Flavonoids are secondary metabolites that are important in plant defense, protection, and human health. Most naturally-occurring flavonoids are found in glucosylated forms. Glucosyltransferases catalyze the transfer of glucose from high-energy sugar donors to an acceptor molecule. The grapefruit flavonol-specific 3-O-glucosyltransferase (F3-O-GT) is highly substrate and regio-specific. The goal of this research is to unravel the amino acid residues responsible for the grapefruit enzyme’s rigid specificity, while attempting to alter the regiospecific glucosylation pattern through site-directed mutagenesis and homology modeling. This research tested the hypothesis that substitution of potential key amino acid residues within the grapefruit Cp-F3-O-GT with position equivalent residues within F7-O-GTs would alter the 3-O-glucosylation of the enzyme. Results reveal that specific single point mutations of residues are capable of abolishing enzymatic activity. Recombinant mutant G392E retained activity and showed an increased affinity for kaempferol relative to the wild-type; however, the rigid regiospecific glucosylation pattern of the enzyme was retained.

No description available.

Mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator protein (CFTR) cause cystic fibrosis (CF), the most common life-shortening genetic disease among Caucasians. Although general features of the structure of CFTR have been predicted from homology models, the conformational changes that result in channel opening and closing have yet to be resolved. We created new closed- and open-state homology models of CFTR, and performed targeted molecular dynamics simulations of the conformational transitions in a channel opening event. The simulations predict a conformational wave that starts at the nucleotide binding domains and ends with the formation of an open conduction pathway. Experimentally confirmed changes in side-chain interactions are observed in all major domains of the protein. We also identified unique-to-CFTR substitutions that may have led to channel activity in CFTR. Molecular modeling and simulations are used to compare the effects of these substitutions against a canonical ABC transporter, and suggest that gain of channel function in CFTR may have risen from loss of ATPase function at its NBDs. The models and simulation add to our understanding of the mechanism of ATP-dependent gating in this disease-relevant ion channel.

<p>Although it has been known for many years that B-cyclin/CDK complexes regulate the assembly of the mitotic spindle and entry into mitosis, the full complement of relevant CDK targets has not been identified. It has previously been shown in a variety of model systems that B-type cyclin/CDK complexes, kinesin-5 motors, and the SCF<super>Cdc4</super> ubiquitin ligase are required for the separation of spindle poles and assembly of a bipolar spindle. It has been suggested that in the budding yeast,<italic> Saccharomyces cerevisiae</italic>, B-type cyclin/CDK (Clb/Cdc28) complexes promote spindle pole separation by inhibiting the degradation of the kinesins-5 Kip1 and Cin8 by the anaphase-promoting complex (APC<super>Cdh1</super>). I have determined, however, that the Kip1 and Cin8 proteins are actually present at wild-type levels in yeast in the absence of Clb/Cdc28 kinase activity. Here, I show that Kip1 and Cin8 are in vitro targets of Clb2/Cdc28, and that the mutation of conserved CDK phosphorylation sites on Kip1 inhibits spindle pole separation without affecting the protein's <italic>in vivo</italic> localization or abundance. Mass spectrometry analysis confirms that two CDK sites in the tail domain of Kip1 are phosphorylated in vivo. In addition, I have determined that Sic1, a Clb/Cdc28-specific inhibitor, is the SCF<super>Cdc4</super> target that inhibits spindle pole separation in cells lacking functional Cdc4. Based on these findings, I propose that Clb/Cdc28 drives spindle pole separation by direct phosphorylation of kinesin-5 motors. </p><p>In addition to the positive regulation of kinesin-5 function in spindle assembly, I have also found evidence that suggests CDK phosphorylation of kinesin-5 motors at different sites negatively regulates kinesin-5 activity to prevent premature spindle pole separation. I have also begun to characterize a novel putative role for the kinesins-5 in mitochondrial genome inheritance in <italic>S. cerevisiae</italic> that may also be