Universiẗat, Diss., 2003--Freiburg (Breisgau).

Although F1-ATPase is extremely conserved among organisms, a putative subunit p18 was identified in Trypanosoma brucei F1-ATPase complex. To explore its function in the procylic, bloodstream and dyskinetoplastic trypanosomes, three different RNAi cell lines were created. Upon p18 silencing the F1-moiety structural integrity was impaired suggesting that p18 is indeed a bona fide subunit of this complex. Since F1-ATPase is crucial for the bloodstream form survival, its potential inhibitor from the 4-oxopiperidine-3,5-dicarboxylates class (JK-11) was examined. JK-11 inhibited growth of the bloodstream trypanosomes, decreased mitochondrial membrane potential and reduced ATPase and ATP synthase activity in mitochondrial lysates. Our results suggest that JK-11 may act on FoF1-ATP synthase/ATPase and its inhibition may contribute to the cytotoxicity of this drug.

Living organisms rely on many different mechanisms to adapt to changes within their environment. Protein phosphorylation and dephosphorylation events are one such way cells can communicate to generate a response to environmental changes. In the Kennelly laboratory we hope to gain insight on phosphorylation events in the domain Archaea through the study of the acidothermophilic organism Sulfolobus solfataricus. Such findings may provide answers into evolutionary relationships and facilitate an understanding of phosphate transfer via proteins in more elaborate systems where pathway disturbances can lead to disease processes. A λ-phage expression library was generated from S. solfataricus genomic DNA. The immobilized expression products were probed with a purified protein kinase, SsoPK4, and radiolabeled ATP to identify potential native substrates. A protein fragment of the ORF sso0563, the catalytic A-type ATPase subunit A (AtpA), was phosphorylated by SsoPK4. Full length and truncated forms of AtpA were overexpressed in E. coli. Additional subunits of the ATPase were also overexpressed and ATPase activity reconstituted in vitro. Phosphoamino acid analysis and MS identified the phosphorylation sites on AtpA. Several variants of AtpA were derived via site-directed mutagenesis and assayed for ATPase activity. Chemical cross-linking was employed to determine possible ATPase subunit interactions; tryptic digests of AtpA and its mutant variants were performed to examine protein folding. The phosphorylated-mimic variant of AtpA, T98D, resulted in an inactive ATPase complex as determined by ATPase activity assays and native-PAGE indicating potential phosphoregulation by SsoPK4 on enzyme activity. Ultimately, any findings would need verification with in vivo studies. / Ph. D.

