Orientador: Jorg Kobarg / Tese (doutorado) - Universidade Estadual de Campoinas, Instituto de Biologia / Made available in DSpace on 2018-08-17T07:25:05Z (GMT). No. of bitstreams: 1 Nakahira_Marcel_D.pdf: 11988351 bytes, checksum: e05bc17d15fd4fe6b9d016e36caed880 (MD5) Previous issue date: 2010 / Resumo: Septinas são proteínas que apresentam um domínio bem característico de ligação ao nucleotídeo GTP (GTPase), bem como outros dois domínios variáveis (N e C-terminais). Sua principal característica é a habilidade de interagir entre si (septinas de grupos diferentes) e de formar filamentos. Esse fato está intimamente relacionado com as funções que desempenham na citocinese, exocitose, apoptose, entre outras. Além disso, elas são direta ou indiretamente envolvidas com situações patológicas, como o mal de Alzheimer e câncer. Acredita-se que uma das suas funções moleculares é a de atuar como "andaime" (scqffòld), promovendo assim a interação entre proteínas. Com isso as funções das septinas se tornaram muito mais amplas do que se acreditava inicialmente. Por isso nosso objetivo é identificar a diversidade de proteínas que interagem com as septinas 6 e 8. Achamos que essas duas septinas interagem com quase todas as outras septinas, exceto aquelas pertencentes ao mesmo "grupo 6". As septinas presas sempre apresentavam o domínio GTPase inteiro, mostrando sua importância na interação. Com isso propusemos baseado também em informação na literatura, um modelo para as unidades formadoras (trímero) dos filamentos, onde as septinas 6 e 8 possivelmente estejam sempre na unidade central do trímero, podendo ser permutadas por outras septinas do mesmo grupo (grupo 6). Ainda identificamos várias outras proteínas que sugerem um envolvimento das septinas em processos como a divisão celular, metabolismo, transcrição, e a degradação de proteínas, entre outros. A análise da presença das septinas 6,7,8 e 9 em células de mamíferos sugere que elas sejam encontradas em estruturas que parecem ser centrossomos, os quais são realacíonados com a divisão celular. Outro estudo realizado com a septina 1 inteira e sua região GTPase mostrou que ela se encontra em solução não como monômero mas sim como um trimero/tetrâmero. O domínio GTPase assim como a presença do nucleotídeo GTP no mesmo são fundamentais para a sua multimerização e estabilidade. Em comparação com dados da literatura a SEPT1 apresenta maior estabilidade sendo mais resistente ao desenovelamento térmico. Por fim, esses e outros resultados auxiliam na compreensão das funções das septinas e sua relação com os processos celulares. / Abstract: Septins have a central domain which binds GTP (GTPase domain) and two other variable domains at their N- and C-termim Their principal characteristic is the ability to bind to other septins, thereby forming filaments. This is intimately related to their functions in cytokinesis, exocytosis, and apoptosis, among others. They are also directly or indirectly associated to pathological processes such as the Alzheimer disease and cancer. It has been suggested that one of its molecular functions may be to act as a '"scaffold" protein to promote interactions among proteins. Thereby the functions of septins have turned out to be more diverse than initially predicted. Based on this our main objective here is lo identify the diversity of proteins thai interact with the human septins 6 and 8. We found that both interact with many other different septins, including almost all of them, except for septins of the same "group 6" (septins 6,8,10,11). The prey septins identified always contained the entire GTPase domain, indicating the importance of this domain for the observed interactions. Therefore, taking also into account data from the literature, we propose a model where the central unit of the trimeric septin is always occupied by septins of the group 6, specially septins 6 and 8. We also identified several other proteins to interact with septins 6 and 8, suggest involvement in processes such as cell division, metabolism, transcription, protein degradation, among others. The analysis of the expression of the septins 6,7,8 and 9 in mammalian cells suggests that they maybe localized to centrossomal structures, which are involved in cell division. Another study which involved full length as well as only the GTPase domain of Septin 1 showed that this septin is not found as a monomer but as a trimer/tetramer in solution. The GTPase domain as well as the presence of the bound nucleotide GTP, are fundamental for its multimerizalion and stability. In comparison to data from the literature, SEPT1 presents an elevated resistance to thermal denaturation. In summary, these and other data help us to understand the function of the septins and their relationship to cellular processes. / Doutorado / Bioquimica / Doutor em Biologia Funcional e Molecular