regulated by CDK phosphorylation. </p><p>In the course of my dissertation research, I encountered problems with several established molecular biology tools used by yeast researchers that I have tried to address. I have constructed a set of 42 plasmid shuttle vectors based on the widely used pRS series for use in <italic>S. cerevisiae</italic> that can be propagated in the bacterium Escherichia coli. This set of pRSII plasmids includes new shuttle vectors that can be used with histidine and adenine auxotrophic laboratory yeast strains carrying mutations in the genes <italic>HIS2</italic> and <italic>ADE1</italic>, respectively. My new pRSII plasmids also include updated versions of commonly used pRS plasmids from which common restriction sites that occur within their yeast-selectable biosynthetic marker genes have been removed in order to increase the availability of unique restriction sites within their polylinker regions. Hence, my pRSII plasmids are a complete set of integrating, centromere and 2&#61549; episomal plasmids with the biosynthetic marker genes <italic>ADE2</italic>, <italic>HIS3</italic>, <italic>TRP1</italic>, <italic>LEU2</italic>, <italic>URA3</italic>, <italic>HIS2</italic> and <italic>ADE1</italic> and a standardized selection of at least 16 unique restriction sites in their polylinkers. Additionally, I have expanded the range of drug selection options that can be used for PCR-mediated homologous replacement using pRS plasmid templates by replacing the G418-resistance kanMX4 cassette of pRS400 with MX4 cassettes encoding resistance to phleomycin, hygromycin B, nourseothricin and bialaphos. Finally, in the process of generating the new plasmids, I have determined several errors in existing publicly available sequences for several commonly used yeast plasmids. Using updated plasmid sequences, I constructed pRS plasmid backbones with a unique restriction site for inserting new markers in order to facilitate future expansion of the pRS/pRSII series.</p> / Dissertation

Submitted by Rosana Amâncio (rosana.amancio@ufcg.edu.br) on 2018-07-12T22:11:47Z No. of bitstreams: 1 ERICA RENATA NOGUEIRA SÁ CAETANO - DISSERTAÇÃO PPGCNBio 2016..pdf: 2506925 bytes, checksum: 2aee1b855d59914fe68902bb6ec5b3fe (MD5) / Made available in DSpace on 2018-07-12T22:11:47Z (GMT). No. of bitstreams: 1 ERICA RENATA NOGUEIRA SÁ CAETANO - DISSERTAÇÃO PPGCNBio 2016..pdf: 2506925 bytes, checksum: 2aee1b855d59914fe68902bb6ec5b3fe (MD5) Previous issue date: 2016-07-14 / CNPq / Miraculina é uma glicoproteína que possui uma incrível propriedade de converter o sabor amargo em doce. Como a miraculina não apresenta sabor algum e tem um baixo teor calórico, esta proteína pode ser usada como adoçantes direcionados para pacientes com doenças relacionadas ao consumo excessivo de açúcar. Estudos comprovaram que membros da família de proteínas miraculinas também possuem atividade de inibidor de tripsina do tipo Kunitz, atuando como agentes naturais de defesa da planta contra pragas e predadores. Diante disso, proteínas do tipo miraculina são de grande relevância para aplicações biotecnológicas. Esse estudo teve como objetivo geral realizar a caracterização estrutural e funcional comparativa de duas miraculinas de Citrus sinensis, por meio de modelagem e docking molecular. Modelos 3D foram gerados e validados para as miraculinas CsMir1 e CsMir4, tripsina de Acryrthosiphon pisum e para os receptores de sabor doce mT1R2 e T1R3 de Mus musculus. Modelos homodiméricos foram gerados para CsMir1 e CsMir4 e modelo heterodimérico foi gerado para mT1R2-T1R3. Estudos da atividade de inibidor de tripsina foram feitos para CsMir1 e CsMir4 por interação com tripsina. Para analisar a atividade de modificação de sabor doce, foi realizada a interação das miraculinas com o receptor mT1R2-T1R3. Como resultados, os modelos dos monômeros e dímeros criados foram considerados bons modelos, válidos e confiáveis, com representações muito próximas das estruturas nativas dessas proteínas. A miraculina CsMir1, na forma monomérica ligou-se a tripsina de A. pisum e na sua forma dimérica ligou-se ao receptor heterodimérico mT1R2-T1R3 através do domínio ATD da subunidade T1R2, entretanto o potencial para as atividades de inibição de proteases e de indução ou inibição a modificação de sabor amargo/azedo em doce é menor do que para a CsMir4. A miraculina CsMir4, na sua forma monomérica ligou-se a tripsina de A. pisum, possivelmente