Les travaux décrits dans ce manuscrit concernent la synthèse, l’étude structurale et l’évaluation biologique d’oligopeptides abiotiques incorporant le gamma-aminoacide hétérocyclique nommé ATC (acide-4-Aminométhyl-1,3-Thiazole-5-Carboxylique). Les ATCs sont construits autour d’un noyau thiazole et présentent deux points de diversité structurale. De précédents travaux ont déterminé que la présence du noyau thiazole entre les positions alpha et béta bloquait l'angle zéta autour de 0°, structurant les homo-oligomères de poly-(S)-ATCs en une hélice 9 droite et les faisant ainsi entrer dans le domaine des foldamères. Dans une première partie, nous avons entrepris de développer une voie de synthèse simple, flexible et énantiosélective permettant d’obtenir les ATCs stéréochimiquement purs sur une échelle de plusieurs grammes à partir d'alpha-aminoacides commerciaux. L’introduction de la diversité chimique est réalisée via deux étapes-clés que sont la condensation croisée de Claisen et la réaction de cyclisation de Hantzsch. Puis l’identification des marqueurs de structuration RMN et IR-TF des oligomères d'ATCs a été mise à profit pour caractériser le repliement d’hétéro-oligomères combinant ATCs et alpha-aminoacides. Ainsi, une étude structurale par RMN, IR-TF, cristallographie RX et dichroïsme circulaire a démontré que l’enchaînement 1:1 (L)-alpha:(S)-ATC se structurait en un ruban, stabilisé par un réseau intramoléculaire de liaisons hydrogène bifides formant des pseudocycles à 9 et 12 chaînons. La distribution des chaînes latérales le long du squelette principal présente une forte analogie avec l’hélice alpha, ce qui pourrait constituer un atout majeur pour le développement de composés à finalité thérapeutique. La dernière partie de ce travail a porté sur la conception de pseudo-peptides amphipatiques pour des applications en temps qu'antimicrobiens. / This manuscript describes the synthesis, the structural study and the biological evaluation of abiotic oligopeptides incorporating the heterocyclic gamma-amino acid ATC (4-Aminomethyl-1,3-Thiazole-5 Carboxylic acid). This original block is built around a thiazole ring and displays two lateral chains. Previous work in our laboratory highlighted that the presence of the thiazole ring between the positions alpha and beta implied that zeta angle was blocked around 0°, thus structuring poly-(S)-ATCs homo-oligomers in a right-handed 9-helix foldamer. First, development of a simple, flexible and enantioselective synthesis on a few grams scale has allowed to get access of a highly diverse ATC library from commercial alpha-amino acids. Introduction of the chemical diversity occurs via two key steps implying a cross-Claisen condensation and a Hantzsch cyclization. Then identification of NMR and FT-IR structural markers of ATC-containing oligomers was used to characterize the folding propensity of hybrid α:ATC oligomers. We demonstrated that 1:1 (L)-alpha:(S)-ATC heterochiral oligomers are structured in solution in a new ribbon-like shape stabilized by a bidentate intramolecular hydrogen bond network forming 9- and 12-membered pseudorings. The distribution of lateral chains along the main skeleton shows a high analogy with alpha-helix thus constituting a major advantage for potential medicinal applications. The last part of this work has focused on the design of amphipathic ATC-containing pseudo-peptides as antimicrobial agents.