La polymérase NS5B du virus de l’hépatite C (VHC) porte une activité ARN polymérase ARN-dépendante essentielle pour la réplication de l'ARN génomique viral. Cette réplication implique la synthèse d'un intermédiaire de réplication de polarité négative. In vitro et probablement in vivo, la NS5B initie la synthèse d'ARN par un mécanisme de novo qui nécessite des interactions spécifiques entre la polymérase virale et des éléments des ARN viraux. Dans une première partie nous avons étudié le rôle du GTP et d’un domaine C-terminal nommé linker de la polymérase. Nos résultats démontrent que des concentrations élevées de GTP sont nécessaires pour la transition de l'initiation à l'élongation de la synthèse de l'ARN. Des mutations dans le linker à la position 556 ne modifient pas la concentration de GTP nécessaire pour la transition. Toutefois, l'initiation de la synthèse d'ARN est augmentée par la mutation S556K. Une analyse structurale menée en parallèle suggère une implication directe du linker dans l'initiation de novo de la synthèse de l'ARN. Dans les deuxièmes et troisièmes parties, nous avons étudié le rôle de motifs ARN dans la traduction et la synthèse de l’'ARN du VHC. Nous avons démontré que la tige boucle SL-E1 formée par la région entre les nt 177 et 222 de l'extrémité 3' de l’ARN (-) est importante pour la synthèse d'ARN in vitro par la NS5B recombinante et dans les cellules Huh7 exprimant le complexe de réplication (RC) du VHC. SL-E1 est impliquée dans l’initiation de la synthèse d’ARN, au moins in vitro. Nous avons également étudié le rôle des tiges boucles SLV et SLVI du gène core. Nos données n'ont pas montré de rôle évident de ces séquences ou de leur complément dans la synthèse de l'ARN in vitro par la NS5B recombinante et en culture cellulaire par le RC du VHC. Nous avons confirmé leur effet négatif sur la traduction IRES dépendante par interaction ARN-ARN longue distance entre SL-VI et le 5'UTR et démontré que le miR122 ne peut pas empêcher cet interaction. Par contre, la présence de SL-VI prévient l’inhibition de la traduction induite par l’interaction entre le domaine III de l’IRES et la tige boucle 5BSL3.2 en 3’ du génome. Ces résultats démontrent la complexité des interactions ARN/ARN et ARN/protéines dans la régulation de la réplication virale. / The hepatitis C virus (HCV) NS5B protein displays a RNA-dependent RNA polymerase activity essential for replication of the viral RNA genome. This replication involves the synthesis of a replication intermediate of negative polarity. In vitro and likely in vivo, the NS5B initiates RNA synthesis by a de novo mechanism which requires specific interactions between the polymerase and viral RNA elements. In the first part of results, we described a combined structural and functional analysis of HCV-NS5B to study the role of a C-terminal segment (termed linker) and of GTP in RNA synthesis. Our results demonstrated that high GTP concentrations are necessary for the transition from the initiation to the elongation of RNA synthesis, and that linker mutations at position S556 did not modify the GTP requirement of NS5B for this transition. However, the initiation of RNA synthesis was greatly enhanced by a S556K mutation. These results together with a structural analysis point to the direct involvement of the linker in the de novo initiation of RNA synthesis. In the second and third parts of results, we studied the role of RNA elements in RNA synthesis. We demonstrated that the SL-E1 stem–loop formed by nucleotides 177–222 from the 3’-end of the HCV (-) RNA is important for RNA synthesis both in vitro by the recombinant NS5B and in Huh7 cells by HCV replication complex (RC). We also showed that SL-E1 is involved in initiation of RNA synthesis, at least in vitro. Then we studied the role of other viral RNA elements in core coding sequences (SLV and SLVI stem loops) and the involvement of the microRNA miR122 in RNA translation and RNA synthesis. For SLV and SLVI, our data did not show any clear role of these core-coding sequences or of their complement in the (-) RNA in RNA synthesis both in vitro by the recombinant NS5B and in cell culture by HCV-RC. We confirmed their negative effect on HCV-IRES translation through long range RNA-RNA interaction between SL-VI sequences and the 5’UTR and demonstrated that miR122 cannot disrupted this interaction and switches the region to an open conformation. Conversely, our data indicated that the SL-VI domain can counteract the negative effect of the interaction between the domain III of IRES and the 5BSL3.2 stem loop localized at the 3’end of the genome. These results point to the complexity of RNA/RNA and RNA/proteins interactions in the HCV replication cycle.

