The aim of this essay is to investigate what sort of political regimes that have been taking form in Russia and Turkey during the 21st century. Hence, it studies the development that has been taking place in both countries during the last ten years. This essay is doing so by using a comparative approach. The theoretical frame of the essay is inspired by Silander’s (2012) dimensions for a democratic regime. The dimensions are leadership, political parties and civil society. Furthermore, it dives into deeper studies about the political system of each country.         The study demonstrates that neither Russia nor Turkey are able to meet the standards of a democracy as of today. Furthermore, it shows that Russia falls within the frame of an authoritarian regime. Turkey is listed as ”partly free” according to this study, hence it is a hybrid regime with limitations.

Soit Г un graphe de Coxeter. Soient W le groupe de Coxeter, A le groupe d'Artin, et A+ le monoïde d'Artin, associés à Г. Soit G un groupe de symétries du graphe de Coxeter Г. Alors G agit sur W, A et A+, et il est connu que le sous-groupe fixe, WG, est un groupe de Coxeter, le sous-monoïde fixe, A+G, est un monoïde d'Artin, et, lorsque Г est de type sphérique, le sous-groupe fixe, AG, est un groupe d'Artin. Cette thèse étudie le comportement de WG, A+G et AG par rapport à des représentations fidèles de W, A et A+, respectivement.Dans un premier temps nous considérons les représentations enracinées introduites par Krammer dans sa thèse. Ce sont une généralisation des représentations canoniques. On se donne une telle représentation f : W → GL(V ) et on suppose que l'action de G sur les racines simples s'étend à V . Dans ce cas f induit une représentation linéaire fG : WG → GL(V G). Nous démontrons que cette représentation est aussi une représentation enracinée. En particulier, elle est fidèle.Dans un second temps nous supposons que Г est simplement lacé, c'est-à-dire que les arêtes de Г n'ont pas de poids. Nous considérons une représentation linéaire fidèle ψ : A+ → GL(E) introduite par Paris. Si Г est de type sphérique, alors cette représentation induit une représentation fidèle ψ : A → GL(E) du groupe. Dans le cas des groupe de tresses, c'est la célèbre représentation linéaire fidèle étudiée par Bigelow et Krammer. Nous démontrons que G agit aussi sur E, que la représentation ψ : A+ → GL(E) est équivariante, et qu'elle induit une représentation fidèle ψ : A+G → GL(EG). Si Г est de type sphérique, alors on obtient une représentation fidèle du groupe fixe, ψ : AG → GL(EG). Finalement, nous déterminons les cas où EG admet une base naturelle en bijection avec le système de racines positives de WG. Ce dernier résultat est motivé par la recherche d'une extension de la représentation ψ : A+ → GL(E) aux graphes qui ne sont pas simplement lacés. / Let Г be a Coxeter graph. Let W be the Coxeter group, A be the Artin group, and A+ be the Artin monoid associated with Г. Let G be a group of symmetries of Г. Then G acts on W, A and A+. The fixed subgroup WG is known to be a Coxeter group, the fixed submonoid A+G is known to be an Artin monoid, and, when Г is of spherical type, the fixed subgroup AG is known to be an Artin group. This thesis studies the behavior of WG, A+G and AG with respect to some faithful linear representations of W, A and A+, respectively.Firstly, we consider the rooted representations of the Coxeter groups introduced by Krammer in his Ph. D. Thesis. These are a generalization of the canonical representations. We take such a linear representation f : W → GL(V ), assuming that the action of G on the simple roots extends to V . Then f induces a linear representation fG : WG → GL(V G). We prove that fGis a rooted representation of WG. In particular, fG is faithful.Afterwards, we assume that Г is simply laced, that is, all the edges of Г are label free. Then we consider a faithful linear representation ψ : A+ → GL(E) introduced by Paris. If Г is of spherical type, this representation extends to a faithful linear representation ψ : A → GL(E) of the Artin group. In the case of the braid groups, it is the celebrated representation studiedby Bigelow and Krammer. Take a group G of symmetries of Г. We prove that G acts on E, that the representation ψ : A+ → GL(E) is equivariant, and that it induces a faithful linear representation ψ : A+G → GL(EG). If Г is of spherical type, then we get a faithful linear representation ψ : AG → GL(EG) of the fixed subgroup. Finally, we determine the cases where EG admits a natural basis in one-to-one correspondence with the positive root system of WG. This last result is motivated by the search of an extension of the linear representation ψ : A+ → GL(E) to Artin monoids (or groups) that are not simply laced.

