Le coenzyme Q est une molécule lipophile rédox rencontrée chez les eucaryotes et chez la plupart des procaryotes. La structure de Q correspond à une benzoquinone substituée par une chaîne polyisoprényle dont la longueur varie selon les organismes. Q joue le rôle de transporteur d'électrons dans les chaînes respiratoires d'où provient la plupart de l'énergie de la cellule. La biosynthèse de Q chez la bactérie Escherichia coli comporte huit étapes et implique au moins neuf protéines (UbiA-UbiH et UbiX). Trois réactions d'hydroxylation sont nécessaires pour la biosynthèse de Q8 en conditions aérobies. Alors que les protéines UbiH et UbiF présentent des homologies de séquence avec des monooxygénases à flavine connues pour catalyser des réactions d'hydroxylation, UbiB qui a été proposée comme étant la troisième hydroxylase, présente uniquement une homologie de séquence avec des kinases. Nous rapportons dans ce travail que la protéine VisC, renommée UbiI, catalyse la réaction d'hydroxylation auparavant attribuée à UbiB. Nous avons également identifié deux nouvelles protéines (YigP et YqiC, renommées respectivement UbiJ et UbiK) importantes pour le métabolisme de Q chez Escherichia coli puisque leur mutation diminue fortement le contenu en Q des souches mutantes. Ces protéines interagissent avec la plupart des protéines connues pour participer à la biosynthèse de Q ce qui implique l'existence d'un complexe de biosynthèse de Q. En utilisant des approches biochimiques et protéomiques, nous avons pu mettre en évidence un complexe impliquant plusieurs protéines Ubi et notamment UbiJ et UbiK. Ces deux protéines semblent avoir un rôle dans l'assemblage et/ou la stabilisation de ce complexe multiprotéique. Enfin, nous nous sommes intéressés à la biosynthèse de Q dans des conditions de cultures anaérobies. Nos résultats montrent l'existence « d'hydroxylases anaérobies », inconnues à ce jour, qui remplaçent les hydroxylases aérobies UbiH, UbiI et UbiF. Grâce à une approche phylogénétique, nous identifions un gène important pour la biosynthèse de Q uniquement en conditions anaérobies suggérant une réorganisation de la biosynthèse de Q entre ces deux environnements fréquemment rencontrés par E. coli. L'ensemble de nos résultats a permis d'améliorer notre connaissance de la voie de biosynthèse procaryote de Q grâce à la découverte de nouveaux gènes impliqués dans ce processus et grâce à l'identification de la fonction moléculaire de certaines protéines. / Ubiquinone (Q) is a lipophilic compound that plays an important role in electron and proton transport in the respiratory chains of Escherichia coli. Besides this important role in energy production, Q also functions as a membrane soluble antioxidant. The biosynthesis of Q8 requires eight reactions and involves at least nine proteins (UbiA-UbiH and UbiX) in Escherichia coli. Three of these reactions are hydroxylations resulting in the introduction of a hydroxyl group on carbon atoms at position 1, 5 and 6 of the aromatic ring. The C1 and C6 hydroxylation are well characterized whereas the C5 hydroxylation has been proposed to involve UbiB, a protein kinase without any sequence homology with monooxygenase. In this work, by genetic and biochemical methods we provide evidence that VisC which we renamed UbiI, displays sequence homology with monooxygenases and catalyzes the C5 hydroxylation, not UbiB. We have identified two new genes, yqiC and yigP (renammed UbiJ and UbiK) which are required only for Q8 biosynthesis in aerobic conditions. The exact role of the corresponding proteins, renamed UbiJ and UbiK, remains unknown. These proteins are able to interact with other Ubi proteins to be able to produce Q supporting the protein complex hypothesis. Our progress on the characterization of an Ubi-complex regrouping several Ubi proteins suggest that UbiJ and UbiK may fulfill functions related to the Ubi-complex stability. Mutants affected in hydroxylation steps are deficient for Q8 in aerobic conditions but recover a wild type Q8 content when grown in anaerobic conditions. This intriguing observation supports the existence of an alternative hydroxylation system independent from dioxygen which has not been characterized so far. By phylogenetic studies, we have identified a new gene in which the deletion affect the biosynthesis of Q only in anaerobic conditions suggesting a reorganization of Q biosynthesis in these two conditions. Our results has improved our knowledge of the prokaryotic Q biosynthetic pathway through the discovery of new genes involved in this process and through the identification of the molecular function of some proteins.