Orientadores: Carla Fernanda Franco Penteado, Fernando Ferreira Costa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-26T18:17:52Z (GMT). No. of bitstreams: 1 Pallis_FlaviaRubia_D.pdf: 2236341 bytes, checksum: 3d0b519ba21fcfbc645749dccc82a06a (MD5) Previous issue date: 2015 / Resumo: A vaso-oclusão compreende um processo complexo e multicelular iniciado pela adesão de hemácias e leucócitos ao endotélio ativado, causando a obstrução vascular, ativação de células endoteliais vasculares e lesões que podem induzir uma resposta inflamatória contínua na anemia falciforme (AF). Estudos preliminares mostraram que os eosinófilos de pacientes com AF encontram-se ativados no sangue periférico, porém o envolvimento dessa célula no processo de vaso-oclusão ainda não está bem caracterizado. Pouco se sabe sobre o papel das proteínas da via das Rho GTPases na adesão dos eosinófilos ao endotélio vascular, bem como nas complicações pulmonares da doença. O objetivo desse trabalho foi avaliar in vitro o papel dos eosinófilos e das proteínas pertencentes à família das Rho GTPases na fisiopatologia da AF, e avaliar in vivo o papel dessa via na resposta inflamatória pulmonar induzida pela OVA em camundongos com AF. Sangue periférico de indivíduos saudáveis (controles) e pacientes com AF, em terapia com hidroxiureia (SSHU) ou não (SS), foi coletado para avaliar a adesão estática e em fluxo. A adesão dos eosinófilos de pacientes com AF à HUVEC estimulada com TNF-'alfa' foi significativamente maior quando comparado a adesão dos eosinófilos á HUVEC de indivíduos controle, em condições de fluxo e estática. No entanto, a adesão dessas células à HUVEC estimulada com TNF-? foi menor nos pacientes SSHU, quando comparada com o com aos SS. O pré-tratamento das HUVEC com o inibidor de Rac1, reduziu a adesão dos eosinófilos de pacientes SS ou SSHU. Em condições de fluxo, o número de eosinófilos aderidos à HUVEC reduziu significativamente quando estas foram tratadas com Y-27632 ou NSC23766 nos três grupos avaliados, porém essa inibição foi maior no grupo SS. In vivo a OVA induziu inflamação pulmonar caracterizada pelo aumento na contagem de leucócitos, principalmente eosinófilos, no lavado broncoalveolar dos camundongos. Essa inflamação foi potencializada nos camundongos com AF (Berkeley e Transplantados) quando comparados aos controles (C57BL6). Os camundongos Transplantados apresentaram níveis elevados de mediadores pró-inflamatórios, tais como, IL-4, IL-5, IL-6, IL-13, RANTES, Eotaxina, MCP-1, MMP-9 e TIMP-1 quando comparados aos camundongos do grupo não sensibilizado (NS). Nenhuma diferença foi observada nos níves de RNAm pulmonar das metaloproteinases e seus inibidores quando comparados os camundongos Transplantados do grupo OVA com os NS, porém a expressão de IL-6 é significativamente maior no pulmão dos animais falciformes desafiados com OVA. Na avaliação funcional dos brônquios, os dados mostraram que a potência para metacolina foi maior nos camundongos Berkeley, quando comparados aos Transplantados e ainda maior quando comparados com os C57BL6. Os animais que foram tratados com os inibidores da via RhoA/ROCK, Y-27632 ou Fasudil, apresentaram menor contagem total e diferencial das células que migraram para os pulmões e níveis reduzidos dos mediadores pró-inflamatórios avaliados. O pré-tratamento com o Fasudil reduziu a potência e a resposta máxima para metacolina dos brônquios da linhagem Berkeley. Não foi observada diferença na avaliação funcional da reatividade da traqueia no modelo de asma experimental nos grupos avaliados. Tomados em conjunto, os resultados indicam que a via RhoA/ROCK tem papel importante na adesão dos eosinófilos ao endotélio e que a inibição dessa via pode atenuar a asma associada a doença falciforme. Deste modo, sugerimos que os inibidores dessa via podem ser novos agentes terapêuticos para o tratamento das manifestações clínicas da AF / Abstract: Vaso-occlusion, comprising a complex and multicellular process, initiated by the adhesion of erythrocytes and leukocytes to the activated endothelium, leading to vascular obstruction, activation of vascular endothelial cells and continuous