Septinas são proteínas pertencentes à família das GTPases que estão envolvidas em uma variedade de funções celulares. Verificamos através de análises bioinformáticas que Schistosoma mansoni, um dos principais agentes etiológicos da esquistossomose, possui quatro genes que codificam septinas (SmSept5, SmSept10, SmSept7.1 e SmSept7.2). O objetivo deste trabalho foi a produção heteróloga das proteínas codificadas por estes genes, visando estudos estruturais e funcionais das mesmas. As septinas SmSEPT5 e SmSEPT10 foram expressas em sistema recombinante e foi possível a obtenção de formas solúveis destas proteínas. Experimentos de gel filtração e cross-linking mostraram que elas são diméricas em solução e estáveis em ampla faixa de pH, embora agregados proteicos tenham sido observados com o aumento da temperatura. Ambas as proteínas foram capazes de ligar GTP e GDP, embora apenas SmSEPT5 tenha apresentado atividade GTPásica. Mg2+ se mostrou essencial para a ligação de GTP a ambas as proteínas, enquanto a ligação do GDP foi independente da presença deste cofator. Ensaios de cristalização com o domínio GTPase de SmSEPT10 resultaram em cristais de ótima qualidade cuja difração resultou na obtenção da estrutura com melhor resolução alcançada até o momento para septinas: 1.9 Å para a forma ligada a GDP e 2.1 Å para a forma ligada a GTP. A análise da sobreposição das estruturas obtidas resultou na observação do deslizamento de uma fita β em relação às demais, que acreditamos estar envolvido com o mecanismo de associação destas proteínas à membranas. Um sistema de coexpressão foi construído em que SmSEPT5, SmSEPT10 e SmSEPT7.2 foram coexpressas e copurificadas, resultando na verificação da formação de hetero-oligômeros e filamentos por estas proteínas. Tratamento de diversas fases do ciclo de vida do parasito com um composto (FCF) que afeta a dinâmica de filamentos de septina, resultou em um fenótipo reversível de paralisia no parasito. Estudos de imunolocalização revelaram a colocalização de septinas e actina em fibras musculares do parasito, sugerindo que a interação entre filamentos de septina e actina pode ter um papel importante nas funções motoras do parasita. A imunolocalização revelou ainda a presença de septinas em placas epiteliais ciliadas de miracídios, células germinativas de miracídios e esporocistos e protonefrídios de cercárias. Os resultados apresentados aqui constituem a primeira descrição de septinas em platelmintos e nos possibilitam o estabelecimento de correlações estruturais e funcionais entre septinas de S. mansoni e complexos análogos de septinas de outros organismos, contribuindo para a elucidação da função desta família de proteínas. / Septins belong to the GTPase family of proteins and are involved in a variety of cellular processes. We have identified four genes encoding septins in Schistosoma mansoni, one of the main causative agents of schistosomiasis, these genes were named SmSept5, SmSept10, SmSept7.1 e SmSept7.2. The aim of this study was to clone the cDNA of these genes in order to subject the resulting proteins to a set of biophysical and functional studies. Biophysical characterizations were undertaken with SmSEPT5 and SmSEPT10 because of the higher solubility of these proteins, which were dimeric in solution and stable over a wide range of pH, although increasing temperatures promoted the aggregation of these proteins. The nucleotide binding assays revealed that both were capable of binding GTP and GDP, although only SmSEPT5 presented GTPase activity. Mg2+ has shown to be essential for GTP binding in both proteins while GDP binding was independent of this cofactor. Crystallization assays with the GTPase domain of SmSEPT10 have resulted in crystals of high quality and consequently high resolution structures were obtained: 1.9 Å to the GDP bound form and 2.1 Å to the GTP bound form, the best resolution achieved to date for any septin member. The sobreposition of the structures obtained enabled us to observe a strand slippage in β3 strand suggesting that it might be part of an activation mechanism involved in the association of these proteins to membranes. A coexpression system was produced, in which SmSEPT5, SmSEPT10 and SmSEPT7.2 were coexpressed and copurified. These proteins were able to assemble into heterocomplexes that further polymerize into filaments. Functional studies performed with a drug (FCF) that affects the dynamics of septin filaments have resulted in a reversible paralysis phenotype in the parasite. Immunolocalization experiments revealed the colocalization of septins and actin in muscular structures of the parasite, suggesting that the interaction of septin and actin filaments might have an important role in the motor activity of the parasite. The immunolocalization also revealed the presence of septins in the ephitelial plates of miracidia, germ cells of miracidia and sporocysts and protonephridia of cercariae. The results presented here constitute the first description of septins in phatyhelmintes and enabled us the establishment of structural and functional relaltionships among septins from S. mansoni and analogous septin complexes in other organisms, contributing to elucidate the function of this family of proteins.