Made available in DSpace on 2014-06-11T19:32:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-06-25Bitstream added on 2014-06-13T20:04:12Z : No. of bitstreams: 1 paiva_ptp_dr_sjrp.pdf: 1878177 bytes, checksum: b4fe38adb188f6058a25aaeef28f8e39 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este estudo compara termos médicos com base em palavras-chave em português e seus equivalentes em inglês extraídos de dois subcorpora paralelos de textos nas subáreas médicas de cardiologia e cirurgia cardiovascular. A investigação também observou traços de simplificação e de explicitação apresentados pelos tradutores de cada subárea. Além disso, foram comparados resultados a partir dos textos produzidos pelos dois tradutores deste estudo com os resultados dos textos produzidos por tradutores de outras duas subáreas médicas observados em estudo anterior (Paiva, 2006). Para tanto, foi adotada como fundamentação teórica a proposta dos estudos da tradução baseados em corpus (Baker, 1993, 1995, 1996, 2000; Camargo, 2005, 2007), a metodologia da lingüística de corpus (Berber Sardinha, 2000, 2004; Tognini-Bonelli, 2001) e, em parte, princípios da terminologia (Aubert, 1996; Barros, 2004; Krieger & Finatto, 2004). Para a compilação do corpus de estudo foram utilizados artigos científicos extraídos de revistas brasileiras bilíngües da área médica, e para os corpora comparáveis foram coletados artigos de revistas médicas brasileiras e estrangeiras de renome nas comunidades médicas das respectivas subáreas. A pesquisa contou com o auxílio do programa de análise lexical WordSmith Tools versão 3.0. O levantamento de termos médicos com base em palavras-chave em português para cada subárea permitiu a elaboração de dois glossários com os respectivos termos equivalentes em inglês, acompanhados do seu contexto em ambas as línguas, que foram, em seguida, inseridos em um programa de memórias de tradução. Como a tradutora de cardiologia é falante nativa de língua portuguesa e o tradutor de cirurgia cardiovascular é falante nativo de língua inglesa, também foi possível comparar o uso de estratégias lingüísticas adotadas por parte de cada tradutor. / This study compares medical terms based on keywords in Portuguese and their equivalents in English extracted from two parallel subcorpora of medical journals of Cardiology and Cardiovascular Surgery. In this investigation, features of simplification and explicitation were also observed in articles translated by two professional translators in each area. Moreover, the results from these two translators were compared to those from the translators of two other medical areas observed in a previous study (Paiva, 2006). The theoretical approach used was that of corpus-based translation studies (Baker, 1993, 1995,1996, 2000; Camargo, 2005, 2007), the methodology of corpus linguistics (Berber Sardinha, 2000, 2004; Tognini-Bonelli, 2001) and some principles of terminology (Aubert, 1996; Barros, 2004; Krieger and Finatto, 2004). For compiling the parallel subcorpora we used scientific articles from well-known bilingual Brazilian journals, and for the comparable corpora we used international journals in the same medical areas. The software WordSmith Tools, version 3.0 was applied in order to extract medical terms based on keywords in Portuguese for each area. This process led to the compilation of two glossaries containing medical terms in Portuguese, their English equivalents, as well as their contexts in both languages. Both glossaries were inserted into and tested in a program of translation memories. As the translator of Cardiology is a Portuguese native speaker and the translator of Cardiovascular Surgery is an English native speaker, it was also possible to compare some of their strategies.