Malgré la relocalisation au noyau d'une majorité des gènes du procaryote ancestral à l'origine des mitochondries, une poignée de gènes réside encore dans l'organite après près de deux milliards d'années d'évolution. Les raisons du maintien d'un génome mitochondrial sont mal comprises. Je me suis intéressé à cette problématique via des expériences de relocalisation artificielle de gènes mitochondriaux chez la levure Saccharomyces cerevisiae. Nous avons réussi, pour la première, à exprimer de manière fonctionnelle depuis le noyau le gène ATP9 qui encode une petite protéine hydrophobe essentielle au canal à protons de l'ATP synthase. Majoritairement mitochondrial chez les eucaryotes, comme S.cerevisiae, ce gène est retrouvé dans le génome nucléaire de la majorité des métazoaires, des algues vertes chlorophycées et des champignons filamenteux ascomycètes tel que Podospora anserina. Nos résultats montrent que l'hydrophobicité de la sous-unité Atp9p doit être diminuée pour qu'elle puisse être importée dans la mitochondrie depuis le cytosol. Nous avons également identifié un certain nombre d'autres adaptations pour optimiser l'expression du gène ATP9 relocalisé. Il apparaît donc que si le transfert du gène ATP9 est en principe possible chez la levure, il s'agit d'un processus très complexe. Une telle évolution n'a donc que peu de chances de se produire et d'être maintenue par la sélection naturelle, à moins que le transfert du gène ATP9 au noyau ne confère quelque avantage à l'organisme. Nous avons confirmé cette hypothèse par une étude menée chez P.anserina où nous avons montré que la relocalisation au noyau du gène ATP9, qui s'est produite naturellement au cours de l'évolution, a permis la mise en place de régulations spécifiques permettant d'ajuster les besoins en ATP synthase au cours du cycle de vie de ce champignon. Les résultats de cette étude nous amènent à introduire une nouvelle hypothèse selon laquelle les variations de contenu en gènes des génomes mitochondriaux ne sont pas influencées uniquement par des contraintes au niveau de la structure de leur produits, mais aussi par le mode de vie de l'organisme. / Despite the nuclear relocation of most genes of the ancestral procaryotic genome which gave birth to mitochondria, a small set of genes still remains into the organite after 2 billions years of evolution. The reasons for this maintenance of mitochondrial genome are currently not clear. I studied these questions by experimenting artificial relocations of mitochondrial genes in the yeast Saccharomyces cerevisiae. We managed, for the first, to functionally express the ATP9 gene from the nucleus, which encodes a small hydrophobic essential subunit of the proton chanel of the ATP synthase. Mostly mitochondrial within eukaryotes like S.cerevisiae, this gene can be found in the nuclear genome in most metazoans, chlorophyceans green algae and ascomycota filamentous fungi like Podospora anserina. Our results show that the hydrophobicity of the Atp9p subunit has to be decreased to be imported into the mitochondria from the cytosol. We also identified some adaptations optimizing the expression of the relocated ATP9 gene. It seems that if the ATP9 gene relocation is possible within the yeast, yet it is a complex and difficult process. Such an evolution has only few chances to occur and to be maintained by natural selection, unless it could confer some advantage to the organism. We have confirmed this hypothesis in a study made on P.anserina, in which we showed that the natural ATP9 relocation to the nucleus that appeared during its evolution allowed the setting up of specific regulations modulating the ATP synthase needs during the life-cycle of this fungus. The results presented here lead us to introduce a new hypothesis postulating that the variations of the set of genes contained in the mitochondrial genome are influenced not only by the constraints generated by their products structure, but also by the lifestyle of the organism.

Dans un premier temps, je me suis intéressé à la sous-unité ε de l’ATP synthase mitochondriale chez la levure, un organisme qui se prête bien à l’étude des fonctions mitochondriales. Cette protéine fait partie d’un élément de l’ATP synthase appelé la tige centrale. Celui-ci permet de coupler le domaine translocateur de protons de cette enzyme (FO) à son secteur catalytique (F1) où l’ATP est synthétisé. En utilisant un système d’expression régulable (répressible par la doxycycline), j’ai montré qu’en l’absence de la sous-unité ε les secteurs F1 et FO ne sont plus couplés, avec pour résultat des fuites massives de protons à travers la membrane interne des mitochondries. J’ai ensuite montré que l’absence de la sous-unité ε peut être compensée par des mutations ralentissant l’activité du FO. Ces données permettent de conclure que la sous-unité ε est nécessaire au maintien de l’intégrité physique de l’ATP synthase lors de son fonctionnement. Dans un second temps, j’ai cherché à identifier de nouveaux facteurs intervenant dans la biogenèse du FO. Pour cela, j’ai utilisé un crible génétique où la survie des cellules de levure est conditionnée à des mutations inactivation le FO. Un millier d’isolats a été analysé. Les mutations ont été localisées dans les génomes mitochondrial et nucléaire. Dix-huit clones, issus de mutations n’affectant pas des facteurs connus pour être nécessaires à l’expression de l’ATP synthase, ont été entièrement séquencés. Plusieurs nouveaux systèmes cellulaires potentiellement impliqués dans la biogenèse du FO ont été identifiés. / At first, I am interested in the ε subunit of mitochondrial ATP synthase in yeast, an organism that is well suited for the study of mitochondrial functions. This protein is a part of the ATP synthase called central stalk. This allows the coupling of proton translocator domain of this enzyme (FO) to its catalytic domain (F1) where ATP is synthesized. Using a tetO expression system, I showed that in the absence of the ε subunit, F1 and FO domains are no longer coupled. It results in a massive proton leakage across the inner membrane of mitochondria. I then showed that the absence of the ε subunit can be compensated by mutations slowing the activity of FO. These data allow to conclude that the ε subunit is necessary to maintain the physical integrity of the ATP synthase for oxydative phosphorylation. Later, I tried to identify new factors involved in the biogenesis of the FO. For this, I used a genetic screen where the survival of yeast cells is conditioned by mutations inactivating the FO. About a thousand clones were analyzed. The mutations were localized in mitochondrial and nuclear genomes. Eighteen clones with mutations in genes encoding not yet known ATP synthase expression factors were completely sequenced. Several new cellular systems that are potentially involved in the biogenesis of FO were identified.

