and reconstitution of subunits reveals that the 70, 58, 40 and 33 kDa components are required, in composite, to form a functional ATP-hydrolytic core, and that no single subunit or subcomplex deficient in these subunits can catalyse ATP hydrolysis.

Fluorescence quenching by nucleotides of the plasma membrane H+-ATPase from Kluyveromyces lactis

The yeast plasma membrane H+-ATPase isolation procedure was improved; a highly pure enzyme (90-95%) was obtained after centrifugation on a trehalose concentration gradient. H+-ATPase kinetics was slightly cooperative: Hill number = 1.5, S0.5 = 800 microM ATP, and turnover number = 36 s-1. In contrast to those of other P-type ATPases, H+-ATPase fluorescence was highly sensitive to nucleotide binding; the fluorescence decreased 60% in the presence of both 5 mM ADP and AMP-PNP. Fluorescence titration with nucleotides allowed calculation of dissociation constants (Kd) from the binding site; Kd values for ATP and ADP were 700 and 800 microM, respectively. On the basis of amino acid sequence and homology model analysis, we propose that binding of the nucleotide to the N-domain is coupled to the movement of a loop beta structure and to the exposure of the Trp505 residue located in the loop. The recombinant N-domain also displayed a large hyperbolic fluorescence quenching when ATP binds; however, it displayed a higher affinity for ATP (Kd = 100 microM). We propose for P-type ATPases that structural movements during nucleotide binding could be followed if a Trp residue is properly located in the N-domain. Further, we propose the use of trehalose in enzyme purification protocols to increase the purity and quality of the isolated protein and to perform structural studies.

Ca2+ -dependent interaction of S100A1 with F1-ATPase leads to an increased ATP content in cardiomyocytes

S100A1, a Ca(2+)-sensing protein of the EF-hand family that is expressed predominantly in cardiac muscle, plays a pivotal role in cardiac contractility in vitro and in vivo. It has recently been demonstrated that by restoring Ca(2+) homeostasis, S100A1 was able to rescue contractile dysfunction in failing rat hearts. Myocardial contractility is regulated not only by Ca(2+) homeostasis but also by energy metabolism, in particular the production of ATP. Here, we report a novel interaction of S100A1 with mitochondrial F(1)-ATPase, which affects F(1)-ATPase activity and cellular ATP production. In particular, cardiomyocytes that overexpress S100A1 exhibited a higher ATP content than control cells, whereas knockdown of S100A1 expression decreased ATP levels. In pull-down experiments, we identified the alpha- and beta-chain of F(1)-ATPase to interact with S100A1 in a Ca(2+)-dependent manner. The interaction was confirmed by colocalization studies of S100A1 and F(1)-ATPase and the analysis of the S100A1-F(1)-ATPase complex by gel filtration chromatography. The functional impact of this association is highlighted by an S100A1-mediated increase of F(1)-ATPase activity. Consistently, ATP synthase activity is reduced in cardiomyocytes from S100A1 knockout mice. Our data indicate that S100A1 might play a key role in cardiac energy metabolism.

Dimeric Core Structure of Modular Stator Subunit E of Archaeal H+-ATPase

Archaeal H(+)-ATPase (A-ATPase) is composed of an A(1) region that hydrolyzes ATP and an integral membrane part A(0) that conducts protons. Subunit E is a component of peripheral stator(s) that physically links A(1) and A(0) parts of the A-ATPase. Here we report the first crystal structure of subunit E of A-ATPase from Pyrococcus horikoshii OT3 at 1.85 A resolution. The protomer structure of subunit E represents a novel fold. The quaternary structure of subunit E is a homodimer, which may constitute the core part of the stator. To investigate the relationship with other stator subunit H, the complex of subunits EH was prepared and characterized using electrophoresis, mass spectrometry, N-terminal sequencing and circular dichroism spectroscopy, which revealed the polymeric and highly helical nature of the EH complex with equimolar stoichiometry of both the subunits. On the basis of the modular architecture of stator subunits, it is suggested that both cytoplasm and membrane sides of the EH complex may interact with other subunits to link A(1) and A(0) parts.

Small-Angle X-ray Scattering Reveals the Solution Structure of the Peripheral Stalk Subunit H of the A1AO ATP Synthase from Methanocaldococcus jannaschii and Its Binding to the Catalytic A Subunit

The H subunit of the A1AO ATP synthase is a component of one of the peripheral stalks connecting the A1 and AO domain. Subunit H of the Methanocaldococcus jannaschii A1AO ATP synthase was analyzed by small-angle X-ray scattering (SAXS) in order to determine the first low-resolution structure of this molecule in solution. Independent to the concentration used, the protein is dimeric and has a boomerang-like shape, divided into two arms of 12.0 and 6.8 nm in length. Circular dichroism (CD) spectroscopy revealed that subunit H is comprised of 78% alpha-helix and a coiled-coil arrangement. To understand the orientation of the helices and the localization of the N- and C-termini inside the dimer, three truncated forms of subunit H (H8-104, H1-98, and H8-98) were expressed, purified, and analyzed by CD. SAXS experiments of H1-98 show that the maximum dimension of the truncated protein dropped to 15.1 nm. Comparison of the low-resolution shapes of H and H1-98 indicates that this goes along with structural changes in the C-terminal arm of the boomerang-like structure. Together with the result of a disulfide formation of a fourth truncated form, H1-47, with a cysteine at position 47, the data suggest a parallel alpha-helical interaction. In addition, all four truncated proteins are dimeric in solution. Tryptophan emission spectra showed specific binding of H and H8-104 to the neighboring, catalytic A subunit, which could not be detected in the presence of H1-98. Finally, the arrangement of H within the A1AO ATP synthase is presented.