lesions in patients with sickle cell anemia (SCA). Preliminary results demonstrated that eosinophils from SCA patients exist in an activated state, however the participation of this cell in the vasooclusive process in not well establish. The role of proteins via the Rho GTPases in the adhesion of eosinophils to the vascular endothelium and in the pulmonary complications of SCA disease it is unknown. The aim of this study was to evaluate in vitro the role of the eosinophils and proteins belonging to the Rho GTPases family in SCA pathophysiology, and evaluate in vivo the role of this pathway in pulmonary inflammatory responses induced by OVA in SCA mice. Peripheral blood of healthy individuals (controls) and SCA patients in therapy or not with hydroxyurea (SCAHU) was collected for static and flow adhesion experiments. For static adhesion assays, eosinophils were isolated from control subjects or SCA patients on or off HU therapy. Adhesion of SCA eosinophils to HUVEC (Human Umbilical Vein Endothelial Cells) under TNF-'alfa'-stimulated conditions was higher when compared with control eosinophils, in flow conditions and static assay. Furthermore, SCAHU eosinophils demonstrated significantly lower adhesive properties, compared to SCA eosinophils. The adhesion of eosinophils from SCA or SCAHU patients were reduced when HUVEC were pretreated with NSC23766 inhibitor, compared to non-treated HUVEC. Under flow conditions, the number of eosinophils adhered to HUVEC cells was reduced when they were treated with Y-27632 or NSC23766 in the three groups investigated, however this inhibition was higher in the SCA patients. In vivo OVA induced lung inflammation, characterized by increased leukocyte particularly eosinophils, counts in the mice bronchoalveolar fuid (BALF). This inflammation was enhanced in SCA mice (Berkeley and Transplanted) when compared to controls (C57BL6). Transplanted mice showed high levels of pro-inflammatory mediators such as IL-4, IL-5, IL-6, IL-13, RANTES, Eotaxin, MCP-1, MMP-9 and TIMP-1 as compared to the control mice group (NS). Furthermore, the SCA mice induced with OVA showed higher lung gene expression of IL-6; however, there was no difference in the expression of MMP-2, MMP-8, MMP-9, MMP-12, TIMP-1 and TIMP-2, compared to NS. In the functional assessment of the bronchi reactivy, data showed that the potency to methacholine in asthmatic model was was greater in the SCA mice (Berkeley), compared to the Transplanted SCA mice, and even greater when compared to C57BL6. The animals treated with the inhibitors of the RhoA/ROCK pathway, Y-27632 or Fasudil, showed lower total and differential cells counts due to migration to the lungs. Pretreatment with the RhoA/ROCK pathway inhibitor significantly reduced the proinflammatory mediator levels evaluated. Treatment with Fasudil reduced maximal response for methacholine in bronchi from Berkeley model. No significant difference was observed in the tracheal reactivity after OVA challenge in all groups investigated. Taken together, our data indicated that RhoA/ROCK pathway play an important role in the eosinophil adhesion to the endothelium and, the inhibition of this pathway could alleviates asthma in SCA patients. Thus, we suggest that RhoA/ROCK inhibitors represents novel therapeutic agents for the treatment of SCA clinical manifestations / Doutorado

Esta tese trata do desenvolvimento de métodos bioanalíticos, baseados na técnica de eletroforese capilar, para duas aplicações distintas: a análise de complexos formados pela ligação entre proteínas e DNA e detecção e monitoramento de hidrólise de GTP catalisada por enzimas. No primeiro capítulo descreve-se uma investigação sobre a viabilidade de ensaios tipo EMSA (?electrophoretic mobility shift assay?) em chips com microcanais para eletroforese. Os fatores de transcrição purificados c-Jun(AP1) e p-50(NFkB) foram usados nos estudos de ligação a sondas de DNA fita dupla contendo as seqüências consenso de ligação dos fatores AP1, NFkB e AP2. As sondas de DNA sintéticas continham como modificação a marcação com o corante fluorescente Cy5 ligado à extremidade 5?, sendo que as