apresentando atividade de inibição de proteases. CsMir4, na sua forma dimérica, ligou-se ao receptor heterodimérico mT1R2-T1R3, através do domínio ATD da subunidade T1R2, potencialmente apresentando atividade de indução ou inibição a modificação de sabor amargo/azedo em doce em M. musculus. / Miraculins are glycoproteins that displays a remarkable property in bitter to sweet taste conversion. As miraculin does not have any taste and has a low calorie, this protein can be used as sweeteners targeted to patients with diseases related to excessive sugar consumption. Studies have shown that members of miraculins protein family also display inhibitor activity against the Kunitz trypsin, acting as natural agents of plant defense against pests and predators. In this context, miraculin proteins are of great relevance for biotechnological applications. The aim of this research was to characterize structurally and functionally two miraculins of Citrus sinensis using in silico tools. Tridimensional models were built and validated for CsMir1 and CsMir4 miraculins, Acryrthosiphon pisum trypsin and for Mus musculus mT1R2-T1R3 receptor. Homodimeric and hetrodimeric models were generated for miraculins (CsMir1, CsMir4) and mT1R2-T1R3, respectively. Molecular docking simulations were performed to investigate the trypsin inhibitory activity and taste conversion activity of CsMir1 and CsMir4. The results showed that the predicted models were reliable and presented good quality parameters. The monomeric CsMir1 miraculin bound to A. pisum trypsin, while its dimeric form bound to ATD domain of the mT1R2-T1R3, although its potential as trypsin inhibitor and bitter/sweet taste modifier were minor than that presented by its homologous CsMir4. The dimeric form of CsMir4 bound to mT1R2-T1R3 receptor in the ATD domain, which strongly suggests bitter/sweet taste modifier activity in M. musculus.

Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-09-20T14:33:37Z No. of bitstreams: 1 TeseDSC.pdf: 4230414 bytes, checksum: d505357e4ed13e446578eb00507beec7 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-21T12:36:04Z (GMT) No. of bitstreams: 1 TeseDSC.pdf: 4230414 bytes, checksum: d505357e4ed13e446578eb00507beec7 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-21T12:36:19Z (GMT) No. of bitstreams: 1 TeseDSC.pdf: 4230414 bytes, checksum: d505357e4ed13e446578eb00507beec7 (MD5) / Made available in DSpace on 2016-09-21T12:36:27Z (GMT). No. of bitstreams: 1 TeseDSC.pdf: 4230414 bytes, checksum: d505357e4ed13e446578eb00507beec7 (MD5) Previous issue date: 2015-06-16 / Não recebi financiamento / Malaria is an acute febrile disease caused by protozoan parasites of the genus Plasmodium, being the species P. falciparum responsible for the most severe forms and deaths caused by the disease. These parasites have developed resistance to commonly used drugs and therefore there is a need to develop new antimalarial agents. Aryltetralone lignans are compounds that show antiplasmodial activity in vitro against P. falciparum, but its mechanism of action is still not fully understood. In this work, we postulate a plausible mode of action of some aryltetralone lignans and according to the obtained results we suggest modifications to the ligands for a better biological activity. In order to achieve our objectives we first performed a search for similar chemical compounds, for which their macromolecular targets were known. From the results obtained, P. falciparum tubulin was selected as a potential target for these lignans. Since there is no experimentally determined three-dimensional structure for this protein, we performed a molecular homology modeling of P. falciparum tubulin and the structure of bovine tubulin complexed with colchicine was selected as template. The analysis of the obtained model showed that the three dimensional structure of Plasmodium tubulin is conserved in relation to the bovine tubulin with some important substitutions occurring in the colchicine binding site region: Ala250B by Ser248B, Ala316B by Cys314B and Ile318B by Met316B. Then, molecular docking of the aryltetralone lignans, colchicine and podophyllotoxin was performed in the modeled P. falciparum tubulin. The docking calculations results allowed to conclude firstly that, although the amino acid substitutions in the binding site, the colchicine binding mode in the P. falciparum tubulin is exactly the same as that already described in the literature for bovine tubulin. As for podophyllotoxin, a different binding mode from that described in the literature for bovine tubulin was obtained due to the replacement of Ala250B by Ser248B and the Val318B by Met316B. For the aryltetralone lignans studied, three different binding modes were obtained: one exhibited by compounds 1, 2 and 3, another by 4 and 6, and a third one by 5. The lignans 1, 2 and 3 are oriented in a way so that the C ring containing the dimethoxy or methylenedioxy group is positioned in the same region obtained for the ring containing the trimethoxy group in the case of colchicine and podophyllotoxin, performing a C-H...