Self-association of isolated large cytoplasmic domain of plasma membrane H+ -ATPase from Saccharomyces cerevisiae: role of the phosphorylation domain in a general dimeric model for P-ATPases

Large cytoplasmic domain (LCD) plasma membrane H+ -ATPase from S. cerevisiae was expressed as two fusion polypeptides in E. coli: a DNA sequence coding for Leu353-Ileu674 (LCDh), comprising both nucleotide (N) and phosphorylation (P) domains, and a DNA sequence coding for Leu353-Thr543 (LCDDeltah, lacking the C-terminus of P domain), were inserted in expression vectors pDEST-17, yielding the respective recombinant plasmids. Overexpressed fusion polypeptides were solubilized with 6 M urea and purified on affinity columns, and urea was removed by dialysis. Their predicted secondary structure contents were confirmed by CD spectra. In addition, both recombinant polypeptides exhibited high-affinity 2',3'-O-(2,4,6-trinitrophenyl)adenosine-5'-triphosphate (TNP-ATP) binding (Kd = 1.9 microM and 2.9 microM for LCDh and LCDDeltah, respectively), suggesting that they have native-like folding. The gel filtration profile (HPLC) of purified LCDh showed two main peaks, with molecular weights of 95 kDa and 39 kDa, compatible with dimeric and monomeric forms, respectively. However, a single elution peak was observed for purified LCDDeltah, with an estimated molecular weight of 29 kDa, as expected for a monomer. Together, these data suggest that LCDh exist in monomer-dimer equilibrium, and that the C-terminus of P domain is necessary for self-association. We propose that such association is due to interaction between vicinal P domains, which may be of functional relevance for H+ -ATPase in native membranes. We discuss a general dimeric model for P-ATPases with interacting P domains, based on published crystallography and cryo-electron microscopy evidence.

Biochemical and molecular characterization of a Na+-translocating F1Fo-ATPase from the thermoalkaliphilic bacterium Clostridium paradoxum

Clostridium paradoxum is an anaerobic thermoalkaliphilic bacterium that grows rapidly at pH 9.8 and 56 degrees C. Under these conditions, growth is sensitive to the F-type ATP synthase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD), suggesting an important role for this enzyme in the physiology of C. paradoxum. The ATP synthase was characterized at the biochemical and molecular levels. The purified enzyme (30-fold purification) displayed the typical subunit pattern for an F1Fo-ATP synthase but also included the presence of a stable oligomeric c-ring that could be dissociated by trichloroacetic acid treatment into its monomeric c subunits. The purified ATPase was stimulated by sodium ions, and sodium provided protection against inhibition by DCCD that was pH dependent. ATP synthesis in inverted membrane vesicles was driven by an artificially imposed chemical gradient of sodium ions in the presence of a transmembrane electrical potential that was sensitive to monensin. Cloning and sequencing of the atp operon revealed the presence of a sodium-binding motif in the membrane-bound c subunit (viz., Q28, E61, and S62). On the basis of these properties, the F1Fo-ATP synthase of C. paradoxum is a sodium-translocating ATPase that is used to generate an electrochemical gradient of + that could be used to drive other membrane-bound bioenergetic processes (e.g., solute transport or flagellar rotation). In support of this proposal are the low rates of ATP synthesis catalyzed by the enzyme and the lack of the C-terminal region of the epsilon subunit that has been shown to be essential for coupled ATP synthesis.

Probing conformations of the beta subunit of F0F1-ATP synthase in catalysis

A subcomplex of F0F1-ATP synthase (F0F1), alpha3beta3gamma, was shown to undergo the conformation(s) during ATP hydrolysis in which two of the three beta subunits have the "Closed" conformation simultaneously (CC conformation) [S.P. Tsunoda, E. Muneyuki, T. Amano, M. Yoshida, H. Noji, Cross-linking of two beta subunits in the closed conformation in F1-ATPase, J. Biol. Chem. 274 (1999) 5701-5706]. This was examined by the inter-subunit disulfide cross-linking between two mutant beta(I386C)s that was formed readily only when the enzyme was in the CC conformation. Here, we adopted the same method for the holoenzyme F0F1 from Bacillus PS3 and found that the CC conformation was generated during ATP hydrolysis but barely during ATP synthesis. The experiments using F0F1 with the epsilon subunit lacking C-terminal helices further suggest that this difference is related to dynamic nature of the epsilon subunit and that ATP synthesis is accelerated when it takes the pathway involving the CC conformation.

Isolation of yeast plasma membranes

The plasma membrane is dynamic, with both its lipid and protein composition changing to facilitate adaptation to the ambient conditions. Biochemical activities to pre-existing proteins will also change. To monitor these variations, the cell membrane must be isolated. Moreover, the preparations must be free of contamination from the variety of other membranes in the cell, principally those associated with the golgi, endoplasmic reticulum (ER), the nucleus, and the vacuole. We describe a method for isolating plasma membranes that avoids incubation with enzymes that degrade the cell wall, thereby avoiding physiological changes that may lead to alteration in profile and activity of membrane proteins as well as avoiding changes that may alter lipid composition. We have used this method to show that, in response to heat shock, the plasma membrane acquires a novel heat-shock protein (HSP) and displays a decline in the levels of the abundant H+ translocating ATPase.

Purification and biochemical characterization of the F1-ATPase from Acidithiobacillus ferrooxidans NASF-1 and analysis of the atp operon

ATPase was purified 51-fold from a chemoautotrophic, obligately acidophilic iron-oxidizing bacterium, Acidithiobacillus ferrooxidans NASF-1. The purified ATPase showed the typical subunit pattern of the F1-ATPase on a polyacrylamide gel containing sodium dodecyl sulfate, with 5 subunits of apparent molecular masses of 55, 50, 33, 20, and 18 kDa. The enzyme hydrolyzed ATP, GTP, and ITP, but neither UTP nor ADP. The K(m) value for ATP was 1.8 mM. ATPase activity was optimum at pH 8.5 at 45 degrees C, and was activated by sulfite. Azide strongly inhibited the enzyme activity, whereas the enzyme was relatively resistant to vanadate, nitrate, and N,N'-dicyclohexylcarbodiimide. The genes encoding the subunits for the F1F(O)-ATPase from A. ferrooxidans NASF-1 were cloned as three overlapping fragments by PCR cloning and sequenced. The molecular masses of the alpha, beta, gamma, delta, and epsilon subunits of the F1 portion were deduced from the amino acid sequences to be 55.5, 50.5, 33.1, 19.2, and 15.1 kDa, respectively.

Isolation, cloning and expression analysis of EcPMA1, a putative plasma membrane H+ -ATPase transporter gene from the biotrophic pathogenic fungus Erysiphe cichoracearum

Little is known at the molecular level about the transporters involved in nutrient transfer in the plant/powdery mildew interaction. A PCR-based approach was used to identify and isolate a partial-length cDNA coding for an isoform of the plasma membrane H+ -ATPase (EcPMA1) in the biotrophic pathogenic fungus Erysiphe cichoracearum. Southern analysis suggests that EcPMA1 exists as a single-copy gene. Sequence analysis indicated a high similarity of EcPMA1 to other fungal H+ -ATPases. Expression of EcPMA1 increases in infected Arabidopsis leaves as the disease progresses, correlating with the growth of the pathogen.