Le coenzyme Q (ubiquinone ou Q) est une molécule organique lipophile composée d'une benzoquinone substituée et d'une chaîne polyisoprényle contenant 6 unités chez Saccharomyces cerevisiae (Q6), 8 chez Escherichia coli (Q8) et 10 chez l'homme (Q10). Q a un rôle bien connu de transporteur d'électrons dans les chaînes respiratoires et fonctionne également comme un antioxydant membranaire. La déficience primaire en Q10 a maintenant été attribuée à des mutations dans 6 gènes de la biosynthèse de Q10 et cause des pathologies sévères. La biosynthèse de Q6 est mitochondriale et nécessite au moins 9 protéines organisées au sein d'un complexe multiprotéique chez la levure (Coq1-Coq9). L'acide 4-hydroxybenzoique (4-HB) et l'acide para-aminobenzoique (pABA) sont les deux précurseurs connus du noyau aromatique de Q6. Malgré de nombreuses recherches et l'importance cruciale de Q dans le métabolisme eucaryote, certaines étapes de la voie de biosynthèse de Q ne sont pas connues. L'étude présentée dans ce manuscrit a permis de montrer l'implication de la protéine Coq6, proposée comme étant une mono-oxygénase à flavine, dans une seule des trois réactions d'hydroxylation que compte la voie de biosynthèse de Q6: l'hydroxylation en C5. De plus, notre étude sur Coq8, une protéine kinase dont sa surexpression stabilise le complexe multiprotéique, nous a permis de confirmer les fonctions de certaines protéines Coq (Coq5, Coq7), de découvrir la fonction de Coq6 et d'éclaircir le rôle des autres (Coq4, Coq9). Nous rapportons également que des analogues hydroxylés ou méthoxylés de 4-HB et du pABA peuvent court-circuiter des étapes déficientes des mutants particuliers conduisant ainsi à la synthèse du coenzyme Q6 dans ces derniers. Ce résultat ouvre de nouvelles perspectives pour traiter les déficiences en coenzyme Q10 qui jusqu'à présent sont traitées par supplémentation en Q. Finalement, la réaction de déamination, essentielle à la biosynthèse de Q6 à partir du pABA, reste incomprise mais nos résultats suggèrent fortement l'implication de Coq6 dans cette étape. / Coenzyme Q (ubiquinone or Q) is a lipophilic organic molecule composed of a substituted benzoquinone and a polyisoprenyl chain containing 6 units in Saccharomyces cerevisiae (Q6), 8 in Escherichia coli (Q8) and 10 in humans (Q10). Q has a well known role as an electron carrier in the mitochondrial respiratory chain and also functions as a membrane soluble antioxidant. Primary Q10 deficiency has now been linked to mutations in six genes of Q biosynthesis and results in severe pathologies. The biosynthesis of Q is mitochondrial and requires at least nine proteins in yeast (Coq1-Coq9). 4-hydroxybenzoate (4-HB) and para-aminobenzoic acid (pABA) are the long-known aromatic precursors of the benzoquinone ring of Q. Despite intensive research efforts and the biological importance of Q, some biosynthetic steps are still uncharacterized. Herein we report that Coq6, a predicted flavin-dependent monooxygenase, is involved exclusively in the C5-hydroxylation reaction. We also demonstrate that the overexpression of the protein Coq8, which is proposed to be a kinase, in Δcoq strains restores steady state levels of the unstable Coq proteins. Moreover, we provide evidence that the kinase activity is essential for the stabilizing effect of Coq8 in the Δcoq strains. The overexpression of Coq8 helped us clarify the role of some proteins (Coq4, Coq9). We also show that using synthetic analogues of 4-HB and pABA allows bypassing deficient biosynthetic steps in some mutants. This result opens new perspectives to address the deficiencies in coenzyme Q which until now are processed by Q supplementation. Finally, the deamination reaction, which is essential for Q6 biosynthesis from pABA remains misunderstood but our results strongly suggest the involvement of Coq6 in this step.

