Os nossos resultados demonstraram a atividade enzimática prolina desidrogenase (PRODH) do produto do gene anotado como codificante de uma prolina oxidase na base dados do genoma de Trypanosoma cruzi. A atividade da proteína codificada por esse gene foi avaliada inicialmente por complementação de uma linhagem de S. cerevisiae deficiente na expressão funcional da PRODH endógena, e posteriormente mediante a obtenção da enzima recombinante ativa expressa em um sistema bacteriano. Nos estudos feitos tanto com leveduras complementadas com o gene PRODH, quanto com as formas epimastigotas de T. cruzi, observamos que nesses organismos há uma correlação positiva entre o nível intracelular de prolina livre e a resistência ao estresse oxidativo. Através dos ensaios de RT-PCR quantitativo observamos que o RNAm do gene da PRODH é regulado ao longo do ciclo de vida do T. cruzi, com maior nível de expressão no estágio epimastigota intracelular, perfil apresentado também em experimentos de Western Blotting, o que é concordante com o papel fundamental desse aminoácido na diferenciação dessa forma para as forma tripomastigota. Nos diferentes ensaios de localização subcelular observou-se que a proteína PRODH está presente na mitocôndria. A seqüência da PRODH apresenta um sítio EF-hand de ligação a Ca2+. Mostramos experimentalmente a funcionalidade desse sítio e a sua função na regulação da atividade por Ca2+. Em ensaios de respiração mitocondrial, utilizando prolina como substrato, foi mostrado que a prolina fornece elétrons à cadeia respiratória através da PRODH, transferindo elétrons e gerando FADH2 no mesmo nível e com a mesma eficiência que o complexo II (succinato desidrogenase). O análogo de prolina T4C, inibidor do transporte de prolina, causa uma diminuição do conteúdo de prolina livre intracelular, o que foi relacionado com uma diminuição significativa da sobrevivência do parasito em combinação com o estresse nutricional e oxidativo, mostrando a participação do metabolismo de prolina na resistência a esses estresses. Todos esses dados sugerem ademais que o transportador de prolina do parasita pode ser um alvo para drogas terapêuticas de interesse quando combinada com outras drogas que agem via geração de espécies reativas de oxigênio. / In the present work, we demonstrated the proline dehydrogenase enzymatic activity (PRODH) for the protein encoded by a gene annotated as a proline oxidase in the T. cruzi genome data base. This activity was shown firstly through complementation of a S. cerevisiae lineage lacking its endogenous PRODH gene. The PRODH gene was also expressed in a bacterial system and the active recombinant protein was obtained. Experiments performed with both, complemented yeasts and T. cruzi epimastigotes, showed a correlation between the intracellular free proline levels and the oxidative stress resistance. Quantitative RT-PCR assay revealed that the PRODH gene is differentially expressed across T. cruzi life cycle, being the highest expression level shown by the intracellular epimastigote form, this result was confirmed by Western blotting. Both results are in accordance with the fact that proline is essential for the differentiation of the intracellular epimastigote into trypomastigote. Subcellular localization assays showed that PRODH is present preferentially in the mitochondria. In silico analyses of the PRODH peptidic sequence indicated the presence of an EF-hand domain, wich is, usually, involved in Ca2+ binding. In fact, our results confirm not only the ability of such domain of binding Ca2+ but also its function in the activity regulation. Mitochondrial respiration assays using proline as substrate showed that PRODH transfers electrons and generates FADH2, with an eficience comparable to that of the complex II (Succinate dehydrogenase). Experiments using the T4C, an analogue of proline that inhibits the proline uptake, caused the depletion of the intracellular free proline, which was followed by the significantly decrement of the cellular viability of the parasites under nutritional and oxidative stresses. Taken together, this data suggest that proline transporters are promising drug targets when combined with other drugs that act by generating reactive oxygen species.