The c15 ring of the Spirulina platensis F-ATP synthase: F1/F0 symmetry mismatch is not obligatory

The oligomeric c ring of the F-ATP synthase from the alkaliphilic cyanobacterium Spirulina platensis was isolated and characterized. Mass spectroscopy analysis indicated a mass of 8,210 Da, reflecting that of a c monomer. The mass increased by 206 Da after treatment with the c-subunit-specific inhibitor dicyclohexylcarbodiimide (DCCD), which indicated modification of the ion-binding carboxylate by DCCD. Atomic force microscopy topographs of c rings from S. platensis showed 15 symmetrically assembled subunits. The c15-mer reported here is the largest c ring that is isolated and does not show the classical c-ring mismatch to the three-fold symmetry of the F1 domain.

Purification, crystallization, and properties of F1-ATPase complexes from the thermoalkaliphilic Bacillus sp. strain TA2.A1

Recently, we reported the cloning of the atp operon encoding for the F(1)F(0)-ATP synthase from the extremely thermoalkaliphilic bacterium Bacillus sp. strain TA2.A1. In this study, the genes encoding the F(1) moiety of the enzyme complex were cloned from the atp operon into the vector pTrc99A and expressed in Escherichia coli in two variant complexes, F(1)-wt consisting of subunits alpha(3)beta(3)gammadeltaepsilon and F(1)Deltadelta lacking the entire delta-subunit as a prerequisite for overproduction and crystallization trials. Both F(1)-wt and F(1)Deltadelta were successfully overproduced in E. coli and purified in high yield and purity. F(1)Deltadelta was crystallized by micro-batch screening yielding three-dimensional crystals that diffracted to a resolution of 3.1A using a synchrotron radiation source. After establishing cryo and dehydrating conditions, a complete set of diffraction data was collected from a single crystal. No crystals were obtained with F(1)-wt. Data processing of diffraction patterns showed that F(1)Deltadelta crystals belong to the orthorhombic space group P2(1)2(1)2(1) with unit cell parameters of a=121.70, b=174.80, and c=223.50A, alpha, beta, gamma=90.000. The asymmetric unit contained one molecule of bacterial F(1)Deltadelta with a corresponding volume per protein weight (V(M)) of 3.25A(3) Da(-1) and a solvent content of 62.1%. Silver staining of single crystals of F(1)Deltadelta analyzed by SDS-PAGE revealed four bands alpha, beta, gamma, and epsilon with identical M(r)-values as those found in the native F(1)F(0)-ATP synthase isolated from strain TA2.A1 membranes. ATPase assays of F(1)Deltadelta crystals exhibited latent ATP hydrolytic activity that was highly stimulated by lauryldimethylamine oxide, a hallmark of the native enzyme.

Differential effect of phosphatidylethanolamine depletion on raft proteins

A considerable amount of evidence supports the idea that lipid rafts are involved in many cellular processes, including protein sorting and trafficking. We show that, in this process, also a non-raft lipid, phosphatidylethanolamine (PE), has an indispensable function. The depletion of this phospholipid results in an accumulation of a typical raft-resident, the arginine transporter Can1p, in the membranes of Golgi, while the trafficking of another plasma membrane transporter, Pma1p, is interrupted at the level of the ER. Both these transporters associate with a Triton (TX-100) resistant membrane fraction before their intracellular transport is arrested in the respective organelles. The Can1p undelivered to the plasma membrane is fully active when reconstituted to a PE-containing vesicle system in vitro. We further demonstrate that, in addition to the TX-100 resistance at 4 degrees C, Can1p and Pma1pa exhibit different accessibility to nonyl glucoside (NG), which points to distinct intimate lipid surroundings of these two proteins. Also, at 20 degrees C, these two proteins are extracted by TX-100 differentially. The features above suggest that Pma1p and Can1p are associated with different compartments. This is independently supported by the observations made by confocal microscopy. In addition we show that PE is involved in the stability of Can1p-raft association.

Ultrafast purification and reconstitution of His-tagged cysteine-less Escherichia coli F1Fo ATP synthase

His-tagged cysteine-less F1Fo ATP synthase from Escherichia coli was purified using Ni-NTA affinity chromatography. During the purification procedure the loss of total ATPase activity did not exceed 50%, and the extent of purification was about 80-fold. The purified enzyme was essentially free of other proteins, was highly active in ATP hydrolysis (75 units/mg at pH 8 and 37 degrees C), and was sensitive to N,N'-dicyclohexylcarbodiimide (70%). Incorporation of F1Fo into soybean liposomes yielded well-coupled and highly active proteoliposomes. The entire procedure, from the disruption of cells by French press to the preparation of proteoliposomes, took only about 8 h. Some improvements in procedures for the estimation of rates of both ATP hydrolysis and ATP-dependent 9-amino-6-chloro-2-methoxyacridine (ACMA) fluorescence quenching are described.

Functional expression of hexahistidine-tagged beta-subunit of yeast F1-ATPase and isolation of the enzyme by immobilized metal affinity chromatography

Mitochondrial ATP synthase (F1Fo-ATPase) catalyzes the terminal step of oxidative phosphorylation. In this paper, we demonstrate the functional expression of the hexahistidine-tagged beta-subunit of yeast ATP synthase and the purification of the F1-ATPase from yeast cells. A gene encoding the beta-subunit from Saccharomyces cerevisiae was modified to encode a protein of which the original N-terminus import signal sequence was replaced by a sequence containing the import signal sequence of a mitochondrial ATPase inhibitor, its processing site, and six consecutive histidines. Expression of the modified gene generated a functional F1Fo complex in host yeast cells lacking a functional copy of the endogenous ATP2 gene, as judged by growth of rescued cells on lactate medium. F1 was extracted from the yeast mitochondria by chloroform treatment and purified by immobilized metal affinity chromatography and gel filtration chromatography. The specific activity of the purified F1 was comparable to that of the wild-type enzyme, and the F1 contained all of the 5 known subunits (alpha, beta, gamma, delta, and epsilon). Moreover, the activity of the F1 was completely inhibited by the specific ATPase inhibitor protein, IF1. These results indicate that F1 containing the tagged beta-subunit is fully assembled and active. The application of this novel procedure simplifies the number of steps required for the isolation of F1 used for studying the molecular mechanism of catalysis and regulation of the enzyme.