ARCA2 est une ataxie récessive qui se caractérise par une atrophie du cervelet et un léger déficit en coenzyme Q10. Des mutations dans le gène ADCK3 ont été récemment identifiées comme étant la cause d’ARCA2. ADCK3 code pour une kinase mitochondriale atypique, qui pourrait être impliquée dans la biosynthèse du coenzyme Q10. L’objectif de mon projet de thèse était d’élucider la physiopathologie d’ARCA2 en utilisant le modèle murin knockout pour Adck3. J’ai ainsi pu montrer que les souris Adck3-/- reproduisent de nombreux symptômes associés à ARCA2 et constituent un bon modèle pour étudier ARCA2. Au niveau du cervelet, les cellules de Purkinje sont spécifiquement touchées et présentent des anomalies morphologiques et fonctionnelles. Un léger défaut mitochondrial a été observé dans les muscles squelettiques des souris Adck3-/-. Enfin, une analyse transcriptomique de ces deux tissus a révélé des altérations de nombreuses voies, impliquant ADCK3 dans de nouveaux processus cellulaires. / ARCA2 is a form of recessive ataxia characterized by a slow progression of the ataxic phenotype, cerebellar atrophy and mild deficit in Coenzyme Q10. ARCA2 was recently found associated with mutations in the ADCK3 gene that encodes a putativemitochondrial kinase homologous to the yeast Coq8 and the bacterial UbiB proteins, which are required for Coenzyme Q biosynthesis. In order to elucidate the pathophysiology of ARCA2, a constitutive knockout mouse for Adck3 was generated.Adck3-/- mice reproduce many ARCA2 symptoms such as slow progression of the ataxic phenotype and mild Coenzyme Q deficit, suggesting that Adck3-/- mice are a good model to study ARCA2. Strikingly, a morphological and functional impairmentwas found in cerebellar Adck3-/- Purkinje cells, whereas a mild mitochondrial defect was observed in the skeletal muscle of Adck3-/- mice. Interestingly, transcriptomic analyses revealed alteration in a number of molecular pathways implicating ADCK3in novel cellular processes.

ARCA2 est une ataxie autosomique récessive rare, caractérisée par une atrophie du cervelet et un léger déficit en Coenzyme Q10 (CoQ). La majorité des patients présentent des signes neurologiques supplémentaires comme l’épilepsie ou l’intolérance à l’exercice. La maladie est due à des mutations dans le gène COQ8A qui semble encoder une protéine kinase-like atypique, impliquée dans la biosynthèse du CoQ. Pour comprendre les mécanismes physiopathologiques, une souris Coq8a knock-out (KO) constitutif a été générée et récapitule les symptômes observés chez les patients. Le but de ce travail de thèse était de mieux comprendre certains aspects, notamment l’intolérance à l’exercice et l’ataxie. Malgré un déficit en CoQ dans les muscles, aucun défaut de respiration mitochondriale n’a été détecté dans un modèle cellulaire de muscle. Néanmoins, dans le cervelet, les niveaux de transcrits de 27 gènes sont dérégulés, précocement dans l’apparition de la pathologie chez les souris KO. Les voies métaboliques vont être explorées, ce qui devrait permettre de relier la fonction de COQ8A au taux de CoQ et aux symptômes observés chez les patients. / ARCA2, a rare form of recessive ataxia, is characterized by early onset progressive ataxia, cerebellar atrophy and a mild Coenzyme Q10 deficiency. Most of the patients show additional neurological signs such as epilepsy and exercise intolerance. Mutations in the COQ8A gene lead to ARCA2. COQ8A is suggested as being an unorthodox protein kinase like, with a regulatory role in CoQ biosynthesis, in mammals. To better understand ARCA2, a constitutive Coq8a knock-out (KO) mouse model was generated, which recapitulates most of the patient’s symptoms. Here we report the use of cellular models and the affected tissues to uncover the molecular signature of COQ8A loss and CoQ deficit. Despite CoQ deficit in the muscle, no mitochondrial bioenergetics defect was uncovered. In parallel, we have identified, by RT-qPCR, a key set of genes that are dysregulated in cerebellum, very early on in the pathology. We are currently investigating these pathways to uncover the link with COQ8A function. Altogether, our experiments will shed light on the early molecular events that lead to ARCA2 and may help draw a link between COQ8A function, CoQ pools and the symptoms observed in patients.