π interaction with Leu246B. Lignans 4 and 6 orient themselves with the aromatic ring C between Ala180A and Leu246B and being held in this position by C-H...π interactions. Lignan 5 is oriented with the aromatic ring C between Leu246B and Leu253B, performing C-H...π interactions with these residues, in a similar way to what was obtained with colchicine in this site. So the likely mechanism of action of the aryltetralone lignans studied here would be their binding to the same colchicine binding site in the tubulin protein of P. falciparum and thereby interrupting the divisions and other cellular functions. / A malária é uma doença febril aguda causada por protozoários parasitas pertencentes ao gênero Plasmodium, sendo a espécie P. falciparum a responsável pela maioria das formas severas e mortes pela doença. Estes parasitas desenvolveram resistência aos fármacos comumente utilizados e, portanto, existe a necessidade de se desenvolver novos agentes antimaláricos. Lignanas ariltetralônicas são compostos que apresentam atividade antiplasmodial in vitro contra o P. falciparum, porém seu mecanismo de ação ainda não é totalmente compreendido. Neste trabalho, conseguimos postular o modo de ação de algumas lignanas ariltetralônicas e, a partir dos resultados obtidos, sugerimos modificações nestes compostos de modo a obter uma melhoria na sua atividade biológica. Para isso, primeiramente foi realizada uma busca por compostos químicos semelhantes, cujos alvos macromoleculares eram conhecidos. A partir dos resultados obtidos, selecionou-se a tubulina do P. falciparum como potencial alvo para estas lignanas. Como não há estrutura tridimensional determinada experimentalmente para esta proteína, foi realizada a modelagem molecular por homologia da tubulina do P. falciparum, selecionando como molde a estrutura da tubulina bovina complexada com colchicina. A partir da análise do modelo construído, verificou-se que a estrutura tridimensional da tubulina do Plasmodium é conservada em relação à tubulina bovina e que ocorrem algumas substituições importantes na região do sítio de ligação da colchicina: Ala250B por Ser248B, Ala316B por Cys314B e Ile318B por Met316B. Em seguida, foi realizado o docking molecular das lignanas ariltetralônicas, da colchicina e da podofilotoxina na tubulina do P. falciparum. Os resultados do docking permitiram concluir primeiramente que, embora ocorram algumas substituições de aminoácidos no sítio, o modo de ligação da colchicina na tubulina do P. falciparum é exatamente o mesmo ao já descrito na literatura para a tubulina bovina. Já para a podofilotoxina, foi obtido um modo de ligação diferente do descrito na literatura para a tubulina bovina, devido à substituição da Ala250B pela Ser248B e da Val318B pela Met316B. Para as lignanas ariltetralônicas estudadas, foram obtidos três modos de ligação diferentes: um exibido pelos compostos 1, 2 e 3, outro para 4 e 6 e um terceiro modo exclusivo para 5. As lignanas 1, 2 e 3 orientam-se de modo que o anel C, que contém o grupo dimetóxi ou metilenodióxi, se posiciona na mesma região do sítio obtida para o anel contendo o grupo trimetóxi da colchicina e da podofilotoxina, realizando uma interação C–H...π com a Leu246B. As lignanas 4 e 6 orientam-se com o anel aromático C entre a Ala180A e a Leu246B, sendo mantido nesta posição por interações C–H...π. No caso da lignana 5, esta se orienta com o anel aromático C entre a Leu246B e Leu253B, realizando interações C– H...π com estes resíduos, semelhante ao que foi obtido para a colchicina neste sítio. Assim, o mecanismo provável de ação das lignanas ariltetralônicas aqui estudadas passaria pela sua ligação ao mesmo sítio de ligação da colchicina na proteína tubulina do P. falciparum e, com isso, interrompendo as divisões e outras funções celulares.