mesmas seqüências não marcadas foram usadas para experimentos de competição. Ensaios tipo EMSA em chip puderam ser realizados em cerca de 2 h com baixo consumo de amostra e sem a necessidade de usar marcação com material radioativo. A sondas de DNA e os complexos formados nas reações de ligação foram analisados no Bioanalyzer usando tanto o procedimento padrão para a análise de DNA quanto um protocolo modificado. Nesta modificação não foi usado corante de intercalação mas 4,9 nM de Cy5-dCTP que foi adicionado ao gel, permitindo apenas a detecção de DNA previamente marcado. Apesar da necessidade de ajustes no método para cada proteína testada, foi mostrado o potencial de se substituir o método de EMSA em gel por métodos baseados em eletroforese em chip. Um experimento de competição foi realizado com sucesso mostrando a ligação do fator de transcrição p-50 à sonda contendo a seqüência consenso NFkB. Este experimento foi considerado como prova de princípio para a hipótese estudada. No segundo capítulo relata-se o desenvolvimento de um método para a detecção e monitoramento in vitro de atividade nucleotídeo-trifosfatase. O método que se mostrou robusto e reprodutível foi aplicado para investigar a atividade GTPase de uma proteína recombinante contendo o domínio catalítico de uma septina humana SEPT4 / Bradeiona (GST-rDGTPase). O exemplo de aplicação demonstra que a técnica de eletroforese capilar pode substituir o método tradicionalmente usado com marcação radioativa para detecção de atividade GTPase inclusive em estudos de cinética enzimática. Os parâmetros cinéticos determinados para a GST-rDGTPase foram: vmax = 1.7 μ M min-1 ± 0.1 and Km = 1.0 mM ± 0.3; kcat = 9 x 10-3 SM-1. O efeito de co-fatores como Mg2+ and Mn2+ também foi estudado. O método analítico descrito também se mostrou útil para a análise de di- e trifosfatos de outros nucleotídeos. / This Thesis concerns on the development of capillary electrophoresis-based bioanalytical methods for two distinct applications: DNA-protein binding analysis and monitoring of enzyme-catalyzed GTP hydrolysis. In the first chapter, the feasibility of on-chip electrophoretic mobility-shift assays (EMSA) is investigated. Purified transcription factors c-Jun(AP1) and p-50(NFkB) were used for binding studies to dsDNA probes containing the consensus sequences from AP1, NFkB and AP2 regulatory sequences. DNA probes were modified at the 5?-end with the Cy5 and unlabeled oligos were used for competition experiments. On-chip-EMSA could be carried out within ca. 2 h with low sample consumption and no need to handle radioactive material. Both, the dsDNA probes and the shifted oligos from binding reactions were analyzed on the ?2100 Bioanalyzer? using either, the standard procedure for DNA analysis or a modified protocol, in which no intercalating dye was used. Instead, 4.9 nM Cy5-dCTP was added to the gel matrix allowing the detection of only Cy5-labeled DNA. Despite the need of specific adjustments for each protein, we have shown the potential for replacing slab gel-based EMSA for on-chip methods. A competition experiment to show sequence specific binding of the transcription factor p-50 to the consensus sequence NFkB is presented as a proof of principle. In chapter II, a capillary electrophoresis-based method for in vitro detection and monitoring of nucleotide-triphosphatase activity is described. This robust and reproducible method was used to investigate GTPase activity of a recombinant protein construct containing the catalytic domain of Human SEPT4 /Bradeion ? (GST-rDGTPase). The application example demonstrates that the capillary electrophoresis technique can replace classical radioactive methods for GTPase activity assays and may be used as a routine analytical tool. Enzyme kinetics of GST-rDGTPase was studied and yielded the following kinetic parameters: vmax = 1.7 μM min-1 ± 0.1 and Km = 1.0 mM ± 0.3; kcat = 9 x 10-3 s-1. In addition the effect of co-factors such as Mg2+ and Mn2+ in the catalytic activity was investigated. The described analytical method was also shown to be useful to analyze di- and triphosphated forms of other nucleotides.