Orientador: Diva Cardoso de Camargo / Banca: Ieda Maria Alves / Banca: João Azenha Junior / Banca: Nelson Luís Ramos / Banca: Peter James Harris / Resumo: Este estudo compara termos médicos com base em palavras-chave em português e seus equivalentes em inglês extraídos de dois subcorpora paralelos de textos nas subáreas médicas de cardiologia e cirurgia cardiovascular. A investigação também observou traços de simplificação e de explicitação apresentados pelos tradutores de cada subárea. Além disso, foram comparados resultados a partir dos textos produzidos pelos dois tradutores deste estudo com os resultados dos textos produzidos por tradutores de outras duas subáreas médicas observados em estudo anterior (Paiva, 2006). Para tanto, foi adotada como fundamentação teórica a proposta dos estudos da tradução baseados em corpus (Baker, 1993, 1995, 1996, 2000; Camargo, 2005, 2007), a metodologia da lingüística de corpus (Berber Sardinha, 2000, 2004; Tognini-Bonelli, 2001) e, em parte, princípios da terminologia (Aubert, 1996; Barros, 2004; Krieger & Finatto, 2004). Para a compilação do corpus de estudo foram utilizados artigos científicos extraídos de revistas brasileiras bilíngües da área médica, e para os corpora comparáveis foram coletados artigos de revistas médicas brasileiras e estrangeiras de renome nas comunidades médicas das respectivas subáreas. A pesquisa contou com o auxílio do programa de análise lexical WordSmith Tools versão 3.0. O levantamento de termos médicos com base em palavras-chave em português para cada subárea permitiu a elaboração de dois glossários com os respectivos termos equivalentes em inglês, acompanhados do seu contexto em ambas as línguas, que foram, em seguida, inseridos em um programa de memórias de tradução. Como a tradutora de cardiologia é falante nativa de língua portuguesa e o tradutor de cirurgia cardiovascular é falante nativo de língua inglesa, também foi possível comparar o uso de estratégias lingüísticas adotadas por parte de cada tradutor. / Abstract: This study compares medical terms based on keywords in Portuguese and their equivalents in English extracted from two parallel subcorpora of medical journals of Cardiology and Cardiovascular Surgery. In this investigation, features of simplification and explicitation were also observed in articles translated by two professional translators in each area. Moreover, the results from these two translators were compared to those from the translators of two other medical areas observed in a previous study (Paiva, 2006). The theoretical approach used was that of corpus-based translation studies (Baker, 1993, 1995,1996, 2000; Camargo, 2005, 2007), the methodology of corpus linguistics (Berber Sardinha, 2000, 2004; Tognini-Bonelli, 2001) and some principles of terminology (Aubert, 1996; Barros, 2004; Krieger and Finatto, 2004). For compiling the parallel subcorpora we used scientific articles from well-known bilingual Brazilian journals, and for the comparable corpora we used international journals in the same medical areas. The software WordSmith Tools, version 3.0 was applied in order to extract medical terms based on keywords in Portuguese for each area. This process led to the compilation of two glossaries containing medical terms in Portuguese, their English equivalents, as well as their contexts in both languages. Both glossaries were inserted into and tested in a program of translation memories. As the translator of Cardiology is a Portuguese native speaker and the translator of Cardiovascular Surgery is an English native speaker, it was also possible to compare some of their strategies. / Doutor

Tripneustes ventricosus (Lamarck 1816), a major near-shore herbivore in the Atlantic and Caribbean, has been harvested for human consumption in the Caribbean for centuries (Lawrence 2001a, b), occasionally at rates that exceed sustainability (Smith & Berkes 1991), and is among the species having economic importance (Lawrence & Bazhin 1998). Tripneustes ventricosus has recently been observed on the forereef controlling macroalgal growth in the absence of Diadema antillarum (Woodley 1999, Aronson & Precht 2000, Haley & Solandt 2001). Large-scale culturing has the potential to produce T. ventricosus in sufficient numbers to be used for: bioremediation of coral reef degradation, restocking of nearshore habitats, and the development of an aquaculture industry for one or more Caribbean islands. Heretofore, T. ventricosus has never been cultured from fertilization to exotrophic (feeding) juvenile. This work presents the results of experiments designed to measure the effectiveness of aeration methods and diets applicable for large-scale larval culture. Airlift aeration, used successfully in larger scale systems, was not effective in the 3.78-L (1-gallon) jars used for my experiments. Success was obtained in cultures reared without mechanical aeration. Fifteen percent of the larvae survived to day 33 and the 6-armed stage was reached. However, paddle aeration, used successfully in many small-scale experimental designs, produced the highest survival rates. Rhodomonas sp. produced the most rapid development (23 days to metamorphosis). Isochrysis aff. galbana (Tahitian strain) supported slower development (36 days to metamorphosis), but produced the highest (48%) survival rate. Cryptomonas sp., a mixture of Dunaliella tertiolecta and Isochrysis, and a mixture of Rhodomonas and Isochrysis were also tested and found to be inferior to the results produced with Isochrysis. Conclusions include: Tripneustes ventricosus larvae can be successfully cultured. While more rapid development occurs when the larvae are fed Rhodomonas, Isochrysis offers a more favorable combination of survival rate and development time. The perimetamorphic period, from rudiment formation to feeding juvenile, included a life stage heretofore unreported for T. ventricosus. Referred to as echinoporculus for its fanciful resemblance to a young pig, this stage was observed as the immediate metamorphic result in nearly half of the metamorphosed animals. Covering was observed in juveniles as small as 1.5 mm. The adornment remained on the aboral surface regardless of the juvenile’s orientation.