Os hormônios tireoidianos estão envolvidos em vários efeitos regulatórios, em órgãos diversos. Suas variações no organismo estão relacionadas a quadros clínicos de grande relevância. A presente dissertação trata do estudo de duas proteínas diretamente relacionadas ao complexo sistema regulatório associado a tais hormônios. A primeira delas é a globulina de ligação à tiroxina (TBG), responsável pelo transporte da grande maioria dos hormônios tireoidianos circulantes, e cujas alterações estão relacionadas a falhas na interpretação de testes de avaliação da função tireoidiana, podendo levar a tratamentos desnecessários. A segunda proteína é o receptor tireoidiano (TR), responsável pela mediação dos efeitos regulatórios do hormônio tireoidiano, tendo sua estimulação de atividade transcricional relacionada à ligação do hormônio em um de seus domínios. A TBG foi estudada através da técnica computacional conhecida como modelagem molecular por homologia, aplicada à proteína em sua forma selvagem e a mutantes observados no Brasil, com o intuito de relacionar a inviabilidade de tais mutantes a aspectos estruturais. Foi proposto que, para dois dos mutantes estudados, a formação das estruturas secundárias como na forma nativa da proteína seria inviável, enquanto que para o terceiro mutante a inviabilidade poderia ser causada por enovelamento incorreto causado por uma possível interação entre um resíduo de cisteína adveniente da mutação e outros resíduos do mesmo aminoácido em posição fisicamente próxima. O estudo do TR teve como base as estruturas cristalográficas das duas isoformas humanas do receptor (hTR &#945; e hTR &#946;) quando ligadas ao tiromimético GC-1. Esse composto tem a propriedade de ligar-se preferencialmente à isoforma &#946;, o que pode ter interessantes aplicações farmacológicas. A análise comparativa da ligação do GC-1 às duas isoformas mostrou que, para tal composto, a seletividade se deve a mudanças consideráveis no modo de ligação ao hTR &#945; e hTR &#946;. Para a isoforma , há dois modos de ligação, envolvendo conformações alternativas de ligante e proteína, onde em uma delas a ligação é mais favorável e semelhante à ligação do composto à isoforma , enquanto no outro modo de ligação há a perda de uma interação direta entre composto e proteína, explicando a mais baixa afinidade do GC-1 à isoforma quando comparado à isoforma . O mecanismo de -seletividade para esse composto está relacionado a um átomo de oxigênio específico que não existe no ligante natural do receptor, o que fornece úteis informações para a criação de novos compostos. / The thyroid hormones are involved in various regulatory effects, on diverse organs. Their fluctuations on the body are related to clinical scenarios of great relevance. This work deals with the study of two proteins which are directly related to the regulatory system associated to these hormones. The first one is the thyroxine-binding globulin (TBG), responsible for the transport of a large part of the thyroid hormones in serum, and whose variations are related to misinterpretation of thyroid function tests. The second protein is the thyroid receptor (TR), responsible for the mediation of the thyroid hormone regulatory effects . the transcriptional activity being related to ligand binding to one of the protein domains. The wild-type TBG and three mutants discovered in Brazil were studied by the computational technique known as homology modeling. The purpose of this investigation was to relate protein unviability to structural aspects. It was proposed that, for two mutants, the unviability was related to the impossibility of secondary structure formation as needed to form the native folding, while the third mutant the cause could be the formation of an incorrect folding due to possible interactions involving a cysteine residue created by the mutation and other nearby cysteine residues. The thyroid receptor was studied in the light of the x-ray structures of the two isoforms of the protein (hTR &#945; and hTR&#946;) bound to GC-1, a synthesized compound which resembles the thyroid