Thesis (M.Sc.). / Written for the Dept. of Anatomy and Cell Biology. Title from title page of PDF (viewed 2008/07/30). Includes bibliographical references.

Esta tese trata do desenvolvimento de métodos bioanalíticos, baseados na técnica de eletroforese capilar, para duas aplicações distintas: a análise de complexos formados pela ligação entre proteínas e DNA e detecção e monitoramento de hidrólise de GTP catalisada por enzimas. No primeiro capítulo descreve-se uma investigação sobre a viabilidade de ensaios tipo EMSA (?electrophoretic mobility shift assay?) em chips com microcanais para eletroforese. Os fatores de transcrição purificados c-Jun(AP1) e p-50(NFkB) foram usados nos estudos de ligação a sondas de DNA fita dupla contendo as seqüências consenso de ligação dos fatores AP1, NFkB e AP2. As sondas de DNA sintéticas continham como modificação a marcação com o corante fluorescente Cy5 ligado à extremidade 5?, sendo que as mesmas seqüências não marcadas foram usadas para experimentos de competição. Ensaios tipo EMSA em chip puderam ser realizados em cerca de 2 h com baixo consumo de amostra e sem a necessidade de usar marcação com material radioativo. A sondas de DNA e os complexos formados nas reações de ligação foram analisados no Bioanalyzer usando tanto o procedimento padrão para a análise de DNA quanto um protocolo modificado. Nesta modificação não foi usado corante de intercalação mas 4,9 nM de Cy5-dCTP que foi adicionado ao gel, permitindo apenas a detecção de DNA previamente marcado. Apesar da necessidade de ajustes no método para cada proteína testada, foi mostrado o potencial de se substituir o método de EMSA em gel por métodos baseados em eletroforese em chip. Um experimento de competição foi realizado com sucesso mostrando a ligação do fator de transcrição p-50 à sonda contendo a seqüência consenso NFkB. Este experimento foi considerado como prova de princípio para a hipótese estudada. No segundo capítulo relata-se o desenvolvimento de um método para a detecção e monitoramento in vitro de atividade nucleotídeo-trifosfatase. O método que se mostrou robusto e reprodutível foi aplicado para investigar a atividade GTPase de uma proteína recombinante contendo o domínio catalítico de uma septina humana SEPT4 / Bradeiona (GST-rDGTPase). O exemplo de aplicação demonstra que a técnica de eletroforese capilar pode substituir o método tradicionalmente usado com marcação radioativa para detecção de atividade GTPase inclusive em estudos de cinética enzimática. Os parâmetros cinéticos determinados para a GST-rDGTPase foram: vmax = 1.7 μ M min-1 ± 0.1 and Km = 1.0 mM ± 0.3; kcat = 9 x 10-3 SM-1. O efeito de co-fatores como Mg2+ and Mn2+ também foi estudado. O método analítico descrito também se mostrou útil para a análise de di- e trifosfatos de outros nucleotídeos. / This Thesis concerns on the development of capillary electrophoresis-based bioanalytical methods for two distinct applications: DNA-protein binding analysis and monitoring of enzyme-catalyzed GTP hydrolysis. In the first chapter, the feasibility of on-chip electrophoretic mobility-shift assays (EMSA) is investigated. Purified transcription factors c-Jun(AP1) and p-50(NFkB) were used for binding studies to dsDNA probes containing the consensus sequences from AP1, NFkB and AP2 regulatory sequences. DNA probes were modified at the 5?-end with the Cy5 and unlabeled oligos were used for competition experiments. On-chip-EMSA could be carried out within ca. 2 h with low sample consumption and no need to handle radioactive material. Both, the dsDNA probes and the shifted oligos from binding reactions were analyzed on the ?2100 Bioanalyzer? using either, the standard procedure for DNA analysis or a modified protocol, in which no intercalating dye was used. Instead, 4.9 nM Cy5-dCTP was added to the gel matrix allowing the detection of only Cy5-labeled DNA. Despite the need of specific adjustments for each protein, we have shown the potential for replacing slab gel-based EMSA for on-chip