O gene hrcA é encontrado em quase todos os ramos da árvore filogenética das eubactérias, e seu produto, a proteína HrcA, funciona como repressor da expressão dos operons de choque térmico groESL e dnaKJ, ligando-se à seqüência repetida invertida denominada CIRCE (controlling inverted repeat of chaperonin expression) presente na região regulatória destes operons. O sistema HrcA-CIRCE está, portanto, amplamente representado nas eubactérias. Particularmente, em Caulobacter crescentus, uma α-proteobactéria, este sistema está envolvido no controle da expressão do operon groESL durante o ciclo celular da bactéria. Conhecer a estrutura e as interações de HrcA é importante para entender este processo. Neste trabalho são apresentadas as análises de seqüência das HrcA\'s de C. crescentus e de Xylella fastidiosa, uma proteobactéria do grupo γ, as quais são muito similares. Este estudo levou à proposta de um modelo estrutural com a delimitação dos domínios da proteína, os dobramentos de cada domínio, com base nas interações da HrcA de C. crescentus com o elemento CIRCE e ATP, que estão sendo caracterizadas em nosso laboratório, assim como a atribuição de aminoácidos e motivos conservados funcionais. Adicionalmente, embora a expressão da HrcA recombinante de X. fastidiosa não tenha tido sucesso, a HrcA recombinante de C. crescentus purificada tem se prestado aos ensaios espectroscópicos, ainda que tenha sido detectada uma microagregação que está sendo enfrentada com um protocolo de purificação baseado no uso de α ciclodextrina. Os estudos espectroscópicos preliminares da HrcA C. crescentus dão suporte ao modelo estrutural proposto. / The hrcA gene is found in almost all branches of the filogenetic tree of eubacteria, and its product, the protein HrcA, functions as a repressor regulating the expression of the heat shock operons groESL and dnaKJ, by binding to the inverted repeat sequence called CIRCE (controlling inverted repeat of chaperonin expression). The system HrcA-CIRCE, therefore, is widely represented in eubacteria. Specifically in Caulobacter crescentus, an α-proteobacterium, this system is involved in the cell-cycle control of groESL expression (Baldini et al, 1998). Knowledge of the structure of HrcA and its interactions is important to understand this process. This work presents the analysis of the sequences of HrcA from C. crescentus and Xylella fastidiosa, a proteobacterium of the γ group, which are very similar. A structural model has been proposed, with protein domain delimitation, specific domain folding, based on known interactions of C. crescentus HrcA with the CIRCE element and ATP, obtained in our laboratory, as well as assignment of functional residues and conserved motifs. Additionally, even though no sucess was obtained the expression of recombinant HrcA from X. fastidiosa, purified recombinant HrcA from C. crescentus has been shown to be suitable for spectroscopic studies, in spite of microagregation observed, which is being faced with a purification protocol based on the use of α cyclodextrin. The preliminary spectroscopic studies of HrcA from C. crescentus support the proposed structural model.

