F1-like ATPase from anaerobic bacterium Lactobacillus casei contains six similar subunits

Electron microscopy of the F1F0 ATP synthase: from structure to function

The F1F0 ATP synthase is the large multisubunit complex which uses the proton gradient of energetically active membranes to synthesize ATP. While biochemical and genetic approaches have characterized the composition of the enzyme and elucidated many details of its mechanism and assembly, electron microscopy has been the tool of primary importance in determining the arrangement of the many subunits which comprise the F1F0. The highly cooperative catalytic mechanism is tightly coupled to transmembrane proton translocation in a separate and rather distant sector of the complex. An understanding of this intricate process and its control requires an appreciation of subunit interactions, starting with their locations relative to one another. Electron microscopy has provided most of the available structural information on the F1F0, and recent applications of cryo-electron microscopy have captured different functionally relevant configurations which may finally address longstanding questions about subunit rearrangements during the catalytic cycle.

Polymerase chain reaction amplification, cloning, sequence determination and homologies of streptococcal ATPase-encoding DNAs

The highly conserved portion of the catalytic subunit (beta-subunit) of the membrane-bound, proton-translocating ATPase from three strains of oral streptococci has been amplified via the polymerase chain reaction. Hybridization studies demonstrated the existence of homology between Escherichia coli and Bacillus megaterium beta-subunit probes at the streptococcal DNA level. Highly degenerate primers, based on the E. coli and B. megaterium amino acid (aa) sequences, were used to amplify the homologues in Streptococcus mutans, S. sanguis and S. sobrinus. The 600 bp fragment from S. sobrinus has been cloned and its nucleotide (nt) sequence determined. Comparison of its nt and deduced aa sequence to that of E. coli and B. megaterium reveals a high degree of homology at the aa level.

The F1-type ATPase in anaerobic Lactobacillus casei

An ATPase from anaerobic Lactobacillus casei has been isolated and 100-times purified. The 400 kDa enzyme molecule was found to have a hexagonal structure 10 nm in diameter composed of at least six protein masses. SDS-electrophoresis reveals four or, under certain conditions, five types of subunit, of apparent molecular masses 57 (alpha), 55 (beta), 40 (gamma), 22 (delta) and 14 (epsilon) kDa with stoichiometry of 3 alpha, 3 beta, gamma, delta, epsilon. The following features resembling F1-ATPases from other sources were found to be inherent in the solubilized L. casei ATPase. (i) Detachment from the membrane desensitizes ATPase to low DCCD concentrations and sensitizes it to water-soluble carbodiimide. (ii) Soluble ATPase is inhibited by Nbf chloride and azide, is resistant to SH-modifiers and is activated by sulfite and octyl glucoside, the activating effect being much stronger than in the case of the membrane-bound ATPase. Substrate specificity of the enzyme is also similar to that of other factors F1. Divalent cations strongly activate the soluble enzyme when added at a concentration equal to that of ATP. An excess of Mn2+, Mg2+ or Co2+ inhibits ATPase activity of F1, whereas that of Ca2+ induces its further activation. No other F1-like ATPases are found in L. casei. It is concluded that this anaerobic bacterium possesses a typical F1-ATPase similar to those in mitochondria, chloroplasts, aerobic and photosynthetic eubacteria.

Negative staining of proteins

Negative staining, some closely related alternative preparation techniques and radiation stability are considered. An attempt is made to clarify the mechanism of action and ultimate resolution limit of negative staining. The results of electron diffraction investigation of thermitase microcrystals embedded in glucose and glucose + stains are presented. It is shown that at doses not exceeding 10 electrons/nm2 electron diffraction from thermitase crystals demonstrate diffraction fields up to 0.2 nm. When adding heavy-atom salts to glucose or using negative staining, the relative intensities of reflections change and electron diffraction patterns for every type of heavy-atom additive (or negative stain) have their specific features. Such characteristic changes of reflection intensities indicate specific interaction of these additives (or stains) with the object. In the case of electron diffraction from the crystals stained using the routine negative staining technique the ordering was preserved down to 0.4-0.5 nm. Increasing the dose up to the normal value results in fading of distant reflections. Thus, negative staining with radiation doses less than the critical one could yield resolution down to 0.4 nm. Yet, the structure may change due to interaction with the stain. Nevertheless, the possibility that such resolution could be obtained for a limited number of objects should not be excluded. Some examples of the application of negative staining for investigation of quaternary and domain structure of proteins (nitrogenase, glutamine synthetase, mitochondrial ATP-synthase, membrane monooxygenase enzymes), tubular and two-dimensional protein crystals (catalase, phosphorylase, HWV protein, hydrogenase), as well as ribosomes and bacteriophages are given in the review.