methods. A competition experiment to show sequence specific binding of the transcription factor p-50 to the consensus sequence NFkB is presented as a proof of principle. In chapter II, a capillary electrophoresis-based method for in vitro detection and monitoring of nucleotide-triphosphatase activity is described. This robust and reproducible method was used to investigate GTPase activity of a recombinant protein construct containing the catalytic domain of Human SEPT4 /Bradeion ? (GST-rDGTPase). The application example demonstrates that the capillary electrophoresis technique can replace classical radioactive methods for GTPase activity assays and may be used as a routine analytical tool. Enzyme kinetics of GST-rDGTPase was studied and yielded the following kinetic parameters: vmax = 1.7 μM min-1 ± 0.1 and Km = 1.0 mM ± 0.3; kcat = 9 x 10-3 s-1. In addition the effect of co-factors such as Mg2+ and Mn2+ in the catalytic activity was investigated. The described analytical method was also shown to be useful to analyze di- and triphosphated forms of other nucleotides.

The glyoxalase system mediates the conversion of methylglyoxal, a toxic ketoaldehyde, to D-lactic acid. The system is composed of two enzymes, glyoxalase I (Glo-I) and glyoxalase II (Glo-II), and exhibits an absolute requirement for a catalytic quantity of glutathione (GSH). Glo-I catalyzes the isomerization of a hemithioacetal, formed non-enzymatically from methylglyoxal and GSH, to the corresponding a -D-hydroxyacid thioester, s-D-lactoylglutathione (SLG). Glo-II catalyzes the irreversible breakdown of SLG to D-lactate and GSH. We have observed that ATP or GTP significantly inhibits the Glo-II activity of tissue homogenates from various sources. We have developed a rapid, one step chromatography procedure to purify Glo-II such that the purified enzyme remains "sensitive" to inhibition by ATP or GTP (Glo-II-s). Studies indicate that inhibition of Glo-II-s by nucleotides is restricted to ATP, GTP, ADP, and GDP, with ATP appearing most effective. Kinetics studies have shown that ATP acts as a partial non-competitive inhibitor of Glo-II-s activity, and further suggest that two kinetically distinguishable forms of the enzyme exist. The sensitivity of pure Glo-II-s to nucleotide inhibition is slowly lost on storage even at -80° C. This loss is accelerated at higher temperatures or in the presence of ATP. Kinetics studies on the resultant "insensitive" enzyme (Glo-II-i) show that a significant reduction of the affinity of the enzyme for the substrate, SLG, occurs and further suggest that only one form of the enzyme is kinetically distinguishable after "de-sensitization". Tryptophan fluorescence studies of the two enzyme preparations suggest that a subtle conformational change in the enzyme has occurred during de-sensitization. We have also observed that Glo-II-i is "resensitized" to nucleotide inhibition after incubation in the presence of a reagent that reduces disulfide bonds. The resensitized enzyme exhibits an increased KM value similar to that of the original Glo-II-s. Kinetics studies show that ATP or GTP again act as partial non-competitive inhibitors of the resensitized enzyme and suggest that only one form of the enzyme is present. The physiological significance of the two enzyme forms is discussed.

Systematic calculations were performed to uncover the free energy surfaces for hydrolytic reactions of methyl-diphosphate (in vacuum and implicit solvents) and GTP in EF-Tu active site. Density functional theory and ONIOM extrapolative QM/MM scheme were adopted for the assay. In accordance with experiments, the catalytic effect of the sodium cation was mild. It changes the conformation of GTP attracting its negatively charged oxygen atoms. hydrolýze GTP. The Na+ also equilibrates the charges of all phosphate groups of the GTP mostly by transferring electrons from gamma to beta-phosphate group, which is characteristic for the intermediate states during the hydrolytic reaction.