The structure of bovine F1-ATPase inhibited by ADP and beryllium fluoride

The structure of bovine F1-ATPase inhibited with ADP and beryllium fluoride at 2.0 angstroms resolution contains two ADP.BeF3- complexes mimicking ATP, bound in the catalytic sites of the beta(TP) and beta(DP) subunits. Except for a 1 angstrom shift in the guanidinium of alphaArg373, the conformations of catalytic side chains are very similar in both sites. However, the ordered water molecule that carries out nucleophilic attack on the gamma-phosphate of ATP during hydrolysis is 2.6 angstroms from the beryllium in the beta(DP) subunit and 3.8 angstroms away in the beta(TP) subunit, strongly indicating that the beta(DP) subunit is the catalytically active conformation. In the structure of F1-ATPase with five bound ADP molecules (three in alpha-subunits, one each in the beta(TP) and beta(DP) subunits), which has also been determined, the conformation of alphaArg373 suggests that it senses the presence (or absence) of the gamma-phosphate of ATP. Two catalytic schemes are discussed concerning the various structures of bovine F1-ATPase.

Isolation of intact vacuoles and proteomic analysis of tonoplast from suspension-cultured cells of Arabidopsis thaliana

A large number of proteins in the tonoplast, including pumps, carriers, ion channels and receptors support the various functions of the plant vacuole. To date, few proteins involved in these activities have been identified at the molecular level. In this study, proteomic analysis was used to identify new tonoplast proteins. A primary requirement of any organelle analysis by proteomics is that the purity of the isolated organelle needs to be high. Using suspension-cultured Arabidopsis cells (Arabidopsis Col-0 cell suspension), a method was developed for the isolation of intact highly purified vacuoles. No plasma membrane proteins were detected in Western blots of the isolated vacuole fraction, and only a few proteins from the Golgi and endoplasmic reticulum. The proteomic analysis of the purified tonoplast involved fractionation of the proteins by SDS-PAGE and analysis by LC-MS/MS. Using this approach, it was possible to identify 163 proteins. These included well-characterized tonoplast proteins such as V-type H+ -ATPases and V-type H+ -PPases, and others with functions reasonably expected to be related to the tonoplast. There were also a number of proteins for which a function has not yet been deduced.

Cytokinin stimulates polyribosome loading of nuclear-encoded mRNAs for the plastid ATP synthase in etioplasts of Lupinus luteus: the complex accumulates in the inner-envelope membrane with the CF(1) moiety located towards the stromal space

Three of the nine subunits of the plastid ATP synthase, including the subunit of the CF(1) moiety (gene AtpC), are encoded in the nucleus. Application of cytokinin to etiolated lupine seedlings induces polyribosome association of their mRNAs. This appears to be specific as no such regulation was observed for messages for three ribosomal proteins. Cytokinin-mediated polyribosome loading was also observed for the spinach AtpC message in etiolated transgenic tobacco seedlings. Analysis of various spinach AtpC mRNA derivatives uncovered that the 5' untranslated region (5' UTR) of this message is sufficient to direct polyribosome loading, and that sequences at the 3' end of the AtpC 5' UTR, including an UC-rich motif, are crucial for this regulation. The increase in polyribosome loading of the AtpC message correlated with an increased synthesis of the polypeptide. The subunit, together with the ATP synthase complex, accumulates in the inner-envelope membrane with the CF(1) moiety located towards the stromal space of the etioplast. These results suggest that cytokinin promotes accumulation of the ATP synthase in the inner-envelope membrane of lupine etioplasts by stimulating the translation efficiency of their nuclear-encoded messages.

Expression, Isolation, and Crystallization of the Catalytic Domain of CopB, a Putative Copper Transporting ATPase from the Thermoacidophilic Archaeon Sulfolobus solfataricus

The P-type CPX-ATPases are responsible for the transport of heavy metal ions in archaea, bacteria, and eukaryotes. We have chosen one of the two CPX-ATPases of the thermophile Sulfolobus solfataricus, CopB (= SSO2896) for the investigation of the molecular mechanism of this integral membrane protein. We recombinately expressed three different soluble domains of this protein (named CopB-A, CopB-B, and CopB-C) in Escherichia coli and purified them to homogeneity. 3D crystals of CopB-B, the 29 kDa catalytic ATP binding/phosphorylation domain were produced, which diffracted to a resolution of 2.2 A. CopB-B has heavy metal stimulated phosphatase activity, which was half maximal in the presence of 80 microM Cu2+. The protein forms a phosphorylated intermediate with the substrate gamma-(32P)-ATP. No specific activation of the polypeptide was observed, when CopB-B phosphatase activity was tested in the presence of the purified CopB-C and CopB-A proteins, which provide the cation binding and the phosphatase domains. We conclude that CopB is a putatively copper translocating ATPase, in which structural elements integrally located in the membrane are required for full, coordinated activation of the catalytic ATP binding domain.

Biochemical characteristics of a mutant of the methanoarchaeon Methanothermobacter thermautotrophicus resistant to the protonophoric uncoupler TCS

In an attempt to more closely define a protein basis of differences in ATPase and ATP synthase activities in a mutant of the methanoarchaeon Methanothermobacter thermautotrophicus resistant to the protonophoric uncoupler TCS (3,3',4',5-tetrachlorosalicylanilide), the composition of membrane associated proteins from the wild-type and mutant strains has been compared. The uncoupler-resistance in the mutant strain was not accompanied by changes in a protein size or changes in the level of subunits A, B and c (proteolipid) of the A1A0-type ATPase-synthase. On the other hand, we revealed a 670-kDa membrane-associated protein complex that is abundantly present only in the mutant strain; it is composed of at least 5 different subunits of 95, 52, 42, 29 and 22 kDa.

The molecular chaperone, Atp12p, from Homo sapiens. In vitro studies with purified wild type and mutant (E240K) proteins

Work in Saccharomyces cerevisiae has shown that Atp12p binds to unassembled alpha subunits of F(1) and in so doing prevents the alpha subunit from associating with itself in non-productive complexes during assembly of the F(1) moiety of the mitochondrial ATP synthase. We have developed a method to prepare recombinant Atp12p after expression of its human cDNA in bacterial cells. The molecular chaperone activity of HuAtp12p was studied using citrate synthase as a model substrate. Wild type HuAtp12p suppresses the aggregation of thermally inactivated citrate synthase. In contrast, the mutant protein HuAtp12p(E240K), which harbors a lysine at the position of the highly conserved Glu-240, fails to prevent citrate synthase aggregation at 43 degrees C. No significant differences were observed between the wild type and the mutant proteins as judged by sedimentation analysis, cysteine titration, tryptophan emission spectra, or limited proteolysis, which suggests that the E240K mutation alters the activity of HuAtp12p with minimal effects on the physical integrity of the protein. An additional important finding of this work is that the equilibrium chemical denaturation curve of HuAtp12p shows two components, the first of which is associated with protein aggregation. This result is consistent with a model for Atp12p structure in which there is a hydrophobic chaperone domain that is buried within the protein interior.