Le pore de transition de perméabilité mitochondriale (PTPm) joue un rôle majeur dans la mort cellulaire et dans la cardioprotection. Notre hypothèse est que le complexe I de la chaîne respiratoire est impliqué dans la régulation de l’ouverture du PTPm. Sur des mitochondries isolées de cœurs des rongeurs, nous avons pu démontrer que le PTPm est désensibilisé par la cyclosporine A, un inhibiteur de la cyclophiline D (CyP-D), et cet effet est largement amplifié en présence de la roténone, un inhibiteur du complexe I. Ces résultats ont été confirmés chez la souris CyP-D déficiente. L’étude de plusieurs types cellulaires a aussi confirmé l’effet de la roténone dans la régulation du PTPm. Ainsi, nous avons pu montrer que le flux d’électrons travers le complexe I est capable de réagir sur un site de régulation du PTPm cardiaque masqué par la CyP-D. De plus, les analogues de l’ubiquinone, élément de la chaîne respiratoire impliqué dans le transfert d’électrons entre les complexes I, II et III, modulent la susceptibilité du PTPm vis-à-vis du Ca2+. Par ailleurs, dans un modèle de cœur isolé du rat, le postconditionnement par le perindoprilate, un inhibiteur de l’enzyme de conversion, diminue la taille de l’infarctus après l’ischémie-reperfusion d’une façon NO-dépendant. L’ensemble de nos résultats ouvre de nouvelles perspectives thérapeutiques dans la cardioprotection et montre l’importance du complexe I et de la CyP-D comme cibles moléculaires incontournables dans la cardioprotection / The mitochondrial permeability transition pore (mPTP) plays an important role in cell death and cardioprotection. Our hypothesis is that the complex I of mitochondrial respiratory chain regulates the opening of mPTP. We showed that the opening of mPTP was inhibited by Cyclosporin A (CsA), a cyclophilin D (CyP-D) inhibitor, in mitochondria isolated from rodent heart, and this effect was largely amplified by rotenone, a complex I inhibitor. These results were confirmed in mitochondria devoid of CyP-D. A study realised in several cell lines also confirmed the effect of rotenone in mPTP regulation. We concluded that the electron flow through the respiratory chain complex I regulate mPTP opening and the regulatory site is masked by CyP-D in cardiac mitochondria. Moreover, two analogues of ubiquinone, mobile carrier of electrons between complex I, II and complex III, modulate the susceptibility of mPTP. In addition, in a model of isolated rat heart, postconditioning with Perindoprilat, an angiotensin converting enzyme inhibitor, protects the heart from ischemia-reperfusion injury in an NO-dependant manner. The findings of the present work put new therapic perspectives in cardioprotection

A hiperglicemia crônica favorece a ocorrência da nefropatia induzida por contraste iodado (NIC). Diabetes Mellitus (DM) e NIC compartilham mecanismos de lesão oxidativa e indução de enzimas de proteção e adaptação celular como a coenzima Q-10 (COQ-10). O objetivo deste estudo foi avaliar o papel da COQ-10 na função e hemodinâmica renal, perfil oxidativo e histologia renal em ratos diabéticos submetidos ao modelo de NIC. Métodos: Ratos Wistar, machos, 250 a 290 g, foram randomizados nos grupos: Citrato: animais que receberam tampão citrato 0,01M, (veículo da estreptozotocina), 0,4 ml intravenoso (i.v), 1 vez; Tween 80: animais que receberam Tween 80, 1%, (veículo da COQ-10), 0,5 ml, intraperitoneal (i.p.), 1 vez; DM: animais que receberam estreptozotocina (65 mg/kg), i.v., 1 vez, no 1º dia do protocolo; DM+CI: animais DM que no 26º dia de protocolo receberam contraste iodado (CI, 6 ml/kg), i.p., 1 vez; DM+CI+COQ-10: animais DM com pré-condicionamento com COQ-10 (10 mg/kg), 1 vez por 6 dias a partir do 22º dia de protocolo, e o tratamento com CI. O protocolo de todos os grupos teve duração de 4 semanas. Foram avaliados parâmetros fisiológicos (ingestão de ração e água, peso, glicemia, razão peso do rim e peso do animal), a função renal (clearance de inulina), a hemodinâmica renal (fluxo sanguíneo renal e resistência vascular renal), o perfil oxidativo (peróxidos, óxido nítrico e substâncias reativas ao ácido tiobarbitúrico na urina, tióis no tecido renal) e análise histológica renal. Resultados: Animais DM apresentaram hiperglicemia, polidipsia, poliúria, polifagia, perda de peso e aumento da relação peso rim/animal, com redução da função renal, além de redução do fluxo sanguíneo renal, elevação da resistência vascular renal, com aumento na excreção de metabólitos oxidativos e consumo de reserva antioxidante endógena. O grupo DM+CI demonstrou redução adicional na função, alterações na hemodinâmica renal e aumento nos parâmetros de estresse oxidativo. A administração de COQ-10 atenuou a redução da função renal, preveniu alterações hemodinâmicas renais e reduziu o estresse oxidativo no grupo DM+CI. As alterações histológicas no DM e DM+CI foram discretas e o tratamento