The alpha regulatory subunit of the mitochondrial F1-ATPase complex is a heat-shock protein. Identification of two highly conserved amino acid sequences among the alpha-subunits and molecular chaperones

Interaction between extracellular ATP5A1 and LPS alleviates LPS-induced neuroinflammation in mice

Neuroinflammation is one of the main causes of Alzheimer's disease (AD). The presence of Lipopolysaccharide (LPS) in senile plaques (SP) of AD suggests that it plays a role in AD pathogenesis. ATP5A1 (F1F0-ATP synthase F1 α subunit) is abundant in SP. Further, the protein has recently been found to have an anti-infection role in zebrafish embryos. In the present study, we observed that LPS levels were higher in the brains of APP/PS1 mice than in control mice, and LPS co-localised with ATP5A1 in amyloid plaques. The interaction of recombinant ATP5A1(rATP5A1) and LPS was evidenced by cellular thermal shift assay and enzyme-linked immunosorbent assay-based binding assay in vitro. Neuroinflammation in the brain of a mouse model was induced by intracerebroventricular injection of LPS. The addition of rATP5A1 relieved LPS-induced reduction of spontaneous locomotor ability, depressive-like behaviour, and working memory impairment. Furthermore, rATP5A1 suppressed the activation of astrocytes and microglia, IL-1β accumulation, and tau phosphorylation induced by LPS. Taken together, findings suggest that ATP5A1 is involved in the regulation of LPS-mediated neuroinflammation in AD.

Dehydroepiandrosterone, molecular chaperones and the epigenetics of primate longevity

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulphate (DHEAS) are the most abundant circulating adrenal steroid hormones. The plasma level of DHEAS correlates with longevity in primates and varies during human development with a maximum in early adulthood and a marked decline during aging. DHEA promotes the expression of molecular chaperones which are housekeeping stress response proteins essential for the processes of folding, translocation, maintenance and repair of proteins, RNA and DNA, as well as for homeostasis, immune response and cancer resistance. The level of chaperone expression correlates with longevity and shows a decline during aging. DHEA-induced promotion of chaperone expression could contribute to the epigenetic evolution of primate longevity.

Thermal sensation and cell adaptability

Whole person adaptive comfort is discussed with reference to recent findings in molecular scale systems biology. The observations are upscaled to hypotheses relating to less traditional interpretations of thermal processes, which have new implications for indoor climate management and design. Arguments are presented for a revision of current focus, model and paradigm. The issue is seen as a problem of integrating theoretical development, conceptual modeling and as an investigation of the extent to which environments and acclimatization can be used to achieve individual fitness and health, not only at the subjective comfort level, as hitherto promoted. It is argued that there are many questions yet to be asked about adaptability before celebrating a particular adaptive state.

β-amyloid peptide binds and regulates ectopic ATP synthase α-chain on neural surface

Accumulation of the amyloid β protein (Aβ) in the brain is an important step in the pathogenesis of Alzheimer's disease. Many molecules could bind with Aβ, among which some molecules mediate Aβ neuronal toxicity. Thus, it is of interest to study the binding proteins of Aβ, and the functions that might be affected by Aβ. In the present study, we observed that accumulation of α-subunit of ATP synthase is associated with aggregates of Aβ proteins in amyloid plaques of amyloid precursor protein/presennillin-1 transgenic mice, and identified the α-subunit of ATP synthase as one of the Aβ binding proteins on the plasma membrane of neural cells by Western blot and mass spectrometry. In order to evaluate the consequences of the interaction between Aβ and surface α-subunit of ATP synthase, the extracellular ATP generation was analyzed, which showed that aggregated Aβ partially inhibited the extracellular generation of ATP, but was unable to significantly induce a decrease in cell surface ATP synthase α on neurons. These results suggest that the cell surface ATP synthase α is a binding protein for Aβ on neural cells, the functional inhibition of surface ATP synthase might be involved in machinery of brain malfunction in Aβ-mediated pathogenesis of Alzheimer's disease.

Thiourea modulates the expression and activity profile of mtATPase under salinity stress in seeds of Brassica juncea

BACKGROUND AND AIMS

Large areas of the globe are becoming saline due to evapotranspiration and poor irrigation practices, and sustainability of agriculture is being seriously affected. Thiourea (TU) has been identified as an effective bioregulator imparting stress tolerance to crops. The molecular mechanisms involved in the TU-mediated response are considered in this study.