The chloroplast genes encoding subunits of the H(+)-ATP synthase

Three CF1 and three CF0 subunits of the chloroplast H(+)-ATP synthase are encoded on the chloroplast genome. The chloroplast atp genes are organized as two operons in plants but not in the green alga, Chlamydomonas reinhardtii. The atpBE or β operon shows a relatively simple organisation and transcription pattern, while the atpIHFA or α operon is transcribed into a large variety of mRNAs. The atp genes are related to those of cyanobacteria and, more distantly, to those of non-photosynthetic bacteria such as E. coli, suggesting a common origin of most F1F0 ATP synthase subunits. Both the chloroplast and cyanobacterial ATP synthases have four F0 subunits, not three as in the E. coli complex. The proton pore of the CF0 is proposed to be formed by the interaction of subunits III and IV.

The F1-ATPase from Streptococcus cremoris: isolation, purification and partial characterization

1. The F1-ATPase from the plasma membrane of Streptococcus cremoris HA was released by low ionic shock wash and purified by gel filtration and ion exchange chromatography. 2. The specific activity of the purified F1-ATPase was 25.8 mumol Pi/mg protein/min. 3. Km for ATP was 0.80 mM, and Ki for ADP as a competetive inhibitor 0.40 mM. 4. The purified F1-ATPase consisted of five subunits, alpha, beta, gamma, delta and epsilon, with molecular masses of 47.0, 45.0, 29.5, 22.0 and 13.0 kDa, respectively. 5. The isoelectric point of the enzyme complex was found to be 4.4.

Electron microscopy and image analysis of the complexes I and V of the mitochondrial respiratory chain

The results of Section IV can be summarized in a simple ATP synthase model. This model implies that either the alpha or the beta subunits must be closer to the membrane. The work of Gao and Bauerlein (1987) indicates that the alpha subunits are closer to the membrane. Although the overall structure is more or less clear, important questions need to be clarified. First, the number and the arrangement of the subunits in the F0 part must be known. Second, the exact shape of F1, and particularly the shape of the large subunits needs to be elucidated. On the basis of fluorescence resonance energy transfer measurements by McCarty and Hammes (1987), a model was presented showing large oblong subunits. Such 'banana-shaped' subunits, which are also presented in the many phantasy models (e.g. Walker et al., 1982), are very unlikely in view of the electron microscopical results, although the large subunits do not need to be exactly spherical. The third and most interesting central question is on the changes in the structure that take place during the different steps in the synthesis of ATP. It can now be taken as proven that the energy transmitted to the ATP synthase is used to induce a conformational change in the latter enzyme, in such a way as to bring about the energy-requiring dissociation of already synthesized ATP (Penefsky, 1985 and reviewed in Slater, 1987). But the way in which the three parts of the ATP synthase are involved is completely unknown. It is rather puzzling that such a long distance exists between the catalytic sites, which are on the interface of the alpha and beta subunits and the F0 part where the proton movements occur, which, according to Mitchell's theory (1961), is the driving force for the synthesis of ATP. Perhaps alternative mechanisms such as the collision hypothesis formulated by Herweijer et al. (1985) are more realistic in describing the mechanism of ATP synthesis. It would bring the complexes I and V close together, not only in the artificial way treated in this paper, but in a useful way for energy conversion.