Rhes (Ras homolog enriched in striatum) has been identified as a novel monomeric G-protein involved in dopaminergic and other signaling in the striatum. Given the many effects of opioids that involve striatal circuitry, genetically engineered mice that are incapable of making Rhes (rhes-/-) and their control littermates (rhes+/+) were subjected to behavioral tests to determine if any differences existed in opioid analgesia, tolerance, withdrawal, reward, and locomotion. Rhes-/- mice showed an increased opioid mediated analgesia, along with an absence of tolerance and decrease in withdrawal when compared with rhes+/+ littermates. However, no significant changes were seen in opioid induced locomotor activation or conditioned place preference. These results provide strong evidence for the implication of Rhes in opioid signaling.

Based on what we have found, we proposed a model for Ni presenting by HypB involved in hydrogenase maturation. HypB binds two Ni ions in the apo- and GDP-bound form. Ni binding also induces dimerization of HypB. Upon GTP binding, HypB can bind an extra Ni ion at the dimeric interface. GTP hydrolysis will release the extra Ni ion, which may be subsequently inserted into hydrogenases during the maturation process. / Furthermore, two Ni binding sites were determined in a monomeric HypB. One is the cluster including C92, H93 and C122, the other is composed of H97 and H101. Upon GTP-dependent dimerization, HypB can bind an extra Ni ion. Our results have shown that the C92/H93/C122 is involved in binding the extra Ni ion, and such binding requires both cysteine residues in the reduced form. Since the GTP-induced dimerization of HypB is coupled to bind an extra Ni, so HypB could act as a GTP-mediated switch that regulate one Ni release from the GTP-bound form to the GDP-bound form. / In the future, we will attempt to crystallize AfHypB in complex with GDP, GTP analogue and AfHypA. Availability of good quality crystals will pave way for the structure determination of AfHypA and AfHypA/HypB complex. And the results obtained will provide a better understanding of the mechanism of functional interaction between HypA and HypB and how HypA and HypB play a role in Ni ion delivery for hydrogenase maturation. / The assembly of the [NiFe]-hydrogenases requires incorporation of Ni ions into the enzyme's metallocenter, which process requires the GTPase activity of HypB and HypA. Due to the essential role in assembly of the active site of hydrogenases, the two proteins were defined as hydrogenase maturation factors. To better understand the mechanism of GTP hydrolysis-dependent Ni delivery accomplished by HypB and HypA, our work focuses on the structure-function study of AfHypB from Archaeoglobus fulgidus and the functional interaction between AfHypA and AfHypB. / The intrinsic GTPase activity of AfHypB is very low, suggesting that AfHypB requires a G-protein activating protein (GAP) to activate its GTPase activity. Although AfHypB can interact with AfHypA to form 1:1 heterodimer, our data suggests that AfHypA is not a GAP for AfHypB. In addition, the FRET results showed that AfHypA could serve as a GEF (G-protein exchange factor) to activate the AfHypB from GDP-bound form to GTP-bound form and facilitate the dissociation of AfHypB dimer in the presence of GMPPNP. / Up to now, we have solved the structure of apo-AfHypB by X-ray crystallography. Crystals of AfHypB were grown using the hanging-drop-vapor-diffusion method and diffracted to ∼2.3 A. It belonged to space group P2(1)2(1)2, with unit cell dimensions a=72.49, b=82.33, c=68.66 A, alpha=beta=gamma=90°. Two molecules of AfHypB were found in an asymmetric unit. Structural comparison between the apo-AfHypB and GTP-bound HypB from M jannachii showed that the GTP binding broke the salt-bridge between K43 and D66, and induced conformational changes in the switch I loop and helix-3, which caused the HypB to form dimer and bind an extra Ni ion. The GTP-bound form of HypB was ready for Ni presenting. And GTP hydrolysis could induce the conformational changes of HypB in the switch I loop and helix-3, which dissociate the HypB dimer into the monomeric GDP-bound form. / Li, Ting. / Adviser: K. B. Wong. / Source: Dissertation Abstracts International, Volume: 70-09, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 98-104). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.