METHODS

Differential display was performed in order to identify TU-modulated transcripts in Brassica juncea seeds exposed to various treatments (distilled water; 1 m NaCl; 1 m NaCl + 500 p.p.m. TU). The differential regulation of these transcripts was validated by quantitative real-time PCR.

KEY RESULTS

Thiourea treatment maintained the viability of seeds exposed to NaCl for 6 h. Expression analysis showed that the transcript level of alpha, beta, gamma, delta and epsilon subunits of mitochondrial ATPase (mtATPase) varied in seeds subjected to the different treatments for 1 h: expression level was significantly altered by 1 m NaCl relative to controls; however, in the NaCl + TU treatment it reverted back in an integrated manner. Similar results were obtained from time-kinetics studies of beta and delta subunits in roots of 8-d-old seedlings. These observations were also confirmed by the mtATPase activity from isolated mitochondria. The reversal in the expression and activity profile of mtATPase through the application of a bioregulator such as TU is a novel finding for any plant system.

CONCLUSIONS

The results suggest that TU treatment maintains the integrity and functioning of mitochondria in seeds as well as seedlings exposed to salinity. Thus, TU has the potential to be used as an effective bioregulator to impart salinity tolerance under field conditions, and might prove to be of high economic importance by opening new avenues for both basic and applied research.

The F1F0-ATPase of Bifidobacterium animalis is involved in bile tolerance

Adaptation and tolerance to bile stress are important factors for the survival of bifidobacteria in the intestinal tract. Bifidobacterium animalis is a probiotic microorganism which has been largely applied in fermented dairy foods due to its technological properties and its health-promoting effects for humans. The effect of the presence of bile on the activity and expression of F(1)F(0)-ATPase, the pool of ATP and the intracellular pH of B. animalis IPLA 4549 and its mutant with acquired resistance to bile B. animalis 4549dOx was determined. The bile-resistant mutant tolerated the acid pH better than its parent strain. Bile induced the expression of the F(1)F(0)-ATPase and increased the membrane-bound H(+)-ATPase activity, in both parent and mutant strains. In acidic conditions (pH 5.0), the expression and the activity of this enzyme were higher in the mutant than in the parent strain when cells were grown in the absence of bile. Total ATP content was higher for the mutant in the absence of bile, whereas the presence of bile induced a decrease of intracellular ATP levels, which was much more pronounced for the parent strain. At pH 4.0, and independently on the presence or absence of bile, the mutant showed a higher intracellular pH than its parent strain. These findings suggest that the bile-adapted B. animalis strain is able to tolerate bile by increasing the intracellular ATP reserve, and by inducing proton pumping by the F(1)F(0)-ATPase, therefore tightly regulating the internal pH, and provide a link between the physiological state of the cell and the response to bile.

Rpm2, the protein subunit of mitochondrial RNase P in Saccharomyces cerevisiae, also has a role in the translation of mitochondrially encoded subunits of cytochrome c oxidase

RPM2 is a Saccharomyces cerevisiae nuclear gene that encodes the protein subunit of mitochondrial RNase P and has an unknown function essential for fermentative growth. Cells lacking mitochondrial RNase P cannot respire and accumulate lesions in their mitochondrial DNA. The effects of a new RPM2 allele, rpm2-100, reveal a novel function of RPM2 in mitochondrial biogenesis. Cells with rpm2-100 as their only source of Rpm2p have correctly processed mitochondrial tRNAs but are still respiratory deficient. Mitochondrial mRNA and rRNA levels are reduced in rpm2-100 cells compared to wild type. The general reduction in mRNA is not reflected in a similar reduction in mitochondrial protein synthesis. Incorporation of labeled precursors into mitochondrially encoded Atp6, Atp8, Atp9, and Cytb protein was enhanced in the mutant relative to wild type, while incorporation into Cox1p, Cox2p, Cox3p, and Var1p was reduced. Pulse-chase analysis of mitochondrial translation revealed decreased rates of translation of COX1, COX2, and COX3 mRNAs. This decrease leads to low steady-state levels of Cox1p, Cox2p, and Cox3p, loss of visible spectra of aa(3) cytochromes, and low cytochrome c oxidase activity in mutant mitochondria. Thus, RPM2 has a previously unrecognized role in mitochondrial biogenesis, in addition to its role as a subunit of mitochondrial RNase P. Moreover, there is a synthetic lethal interaction between the disruption of this novel respiratory function and the loss of wild-type mtDNA. This synthetic interaction explains why a complete deletion of RPM2 is lethal.

