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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

Quantitative Evaluation of Saponin Content in Du Puits Alfalfa Foilage (Medicago sativa L.) with Trichoderma

Li-Chun, Wang 01 May 1969 (has links)
Selections in Du Puits alfalfa (Medicago sativa L. ) were evaluated for saponin content. The data obtained from the Trichoderma bioassay were converted to saponin values by regressions and standard curves. It was necessary to adjust the concentration of alfalfa extract in the bioassay so that the saponin content in alfalfa was estimated in that portion of the curve showing a marked response to saponin. A different regression was established for each group of low and high saponin plants of Du Puits alfalfa. The standard curve prepared with extract of Du Puits alfalfa used on the basis of its saponin content or the commercial purified saponin could be utilized for estimating the saponin content in Du Puits alfalfa, because the results were comparable to the values determined by chemical analysis. Attention should be given to the concentration of extract used when converting the bioassays to actual saponin content, because certain concentrations gave values more similar to the chemical analysis than others. Two cycles of selection for low and high saponin content in Du Puits alfalfa were involved in the tests. The results indicated that the saponin content in low saponin plants was lower and that the saponin content in the high saponin plants was higher than in the unselected plants. They also showed that average saponin values in low and high saponin and the unselected plants were similar between the second and the third cuttings, but different from the first cutting
242

EVALUATION AND FUNCTIONAL CHARACTERIZATION OF BIOCONTROL AGENTS TARGETING SELECT SOILBORNE PATHOGENS OF SOYBEAN

Filgueira Pimentel, Mirian 01 June 2021 (has links) (PDF)
Soybean crops are vulnerable to a wide range of pathogens that reduce yield and cause extensive losses worldwide. In the United States, the soilborne pathogens Pythium spp., causing soybean damping-off, and Fusarium virguliforme, causing sudden death syndrome (SDS) of soybean, have been among the top diseases that most reduced soybean yields. This study demonstrated that biological control using native fungal antagonists could be a powerful tool to integrate with current management strategies for more efficient control of Pythium damping-off and SDS in soybean. Trichoderma spp. and Clonostachys rosea demonstrated the ability to mycoparasitize and antagonize the pathogens using different mechanisms and exhibited a protective effect on soybean in field conditions. The development of an efficient biological control program for disease management relies on a deep understanding of the BCA-pathogen interaction’s biology. This research also uncovered the molecular mechanisms involved in the F. virguliforme-T. afroharzianum interaction by using a dual RNAseq approach. Significant changes in both fungal organisms’ transcriptomes were discovered at different stages in their interaction. The results provided here can contribute to the future implementation of effective biological control programs for soybean. The benefits may also extend to other crops.
243

Application of Nepalese <i>Trichoderma</i> spp. with Anaerobic Soil Disinfestation (ASD) to Control Soil-borne Diseases and Effect of ASD on Weeds

Khadka, Ram Bahadur January 2021 (has links)
No description available.
244

Production of Carbohydrases by Fungus <i>Trichoderma Reesei</i> Grown on Soy-based Media

Coffman, Anthony M. January 2013 (has links)
No description available.
245

Modélisation et optimisation de la production de cellulases par Trichoderma reesei pour les bioraffineries lignocellulosiques