Subunit composition of the H+-ATPase complex from anaerobic bacterium Lactobacillus casei

The H+-ATPase complex has been isolated from the membranes of the anaerobic bacterium Lactobacillus casei by two independent methods. 1. The crossed-immunoelectrophoresis of the 14C-labelled ATPase complex against antibodies to a highly purified soluble ATPase has been used. The subunit composition of the complex has been established by autoradiography. The soluble part of L. casei ATPase, in contrast to coupling factor F1-ATPases of aerobic bacteria, chloroplasts and mitochondria which include two kinds of large subunit (alpha and beta), consists of one kind of large subunit with a molecular mass of 43 kDa. Moreover, a minor polypeptide of 25 kDa has been found in the soluble ATPase. Factor F0 of L. casei ATPase complex consists of a 16-kDa subunit and two subunits with molecular masses less than 14 kDa. 2. A dicyclohexylcarbodiimide-sensitive ATPase complex has been isolated from L. casei membranes by treating them with a mixture of octyl glucoside and sodium cholate. The complex, purified by centrifugation on a sucrose density gradient, contains the main subunits with molecular masses of 43 kDa, 25 kDa and 16 kDa and a dicyclohexylcarbodiimide-binding subunit with a molecular mass less than 14 kDa.

Some peculiarities of functioning of H+-ATPase from the membranes of the anaerobic bacterium Lactobacillus casei

Radiation inactivation analysis gave the target sizes of 176 +/- 5 kDa and 275 +/- 33 kDa for ATPase from anaerobic Lactobacillus casei and aerobic Micrococcus luteus bacteria respectively. The values are close to the known molecular masses of the enzymes. Thus, to function the L. casei ATPase, like the F1-ATPases, requires a complete structure composed of all the enzyme subunits. L. casei ATPase is inhibited by 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole owing to modification of an amino acid residue(s) with pK greater than 8.5. L. casei ATPase consists of six identical subunits and differs from alpha 3 beta 3 gamma delta epsilon-type F1-ATPases in a number of catalytic properties. Namely, ATP hydrolysis under the 'unisite' conditions proceeds at a relatively high rate suggesting the absence of cooperative interactions between the catalytic sites. Contrary to mitochondrial F1-ATPase. L. casei ATPase does not form an inactive complex with ADP. These findings imply essential differences in the operating mechanism for L. casei ATPase and F1 ATPase.

Electron-microscopic studies on location of SH-groups in mitochondrial F1-ATPase using a ferritin label

A new approach has been suggested for electron-microscopic study of the structure of mitochondrial F1-ATPase based on ferritin labeling. By means of sequential treatment with 2-iminothiolane and Nbs2 we obtained a modified ferritin (NbsSPrCNH-Ft) able to react with SH-groups of proteins and to form conjugates in which the protein and ferritin are bound by disulfide bonds. An electron-microscopic investigation of the negatively stained preparations of mitochondrial F1-ATPase, preincubated with modified ferritin, revealed such enzyme-ferritin conjugates. In case of modified ferritin, containing 360 mol SH-groups per mol protein, and F1-ATPase, pretreated with N-ethylmaleimide and then with dithiothreitol, conjugates were obtained in which ferritin molecules are bound to several (as many as four) of the six protein masses, comprising a bilayer molecule of the enzyme. Taking into consideration the biochemical data on the location of accessible SH-groups (only in alpha, gamma or epsilon subunits), it is inferred from the results obtained that one of the protein masses is a complex between beta subunit and at least one of the minor subunits located partially on the molecule's external side. This indicates the nonequivalence of different copies of the major subunits. Averaged images of the particles of the F1-F0 complex from bovine heart mitochondria and bacteria Micrococcus lysodeicticus were obtained. It was found that F0 component is bound to two adjacent protein masses of the F1-ATPase molecule. It is suggested that this binding may be due the nonequivalency of single-type major subunits.

Membrane-associated and solubilized ATPases of Streptococcus mutans and Streptococcus sanguis

The proton-translocating, membrane ATPases of oral streptococci have been implicated in cytoplasmic pH regulation, acidurance, and cariogenicity. Membranes were isolated from Streptococcus mutans GS-5 and Streptococcus sanguis NCTC 10904 following salt-induced lysis of cells treated with lysozyme and mutanolysin. The ATPase activities of these membranes were 1.8 and 1.1 units per mg membrane protein, respectively. F1 ATPases were washed free from the membranes and purified by fast protein liquid chromatography (FPLC). Hydrolytic activities of the F1 ATPases were maximal at pH values between 6.0 and 6.6, whereas the membrane-bound enzymes had pH maxima of 7.5 (S. sanguis) and 6.0 (S. mutans). The F1 ATPases of the streptococci were similar to the well-characterized enzyme of Escherichia coli; they consisted of five different polypeptides and had apparent, aggregate molecular weights of from 335 to 350 Kd. The membrane-bound ATPases were characterized biochemically and found to be similar to those of proton-translocating ATPases of E. coli and Streptococcus faecalis. Km values for the membranes with respect to ATP were found to be 0.9 and 1.0 mmol/L for S. mutans and S. sanguis, respectively. Both enzymes had specificities for purine triphosphates and were active with a variety of divalent cations, although optimal activity occurred with ATP and Mg. The membrane-associated enzymes were sensitive to the inhibitors dicyclohexylcarbodiimide (DCCD) and azide, but insensitive to ouabain and vanadate.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of the N,N'-dicyclohexylcarbodiimide resistant ATPase of Streptococcus cremoris