L'analyse numérique se développe en un outil puissant dans l'étude des équations aux dérivées partielles (EDPs), permettant d'illustrer des théorèmes existants et de trouver des conjectures. En utilisant des techniques sophistiquées, des questions apparaissant inaccessibles avant, comme des oscillations rapides ou un blow-up des solutions, peuvent être étudiées. Des oscillations rapides dans les solutions sont observées dans des EDPs dispersives sans dissipation où les solutions des EDPs correspondantes sans dispersion ont des chocs. Pour résoudre numériquement ces oscillations, l'application de méthodes efficaces introduisant peu de dissipation numérique artificielle est impérative, en particulier pour l'étude d'EDPs en plusieurs dimensions. Comme les EDPs étudiées dans ce contexte sont typiquement raides, l'intégration efficace dans le temps représente le principal problème. Une analyse des intégrants exponentiels et symplectiques a permi de déterminer les méthodes les plus efficaces pour chaque EDP étudiée. L'apprentissage et l'utilisation de techniques de parallélisation de codes numériques permet de nos jours de grandes avancées, plus précisément dans ce travail d'étudier numériquement la stabilité des solutions et l'apparition de blow-up dans l'équation de Davey-Stewartson. / Numerical analysis becomes a powerful resource in the study of partial differential equations (PDEs), allowing to illustrate existing theorems and find conjectures. By using sophisticated methods, questions which seem inaccessible before, like rapid oscillations or blow-up of solutions can be addressed in an approached way. Rapid oscillations in solutions are observed in dispersive PDEs without dissipation where solutions of the corresponding PDEs without dispersion present shocks. To solve numerically these oscillations, the use of efficient methods without using artificial numerical dissipation is necessary, in particular in the study of PDEs in some dimensions, done in this work. As studied PDEs in this context are typically stiff, efficient integration in time is the main problem. An analysis of exponential and symplectic integrators allowed to select and find the more efficient method for each PDE studied. The use of parallel computing permitted to address numerically questions of stability and blow-up in the Davey-Stewartson equation, in both stiff and non-stiff regimes.

Pas de résumé en français / No abstract

Dans ce travail, nous établissons et testons la technique de passage adiabatique parallèle (PAP) qui optimise le passage adiabatique en sélectionnant un trajet spécifique qui permet une dynamique rapide tout en préservant la robustesse standard de la technique adiabatique. L'intuition de PAP est basée sur le fait que l'on s'attend à une probabilité de transition nonadiabatique allant vers zéro par analyse Landau-Zener lorsque la courbure relative des deux énergies propres tend vers zéro. Dans ce travail nous testons la robustesse de cette technique et nous montrons sa supériorité par rapport à une dynamique avec un chirp linéaire traditionnel et des impulsions gaussiennes. Nous montrons son extension sur les transitions multiphotons dans les systèmes quantiques multiniveaux, où l'effet Stark joue un rôle important. Nous avons déterminé une forme optimale d'impulsion dans laquelle les décalages des niveaux sont simultanément compensés par la phase programmé de l'impulsion du laser. Ensuite, est présentée la technique de passage adiabatique parallèle local. Cela correspond à une dynamique où la valeur propre de l'état peuplé est parallèle à la plus proche au cours du temps. Nous développons l'idée de transfert de population par passage adiabatique de l'état fondamental à une superposition d'états. Le transfert est exécuté par des impulsions femtosecondes mises en forme dans le domaine spectral. Les états excités sont déplacés de façon dynamique en raison de la présence de composants non-résonnants des canaux différents. Nous montrons que ce décalage Stark peut être compensé par un autre champ ou par une mise en forme spécifique des impulsions appropriées. / In this work we establish and test the