com COQ-10 previniu a progressão de danos histológicos mais extensos nos animais que receberam CI. Conclusão: O tratamento com COQ-10 demonstrou efeito antioxidante na NIC em ratos diabéticos com melhora significativa da função e hemodinâmica renal. / Chronic hyperglycemia favors the occurrence of nephropathy induced by iodinated contrast (CIN). Diabetes Mellitus (DM) and CIN share oxidative damage mechanisms and induction of protective and cellular adaptation enzymes as coenzyme Q-10 (CoQ-10). The aim of this study was to investigate the role of COQ-10 in renal function and hemodynamics, oxidative profile and renal histology in diabetic rats submitted to the NIC model. Methods: Wistar rats, male, weighing 250-290 g, were randomized into two groups: Citrate: animals that received citrate buffer 0.01M (streptozotocin), 0.4 ml, intravenous (i.v.), once; Tween 80: animals that received Tween 80, 1% (CoQ-10 vehicle), 0.5 ml, intraperitoneal (i.p.), once; DM: animals given streptozotocin (65 mg/kg) i.v., once on the first day of the protocol; CI+DM: DM animals, on the 26º day protocol, tretated with iodinated contrast (CI, 6 ml/kg) i.p., once; DM+CI+COQ-10: DM animals preconditioned with COQ-10 (10 mg/kg), once a day, for 6 days from the 22º day and treated with CI. The protocol for all groups lasted 4 weeks. Physiological parameters evaluated were (food and water intake, corporal weight, blood glucose and right kidney weight), renal function (inulin clearance), renal hemodynamics (renal blood flow and renal vascular resistance), the oxidative profile (peroxides, nitric oxide and reactive substances to thiobarbituric acid in urine, thiols in renal tissue) and renal histological analysis. Results: DM animals showed hyperglycemia, polydipsia, polyuria, polyphagia, weight loss and increased weight kidney / animal relationship with reduced renal function, as well as a reduction on renal blood flow, increased renal vascular resistance and changes in oxidative profile with increased the excretion of metabolites and oxidative consumption of endogenous antioxidant reserve. DM+CI promoted further reduction in renal function, exacerbated hemodynamic changes and increase in oxidative stress parameters. COQ-10 administration preserved renal function, prevented hemodynamic changes and reduced oxidative stress in the DM + CI + COQ-10. Histological changes in DM and DM + CI were discrete and treatment with CoQ-10 prevented the progression of the histologic damage in the animals receiving CI. Conclusion: COQ-10 presented an antioxidant effect on the NIC in diabetic rats, by improving function and renal hemodynamics and reducing oxidative stress.

Mutantes respiratórios de Saccharomyces cerevisiae podem apresentar uma ampla variedade de instabilidade do mtDNA. Nós analisamos diferentes classes de mutantes e observamos uma elevada instabilidade nos mutantes que não possuem a coenzima Q (CoQ) funcional. O objetivo desse trabalho foi avaliar os efeitos das alterações no estado redox da coenzima Q sobre a estabilidade do mtDNA de diferentes linhagens de S. cerevisiae. No mutante <font face=\"Symbol\">Dcoq10, que sintetiza CoQ não funcional, a inativação das NADH desidrogenases individuais Ndi1p e Nde1p, resultou numa menor instabilidade do mtDNA, acompanhada por uma diminuição na taxa de liberação de peróxido de hidrogênio (H2O2). Por outro lado, a super-expressão de Nde1p aumentou a instabilidade do mutante <font face=\"Symbol\">Dcoq10. A inativação das NADH desidrogenases na linhagem <font face=\"Symbol\">Dcoq4, deficiente na síntese da CoQ, não reduziu a instabilidade do mtDNA. Juntos, os resultados indicam que alterações no estado de oxido-redução da coenzima Q influenciam a estabilidade do mtDNA, provavelmente através da produção de espécies reativas de oxigênio. / Saccharomyces cerevisiae respiratory mutants can show a wide range of mtDNA instability. We analyze different classes of mutants and observed a higher instability among mutants lacking a functional coenzyme Q (CoQ). The aim of this study was to evaluate the effects of alterations in the redox state of coenzyme Q on the stability of mtDNA mitochondrial in different strains of Saccharomyces cerevisiae. In <font face=\"Symbol\">Dcoq10 mutant, which synthesizes CoQ nonfunctional, inactivation of individual NADH dehydrogenases Ndi1p Nde1p has shown a decreased mtDNA instability, which was accompanied by a decrement in the rate of hydrogen peroxide (H2O2) release. Moreover, overexpression of Nde1p increased instability <font face=\"Symbol\">Dcoq10 mutant. The inactivation of individual NADH dehydrogenases in <font face=\"Symbol\">Dcoq4 strain which is deficient in the synthesis of CoQ, did not reduce the instability of the mtDNA. All the results indicate that changes in the redox state of coenzyme Q influence the stability of mtDNA, probably by the production of reactive oxygen species.