Isolation of a complete A1AO ATP synthase comprising nine subunits from the hyperthermophile Methanococcus jannaschii

Archaeal A(1)A(O) ATP synthase/ATPase operons are highly conserved among species and comprise at least nine genes encoding structural proteins. However, all A(1)A(O) ATPase preparations reported to date contained only three to six subunits and, therefore, the study of this unique class of secondary energy converters is still in its infancy. To improve the quality of A(1)A(O) ATPase preparations, we chose the hyperthermophilic, methanogenic archaeon Methanococcus jannaschii as a model organism. Individual subunits of the A(1)A(O) ATPase from M. jannaschii were produced in E. coli, purified, and antibodies were raised. The antibodies enabled the development of a protocol ensuring purification of the entire nine-subunit A(1)A(O) ATPase. The ATPase was solubilized from membranes of M. jannaschii by Triton X-100 and purified to apparent homogeneity by sucrose density gradient centrifugation, ion exchange chromatography, and gel filtration. Electron micrographs revealed the A(1) and A(O) domains and the central stalk, but also additional masses which could represent a second stalk. Inhibitor studies were used to demonstrate that the A(1) and A(O) domains are functionally coupled. This is the first description of an A(1)A(O) ATPase preparation in which the two domains (A(1) and A(O)) are fully conserved and functionally coupled.

Isolation of H+ -translocating ATPase in tonoplast of Tradescantia virginiana L. leaf cells

The tonoplast of Tradescantia virginiana L. was prepared from leaf cells and then solubilized with deoxycholate (DOC) and n-octyl-beta-D-glucoside (n-OG). Three major polypeptides (68, 60, 16 kDa) and several other minor components were isolated. These polypeptides were reconstituted in soybean phospholipids (asolectin). The H(+) pump activity was investigated with the reconstituted system as well as with the tonoplast. In both cases, the quinacrine-fluorescence quenching was observed in the presence of ATP-Mg(2+), indicating the H(+) pumping. The H(+) pump activity was inhibited by gramicidin D, a channel-forming ionophore, and by KNO(3), an inhibitor specific to tonoplast-type (V-type) H(+)-ATPase.

H+/ATP ratio of proton transport-coupled ATP synthesis and hydrolysis catalysed by CF0F1-liposomes

The H(+)/ATP ratio and the standard Gibbs free energy of ATP synthesis were determined with a new method using a chemiosmotic model system. The purified H(+)-translocating ATP synthase from chloroplasts was reconstituted into phosphatidylcholine/phosphatidic acid liposomes. During reconstitution, the internal phase was equilibrated with the reconstitution medium, and thereby the pH of the internal liposomal phase, pH(in), could be measured with a conventional glass electrode. The rates of ATP synthesis and hydrolysis were measured with the luciferin/luciferase assay after an acid-base transition at different [ATP]/([ADP][P(i)]) ratios as a function of deltapH, analysing the range from the ATP synthesis to the ATP hydrolysis direction and the deltapH at equilibrium, deltapH (eq) (zero net rate), was determined. The analysis of the [ATP]/([ADP][P(i)]) ratio as a function of deltapH (eq) and of the transmembrane electrochemical potential difference, delta micro approximately (H)(+) (eq), resulted in H(+)/ATP ratios of 3.9 +/- 0.2 at pH 8.45 and 4.0 +/- 0.3 at pH 8.05. The standard Gibbs free energies of ATP synthesis were determined to be 37 +/- 2 kJ/mol at pH 8.45 and 36 +/- 3 kJ/mol at pH 8.05.

Characterization of H+,K+-ATPase T cell epitopes in human autoimmune gastritis

Human autoimmune gastritis (AIG) is an organ-specific inflammatory disorder leading to gastric atrophy and pernicious anemia. Gastric H+,K(+)-ATPase was identified as the autoantigen in both human disease and experimental murine AIG (EAIG). Studies of EAIG significantly contributed to current knowledge of human AIG, but to what extent EAIG mimics AIG is still debated, and the autoantigenic epitopes in AIG are yet unknown. This study aimed to identify the H+,K(+)-ATPase epitopes recognized by gastric T cell clones from AIG patients, to define their TCR Vbeta usage and epitope-induced cytokine response. Sixteen H+,K(+)-ATPase-reactive CD4+ gastric T cell clones of four AIG patients were tested for proliferation to overlapping 15-mer peptides spanning the a and beta chains of H+,K(+)-ATPase. We identified 6 epitopes in the a chain and 5 in the beta chain; TCR Vbeta usage was not restricted. Four (36%) of the 11 H+,K(+)-ATPase epitopes recognized in AIG were found to overlap with epitopes that are relevant in EAIG, including a previously described gastritogenic epitope. Gastric T cell recognition of the peptide epitopes resulted in secretion of Th1 cytokines. Our data suggest a striking similarity between human AIG and EAIG, at the epitope level, with regard to cytokine secretion and likely also with regard to pathogenic mechanisms.

Evidence for structural integrity in the undecameric c-rings isolated from sodium ATP synthases

The Na(+)-translocating ATP synthases from Ilyobacter tartaricus and Propionigenium modestum contain undecameric c subunit rings of unusual stability. These c(11) rings have been isolated from both ATP synthases and crystallized in two dimensions. Cryo-transmission electron microscopy projection maps of the c-rings from both organisms were identical at 7A resolution. Different crystal contacts were induced after treatment of the crystals with dicyclohexylcarbodiimide (DCCD), which is consistent with the binding of the inhibitor to glutamate 65 in the C-terminal helix on the outside of the ring. The c subunits of the isolated c(11) ring of I.tartaricus were modified specifically by incubation with DCCD with kinetics that were indistinguishable from those of the F(1)F(o) holoenzyme. The reaction rate increased with decreasing pH but was lower in the presence of Na(+). From the pH profile of the second-order rate constants, the pK of glutamate 65 was deduced to be 6.6 or 6.2 in the absence or presence of 0.5mM NaCl, respectively. These pK values are identical with those determined for the F(1)F(o) complex. The results indicate that the isolated c-ring retains its native structure, and that the glutamate 65, including binding sites near the middle of the membrane, are accessible to Na(+) from the cytoplasm through access channels within the c-ring itself.