1. The specific activity of the membrane-bound ATPase of Streptococcus cremoris HA was 1.30 mumol Pi/mg protein/min. 2. Km for ATP as substrate was 0.8 mM. 3. The pH optimum was 8.0 at +37 degrees C. 4. The ATPase was maximally activated with Mg2+/ATP molar ratio of 1:2. 5. Cations activated the enzyme in order: Mg2+ greater than Co2+ greater than Mn2+ greater than Zn2+ greater than Ca2+ greater than K+ greater than Na+. 6. The enzyme was inhibited by oligomycin (27-77%), sodium azide (13-33%) and ouabain (15-22%). N,N'-dicyclohexylcarbodiimide had no effect on the enzyme activity.

Primary structure and subunit stoichiometry of F1-ATPase from bovine mitochondria

The enzyme complex F1-ATPase has been isolated from bovine heart mitochondria by gel filtration of the enzyme released by chloroform from sub-mitochondrial particles. The five individual subunits alpha, beta, gamma, delta and epsilon that comprise the complex have been purified from it, and their amino acid sequences determined almost entirely by direct protein sequence analysis. A single overlap in the gamma-subunit was obtained by DNA sequence analysis of a complementary DNA clone isolated from a bovine cDNA library using a mixture of 32 oligonucleotides as the hybridization probe. The alpha, beta, gamma, delta and epsilon subunits contain 509, 480, 272, 146 and 50 amino acids, respectively. Two half cystine residues are present in the alpha-subunit and one in each of the gamma- and epsilon-chains; they are absent from the beta- and delta-subunits. The stoichiometry of subunits in the complex is estimated to be alpha 3 beta 3 gamma 1 delta 1 epsilon 1 and the molecular weight of the complex is 371,135. Mild trypsinolysis of the F1-ATPase complex, which has little effect on the hydrolytic activity of the enzyme, releases peptides from the N-terminal regions of the alpha- and beta-chains only; the C-terminal regions are unaffected. Sequence analysis of the released peptides demonstrates that the N terminals of the alpha- and beta-chains are ragged. In 65% of alpha-chains, the terminus is pyrrolidone carboxylic acid; in the remainder this residue is absent and the chains commence at residue 2, i.e. lysine. In the beta-subunit a minority of chains (16%) have N-terminal glutamine, or its deamidation product, glutamic acid (6%), or the cyclized derivative, pyrrolidone carboxylic acid (5%). A further 28% commence at residue 2, alanine, and 45% at residue 3, serine. The delta-chains also are heterogeneous; in 50% of chains the N-terminal alanine residue is absent. The sequences of the alpha- and beta-chains show that they are weakly homologous, as they are in bacterial F1-ATPases. The sequence of the bovine delta-subunit of F1-ATPase shows that it is the counterpart of the bacterial epsilon-subunit. The bovine epsilon-subunit is not related to any known bacterial or chloroplast H+-ATPase subunit, nor to any other known sequence. The counterpart of the bacterial delta-subunit is bovine oligomycin sensitivity conferral protein, which helps to bind F1 to the inner mitochondrial membrane.(ABSTRACT TRUNCATED AT 400 WORDS)

Electron microscopy of beef heart mitochondrial F1-ATPase

The quaternary structure of isolated and membrane-bound F1-ATPase (submitochondrial particles) has been studied by electron microscopy. A model of the molecule has been proposed: six protein masses are arranged in two layers approximately at the vertices of a triangular antiprism. Computer averaging of the images showed that the frontal view of the molecule can be approximately characterized by mirror plane symmetry.