technique of parallel adiabatic passage (PLAP) thatoptimizes the adiabatic passage in the sense that it selects specific paths that allow a fastadiabatic dynamics while preserving the standard robustness of adiabatic techniques. Theintuition of PLAP is based on the fact that the use of eigenvalues that are parallel for alltimes is expected to lead to a small nonadiabatic transition probability from Landau-Zeneranalysis for two-state approximations. In this work we test the robustness of this techniqueand show its superiority to the traditional linearly chirped dynamics with Gaussian pulses. Weshow its extension for two-photon and three-photon transitions on multilevel quantum systems,where the Stark shift plays an important role in a strong field regime. We have determined anoptimal pulse shaping in which the static and dynamic energy level shifts are simultaneouslycompensated by a programmed phase of a laser field. Next the local parallel adiabatic passagetechnique is presented. This corresponds to a dynamics where the eigenvalue of the populatedstate is parallel to the closest one at all times.We extend the idea of population transfer by adiabatic passage from the ground state toa superposition of states. The transfer is executed with spectrally shaped femtosecond laserpulses. The excited states are dynamically shifted in energy due to the presence of nonresonantcomponents of different channels. We show that this Stark shift can be compensated by anotherfield or by shaping appropriately the pulses.

La synthèse des protéines de choc thermique (HSPs) est un moyen de défense développé par la cellule pour faire face aux diverses agressions auxquelles elle peut être soumise. En tant que chaperons, les HSPs participent aux mouvements intracellulaires des protéines, préviennent l'agrégation des protéines altérées, éliminent les protéines anormales et contribuent à la conformation correcte des peptides nouvellement synthétisées. Mon équipe d’accueil s’intéresse aux rôles des HSPs dans des processus cellulaires tels que l’apoptose et la différenciation cellulaire. Le but de mon travail de thèse consiste à étudier le rôle des protéines de choc thermique HSP90 et HSP70 au cours de la différenciation des monocytes en macrophages. J’ai dans un premier temps étudié l’implication de HSP90 dans la différenciation macrophagique. c-IAP1 est un membre de la famille des protéines inhibitrices de l’apoptose impliqué dans la régulation de l’apoptose, dans le cycle cellulaire et dans la signalisation cellulaire. Nous avons précédemment montré que c-IAP1 migre du noyau vers le cytoplasme au cours de la différenciation cellulaire. Nous démontrons dans ce travail que c-IAP1 est une protéine cliente de la protéine de choc thermique HSP90β. Dans trois différents modèles de différenciation, ces protéines interagissent et migrent ensemble du noyau vers le cytoplasme au cours de la différenciation cellulaire. L’inhibition de HSP90 ou la déplétion spécifique de l’isoforme β par des siRNA conduisent à sa dégradation par le protéasome. La fonction de chaperon moléculaire de HSP90 envers c-IAP1 est spécifique de l’isoforme β car la déplétion de l’isoforme α n’a pas d’effets sur c-IAP1. De plus l’inhibition de HSP90 ou la déplétion de HSP90β bloquent la différenciation cellulaire tout comme la déplétion de c-IAP1 par siRNA. La deuxième partie de montre travail a consisté à étudier le rôle de HSP70 dans la différenciation macrophagique. Nous montrons que cette protéine est fortement induite après stimulation des cellules par le facteur de croissance M-CSF et que son inhibition bloque la différenciation des monocytes en macrophage. HSP70 interagit avec la protéine Spi-1/Pu.1, facteur de transcription clé de la différenciation macrophagique. L’expression de Spi-1/Pu.1 augmente également au cours de la différenciation macrophagique et ce de manière similaire à celle de HSP70. Ceci suggère l’implication des facteurs de transcription responsables de l’induction des HSPs, les Heat Shock Factor (HSF). L’étude du promoteur de Spi-1/Pu.1 a révélé la présence d’une séquence ressemblant fortement aux éléments de réponse classiques