La F1 Fo ATP synthase est un complexe enzymatique localisé au sein de la membrane interne mitochondriale qui utilise le gradient électrochimique en protons formé par la chaîne respiratoire pour synthétiser de l'ATP à partir d'ADP et de Pi. Cette enzyme conservée de la levure S. cerevisiae aux cellules de mammifères s'organise dans les membranes internes mitochondriales sous forme de structures supramoléculaires d'ATP synthases. Chez la levure, il est aujourd'hui parfaitement identifiée que cette organisation nécessite la présence de deux sous-unités accessoires de l'enzyme : les sous-unités e et g.Les travaux présentés dans ce manuscrit visaient à étudier l'implication des sous-unités e et g dans les mécanismes de dimérisation et d'oligomérisation des ATP synthases ainsi que dans la morphogénèse des crêtes mitochondriales chez la levure S. cerevisiae et dans les cellules humaines en culture.Chez la levure, l'étude réalisée nous a permis de déterminer la stœchiométrie des sous-unités e et g, élément indispensable à la modélisation de l'agencement des sous-unités membranaires de l'enzyme dans la membrane interne mitochondriale.Dans les cellules humaines en culture, nous avons pu établir que les sous-unités e et g participent à la stabilité des dimères d'ATP synthases. Cependant l'implication de ces sous-unités dans la stabilité de l'enzyme semble différente des observations effectuées dans les cellules de levure / The F1Fo ATP synthase is an enzymatic complex embedded in the inner mitochondrial membrane which use the electrochemical proton gradient generated by the phosphorylation oxydative pathway to synthesize ATP from ADP and inorganic phosphate. This enzyme is conserved from yeast to mammalian cells and displays supramolecular organization in the inner mitochondrial membrane. In yeast, it is actually well-known that the supramolecular assembly required two accessory subunits : e and g subunits.The present work was realized to understand the involvement of subunits e and g in dimerization and oligomerization of mitochondrial ATP synthases as well as their effect on mitochondrial inner membrane morphogenesis in yeast S. cerevisiae and human cultured cells.In yeast, this study led us to determine subunits e and g stoechiometry, which was cruelly missing to establish a model of the ATP synthases membranous subunits layout in the inner mitochondrial membrane.In human cells, we have demonstrated that subunits e and g are implicated in ATP synthase dimer stabilization. However, their involvement in this stabilization seems to be quietly different of what have been observed in yeast cells.

La mitochondrie forme un réseau dynamique de tubules, dont la morphologie et la distribution sont étroitement régulées. Les mitochondries sont des organelles à double membrane dont l’architecture interne est complexe. Les crêtes mitochondriales forment des invaginations de la membrane interne. Elles sont le lieu des phosphorylations oxydatives, réactions par lesquelles l’ATP synthase produit l’ATP. L’ATP synthase est également connue pour son rôle clé dans la morphogenèse des crêtes. Dans cette étude j’ai mis en évidence in vivo la localisation en cluster de l’ATP synthase au sein du réseau mitochondrial de S. cerevisiae se développant sur substrat fermentescible. Mes résultats suggèrent que ces clusters correspondent aux crêtes mitochondriales, ce qui ouvre de nouvelles perspectives pour l’étude du remaniement de la membrane interne.La morphologie du réseau mitochondrial est maintenue par un équilibre entre les processus de fusion et de fission des tubules mitochondriaux. Dans la deuxième partie de ma thèse, j’ai mis en évidence une fragmentation progressive du réseau mitochondrial lors de l’entrée des cellules en quiescence, un état cellulaire non prolifératif réversible. En quiescence, le réseau mitochondrial est constitué de petites vésicules sous corticales immobiles au contenu enzymatique variable. Lors d’un retour à l’état prolifératif ces vésicules fusionnent rapidement pour reformer un réseau tubulaire, et ce, avant l’émergence de la cellule fille. De façon surprenante j’ai mis en évidence que ni les machineries canoniques de fusion ou de fission, ni le cytosquelette d’actine ne sont requis lors du remaniement du réseau mitochondrial dans les transitions entre prolifération et quiescence. / Mitochondria form a dynamic tubular network which organization and distribution is highly regulated.Mitochondria are double membrane organites with a complex internal architecture. Cristae, which areinner membrane invaginations, are the site of oxidative phosphorylation, reactions by which ATP synthaseproduces ATP. ATP synthase also play a key role in cristae morphogenesis. In this study, I have shown thatATP synthase localized as discrete clusters along the mitochondrial network in living S. cerevisiae cellsgrown on a fermentable carbon source. Overall our data suggest that ATP synthase clusers correspond tomitochondrial cristae, opening new avenues to explore the mechanisms involved in inner membraneremodelling.Mitochondrial network morphology is regulated by a dynamic equilibrium between the fusion and fissionof mitochondrial tubules. In the second part of my thesis, I highlight a progressive mitochondrialfragmentation during quiescence establishment, a state defined as a reversible absence of proliferation.Quiescent cells mitochondrial network is composed of immobile small cortical mitochondrial vesicles witha variable enzymatic content. Upon quiescence exit, cortical mitochondrial vesicles rapidly fuse and atubular network is reconstituted prior to bud emergence. Astonishingly, neither the canonical fusion orfission machineries nor the actin cytoskeleton are required for the mitochondrial network modificationduring quiescence / proliferation transition.