Jourdier, Etienne 19 September 2012 (has links)
Dans le contexte énergétique et climatique mondial, le coût élevé des enzymes Cellulolytiques (cellulases) freine le développement des bioraffineries lignocellulosiques, pour produire des biocarburants et composés chimiques à partir d'une matière première végétale renouvelable. L'objectif de ce travail est de caractériser et de modéliser le métabolisme du micro-organisme Trichoderma reesei, afin d'optimiser le protocole industriel de production de cellulases. Cette étude a été réalisée sur des milieux modèles représentatifs de ceux attendus à l'échelle industrielle. Tout d'abord, la stoechiométrie des réactions de croissance et de production a été établie, puis une étude cinétique a été menée pour mesurer précisément le comportement du micro-organisme à forte induction de la production de cellulases. Le modèle résultant a été utilisé pour optimiser le protocole industriel de production. Ensuite, l'intégration de cette étape dans une bioraffinerie lignocellulosique a été étudiée, avec l'effet sur le métabolisme i) des mélanges de sucres disponibles, ii) des composés inhibiteurs issus de la dégradation de la lignocellulose, et iii) du changement d'échelle. Ces travaux ont fait progresser de façon substantielle les connaissances du métabolisme de T. reesei en ce qui concerne la production de cellulases, et les modèles développés sont des outils d'aide rationnelle à la définition d'un procédé de production de cellulases intégré dans une bioraffinerie lignocellulosique. / In the global energetic and climatic context, the high cost of the cellulolytic enzymes (cellulases) postpones the development of lignocellulosic biorefineries, dedicated to produce biofuels and chemical compounds from renewable vegetable feedstocks. The aim of this work was to measure and model the metabolism of the micro-organism Trichoderma reesei, in order to optimize the industrial protocol for the production of cellulase. This study was carried out using synthetic media representative of industrial ones. First, the stoichiometries of growth and protein production reactions were determined. Then, a kinetic study was conducted to precisely measure the specific rates of T. reesei at high induction of cellulase production. The resulting model was used to optimize the industrial production protocol. Finally the integration of this step in a lignocellulosic biorefinery was studied by determining the impacts on the metabolism of i) available sugar mixtures, ii) inhibitory compounds from lignocellulosic biomass degradation, and iii) scale-up. These results significantly contributed to improve the knowledge of T. reesei metabolism on cellulase production. The developed models are rational tools for the optimization of a cellulase production protocol suited to lignocellulosic biorefineries.
246

Estudos por modelagem e dinâmica molecular integradas a técnicas físicas para biomoléculas em solução - interação de receptores nucleares a elementos responsivos no DNA e dinâmica inter-domínios da celobiohidrolase I / Integrated experimental biophysics and molecular dynamics simulations of biomolecules in solution - the interaction of nuclear receptors with DNA response elements and the inter-domain dynamics of Cellobiohydrolase I

Lima, Leonardo Henrique França de 26 September 2011 (has links)
Movimentos coletivos prestam um papel fundamental na dinâmica e energética de biomoléculas em solução. Estes movimentos permitem o acoplamento de regiões significativamente distantes, apresentando considerável influência, por exemplo, no alosterismo para a formação de complexos macromoleculares e no funcionamento integrado de proteínas multidomínios como \"máquinas moleculares\". Neste trabalho de doutoramento, serão apresentados os resultados referentes à aplicação conjunta de técnicas experimentais biofísicas, de modelagem estrutural e de dinâmica molecular no estudo de dois sistemas para os quais estes movimentos coletivos demonstram considerável importância funcional. Para a interação do receptor nuclear do ácido 9-cis-retinóico com seu elemento responsivo específico no DNA (HRE), a comparação de estudos de dinâmica molecular com ensaios de afinidade por anisotropia de fluorescência sugere que a resistência inicial para a associação do monômero, seguida da acentuada colaboratividade na associação do dímero é regida por um impedimento da associação do domínio de ligação ao DNA (DBD) para o primeiro à sequência responsiva devido, em última análise, a uma não complementaridade dos modos coletivos mútuos. Este impedimento para a associação monomérica inicial é mais acentuado para o monômero 5\' (para o qual a menor especificidade de ligação à seqüência específica já é bem documentada), devido aos efeitos conjuntos de um \"defeito\" natural no empacotamento de bases da seqüência responsiva, que se manifesta mais significativamente na interface entre o meio-sítio 5\' e a seqüência espaçadora, e dos modos vibracionais entre os dois sítios decorrentes de seu faseamento relativo na topologia do DNA na seqüência responsiva, caracterizando um mecanismo \"chave e fechadura\" para a interação obrigatoriamente simultânea dos dois monômeros ao DNA. No segundo caso, um estudo integrado utilizando a técnica experimental de espalhamento de raios X a baixos ângulos e uma abordagem de modelagem estrutural baseada em dinâmica molecular foi realizado para a celobiohidrolase I de Trichoderma harziannum. Este estudo permitiu tanto a elaboração de um modelo estrutural de maior resolução para esta enzima de alto potencial biotecnológico como a constatação dos possíveis mecanismos moleculares a partir dos quais as glicosilações no peptídeo conector impõem restrições à orientação e modos vibracionais entre seus dois domínios de forma condizente com sua ação concertada na interação e no deslize da enzima sobre a superfície celulósica, ambos de fundamental importância para a processividade da enzima na hidrólise do substrato microcristalino. / Collective motions play a fundamental role in solution biomolecule dynamics and energetics. These movements can couple very distant regions in the protein structures affection, for instance, allosteric mechanisms, the establishment of macromolecular complexes, and on the integrated function of multidomain proteins as molecullar machines. In this thesis, we present results concerning to the joint use of experimental biophysical techniques, structural modeling and molecular dynamics simulations on the study of two systems for which these collective motions have substantial importance. First, we study the interaction of the nuclear retinoid X receptor with its specific DNA hormone response element (HRE) using a combination of molecular dynamics simulations and affinity assays performed by using fluorescence anisotropy. We find out that collective motions mediate the low binding affinity of monomers and the high cooperative binding of HRE dimers. The lower binding affinity of the monomer is more prominent for 5´ monomers. This occur due to an natural ineffective stacking of the last base pair step at the 5´-half-site and to the phasing of the two binding half-sites in the DNA topology, that impose a collective motions that tends to occlude the 5´ binding site. This behavior, in turn, is concurrent with the well known 3´ polarity and the decreased binding specificity to the 5´ half site for the hRXR&alpha; monomer. This same pattern impose a lock-and-key mechanisms dependent on the binding of the full dimer. Second, an integrated Small angle X ray scattering and molecular dynamics based structural modeling was used to comprehend the interdomain motions of cellobiohydrolase I of Trichoderma harziannum. We manage to build a refined model for this enzime, with important biotechnological potential. We also provide insights into molecular mechanisms of linker and glycosylation imposed restraints on the orientation and vibrational modes of the full-length enzyme, supporting a mechanism of sliding of on the cellulose surface. This mechanism is fundamental for the high processivity on the hydrolysis of microcrystalline cellulose.
247