sur lesquels se fixe HSF1. HSF1 est capable de se fixer sur le promoteur de Spi-1/Pu.1 et l’inhibition de HSF1 bloque l’expression de Spi-1/Pu.1. HSF1 participe donc au contrôle de l’expression de Spi-1/Pu.1 lors de la différenciation macrophagique. HSP90 et HSP70 sont donc essentielles à la différenciation macrophagique. Comprendre les mécanismes cellulaires impliqués dans les voies de différenciation se révèle extrêmement important puisque des altérations des mécanismes de l’hématopoïèse sont retrouvées dans plusieurs types de leucémies (leucémies aiguës myéloblastiques et leucémies myélo-monocytaires chroniques). Connaître le rôle des HSPs dans la différenciation cellulaire permettrait donc de développer de nouvelles stratégies thérapeutiques pour le traitement de ces pathologies. / Heat shock proteins (HSPs) are molecular chaperones whose expression is increased after many different stresses. They have a protective function helping the cell to cope with lethal conditions. These proteins play an essential role as molecular chaperones by assisting the correct folding of nascent and stress-accumulated misfolded proteins and by preventing their aggregation. My team is interested in understanding the roles of HSPs in two physiological related processes: apoptosis and cell differentiation. The aim of my work is to study the functions of HSP90 and HSP70 in macrophagic differentiation. I first studied the role of HSP90 in macrophagic differentiation. We previously reported that cellular inhibitor of apoptosis protein-1 (c-IAP1), migrated from the nucleus to the surface of the Golgi apparatus in cells undergoing differentiation. c-IAP1 is a member of the inhibitor of apoptosis protein (IAP) family which has demonstrated functions in cell death, cell signaling and mitosis. Here, we show that c-IAP1 is a client protein of the stress protein HSP90β. In three distinct cellular models, the two proteins interact and migrate from the nucleus to the cytoplasm during the differentiation process through a leptomycin B-sensitive pathway. Inhibition of HSP90 proteins by small chemical molecules and specific depletion of HSP90isoform by siRNA both leads to c-IAP1 degradation by the proteasomal machinery. This chaperone function of HSP90 towards c-IAP1 is specific of its β isoform as specific depletion of HSP90α isoform does not affect c-IAP1 content. Chemical inhibition of HSP90 or siRNA-mediated depletion of HSP90both inhibit cell differentiation, which can be reproduced by siRNA-mediated depletion of c-IAP1. Altogether, these results suggest that HSP90prevents auto-ubiquitination and degradation of its client protein c-IAP1, whose depletion would be sufficient to inhibit cell differentiation. The second part of my work consisted in the study of the role of HSP70 in macrophagic differentiation. We used two models of differentiation: human peripheral monocytes exposed to M-CSF and THP1 cells induced to differentiate by TPA. We found that in both models, HSP70 expression was induced during differentiation. Interestingly, the expression of Spi-1/Pu.1, a transcription factor essential for monocytes to differentiate, was similarly induced. Upon differentiation, both proteins co-localized in the nucleus and associated. Inhibition or down regulation of HSP70 induced Spi-1/Pu.1 degradation and blocks the differentiation process, indicating that the necessity of Spi-1/Pu.1 to be chaperoned by HSP70 during differentiation. Since Spi-1/Pu.1 promoter has a HSE-like, we studied whether transcription factors responsible for HSPs induction, HSF, could be involved. We show that although HSF2 do not seem involved, HSF1 binds to Spi-1/Pu.1 promoter and its inhibition blocks Spi-1/Pu.1 expression and monocytes differentiation. So HSP90 and HSP70 are essentials for macrophagic differentiation. Understanding monocyte differentiation regulation is important since defects of the differentiation process can lead to the development of leukemias (acute myeloid leukemia, chronic myelomonocytic leukemia). A better understanding of the roles of HSPs may provide new therapeutic strategies for the treatment of these pathologies.