hormones. This ligand binds preferably the isoform, a feature that may have interesting pharmacological applications. The comparative analysis of GC-1 binding to the two isoforms allowed the construction of a structural basis of its -selectivity property, which is due to considerable differences in the binding modes for the two isoforms. This involves two different configurations of ligand and protein conformations for the isoform - on one of them, the ligand docks to the molecule the same way it docks to hTR&#946;, while on the second configuration it loses one direct interaction to the protein, explaining its lower affinity to hTR &#945; when compared to hTR&#946;. The -selectivity mechanism for this compound is related to a specific oxygen atom which doesn?t exist on the receptor endogenous ligand, providing useful information for the development of new compounds.

Marihuana (Cannabis sativa) é uma planta amplamente usada pelo ser humano há séculos e suas várias aplicações têm benefícios importantes. A planta Cannabis sativa tem sido usada pelo homem como comida, em práticas medicinais e rituais religiosos. Seus efeitos incluem analgesia, alteração na percepção, cognição, memória e atividade psicomotora. Os compostos canabinoides têm sido usados na quimioterapia do câncer e AIDS. No entanto, o uso da marijuana é um problema devido aos seus efeitos indesejados, nesse caso, a atividade psicotrópica apresentada pelos compostos canabinoides. Devido ao grande interesse nos efeitos causados pelos compostos extraídos da Cannabis, vários estudos têm sido realizados com o objetivo de melhor entender a relação entre a estrutura química e a atividade biológica de compostos canabinoides, bem como as suas interações com os receptores canabinoides, CB1 e CB2. Ambos são receptores de sete transmembranas (TM) que pertencem à família classe A, como a da rodopsina bovina, dos receptores acoplados à proteína-G (GPCRs). Esta Tese representa um estudo da modelagem molecular do receptor CB1 baseado na estrutura da rodopsina bovina já publicada, uma vez que a maioria dos efeitos terapêuticos dos canabinoides tem sido mostrado serem mediados pelo receptor canabinoide CB1. Esse trabalho fornece, também, uma investigação da interação ligante-receptor e um estudo da ativação do receptor CB1. Ao final, foi feito um estudo de docking a fim de entender as principais interações que ocorrem entre o &#8710;9 -THC, a principal molécula psicoativa presente na Cannabis, e seu receptor CB1. / Marijuana (Cannabis sativa) is a widely used plant and its various applications have important benefits. The plant Cannabis sativa has been used by man for centuries for eating, medicinal practices and religious rituals. In human subjects, its effects include analgesia, alterations in perceptions, cognition, memory and psychomotor activity. The cannabinoid compounds have been used in the cancer chemotherapy and AIDS, but the use of marijuana is a problem due to its unwanted effects (the psychotropic activity presented by the cannabinoid compounds). Due to the great interest in the effects caused by the compounds extracted from the Cannabis, several studies have been carried out with the aim to better understand the relationship between the chemical structure and the biological activity of cannabinoid compounds, as well as their interaction with the cannabinoid receptors (CB1 and CB2). Both are seven-transmembrane (TM) receptors that belong to the rhodopsin-like family Class A of G protein coupled receptors (GPCRs). This work represents a study of molecular modeling of the CB1 receptor based upon the published bovine rhodopsin structure, once the most of the therapeutic effects of cannabinoids compounds have been shown to be mediated through the CB1 cannabinoid receptor. This work also provides an investigation of the CB1 receptor-ligand interaction and a study of the CB1 receptor activation. A docking study was also performed in order to understand the main interactions that occur between &#8710;9 -THC, the principal psychoactive molecule present in cannabis, and its receptor CB1.