Coenzima Q (CoQ) é uma molécula de função essencial na transferência de elétrons da cadeia respiratória mitocondrial. Em Saccharomyces cerevisiae , a CoQ é constituída por um anel de benzeno associado a uma cadeia poliprenil, com 6 unidades de repetição, sendo por isso também denominada CoQ6 ou Q6. Ao todo já foram identificados treze genes (COQ1 COQ11, ARH1 e YAH1) nucleares necessários para biossíntese da CoQ. A maioria dos produtos Coq estão fisicamente associados em um complexo biossintético ancorado na membrana mitocondrial interna. Neste projeto, tentamos descrever resíduos relevantes de Coq3p e Coq7p aliando análises de bioinformática com testes fenotípicos para balizamento funcional. Coq7p é uma proteína com dois centros de ferro com íons carboxilato e catalisa a hidroxilação de demetoxi-Q6 (DMQ6). Neste estudo, indicamos um grupo de resíduos que modulam a atividade e a estabilidade de Coq7p: D53, R57, V111 e S114. Enquanto R57, V111 e S114 são resíduos muito conservados, V111 e S114 estão correlacionados em comunidades de coevolução. Aqui, demonstramos também que o duplo mutante S114A, V111G e o mutante S114E apresentam deficiência respiratória em temperatura não permissiva, além de acumularem o intermediário DMQ6 e sintetizarem baixas quantidades de Q6, concluindo assim que o fosmimético S114E inibe a atividade Coq7p. Dessa forma, propomos que a fosforilação do resíduo S114 promove o deslocamento de uma alça entre as hélices 2 e 3, afetando assim a atividade do centro catalítico Coq7p. Por sua vez, Coq3p atua como uma metiltransferase, catalisando diferentes passos durante a biossíntese da CoQ. Aqui, identificamos resíduos que colaboram para a atividade funcional de Coq3p: E123, S125, C131, G133, G134, H165, D203, E219, K258 e S262. Mutantes carregando as alterações E123A, H165A, D203A, E219A, K258A e S62A apresentam discreto crescimento respiratório e expressão de Coq3p similares à da linhagem selvagem, além de acumularem baixas quantidades de Q6. Enquanto C131, G133 e G134 são resíduos altamente conservados, localizados em uma alça no espaço entre fitas beta, no provável sítio ativo da proteína, mutantes C131A, G133A e G134A se superexpressos apresentam crescimento respiratório em meio contendo fonte de carbono não fermentável, além de acumularem Q6 compatíveis com os níveis de expressão proteica. Propomos assim um modelo para Coq3p, tendo os resíduos C131, G133 e G134 como centro catalítico de Coq3p. / Coenzyme Q (CoQ) is a molecule of essential function in the transfer of electrons of the mitochondrial respiratory chain. In saccharomyces cerevisiae , CoQ is constituted by a benzene ring associated with a polyprenyl chain with 6 repetition units, being therefore also denominated CoQ6 or Q6. Thirteen nuclear genes have already been identified (COQ1 COQ11, ARH1 and YAH1) required for coenzyme Q biosynthesis. Most of Coq products are physically associated in a biosynthetic complex anchored at the mitochondrial internal membrane. In this project, we identified Coq3p and Coq7p residues relevant for their respective role in CoQ synthesis combining bioinformatics analyzes with phenotypic tests for functional mapping. Coq7p is a carboxylate-bridged di-iron protein that catalyzes the hydroxylation of demetoxy-Q6 (DMQ6), the last monooxygenase step in the synthesis of CoQ. In this study, we found a group of residues that modulate the activity and stability of Coq7p: D53, R57, V111 and S114. While R57, V111 