Les travaux décrits dans ce manuscrit concernent la synthèse d’oligomères de γ-amino acides hétérocycliques contraints, appelés ATCs (acides 4-Amino-(méthyl)-1,3-Thiazole-5-Carboxyliques), leur application en catalyse énamine et leur étude structurale. Les monomères d’ATC sont construits autour d’un noyau thiazole inséré entre les carbones Cα-Cβ, permettant de limiter la valeur de l’angle dièdre ζ à 0°. La présence de deux points de substitution, sur le carbone γ asymétrique et en position 2 du noyau aromatique, permet une large diversification structurale des ATCs. Ainsi, plusieurs séries d’oligomères ont été synthétisées par couplages peptidiques sur support solide. Une étude structurale de ces oligomères par RMN, IR-TF, cristallographie RX et dichroïsme circulaire a démontré qu’ils adoptaient une structure en helice C9, résultant d’un réseau de liaisons hydrogène de type COi---NHi+2 s’établissant tout au long de la séquence. L’objectif du projet présenté ici vise à étudier l’impact de la conformation des architectures développées, à la fois sur la sélectivité et sur l’induction asymétrique dans la réaction de nitro-Michael pour trois réactifs différents. Le dernier axe de ce travail a été de développer une méthode de modélisation sous contraintes RMN spécifique à la génération de modèles tridimentionel d’oligomères d’ATCs. / The work described in this manuscript is devoted to the synthesis of heterocyclic constrained γ-amino acids, named ATCs (4-Amino-(methyl)-1,3-Thiazole-5-Carboxylic acids), their application in enamine catalysis and their structural study. ATC monomers are built around a thiazole ring providing a conformational limitation around the Cα and Cβ at 0°. The presence of two diversification points both on the γ asymmetric carbon and on the position 2 of the aromatic ring, allows a large structural diversification of the ATCs. Therefore, several oligomers were synthesized using solid phase peptide synthesis. A structural study of these oligomers, employing NMR, FTIR, circular dichroism and crystallography RX, demonstrated that they adopt a C9-right-handed helix stabilized by a hydrogen bond pattern between COi---NHi+2 along the helix. The objective of the project presented in this manuscript was the design and the structural characterization of molecular edifices with predictable folding properties and the systematic study of structure-function relationships in the nitro-Michael addition reaction, for three different substrates. Eventually, the last part of this work focused on the development of a new methodology, specific to ATC-oligomers, to perform 3D-modelling studies using NMR refinement.

No description available.

Le complexe de la cohésine est requis pour de nombreuses transactions chromosomiques, la cohésion des chromatides soeurs, la réparation des dommages à l'ADN, la régulation de la transcription et le contrôle de l'architecture de la chromatine en 3D. La manière dont la cohésine engage la chromatine est restée une question majeure. Les sous-unités de base de cohesin, Smc1, Smc3, Scc1 assemblent un complexe en forme d’anneau via la connexion des domaines SMC «charnières» hétérodimères fournis par Smc1 et Smc3, et par la liaison des domaines SMC ATPase par Scc1. D'autres facteurs jouent un rôle dans différents aspects de la fonction de la cohésine, tels que Scc3, qui favorise l'association de la cohésine à l'ADN, les complexes de chargement et de déchargement, Scc2-Scc4 et Pds5-Wapl, respectivement responsables du chargement de la cohésine et de sa dissociation de la chromatine. . Au cours de la phase S, une acétyltransférase appelée Eco1 acétyle le domaine ATPase de Smc3 et déclenche l’établissement de la cohésion. Pour augmenter davantage la cohésion, un facteur métazoaire supplémentaire, la sororine forme un complexe avec Pds5 pour empêcher la liaison de Wapl. Pendant la métaphase, la cohésine centromérique est protégée par shugoshin-PP2A. Chez les métazoaires, la cohésine est libérée des chromosomes en deux étapes. La première nécessite la phosphorylation de la cohésine et permet à Wapl de se lier à nouveau à Pds5 afin d'assurer la médiation de la libération de cohésine indépendante du clivage à partir des bras des chromosomes. La seconde se produit lors de la réalisation de l'assemblage de la broche et nécessite l'activation d'une protéase appelée séparase, ce qui entraîne le clivage Scc1, libérant ainsi des chromatides soeurs à séparer dans des cellules filles. Au-delà de la cohésion, il devient également évident que la cohésine joue des rôles plus divers en interagissant avec une multitude d'autres facteurs, notamment la CTCF, une protéine connue comme un isolant, dont il a été rapporté qu'elle collabore à la détermination du génome 3D. structure.Pour comprendre comment la cohesine engage l'ADN, j'ai étudié les propriétés de liaison à l'ADN de sous-complexes précédemment identifiés. En déterminant une structure cristalline de la levure Scc3 liée à un fragment de la sous-unité Scc1 kleisin et de l'ADN, j'ai pu démontrer