Dans le cadre du changement climatique et de l'évolution de la réglementation concernant les intrants azotés, la culture du colza risque d'être fortement pénalisée dans la mesure où c'est une culture qui nécessite d'importants apports azotés pour atteindre son potentiel de rendement. Par ailleurs, comme chez le colza un déficit hydrique induit l'accumulation de certains composés azotés, il est vraisemblable que cela conduise au détournement d'une quantité importante d'azote vers les organes végétatifs aux dépens des organes reproducteurs et donc du rendement. Chez le colza, la réponse métabolique au déficit hydrique se traduit par une très forte accumulation de proline et dans une moindre mesure une augmentation de la teneur en GABA (acide γ-aminobutyrique), deux acides aminés connus chez la plupart des plantes pour leur réponse à de nombreux stress abiotiques. L'objectif de cette thèse est de déterminer comment le métabolisme de ces deux molécules contribue à l'allocation de l'azote au cours du développement de la plante en situation normale comme en condition de stress hydrique et/ou azoté. Pour répondre à cette question nous avons fait le choix de caractériser deux voies enzymatiques majeures impliquées dans le catabolisme de la proline et du GABA : la proline déshydrogénase (ProDH) et la GABA-transaminase (GABA-T) et d'évaluer l'impact de carences hydriques et/ou azotées sur ces voies. Cette étude nécessitait d'identifier au préalable les gènes codant ces enzymes afin d'aborder une approche fonctionnelle. Les résultats montrent l'existence de multiples copies de gènes ProDH et GABA-T dans le génome du colza. L'analyse de leurs profils d'expression suggère que des processus de sub-fonctionnalisation sont en cours conduisant à l'expression spécifique, de certaines copies en réponse aux stress, et d'autres dans les processus développementaux. La comparaison des profils métaboliques avec les profils spécifiques des transcrits a permis d'élaborer des hypothèses sur le rôle de ces voies dans la gestion de l'azote. L'étude conjointe des métabolismes de la proline et du GABA suggère l'existence de régulations connexes entre les deux. Enfin, l'utilisation de plantules a permis - d'approfondir la régulation des gènes étudiés à des stades précoces de développement - et de mettre en évidence les effets délétères de l'inhibition de la GABA-T par une approche pharmacologique. En conclusion ces résultats apportent des précisions sur la régulation de ces deux enzymes et fournissent des éléments de réponse quant au rôle fonctionnel des catabolismes de la proline et du GABA dans les processus de gestion de l'eau et de l'azote chez le colza. Ces travaux constituent donc une première étape dans une démarche de validation de ces gènes comme candidats pour des programmes d'amélioration du colza visant à sélectionner des génotypes mieux adaptés aux conditions environnementales futures. / In the context of climate change and recent regulation concerning nitrogen inputs, the oilseed rape yields may be severely decreased because its crop requires significant nitrogen supply to reach high yield performance. Moreover, as water deficit induces the accumulation of some nitrogen compounds in oilseed rape, it is likely that this could lead to diversion of significant amounts of nitrogen to the vegetative organs at the expense of the reproductive ones and therefore of the yield. In oilseed rape, the metabolic response to water deficit results in a very high proline accumulation and, to a lesser extent, an increased content of GABA (γ-aminobutyric acid), both these amino acids known for their response to many environmental stresses in most species. The objective of the work presented here was to determine how the metabolism of proline and GABA contributes to the nitrogen allocation during plant development under optimal conditions and under water stress and/or nitrogen depletion. To answer this question, we have chosen to characterize two major enzymatic pathways involved in the catabolism of proline and GABA, proline dehydrogenase (ProDH) and GABA transaminase (GABA-T), and assess the impact of water and/or nitrogen deficiency on these pathways. This study has required to preliminary identify the genes encoding these enzymes in order to initiate a functional approach. The results show the presence of multiple copies of ProDH and GABA-T genes in the oilseed rape genome. Analysis of their expression profiles suggests that sub-functionalization processes are occurring, leading to the specific expression of some copies in response to stress, and some in developmental processes. Comparison of metabolic profiles with specific profiles of transcripts allows us to hypothesize about the role of these pathways in management of nitrogen. The combined study of proline and GABA metabolisms suggests the existence of relationships between them. Finally, the use of seedlings allows - further studying the regulation of genes in the early stages of development - and highlighting the deleterious effects of the inhibition of GABA-T by a pharmacological approach. In conclusion these results supply information on the regulation of these two enzymes and provide answers about the functional roles of proline and GABA catabolisms in the management processes of water and nitrogen in oilseed rape. These works constitute a first step in validation process of these genes as putative candidates for oilseed rape breeding programs to select genotypes better adapted to future environmental conditions.