Structural energetics of MgADP binding to the isolated beta subunit of F1-ATPase from thermophilic Bacillus PS3

The energetics of binding of MgADP to the isolated beta subunit of F(1)-ATPase from thermophilic Bacillus (Tbeta) was characterized by high-precision isothermal titration calorimetry. The reaction was enthalpically driven, with a DeltaCp of -36cal(molK)(-1). To gain insight into the molecular basis of this small DeltaCp, we analyzed the changes in accessible surface areas (DeltaASA) between the structures of empty and MgADP-filled beta subunits, extracted from the crystal structure of bovine heart F(1). Consistent with the experimental DeltaCp, the DeltaASA was small (-775A(2)). We used a reported surface area model developed for protein reactions to calculate DeltaCp and DeltaH from DeltaASA, obtaining good agreement with the experimental values. Conversely, using the same model, a DeltaASA of -770A(2) was estimated from experimental DeltaCp and DeltaH for the Tbeta-MgADP complex. Our structural-energetic study indicates that on MgADP binding the isolated Tbeta subunit exhibits intrinsic structural changes similar to those observed in F(1).

Improved purification for thermophilic F1F0 ATP synthase using n-dodecyl beta-D-maltoside

Here we report a fast, simple purification for thermophilic F1F0 ATP synthase (TF1F0) that utilizes a cocktail of stabilizing reagents and the detergent n-dodecyl beta-D-maltoside to yield enzyme with an ATPase activity of 41 micromol/min/mg, 2.5-fold higher than that previously reported. ATPase activity was 80% inhibited by the F0-reactive reagent dicyclohexylcarbodiimide, indicating that F1-F0 interactions were largely intact. To measure ATP-driven proton pumping activity, purified TF1F0 was incorporated into liposomes, and the ATP-induced change in internal pH was measured using the fluorescent probe pyranine. In the presence of valinomycin, a maximum ATP-driven deltapH of 0.8 units was obtained. To measure ATP synthesis activity, TF1F0 was incorporated into liposomes with the light-dependent proton pump bacteriorhodopsin. Proteoliposomes were illuminated to generate an electrochemical gradient, after which ADP and inorganic phosphate were added to initiate ATP synthesis. A steady state ATP synthesis activity of 490 nmol/min/mg was achieved after an initial approximately 30-min lag phase.

Stalk segment 5 of the yeast plasma membrane H(+)-ATPase. Labeling with a fluorescent maleimide reveals a conformational change during glucose activation

Glucose is well known to cause a rapid, reversible activation of the yeast plasma membrane H(+)-ATPase, very likely mediated by phosphorylation of two or more Ser/Thr residues near the C terminus. Recent mutagenesis studies have shown that glucose-dependent activation can be mimicked constitutively by amino acid substitutions in stalk segment 5 (S5), an alpha-helical stretch connecting the catalytic part of the ATPase with transmembrane segment 5 (Miranda, M., Allen, K. E., Pardo, J. P., and Slayman, C. W. (2001) J. Biol. Chem. 276, 22485-22490). In the present work, the fluorescent maleimide Alexa-488 has served as a probe for glucose-dependent changes in the conformation of S5. Experiments were carried out in a "3C" version of the ATPase, from which six of nine native cysteines had been removed by site-directed mutagenesis to eliminate background labeling by Alexa-488. In this construct, three of twelve cysteines introduced at various positions along S5 (A668C, S672C, and D676C) reacted with the Alexa dye in a glucose-independent manner, as shown by fluorescent labeling of the 100 kDa Pma1 polypeptide and by isolation and identification of the corresponding tryptic peptides. Especially significant was the fact that three additional cysteines reacted with Alexa-488 more rapidly (Y689C) or only (V665C and L678C) in plasma membranes from glucose-metabolizing cells. The results support a model in which the S5 alpha-helix undergoes a significant change in conformation to expose positions 665, 678, and 689 during glucose-dependent activation of the ATPase.

F- and V-type ATPases in the hyperthermophilic bacterium Thermotoga neapolitana

Two gene clusters encoding F- or V-type ATPases were found in genomic DNA of the hyperthermophilic bacterium Thermotoga neapolitana. The subunit genes of each ATPase formed an operon. While the gene arrangement in the operon of the F-type ATPase resembled those in eukaryotic organelles and bacteria, that of the V-type ATPase was different from those reported for archaea, bacteria, or eukaryotes. Both ATPases were found to be expressed in the cells of T. neapolitana by Western blot analysis. Although V-type ATPase could not be rendered soluble, F-type ATPase was solubilized with 1% Triton X-100 and characterized. This is the first report of the coexistence of both F- and V-type ATPases in hyperthermophilic bacteria. It has recently been shown by a genome analysis that Thermotoga maritima has no V-type ATPase gene cluster but does have an F-type ATPase gene cluster; however, part of a gene for the D-subunit of the V-type ATPase gene has been reported in the T. maritima genome. Evolution of the two types of ATPases in Thermotoga is discussed.

A functionally active human F1F0 ATPase can be purified by immunocapture from heart tissue and fibroblast cell lines. Subunit structure and activity studies

Human mitochondrial F(1)F(0) ATP synthase was isolated with a one-step immunological approach, using a monoclonal antibody against F(1) in a 96-well microplate activity assay system, to establish a method for fast high throughput screening of inhibitors, toxins, and drugs with very small amounts of enzyme. For preparative purification, mitochondria from human heart tissue as well as cultured fibroblasts were solubilized with dodecyl-beta-d-maltoside, and the F(1)F(0) was isolated with anti-F(1) monoclonal antibody coupled to protein G-agarose beads. The immunoprecipitated F(1)F(0) contained a full complement of subunits that were identified with specific antibodies against five of the subunits (alpha, beta, OSCP, d, and IF(1)) and by MALDI-TOF and/or LC/MS/MS for all subunits except subunit c, which could not be resolved by these methods because of the limits of detection. Microscale immunocapture of F(1)F(0) from detergent-solubilized mitochondria or whole cell fibroblast extracts was performed using anti-F(1) monoclonal antibody immobilized on 96-well microplates. The captured complex V displayed ATP hydrolysis activity that was fully oligomycin and inhibitor protein IF(1)-sensitive. Moreover, IF(1) could be co-isolated with F(1)F(0) when the immunocapture procedure was carried out at pH 6.5 but was absent when the ATP synthase was isolated at pH 8.0. Immunocaptured F(1)F(0) lacking IF(1) could be inhibited by more than 90% by addition of recombinant inhibitor protein, and conversely, F(1)F(0) containing IF(1) could be activated more than 10-fold by brief exposure to pH 8.0, inducing the release of inhibitor protein. With this microplate system an ATP hydrolysis assay of complex V could be carried out with as little as 10 ng of heart mitochondria/well and as few as 3 x 10(4) cells/well from fibroblast cultures. The system is therefore suitable to screen patient-derived samples for alterations in amount or functionality of both the F(1)F(0) ATPase and IF(1).