que Scc3 et Scc1 forment un module d'interaction composite de l'ADN. Le sous-complexe Scc3-Scc1 engage un ADN double brin à travers une surface conservée, chargée positivement. Nous démontrons que ce domaine est requis pour la liaison à l'ADN par Scc3-Scc1 in vitro, ainsi que pour l'enrichissement de la cohésine sur des chromosomes et pour la viabilité cellulaire. Ces résultats suggèrent que l'interface de liaison à l'ADN Scc3-Scc1 joue un rôle central dans le recrutement des complexes de la cohésine sur les chromosomes et donc que cette dernière exécute fidèlement ses fonctions lors de la division cellulaire.Pour étudier les bases moléculaires de la collaboration fonctionnelle signalée entre la cohésine et le CTCF dans la définition de la structure chromosomique 3D, j'ai identifié et déterminé la structure d'un complexe ternaire composé de SA2 humain (un orthologue de Scc3), de Scc1 et de CTCF. La structure révélait un motif de liaison SA2-Scc1 très répandu qui était présent non seulement dans le CTCF, mais aussi dans d’autres facteurs connexes fonctionellement, tels que shugoshin et Wapl. Les tests de compétition déroulants ont indiqué que la liaison de ces facteurs à SA2-Scc1 était mutuellement exclusive, ce qui suggère fortement qu'ils interagissent avec la cohésine via des mécanismes similaires. Pour démontrer ce principe, j'ai pu déterminer une structure de shugoshin en complexe avec SA2-Scc1, ce qui a confirmé que tant le shugoshin que le CTCF se lient à la même surface conservée sur la cohésine. / The cohesin complex is required for numerous chromosomal transactions including sister chromatid cohesion, DNA damage repair, transcriptional regulation and control of 3D chromatin architecture. How cohesin engages chromatin has remained a major question. The basic subunits of cohesin, Smc1, Smc3, Scc1 assemble a ring-shaped complex via connection of the heterodimeric SMC ‘hinge’ domains contributed by of Smc1 and Smc3, and through linkage of the SMC ATPase domains by Scc1. Additional accessory factors play important roles in different aspects of cohesin function, such as Scc3, which promotes the association of cohesin with DNA, the loading and unloading complexes, Scc2-Scc4 and Pds5-Wapl respectively, responsible for cohesin loading and its disassociation from chromatin. During S phase, an acetyltransferase called Eco1 acetylates the ATPase domain of Smc3 and triggers the stabilization, or establishment, of cohesion. To further augment cohesion, an additional metazoan factor, sororin forms a complex with Pds5 to prevent Wapl binding. During metaphase, centromeric cohesin is protected by the shugoshin-PP2A complex. In metazoans, cohesin is released from chromosomes in two major steps. The first requires cohesin phosphorylation and allows Wapl to bind Pds5 again to mediate cleavage-independent release of cohesin from chromosome arms. The second transpires upon fulfilment of spindle assembly and requires activation of a protease called separase, resulting in Scc1 cleavage, thus releasing sister chromatids to be segregated into daughter cells. Beyond cohesion, it is also becoming apparent that cohesin plays more diverse roles by interacting with a plethora of other factors, most notably CTCF, a zinc finger protein that is known as an insulator, which has been reported to collaborate with cohesin in determining 3D genome structure.To understand how cohesin engages DNA, I investigated the DNA binding properties of previously identified globular sub-complexes. By determining a crystal structure of the budding yeast Scc3 bound to a fragment of the Scc1 kleisin subunit and DNA, I could demonstrate that Scc3 and Scc1 form a composite DNA interaction module. The Scc3-Scc1 subcomplex engages double-stranded DNA through a conserved, positively charged surface. We demonstrate that this conserved domain is required for DNA binding by Scc3-Scc1 in vitro, as well as for the enrichment of cohesin on chromosomes and for cell viability. These findings suggest that the Scc3-Scc1 DNA-binding interface plays a central role in the recruitment of cohesin complexes to chromosomes and therefore for cohesin to faithfully execute its functions during cell division.To investigate the molecular basis of the reported functional collaboration between cohesin and CTCF in defining 3D chromosome structure, I identified and determined the structure of a ternary complex composed of human SA2 (an orthologue of Scc3), Scc1 and CTCF. The structure revealed a wide-spread SA2-Scc1 binding motif which was found to be present not only in CTCF, but also other functionally related factors, including shugoshin and Wapl. Competition pulldown assays indicated that binding of these factors to SA2-Scc1 was mutually exclusive, which strongly suggested that they interact with cohesin via similar mechanisms. To demonstrate this principle, I was able to determine a structure of shugoshin in complex with SA2-Scc1, which confirmed that both shugoshin and CTCF bind the same conserved surface on cohesin.