and S114 are highly conserved residues, V111 and S114 are correlated in communities of coevolution. We also demonstrate that the double mutant S114A, V111G and the mutant S114E have respiratory deficiency at non-permissive temperature, in addition to accumulating of the intermediate DMQ6 and low amounts of Q6, thus concluding that phosmimetic S114E inhibits the activity of Coq7p. Hence, we propose that the phosphorylation of S114 is required to move a loop between helices 2 and 3, thus affecting the activity of the catalytic center Coq7p. For its part, Coq3p acts as a methyltransferase, catalyzing different steps during biosynthesis of CoQ. Here we identified residues that collaborate for functional activity of Coq3p: E123, S125, C131, G133, G134, H165, D203, E219, K258 and S262. Mutants E123A, H165A, D203A, E219A, K258A and S62A, have mild respiratory growth, and expression of Coq3p levels similar to the wild strain, in addition to accumulating low amounts of Q6. While C131, G133, and G134 are residues highly conserved, located in a loop in the space between beta sheets, the overexpression of the mutants C131A, G133A and G134A present respiratory growth in medium containing non-fermentable carbon source, in addition to accumulate Q6 compatible with the levels of protein expression. We propose a model for Coq3p, with residues C131, G133 and G134 as part of Coq3p catalytic center.

Le coenzyme Q (ubiquinone ou Q) est une molécule organique lipophile composée d'une benzoquinone substituée et d'une chaîne polyisoprényle contenant 6 unités chez Saccharomyces cerevisiae (Q6), 8 chez Escherichia coli (Q8) et 10 chez l'homme (Q10). Q a un rôle bien connu de transporteur d'électrons dans les chaînes respiratoires et fonctionne également comme un antioxydant membranaire. La déficience primaire en Q10 a maintenant été attribuée à des mutations dans 6 gènes de la biosynthèse de Q10 et cause des pathologies sévères. La biosynthèse de Q6 est mitochondriale et nécessite au moins 9 protéines organisées au sein d'un complexe multiprotéique chez la levure (Coq1-Coq9). L'acide 4-hydroxybenzoique (4-HB) et l'acide para-aminobenzoique (pABA) sont les deux précurseurs connus du noyau aromatique de Q6. Malgré de nombreuses recherches et l'importance cruciale de Q dans le métabolisme eucaryote, certaines étapes de la voie de biosynthèse de Q ne sont pas connues. L'étude présentée dans ce manuscrit a permis de montrer l'implication de la protéine Coq6, proposée comme étant une mono-oxygénase à flavine, dans une seule des trois réactions d'hydroxylation que compte la voie de biosynthèse de Q6: l'hydroxylation en C5. De plus, notre étude sur Coq8, une protéine kinase dont sa surexpression stabilise le complexe multiprotéique, nous a permis de confirmer les fonctions de certaines protéines Coq (Coq5, Coq7), de découvrir la fonction de Coq6 et d'éclaircir le rôle des autres (Coq4, Coq9). Nous rapportons également que des analogues hydroxylés ou méthoxylés de 4-HB et du pABA peuvent court-circuiter des étapes déficientes des mutants particuliers conduisant ainsi à la synthèse du coenzyme Q6 dans ces derniers. Ce résultat ouvre de nouvelles perspectives pour traiter les déficiences en coenzyme Q10 qui jusqu'à présent sont traitées par supplémentation en Q. Finalement, la réaction de déamination, essentielle à la biosynthèse de Q6 à partir du pABA, reste incomprise mais nos résultats suggèrent fortement l'implication de Coq6 dans cette étape.