Heat stress contributes to the enhancement of cardiac mitochondrial complex activity

Hyperthermic stress is known to protect against myocardial dysfunction after ischemia-reperfusion injury. It is unclear however, what energetic mechanisms are affected by the molecular adaptation to heat stress. We hypothesized that mild hyperthermic stress can increase mitochondrial respiratory enzyme activity, affording protection to mitochondrial energetics during prolonged cardiac preservation for transplantation. Rat hearts were excised after heat-stress or sham treatment and subjected to cold cardioplegic arrest and ischemia followed by reperfusion in an ex vivo perfusion system. Cardiac function, mitochondrial respiratory, and complex activities were assessed before and after ischemia. Heat shock protein (Hsp 32, 60, and 72) expression was increased in heat-stressed hearts. This was associated with increased mitochondrial complex activities in heat-stress versus sham-treated groups for complex I-V. During reperfusion, higher complex activities and respiratory control ratios were observed in heat-stressed versus sham-treated groups. Recovery of ventricular function was improved in heat-stressed hearts. Furthermore, mitochondria in reperfused heat-stressed myocardium exhibited intact membranes with packed, parallel, lamellar cristae, whereas in sham-treated myocardium, mitochondria were severely disrupted. This study provides the first evidence of heat-stress-mediated enhancement of mitochondrial energetic capacity. This is associated with increased tolerance to ischemia-reperfusion injury. Protection by heat stress against myocardial dysfunction may be partially due to enhancement of mitochondrial energetics.

Heat shock proteins and inflammatory acne vulgaris: molecular cloning, overexpression and purification of a propionibacterium acnes GroEL and DnaK homologue

Propionibacterium acnes is associated with inflammatory acne. The genes encoding two putative mediators of inflammation, the heat shock proteins GroEL and DnaK, were cloned from this organism and sequenced. groEL and dnaK encode proteins of 56.8 and 66.4 kDa, respectively, which show a high degree of homology (>75% similarity) to the GroEL and DnaK proteins of mycobacteria and streptomycetes. The promoter regions of both genes contain inverted repeat sequences believed to be involved in the transcriptional regulation of heat shock genes. Recombinant P. acnes GroEL and DnaK were overexpressed in Escherichia coli with C-terminal histidine tags. The recombinant proteins were purified from E. coli by metal affinity chromatography. These proteins will now be used in immunological investigations to determine their role in inflammatory acne.

ASC1/RAS2 suppresses the growth defect on glycerol caused by the atp1-2 mutation in the yeast Saccharomyces cerevisiae

To better define the regulatory role of the F(1)-ATPase alpha-subunit in the catalytic cycle of the ATP synthase complex, we isolated suppressors of mutations occurring in ATP1, the gene for the alpha-subunit in Saccharomyces cerevisiae. First, two atp1 mutations (atp1-1 and atp1-2) were characterized that prevent the growth of yeast on non-fermentable carbon sources. Both mutants contained full-length F(1)alpha-subunit proteins in mitochondria, but in lower amounts than that in the parental strain. Both mutants exhibited barely measurable F(1)-ATPase activity. The primary mutations in atp1-1 and atp1-2 were identified as Thr(383) --> Ile and Gly(291) --> Asp, respectively. From recent structural data, position 383 lies within the catalytic site. Position 291 is located near the region affecting subunit-subunit interaction with the F(1)beta-subunit. An unlinked suppressor gene, ASC1 (alpha-subunit complementing) of the atp1-2 mutation (Gly(291) --> Asp) restored the growth defect phenotype on glycerol, but did not suppress either atp1-1 or the deletion mutant Deltaatp1. Sequence analysis revealed that ASC1 was allelic with RAS2, a G-protein growth regulator. The introduction of ASC1/RAS2 into the atp1-2 mutant increased the F(1)-ATPase enzyme activity in this mutant when the transformant was grown on glycerol. The possible mechanisms of ASC1/RAS2 suppression of atp1-2 are discussed; we suggest that RAS2 is part of the regulatory circuit involved in the control of F(1)-ATPase subunit levels in mitochondria.