Due to the extreme properties of diamond, such as extreme hardness, high thermal conductivity, high electrical breakdown strength, high electron and hole mobilities and large band gap, it is of interest to study this material in detail. Before advantage can be taken of diamond’s properties for high-temperature, high-power electronic applications successful doping/ion implantation of diamond must be achieved. This requires an understanding of the types of defects produced during ion irradiation. In the present work, type IIa diamond has been irradiated with various doses of 320keV Xe ions at room temperature. Analytical techniques used are electron spin resonance spectroscopy, Raman spectroscopy, transmission electron microscopy and electron energy loss spectroscopy. Previous models have suggested that upon ion impact, amorphous and/or graphitized clusters are formed in diamond, which will overlap at a critical dose to form a semi-continuous graphitized layer. (For complete abstract open document)

Due to the extreme properties of diamond, such as extreme hardness, high thermal conductivity, high electrical breakdown strength, high electron and hole mobilities and large band gap, it is of interest to study this material in detail. Before advantage can be taken of diamond’s properties for high-temperature, high-power electronic applications successful doping/ion implantation of diamond must be achieved. This requires an understanding of the types of defects produced during ion irradiation. In the present work, type IIa diamond has been irradiated with various doses of 320keV Xe ions at room temperature. Analytical techniques used are electron spin resonance spectroscopy, Raman spectroscopy, transmission electron microscopy and electron energy loss spectroscopy. Previous models have suggested that upon ion impact, amorphous and/or graphitized clusters are formed in diamond, which will overlap at a critical dose to form a semi-continuous graphitized layer. (For complete abstract open document)

L'hydrolyse de l'ATP en ADP constitue la principale source d'énergie de la cellule. Le transport de ce nucléotide depuis son lieu de synthèse vers le cytosol est essentiel pour la plupart des réactions métaboliques et nécessite un passage à travers les membranes. Ainsi, un grand nombre de transporteurs d'ATP/ADP sont présents dans les différents organites tels que les mitochondries, les chloroplastes, et autres types de plastides mais aussi chez les bactéries pathogènes (Rickettsia prowazekii, Protoclamydiae amoebophila) (Trentmann et al, 2007).L'équipe s'intéresse principalement à 2 types de transporteurs d'ADP et d'ATP, la famille des transporteurs mitochondriaux (MCF) et la famille des NTT (plastes et bactéries). Malgré des fonctions similaires, ces 2 familles de transporteurs possèdent des propriétés biochimiques et structurales différentes. De nos jours, il n'existe aucune information structurale disponible sur la famille des NTTs. La détermination de cette structure pourrait permettre de comprendre le mécanisme de transport de ces transporteurs mais plus généralement comprendre le transport de l'ATP et ADP dans les cellules.Une étude a été initiée sur la structure et la fonction de la famille des NTT plus particulièrement des transporteurs chloroplastiques d'Arabidopsis thaliana mais aussi des transporteurs bactériens. Toutefois, ma thèse concerne principalement les transporteurs chloroplastiques NTT1 et NTT2. Ces 2 isoformes sont localisées dans la membrane interne des chloroplastes et permettent de pourvoir le stroma en ATP lorsque la photosynthèse ne peut pas avoir lieu par manque de lumière.Nous avons déterminé et optimisé les conditions de surexpression des 2 isoformes dans un système hétérologue puis de purification en détergent). Nous avons mis au point des méthodes permettant de caractériser le transporteur en solution et de mesurer son activité dans le but d'aboutir à une étude structurale. Des pistes de cristallisation ont également étaient obtenues. / ATP is the main energy currency in the cell and its transport across membranes is essential for most of the metabolic reactions. A large number of ATP/ADP transporters are present in the different cell organelles such as mitochondria, chloroplasts, other types of plastids and some are also found in bacteria (Rickettsia prowazekii, Protoclamydiae amoebophila) (Trentmann et al, 2007). The team