Le récepteur au goût sucré est un hétérodimère composé de 2 sous-unités appelées T1R2 et T1R3. Chaque sous-unité appartient à la famille des récepteurs couplés aux protéines G de la classe C. Les membres de cette famille de récepteurs partagent une architecture commune, constituée d’un domaine N-terminal (DNT) de grande taille lié au domaine transmembranaire par une région riche en cystéine. Il a été montré que les DNT de T1R2 et T1R3 de souris étaient capables de lier des sucres naturels (saccharose et glucose) et le sucralose, avec des affinités distinctes et avec différents changements de conformation du domaine induits la fixation du ligand (Nie et al., Curr Biol, 2005). Cependant, les propriétés de liaison du DNT de T1R3 humain, ainsi que la contribution respective des 2 sous-unités dans la fonctionnalité du récepteur restent encore largement méconnues. Lors de cette étude, nous avons exprimé les DNT de T1R3 humain (DNT-hT1R3) et de souris à l’aide de la bactérie Escherichia coli, sous forme de protéines insolubles, appelés corps d’inclusion (CI). Les CI ont été purifiés puis solubilisés en utilisant un agent chaotrope. Le transfert des DNT dans leur état natif par un repliement in vitro, nécessite un criblage des conditions de repliement. Pour cela nous avons utilisé une approche factorielle en faisant varier des facteurs tels que le tampon, le pH ou la présence d’additifs. Les protéines repliées ont ensuite été caractérisées par différentes approches parmi lesquelles l’électrophorèse, la filtration sur gel, la fluorescence et le dichroïsme circulaire. Leur fonctionnalité a ensuite été vérifiée en mesurant les variations de l’intensité de fluorescence intrinsèque des protéines engendrées par l’ajout de sucralose. Le dosage d’Ellman a permis de déterminer la présence d’une seule cystéine libre dans DNT-hT1R3, qui a été confirmée, par purification, puis analyse des peptides trypsiques de la protéine. La présence de structures secondaires a été montrée par dichroïsme circulaire. Afin de caractériser les propriétés de liaison de DNT-hT1R3, un marquage fluorescent a été réalisé en utilisant une sonde sensible à l’environnement greffée de manière covalente à la protéine. Nous avons montré que la fixation d’un ligand sur la protéine marquée provoque des modifications conformationnelles qui ont permis de mesurer l’affinité du DNT de T1R3 pour diverses molécules sapides, avec des affinités en accord avec les données sensorielles. Cette étude a également permis de montrer que le calcium et le magnésium étaient capables de se lier à la protéine. Enfin, les propriétés de liaison de certains ligands ont été validées par microcalorimétrie. Ces résultats montrent que le DNT de T1R3 joue un rôle important, jusqu’à présent insoupçonné dans la reconnaissance des composés sucrés. / The sweet taste receptor is a heterodimer composed of two subunits called T1R2 and T1R3. Each subunit belongs to the class C of G protein-coupled receptors and is constituted by a large extracellular N-terminal domain (NTD) linked to the transmembrane domain by a cysteine-rich region. It has been shown that T1R2 and T1R3 NTDs are both able to bind natural sugars and sucralose with distinct affinities and undergo ligand-dependent conformational change (Nie et al., Curr Biol, 2005). However, the binding properties of T1R3 NTD and the relative contribution of the two subunits to the heterodimeric receptor function remained largely unknown. To characterize the binding properties of each subunit in greater depth a large quantity of proteins is required to use biochemical, biophysical and structural approaches. To accomplish this goal, we took advantage of bacterial expression strategy, which has been successfully used to produce functional mouse T1R2 and T1R3 NTDs (Nie et al., Curr Biol, 2005). Human T1R3 NTD was expressed in high level in Escherichia coli as insoluble aggregated protein (inclusion bodies). Transferring this protein into its native state by in vitro refolding requires screening to find buffer conditions and suitable additives. We established a factorial screen to detect folded functional T1R3 NTD based on intrinsic tryptophan fluorescence quenching by sucralose (known to bind mT1R3 NTD) and identified positive synergistic interactions between additives on refolding of T1R3 NTD. The soluble T1R3 NTD protein was then purified and characterized using electrophoresis, gel filtration, fluorescence and circular dichroism spectroscopy. T1R3 NTD is properly refolded and able to bind saccharide compounds with physiological relevant affinities. As expected, one free thiol could be measured in T1R3 NTD using Ellman’s assay suggesting that except one, all the cysteines are involved in disulfide linkages. This presence of this free cystein was also confirmed by mass spectrometry identification of the fluorescent peptide resulting from trypsin digestion. This free cysteine was used to covalently attach an environmentally sensitive fluorophore. This study also revealed that calcium and magnesium was able to bind T1R3 NTD. Due to the high quantities of functional NTD T1R3, the interactions with some sweeteners were characterized using microcalorimetry. Interestingly, we confirmed that T1R3 NTD is also able to bind numerous sweeteners with physiological affinities, suggesting that T1R3 NTD plays an important role in sweetener recognition.