The petite mutation in yeasts: 50 years on

Fifty years ago it was reported that baker's yeast, Saccharomyces cerevisiae, can form "petite colonie" mutants when treated with the DNA-targeting drug acriflavin. To mark the jubilee of studies on cytoplasmic inheritance, a review of the early work will be presented together with some observations on current developments. The primary emphasis is to address the questions of how loss of mtDNA leads to lethality (rho 0-lethality) in petite-negative yeasts and how S. cerevisiae tolerates elimination of mtDNA. Recent investigation have revealed that rho 0-lethality can be suppressed by specific mutations in the alpha, beta, and gamma subunits of the mitochondrial F1-ATPase of the petite-negative yeast Kluyveromyces lactis and by the nuclear ptp alleles in Schizosaccharomyces pombe. In contrast, inactivation of genes coding for F1-ATPase alpha and beta subunits and disruption of AAC2, PGS1/PEL1, and YME1 genes in S. cerevisiae convert this petite-positive yeast into a petite-negative form. Studies on nuclear genes affecting dependence on mtDNA have provided important insight into the functions provided by the mitochondrial genome and the maintenance of structural and functional integrity of the mitochondrial inner membrane.

In vivo heat shock protects rat myocardial mitochondria

Heat shock (HS)/stress proteins (HSP) provide protection from a variety of stresses other than HS, including oxidative stress and mitochondria have been implicated as the target of HS-related protection in stressed cultured cells. Here we investigated whether mitochondria also are targets for the HS-mediated protection in vivo. Sprague Dawley rats were exposed, or not, to HS (41 degrees C, 15 min). After a 21 h recovery period, hearts were excised and perfused with or without H2O2 (0.15 mM). Myocardial mitochondria were then isolated, and their oxygen consumption was analyzed. HS prevented H2O2-induced alterations in state 3 respiration while increasing the expression of Hsp70 and heme oxygenase (HO). Thus, in vivo HS protects rat myocardial mitochondrial respiration against the deleterious effects of oxidative injury, a protection relating to Hsp70 and/or HO and targeting state 3 respiration.

Variable peroxisomal and mitochondrial targeting of alanine: glyoxylate aminotransferase in mammalian evolution and disease

Under the putative influence of dietary selection pressure, the subcellular distribution of alanine:glyoxylate aminotransferase 1 (AGT) has changed on many occasions during the evolution of mammals. Depending on the particular species, AGT can be found either in peroxisomes or mitochondria, or in both peroxisomes and mitochondria. This variable localization depends on the differential expression of N-terminal mitochondrial and C-terminal peroxisomal targeting sequences by the use of alternative transcription and translation initiation sites. AGT is peroxisomal in most humans, but it is mistargeted to the mitochondria in a subset of patients suffering from the rare hereditary disease primary hyperoxaluria type 1. Mistargeting is due to the unlikely combination of a normally occurring polymorphism that generates a functionally weak mitochondrial targeting sequence and a disease-specific mutation which, in combination with the polymorphism, inhibits AGT dimerization. The mechanisms by which AGT can be targeted differentially to peroxisomes and/or mitochondria highlight the different molecular requirements for protein import into these two organelles.

Gene structure and cell type-specific expression of the human ATP synthase alpha subunit

The gene structure of the human ATP synthase alpha subunit (hATP1) was determined by cloning and sequencing. This gene is approximately 14 kbp in length and contains 12 exons interrupted by 11 introns. Mapping of the clones of hATP1 and Southern blot analysis of the genomic gene showed that there were a single copy of bona fide hATP1 gene and two pseudogenes. Primer extension and S1 mapping analysis showed the presence of multiple transcription initiation sites of the hATP1 gene. No TATA box or CAAT box was found near the transcription initiation sites. Comparison with the bovine gene showed that the 5'-flanking region of the hATP1 gene has an unconserved guanine-cytosine (GC) rich region, including several binding motifs of transcriptional factors, such as Sp1, AP-2, and GCF. By functional assay of gene expression, the basal promoter activity was located near the GC rich region. Comparison of the 5'-upstream region of the hATP1 gene with those of the genes for bovine ATP synthase alpha, human beta, and human gamma subunits indicated three common sequences, suggesting that putative cis-elements coordinate the expressions of the three subunit genes for the ATP synthase. The enhancer activities derived from the 5'-deletion mutants of a hATP1-CAT chimeric gene were different in cell lines from four different human tissues, suggesting the existence of cell type-specific gene regulation.