Os nossos resultados demonstraram a atividade enzimática prolina desidrogenase (PRODH) do produto do gene anotado como codificante de uma prolina oxidase na base dados do genoma de Trypanosoma cruzi. A atividade da proteína codificada por esse gene foi avaliada inicialmente por complementação de uma linhagem de S. cerevisiae deficiente na expressão funcional da PRODH endógena, e posteriormente mediante a obtenção da enzima recombinante ativa expressa em um sistema bacteriano. Nos estudos feitos tanto com leveduras complementadas com o gene PRODH, quanto com as formas epimastigotas de T. cruzi, observamos que nesses organismos há uma correlação positiva entre o nível intracelular de prolina livre e a resistência ao estresse oxidativo. Através dos ensaios de RT-PCR quantitativo observamos que o RNAm do gene da PRODH é regulado ao longo do ciclo de vida do T. cruzi, com maior nível de expressão no estágio epimastigota intracelular, perfil apresentado também em experimentos de Western Blotting, o que é concordante com o papel fundamental desse aminoácido na diferenciação dessa forma para as forma tripomastigota. Nos diferentes ensaios de localização subcelular observou-se que a proteína PRODH está presente na mitocôndria. A seqüência da PRODH apresenta um sítio EF-hand de ligação a Ca2+. Mostramos experimentalmente a funcionalidade desse sítio e a sua função na regulação da atividade por Ca2+. Em ensaios de respiração mitocondrial, utilizando prolina como substrato, foi mostrado que a prolina fornece elétrons à cadeia respiratória através da PRODH, transferindo elétrons e gerando FADH2 no mesmo nível e com a mesma eficiência que o complexo II (succinato desidrogenase). O análogo de prolina T4C, inibidor do transporte de prolina, causa uma diminuição do conteúdo de prolina livre intracelular, o que foi relacionado com uma diminuição significativa da sobrevivência do parasito em combinação com o estresse nutricional e oxidativo, mostrando a participação do metabolismo de prolina na resistência a esses estresses. Todos esses dados sugerem ademais que o transportador de prolina do parasita pode ser um alvo para drogas terapêuticas de interesse quando combinada com outras drogas que agem via geração de espécies reativas de oxigênio. / In the present work, we demonstrated the proline dehydrogenase enzymatic activity (PRODH) for the protein encoded by a gene annotated as a proline oxidase in the T. cruzi genome data base. This activity was shown firstly through complementation of a S. cerevisiae lineage lacking its endogenous PRODH gene. The PRODH gene was also expressed in a bacterial system and the active recombinant protein was obtained. Experiments performed with both, complemented yeasts and T. cruzi epimastigotes, showed a correlation between the intracellular free proline levels and the oxidative stress resistance. Quantitative RT-PCR assay revealed that the PRODH gene is differentially expressed across T. cruzi life cycle, being the highest expression level shown by the intracellular epimastigote form, this result was confirmed by Western blotting. Both results are in accordance with the fact that proline is essential for the differentiation of the intracellular epimastigote into trypomastigote. Subcellular localization assays showed that PRODH is present preferentially in the mitochondria. In silico analyses of the PRODH peptidic sequence indicated the presence of an EF-hand domain, wich is, usually, involved in Ca2+ binding. In fact, our results confirm not only the ability of such domain of binding Ca2+ but also its function in the activity regulation. Mitochondrial respiration assays using proline as substrate showed that PRODH transfers electrons and generates FADH2, with an eficience comparable to that of the complex II (Succinate dehydrogenase). Experiments using the T4C, an analogue of proline that inhibits the proline uptake, caused the depletion of the intracellular free proline, which was followed by the significantly decrement of the cellular viability of the parasites under nutritional and oxidative stresses. Taken together, this data suggest that proline transporters are promising drug targets when combined with other drugs that act by generating reactive oxygen species.