A hiperglicemia crônica favorece a ocorrência da nefropatia induzida por contraste iodado (NIC). Diabetes Mellitus (DM) e NIC compartilham mecanismos de lesão oxidativa e indução de enzimas de proteção e adaptação celular como a coenzima Q-10 (COQ-10). O objetivo deste estudo foi avaliar o papel da COQ-10 na função e hemodinâmica renal, perfil oxidativo e histologia renal em ratos diabéticos submetidos ao modelo de NIC. Métodos: Ratos Wistar, machos, 250 a 290 g, foram randomizados nos grupos: Citrato: animais que receberam tampão citrato 0,01M, (veículo da estreptozotocina), 0,4 ml intravenoso (i.v), 1 vez; Tween 80: animais que receberam Tween 80, 1%, (veículo da COQ-10), 0,5 ml, intraperitoneal (i.p.), 1 vez; DM: animais que receberam estreptozotocina (65 mg/kg), i.v., 1 vez, no 1º dia do protocolo; DM+CI: animais DM que no 26º dia de protocolo receberam contraste iodado (CI, 6 ml/kg), i.p., 1 vez; DM+CI+COQ-10: animais DM com pré-condicionamento com COQ-10 (10 mg/kg), 1 vez por 6 dias a partir do 22º dia de protocolo, e o tratamento com CI. O protocolo de todos os grupos teve duração de 4 semanas. Foram avaliados parâmetros fisiológicos (ingestão de ração e água, peso, glicemia, razão peso do rim e peso do animal), a função renal (clearance de inulina), a hemodinâmica renal (fluxo sanguíneo renal e resistência vascular renal), o perfil oxidativo (peróxidos, óxido nítrico e substâncias reativas ao ácido tiobarbitúrico na urina, tióis no tecido renal) e análise histológica renal. Resultados: Animais DM apresentaram hiperglicemia, polidipsia, poliúria, polifagia, perda de peso e aumento da relação peso rim/animal, com redução da função renal, além de redução do fluxo sanguíneo renal, elevação da resistência vascular renal, com aumento na excreção de metabólitos oxidativos e consumo de reserva antioxidante endógena. O grupo DM+CI demonstrou redução adicional na função, alterações na hemodinâmica renal e aumento nos parâmetros de estresse oxidativo. A administração de COQ-10 atenuou a redução da função renal, preveniu alterações hemodinâmicas renais e reduziu o estresse oxidativo no grupo DM+CI. As alterações histológicas no DM e DM+CI foram discretas e o tratamento com COQ-10 previniu a progressão de danos histológicos mais extensos nos animais que receberam CI. Conclusão: O tratamento com COQ-10 demonstrou efeito antioxidante na NIC em ratos diabéticos com melhora significativa da função e hemodinâmica renal. / Chronic hyperglycemia favors the occurrence of nephropathy induced by iodinated contrast (CIN). Diabetes Mellitus (DM) and CIN share oxidative damage mechanisms and induction of protective and cellular adaptation enzymes as coenzyme Q-10 (CoQ-10). The aim of this study was to investigate the role of COQ-10 in renal function and hemodynamics, oxidative profile and renal histology in diabetic rats submitted to the NIC model. Methods: Wistar rats, male, weighing 250-290 g, were randomized into two groups: Citrate: animals that received citrate buffer 0.01M (streptozotocin), 0.4 ml, intravenous (i.v.), once; Tween 80: animals that received Tween 80, 1% (CoQ-10 vehicle), 0.5 ml, intraperitoneal (i.p.), once; DM: animals given streptozotocin (65 mg/kg) i.v., once on the first day of the protocol; CI+DM: DM animals, on the 26º day protocol, tretated with iodinated contrast (CI, 6 ml/kg) i.p., once; DM+CI+COQ-10: DM animals preconditioned with COQ-10 (10 mg/kg), once a day, for 6 days from the 22º day and treated with CI. The protocol for all groups lasted 4 weeks. Physiological parameters evaluated were (food and water intake, corporal weight, blood glucose and right kidney weight), renal function (inulin clearance), renal hemodynamics (renal blood flow and renal vascular resistance), the oxidative profile (peroxides, nitric oxide and reactive substances to thiobarbituric acid in urine, thiols in renal tissue) and renal histological analysis. Results: DM animals showed hyperglycemia, polydipsia, polyuria, polyphagia, weight loss and increased weight kidney / animal relationship with reduced renal function, as well as a reduction on renal blood flow, increased renal vascular resistance and changes in oxidative profile with increased the excretion of metabolites and oxidative consumption of endogenous antioxidant reserve. DM+CI promoted further reduction in renal function, exacerbated hemodynamic changes and increase in oxidative stress parameters. COQ-10 administration preserved renal function, prevented hemodynamic changes and reduced oxidative stress in the DM + CI + COQ-10. Histological changes in DM and DM + CI were discrete and treatment with CoQ-10 prevented the progression of the histologic damage in the animals receiving CI. Conclusion: COQ-10 presented an antioxidant effect on the NIC in diabetic rats, by improving function and renal hemodynamics and reducing oxidative stress.