In this review we discuss the role of ATP synthase as a molecular drug target for natural and synthetic antimicrobial/ antitumor peptides. We start with an introduction of the universal nature of the ATP synthase enzyme and its role as a biological nanomotor. Significant structural features required for catalytic activity and motor functions of ATP synthase are described. Relevant details regarding the presence of ATP synthase on the surface of several animal cell types, where it is associated with multiple cellular processes making it a potential drug target with respect to antimicrobial peptides and other inhibitors such as dietary polyphenols, is also reviewed. ATP synthase is known to have about twelve discrete inhibitor binding sites including peptides and other inhibitors located at the interface of α/β subunits on the F1 sector of the enzyme. Molecular interaction of peptides at the β DEELSEED site on ATP synthase is discussed with specific examples. An inhibitory effect of other natural/synthetic inhibitors on ATP is highlighted to explore the therapeutic roles played by peptides and other inhibitors. Lastly, the effect of peptides on the inhibition of the Escherichia coli model system through their action on ATP synthase is presented.

In this review we discuss the role of ATP synthase as a molecular drug target for natural and synthetic antimicrobial/ antitumor peptides. We start with an introduction of the universal nature of the ATP synthase enzyme and its role as a biological nanomotor. Significant structural features required for catalytic activity and motor functions of ATP synthase are described. Relevant details regarding the presence of ATP synthase on the surface of several animal cell types, where it is associated with multiple cellular processes making it a potential drug target with respect to antimicrobial peptides and other inhibitors such as dietary polyphenols, is also reviewed. ATP synthase is known to have about twelve discrete inhibitor binding sites including peptides and other inhibitors located at the interface of α/β subunits on the F1 sector of the enzyme. Molecular interaction of peptides at the β DEELSEED site on ATP synthase is discussed with specific examples. An inhibitory effect of other natural/synthetic inhibitors on ATP is highlighted to explore the therapeutic roles played by peptides and other inhibitors. Lastly, the effect of peptides on the inhibition of the Escherichia coli model system through their action on ATP synthase is presented.

Strap is a DNA damage responsive p53 cofactor, reflecting its control by the DNA damage signalling pathway. This study identified Strap at the mitochondria where it is damage regulated and can augment p53-dependent cytochrome c release leading to apoptosis. Moreover, p53 and Strap facilitate each other’s localisation from the mitochondria to the nucleus during the DNA damage response. Two ATM/ATR phosphorylation consensus sites in Strap were identified by mass spectrometry and phosphorylation of all the ATM/ATR consensus sites resulted in mitochondrial localisation of Strap during DNA damage. Targeting Strap to the mitochondria depletes cellular ATP when cells favour energy production through oxidative phosphorylation and sensitises cells to p53-dependent damage-induced apoptosis. These results thus imply that Strap co-ordinates different arms of the p53 response, and might be responsible for integrating its mitochondrial and nuclear functions.