Characterization of a hyperthermophilic P-type ATPase from Methanococcus jannaschii expressed in yeast

We report on the biochemical and structural properties of a putative P-type H(+)-ATPase, MJ1226p, from the anaerobic hyperthermophilic Archaea Methanococcus jannaschii. An efficient heterologous expression system was developed in Saccharomyces cerevisiae and a four-step purification protocol, using n-dodecyl beta-d-maltoside, led to a homogeneous detergent-solubilized protein fraction with a yield of over 2 mg of protein per liter of culture. The three-dimensional structure of the purified detergent-solubilized protein obtained at 2.4 nm resolution by electron microscopy showed a dimeric organization in which the size and the shape of each monomer was compatible with the reported structures of P-type ATPases. The purified MJ1226p ATPase was inactive at 40 degrees C and was active at elevated temperature reaching high specific activity, up to 180 micromol of P(i) x min(-1) x mg(-1) at 95 degrees C. Maximum ATPase activity was observed at pH 4.2 and required up to 200 mm monovalent salts. The ATPase activity was stable for several days upon storage at 65 degrees C and was highly resistant to urea and guanidine hydrochloride. The protein formed catalytic phosphoenzyme intermediates from MgATP or P(i), a functional characteristic specific of P-type ATPases. The highly purified, homogeneous, stable, and active MJ1226p ATPase provides a new model for further structure-function studies of P-type ATPases.

Stepping rotation of F(1)-ATPase with one, two, or three altered catalytic sites that bind ATP only slowly

F(1)-ATPase is an ATP hydrolysis-driven motor in which the gamma subunit rotates in the stator cylinder alpha(3)beta(3). To know the coordination of three catalytic beta subunits during catalysis, hybrid F(1)-ATPases, each containing one, two, or three "slow" mutant beta subunits that bind ATP very slowly, were prepared, and the rotations were observed with a single molecule level. Each hybrid made one, two, or three steps per 360 degrees revolution, respectively, at 5 microm ATP where the wild-type enzyme rotated continuously without step under the same observing conditions. The observed dwell times of the steps are explained by the slow binding rate of ATP. Except for the steps, properties of rotation, such as the torque forces exerted during rotary movement, were not significantly changed from those of the wild-type enzyme. Thus, it appears that the presence of the slow beta subunit(s) does not seriously affect other normal beta subunit(s) in the same F(1)-ATPase molecule and that the order of sequential catalytic events is faithfully maintained even when ATP binding to one or two of the catalytic sites is retarded.

Modulation of proton pumping across proteoliposome membranes reconstituted with tonoplast H(+)-ATPase from cultured rice (Oryza sativa L. var. Boro) cells by acyl steryl glucoside and steryl glucoside

Tonoplast H(+)-ATPase purified from cultured rice cells (Oryza sativa L. var. Boro) was reconstituted into asolectin liposomes containing steryl glucoside (SG) or acyl steryl glucoside (ASG), and the effects of SG and ASG on proton pumping, ATP-hydrolysis activity and proton permeability of the proteoliposome membranes were investigated. In the proteoliposomes containing 10 mol% SG, proton pumping and ATP-hydrolysis activity were increased to around 140% of those in SG-free proteoliposomes. In the proteoliposomes containing ASG, proton pumping and ATP-hydrolysis activity were decreased to one-tenth of those in ASG-free proteoliposomes at 15 mol% ASG; however, activity increased again slightly in the range between 20 and 40 mol% ASG. The change in proton pumping across the proteoliposome membrane is not due to a change of proteoliposome size nor to the location of the catalytic site of the tonoplast H(+)-ATPase in the proteoliposomes. SG and ASG also reduced the passive proton permeability of the proteoliposomes. These results show that SG and ASG modulate proton pumping across the tonoplast toward stimulation and depression, respectively, and they reduce the passive proton permeability of the tonoplast.

Quantitative determination of binding affinity of delta-subunit in Escherichia coli F1-ATPase: effects of mutation, Mg2+, and pH on Kd

To study the stator function in ATP synthase, a fluorimetric assay has been devised for quantitative determination of binding affinity of delta-subunit to Escherichia coli F(1)-ATPase. The signal used is that of the natural tryptophan at residue delta28, which is enhanced by 50% upon binding of delta-subunit to alpha(3)beta(3)gammaepsilon complex. K(d) for delta binding is 1.4 nm, which is energetically equivalent (50.2 kJ/mol) to that required to resist the rotor strain. Only one site for delta binding was detected. The deltaW28L mutation increased K(d) to 4.6 nm, equivalent to a loss of 2.9 kJ/mol binding energy. While this was insufficient to cause detectable functional impairment, it did facilitate preparation of delta-depleted F(1). The alphaG29D mutation reduced K(d) to 26 nm, equivalent to a loss of 7.2 kJ/mol binding energy. This mutation did cause serious functional impairment, referable to interruption of binding of delta to F(1). Results with the two mutants illuminate how finely balanced is the stator resistance function. delta' fragment, consisting of residues delta1-134, bound with the same K(d) as intact delta, showing that, at least in absence of F(o) subunits, the C-terminal domain of delta contributes zero binding energy. Mg(2+) ions had a strong effect on increasing delta binding affinity, supporting the possibility of bridging metal ion involvement in stator function. High pH environment greatly reduced delta binding affinity, suggesting the involvement of protonatable side-chains in the binding site.

F(0) of ATP synthase is a rotary proton channel. Obligatory coupling of proton translocation with rotation of c-subunit ring

Coupling of proton flow and rotation in the F(0) motor of ATP synthase was investigated using the thermophilic Bacillus PS3 enzyme expressed functionally in Escherichia coli cells. Cysteine residues introduced into the N-terminal regions of subunits b and c of ATP synthase (bL2C/cS2C) were readily oxidized by treating the expressing cells with CuCl(2) to form predominantly a b-c cross-link with b-b and c-c cross-links being minor products. The oxidized ATP synthases, either in the inverted membrane vesicles or in the reconstituted proteoliposomes, showed drastically decreased proton pumping and ATPase activities compared with the reduced ones. Also, the oxidized F(0), either in the F(1)-stripped inverted vesicles or in the reconstituted F(0)-proteoliposomes, hardly mediated passive proton translocation through F(0). Careful analysis using single mutants (bL2C or cS2C) as controls indicated that the b-c cross-link was responsible for these defects. Thus, rotation of the c-oligomer ring relative to subunit b is obligatory for proton translocation; if there is no rotation of the c-ring there is no proton flow through F(0).

pH dependent inactivation of solubilized F1F0 ATP synthase by dicyclohexylcarbodiimide: pK(a) of detergent unmasked aspartyl-61 in Escherichia coli subunit c

The pH dependence of the reaction of dicyclohexylcarbodiimide with the essential aspartyl-61 residue in subunit c of Escherichia coli ATP synthase was compared in membranes and in a detergent dispersed preparation of the enzyme. The rate of reaction was estimated by measuring the inactivation of ATPase activity. The reaction with the detergent dispersed form of the enzyme proved to be pH sensitive with the essential aspartyl group titrating with a pK(a)=8. However, when measured with E. coli membranes, the reaction proved to be pH insensitive. The results suggest that the reacting aspartyl-61 residues are shielded from the bulk aqueous solvent when in the membrane, but then become aqueous-accessible following detergent solubilization.