Genetic and biochemical analysis of Salmonella typhimurium FliI, a flagellar protein related to the catalytic subunit of the F0F1 ATPase and to virulence proteins of mammalian and plant pathogens

FliI is a Salmonella typhimurium protein that is needed for flagellar assembly and may be involved in a specialized protein export pathway that proceeds without signal peptide cleavage. FliI shows extensive sequence similarity to the catalytic beta subunit of the F0F1 ATPase (A. P. Volger, M. Homma, V. M. Irikura, and R. M. Macnab, J. Bacteriol. 173:3564-3572, 1991). It is even more similar to the Spa47 protein of Shigella flexneri (M. M. Venkatesan, J. M. Buysse, and E. V. Oaks, J. Bacteriol. 174:1990-2001, 1992) and the HrpB6 protein of Xanthomonas campestris (S. Fenselau, I. Balbo, and U. Bonas, Mol. Plant-Microbe Interact. 5:390-396, 1992), which are believed to play a role in the export of virulence proteins. Site-directed mutagenesis of residues in FliI that correspond to catalytically important residues in the F1 beta subunit resulted in loss of flagellation, supporting the hypothesis that FliI is an ATPase. FliI was overproduced and purified almost to homogeneity. It demonstrated ATP binding but not hydrolysis. An antibody raised against FliI permitted detection of the protein in wild-type cells and an estimate of about 1,500 subunits per cell. An antibody directed against the F1 beta subunit of Escherichia coli cross-reacted with FliI, confirming that the proteins are structurally related. The relationship between three proteins involved in flagellar assembly (FliI, FlhA, and FliP) and homologs in a variety of virulence systems is discussed.

Added subunit beta of CF1 as well as gamma/delta/epsilon restore photophosphorylation in partially CF1-depleted thylakoids

We investigated the ability of subunits beta, gamma, delta, and epsilon of CF1, the F1-ATPase of chloroplasts, to interact with exposed CF0 in EDTA-treated, partially CF1-depleted thylakoid membranes. We measured the ability of subunits beta, gamma, delta, and epsilon to stimulate the rate of photophosphorylation under continuous light and, for subunit beta, also the ability to diminish the proton leakage through exposed CF0 by deceleration of the decay of electrochromic absorption transients under flashing light. The greatest effect was caused by subunit beta, followed by gamma/delta/epsilon. Pairwise combinations of gamma, delta, and epsilon or each of these subunits alone were only marginally effective. Subunit gamma from the thermophilic bacterium PS 3 in combination with chloroplast delta and epsilon was as effective as chloroplast gamma. The finding that the small CF1 subunits in concert and the beta subunit by itself specifically interacted with the exposed proton channel CF0, qualifies the previous concept of subunit delta acting particularly as a plug to the open CF0 channel. The interactions between the channel and the catalytic portion of the enzyme seem to involve most of the small, and at least beta of the large subunits.

Low translational efficiency of the F1-ATPase beta-subunit mRNA largely accounts for the decreased ATPase content in brown adipose tissue mitochondria

The half-life of the F1-ATPase beta-subunit (F1-beta) mRNA in ATPase-poor brown adipose tissue (BAT) (t1/2 = 9.5 h) was found to be 3-7-fold shorter than in liver (t1/2 = 27 h) and heart (t1/2 = 63 h) of mice. When translated in reticulocyte lysate, a 2-3-fold lower efficiency appeared with F1-beta mRNA from BAT than from other tissues. The in vitro synthesized F1-beta protein precursors of BAT, liver and heart origin were imported and processed by mouse liver mitochondria with equal efficiency. The results indicate that the pool of abundant F1-beta mRNA in BAT is not fully translatable, most likely due to its low metabolic stability.