is mainly interested in two distinct transporters families, the mitochondrial carrier family (MCF) and the NTT family. Despite similar function, mitochondrial ADP/ATP transporters (Pebay-Peyroula et al, 2003) and NTT proteins exhibit different structural and biochemical properties. To date no structural information is available on the NTT family. The determination of a structure would help for understanding the transport mechanism of these carriers and more generally the different mechanisms of the transport of ADP and ATP within the cell.We initiated a structure-function study on the NTT family focusing on chloroplast transporters from Arabidopsis thaliana and also from bacteria. My thesis is focused on chloroplast NTT1 and NTT2. These isoforms are localized in the inner membrane of chloroplast. They transport ATP inside the chloroplast in order to supply the different reactions occurring in the stroma when the photosynthesis does not occur.We have determined and optimized conditions to overexpress these 2 isoforms in heterologous systems and to purify the protein in detergents. We have also set up tools to characterize the carrier in solution and to measure its transport activity opening the way to functional and structural studies. We obtained promising crystallization hits.

Face à l'augmentation générale de la consommation d'énergie, l'exploitation du Gaz Naturel Liquéfié (GNL) connaît un intérêt croissant, d'où un marché en forte expansion avec de nombreux projets d'installation de terminaux méthaniers. Les installations de gaz naturel liquéfié ont la particularité de fonctionner à très basses températures (~ -160°C), ce qui exige l'utilisation de matériaux particuliers présentant des caractéristiques adaptées aux températures extrêmes. Cette étude nous a permis d'évaluer le comportement structural de l'acier 9% Ni métal de base, consistant en une phase ferrique d'un grain martensitique en présence d'austénite, utilisé dans la construction du réservoir interne de stockage du GNL.Ce métal présente des domaines inhomogènes au niveau mésoscopique principalement formés par la phase austénitique riche en Ni mis en évidence par la diffusion des neutrons aux petits angles. Suite à une déformation mécanique, une augmentation du pourcentage de la phase austénitique est observée au niveau de la zone de déformation plastique. Ce phénomène est probablement dû à la diffusion préférentielle du Ni le long des dislocations au cours du traitement mécanique et son accumulation au niveau de cette zone. Au cours du processus de soudage, une diffusion intergranulaire du Ni au sein de la zone affectée thermiquement (ZAT) est observée. Ce phénomène permet de stabiliser la phase austénitique au niveau de la ZAT et d'améliorer les propriétés mécaniques au sein de cette zone. La déformation mécanique appliquée à basse température sur l'acier 9% Ni, ne détériore pas les propriétés structurales de ce matériau. / Due to the overall increase in energy consumption, the use of the Liquefied Natural Gas (LNG) is experiencing an increasing interest, resulting in a rapidly growing market with many LNG terminals installation projects. LNG installations have the particularity of operating at extremely low temperatures (~ -160°C), which requires materials with specific characteristics suitable to extreme temperatures. This study allowed us to evaluate the structural behavior of the base metal 9% Ni steel, consisting of a ferritic phase with a martensitic grain in the presence of residual austenite, used in the construction of the inner wall of LNG storage tank. This metal presents, at the mesoscopic level, non-homogeneous domains formed primarily by the Ni rich austenitic phase revealed by small angle neutron scattering. Due to a mechanical deformation, an increase in the percentage of the austenitic phase is observed at the plastic deformation zone. This phenomenon is probably due to the preferential diffusion of Ni along dislocations during the mechanical treatment and its accumulation at this area. During the welding process, a grain boundary diffusion of Ni in the Heat Affected Zone (HAZ) is observed. This phenomenon allows the stabilization of the austenitic phase at the HAZ and the improvement of the mechanical properties within this area. Mechanical deformation applied at low temperatures on the 9% Ni steel, does not deteriorate the structural properties of the material.