First patch, then catch: measuring the activity and the mRNA transcripts of a proton pump in individual Lilium pollen protoplasts

Combining the patch-clamp method with single-cell reverse transcription polymerase chain reaction (scRT-PCR) a fusicoccin-induced current reflecting the activity of the plasma membrane H(+) ATPase of lily pollen protoplasts was measured and subsequently, the ATPase-encoding mRNAs were collected and amplified. Southern blot signals were observed in all 'patch-catch' experiments and could be detected even in 2560-fold dilutions of the pollen contents. H(+) ATPase mRNAs were detectable only in the vegetative but not in the generative cell of pollen as confirmed by immunolocalisation. In 15% of the scRT-PCR experiments, a random non-reproducibility of the PCR was observed, probably caused by varying amounts of ATPase mRNAs in the protoplasts.

Resolving the DDT target protein in insects as a subunit of the ATP synthase

1,1-bis-(p-Chlorophenyl)-2,2,2-trichloroethane (DDT) inhibited the ATP hydrolytic activity of the ATP synthase from a DDT-susceptible insect (Apis mellifera) as well as a DDT-tolerant insect (Spodoptera littoralis), and from rat liver and bovine heart in a parallel way to its insecticidal properties and selectivity of action. Inhibition of the ATPase activity of these preparations by DDT was parallel to the poisoning of the source organism with DDT. Furthermore, both the inhibition and poisoning of insects were affected similarly by temperature. Inhibition of the insect enzyme activity by DDT was specific and differed from that by oligomycin or N,N-dicyclohexylcarbodi-imide (DCCD). PAGE analysis of the various preparations of the enzyme showed that the inhibition of the enzyme activity by DDT was associated with the presence of a selective protein band with an apparent molecular mass of 23 kDa. This protein band exists in the preparations from the DDT-susceptible insects but was absent from the preparations of the enzyme from the DDT-insensitive sources. Removal of this protein band from the enzyme rendered its activity insensitive to inhibition by DDT. The protein was purified directly from mitochondria and the DDT sensitivity was reconstituted upon its addition to the DDT-insensitive F1-ATPase. We conclude that this identified protein of the ATP synthase is the DDT target protein in insects.

Membrane topography of the coupling ion binding site in Na+-translocating F1F0 ATP synthase

A carbodiimide with a photoactivatable diazirine substituent was synthesized and incubated with the Na(+)-translocating F(1)F(0) ATP synthase from both Propionigenium modestum and Ilyobacter tartaricus. This caused severe inhibition of ATP hydrolysis activity in the absence of Na(+) ions but not in its presence, indicating the specific reaction with the Na(+) binding c-Glu(65) residue. Photocross-linking was investigated with the substituted ATP synthase from both bacteria in reconstituted 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC)-containing proteoliposomes. A subunit c/POPC conjugate was found in the illuminated samples but no a-c cross-links were observed, not even after ATP-induced rotation of the c-ring. Our substituted diazirine moiety on c-Glu(65) was therefore in close contact with phospholipid but does not contact subunit a. Na(+)in/(22)Na(+)out exchange activity of the ATP synthase was not affected by modifying the c-Glu(65) sites with the carbodiimide, but upon photoinduced cross-linking, this activity was abolished. Cross-linking the rotor to lipids apparently arrested rotational mobility required for moving Na(+) ions back and forth across the membrane. The site of cross-linking was analyzed by digestions of the substituted POPC using phospholipases C and A(2) and by mass spectroscopy. The substitutions were found exclusively at the fatty acid side chains, which indicates that c-Glu(65) is located within the core of the membrane.

Two forms of yeast plasma membrane H(+)-ATPase: comparison of yield and effects of inhibitors

Classical isolation procedure for plasma membrane H(+)-ATPase of Saccharomyces cerevisiae based on fractional centrifugation yielded always a roughly two-fold greater amount of membranes when starting from glucitol-preincubated than from glucose-preincubated yeast. This difference persisted all the way to the purified plasma membranes and to the purified H(+)-ATPase. The ATP-hydrolyzing activity by plasma membranes was roughly twice greater in glucose-preincubated cells than in the D-glucitol-preincubated ones while the purified enzyme was 7 times more active after glucose than after glucitol. Effects of diethylstilbestrol, suloctidil, erythrosin B, vanadate and dicarbanonaboranuide were very similar on plasma membrane-localized and purified ATPases of both forms, suggesting that both preparations contain the two ATPase forms, the glucose-preincubated one being richer in the activated form while the glucitol-preincubated one contains less of it.

Two-dimensional gel electrophoresis and FTIR spectroscopy reveal both forms of yeast plasma membrane H(+)-ATPase in activated and basal-level enzyme preparations

Plasma membrane H(+)-ATPase of the yeast Saccharomyces cerevisiae was isolated and purified in its two forms, the activated A-ATPase from glucose-metabolizing cells, and the basal-level B-ATPase from cells with endogenous metabolism only. Using two-dimensional gel electrophoretic analysis, we showed that both enzyme preparations are actually mixtures of the non-active, i.e. non-phosphorylated, and the active, i.e. phosphorylated, forms of the enzyme. Previous deliberations suggesting that the B-ATPase displays some activity which is lower than that of A-ATPase were apparently wrong. It seems that, molecularly speaking, the B-form is actually not active at all, and what activity we measure in our preparation is due to an admixture of the true active form (A-form). Fourier transform infrared spectroscopic study of the secondary structure and particularly thermal denaturation data suggest the possibility that the two enzyme forms interact to form complexes less stable than the single forms. On the whole then, there apparently is a different ratio of the active and inactive forms and/or complexes between the two forms present in all enzyme preparations.