Distribution of RNA editing sites in Oenothera mitochondrial mRNAs and rRNAs

To investigate whether RNA editing in plant mitochondria modifies structural RNAs as well as protein-coding RNAs we compared the genomic-encoded information with the respective transcripts of several genes in Oenothera. The genes analysed are the 5S, 18S and 26 S rRNAs, the alpha-subunit of ATPase (atpA), cytochrome b (cytb), orfB, which is located upstream of cytochrome oxidase subunit III, and the respective leader, trailer and spacer sequences. All open reading frames were found to be edited to some degree. The atpA coding region has the least edited mRNA in Oenothera mitochondria, with only four nucleotides altered in the 1533 nucleotide open reading frame. From this analysis we conclude that frequent RNA editing is indicative of functional protein coding regions in plant mitochondria. The extensive editing in orfB, for example, suggests that this orf codes for a mitochondrial protein. No RNA editing event was found in the 5S rRNA or in the 1824 nucleotides analysed of the 18S rRNA, but two nucleotides were found to be altered in the 1970 nucleotides compared for the 26S rRNA. One nucleotide alteration has changed C to U, the other in reverse U to C. However, only one of five cDNA clones covering this region shows the modifications, similar to many silent editing events in open reading frames. RNA editing in the structural RNAs thus does not seem to be essential for their function in the mitochondrial ribosome.

Gene structure of heat shock proteins 61KDa and 12KDa (thermophilic chaperonins) of thermophilic bacterium PS3

Heat shock proteins 60 (hsp60) and 10 (hsp10) are essential for the formation and restoration of many supramolecular structures. For reconstitution of these structures, we isolated stable hsps of 61kDa and 12kDa, which are similar to hsp60 and hsp10, respectively, from the supernatant fraction of thermophilic bacterium PS3 by ATP-Agarose chromatography. Using synthetic DNA of the deduced sequence, the 1.6kbp double stranded DNA encoding both proteins was obtained by the polymerase chain reaction (PCR). The complete sequence of the resulting reading frames showed high homology to those of the genes encoding GroEL (hsp60) and GroES (hsp10) of E. coli, and hsp60s and hsp10s of several other species. The genes for the 12K and 61K were present in the same operon. 61K was also partially similar to the F1 alpha subunit of thermophilic ATP synthase, which is highly reconstitutable to form the alpha beta complex.

Nucleotide sequence of a cDNA for the alpha subunit of human mitochondrial ATP synthase

A full length cDNA clone of the alpha subunit of mitochondrial ATP synthase (EC 3.6.1.34) has been isolated from a cDNA library prepared from LX-1 human tumor cells in the lambda-Zap vector. The clone is 1883 base pairs (bp) in length and contains a 1659 bp open reading frame encoding a polypeptide of 553 residues. The deduced amino acid sequence is highly homologous to ATP synthase from several other species.

Heat shock proteins and cell proliferation

Heat shock proteins (Hsps) carry out a number of essential functions in the cell. These functions could be utilized, in a developmentally regulated manner, to affect proteins necessary for cell growth and proliferation. Data showing Hsp involvement in cell proliferation under non-stress conditions are perhaps not altogether surprising in view of the important roles of Hsps in cell metabolism. In a number of cases stress can facilitate cell proliferation in cells which could otherwise not be amenable to this developmental pathway. It is proposed that Hsps could play an essential helper role in initiating this process.

Immunological detection of the mitochondrial F1-ATPase alpha subunit in the matrix of rat liver peroxisomes. A protein involved in organelle biogenesis?

Rat liver peroxisomes contain in their matrix the alpha-subunit of the mitochondrial F1-ATPase complex. The identification of this protein in liver peroxisomes has been achieved by immunoelectron microscopy and subcellular fractionation. No beta-subunit of the mitochondrial F1-ATPase complex was detected in the peroxisomal fractions obtained in sucrose gradients or in Nycodenz pelletted peroxisomes. The consensus peroxisomal targeting sequence (Ala-Lys-Leu) is found at the carboxy terminus of the mature alpha-subunit from bovine heart and rat liver mitochondria. Due to the dual subcellular localization of the alpha-subunit and to the structural homologies that exist between this protein and molecular chaperones [(1990) Biol. Chem. 265, 7713-7716] it is suggested that the protein should perform another functional role(s) in both organelles, plus to its characteristic involvement in the regulation of mitochondrial ATPase activity.