Parmi les 57 cytochromes P450 identifiés lors du séquençage complet du génome humain, on en dénombre environ 15 dont on ne connaît pratiquement rien de leurs rôles physiologiques, de leurs substrats, et de leurs structures, d’où le nom de «P450 orphelins». Le CYP2U1 est l’un des cytochromes P450 les plus fortement exprimé au niveau du cerveau et du cervelet mais c’est aussi l’un des plus conservé parmi les différentes espèces du règne animal. Ce travail de thèse a tout d’abord consisté à optimiser les conditions d’expression du CYP2U1 sous une forme active. Un premier système d’expression dans la levure Saccharomyces Cerevisiae a permis une production d’un complexe CYP2U1-P450 réductase catalytiquement actif permettant des études de recherche de substrat. Un second système d’expression dans Escherichia Coli devrait permettre d’obtenir de plus grandes quantités d’enzyme soluble destinée à des études structurales. Dans un second temps, une recherche de substrats a été effectuée à l’aide d’analyse d’incubats par chromatographie liquide couplée à une détection par spectrométrie de masse. A ce jour, un screening dirigé de plus de soixante-dix molécules, substrats de P450s de la famille 2, a permis d’identifier les premiers substrats exogènes du CYP2U1, les analogues de terfénadone et la débrisoquine. D’autre part, une étude par modélisation moléculaire de la structure du CYP2U1 a été effectuée. Cette étude montre que le CYP2U1 diffère de tous les autres P450s par la présence d’un insert très spécifique dans son domaine N-terminal. Des modèles par homologie basés sur les structures cristallographiques des P450s de la famille 2 ont été construits. Ces modèles ont été validés par dynamique moléculaire et ont permis de proposer un mode d’interaction avec la membrane, d’identifier la position des canaux d’accès ainsi que de déterminer la topologie du site actif. Enfin, un docking des premiers substrats exogènes au sein du site actif du CYP2U1 a permis de confirmer la régioselectivité des hydroxylations catalysées par le CYP2U1. / Among the 57 human cytochrome P450 genes that have been identified; substrates, structure and physiologic role of 15 of them is practically unknown. They are called orphan. One of them, CYP2U1 is one of the most expressed cytochrome P450 in the brain and in the cerebellum but also one of the most conserved isoform in the all animal kingdom. This manuscript first describes the optimization of the heterologous expression of an active form of CYP2U1. Expression in a eukaryotic host, yeast Saccharomyces Cerevisiae first allows the production of a catalytic active CYP2U1-P450 reductase complex needed for substrate screening. Another expression system in a prokaryote host Escherichia Coli will allow higher production rate of a truncated and soluble form of the protein which will permit structural studies. Then a directed substrate screening was performed with the liquid chromatography – mass spectrometry analysis of CYP2U1 incubations. To date, 70 molecules, CYP2 family substrates, were tested that allow the identification of the two first exogenous CYP2U1 substrates: débrisoquine and terfenadone analogs. A structural study was achieved using a homology tridimensional model of the enzyme. We have found that CYP2U1 is longer than the other human CYPs, with an N-terminal 20 amino acids insertion, located after the  helical membrane spanning domain. Structural models were built using six crystallized human CYP2s as templates. Molecular dynamics experiments in membrane suggested a specific interaction with the membrane. The active site topology and the access channels were also determined and a docking of the two first exogenous CYP2U1 substrates was performed in order to confirm the regioselective hydroxylation activities observed in vitro.

No description available.