Analyse locale et globale de l'hydrodynamique et du transfert de matière dans des fluides à rhéologie complexe caractéristiques des milieux de fermentation / Local and global study of hydrodynamic and mass transfer in stirred vessels with non Newtonian model fluids

Gabelle, Jean-christophe 05 September 2012 (has links)
La production d’éthanol à partir de biomasse lignocellulosique est reconnue comme une des voies possibles de réduction des émissions de gaz à effet de serre et de remplacement partiel des énergies fossiles. Pour être compétitif, la production d'enzymes à bas coûts est nécessaire. Ces enzymes sont produites par le champignon filamenteux Trichoderma reesei, qui présente, à forte concentration, un comportement fortement rhéofluidifiant pouvant entrainer des limitations de mélange et de transfert de matière lors du changement d'échelle. Dans ce travail, il est proposé de compléter les données de la littérature concernant le temps de mélange, la puissance dissipée et le transfert de matière gaz-liquide (global et local) par des mesures à plusieurs échelles dans des fluides modèles de rhéologie similaire aux milieux biologiques visés. Les modèles et corrélations développés qui en résultent sont directement exploitables pour le design des fermenteurs industriels. Afin d’étudier plus en détail le mélange, le taux de cisaillement et la turbulence, une étude par PIV a été menée sur des milieux transparents. La caractérisation fine de l'hydrodynamique repose sur la dissociation des différentes composantes du mouvement à l’aide de la POD. L'évolution des grandeurs mesurées avec les conditions opératoires permet de fournir des indications précieuses pour l'extrapolation des fermenteurs mettant en œuvre des micro-organismes potentiellement sensibles au cisaillement / Ethanol made from cellulosic biomass is recognized as a promising substitute for fossil fuel and thus as a way to reduce greenhouse gas emissions. To be competitive, low cost cellulosic enzymes produced by the filamentous fungus Trichoderma reesei are required. At high biomass concentration, the culture broth becomes so highly shear-thinning that mixing and mass transfer limitations may be encountered when the process is scaled up.In this study, we propose to complete data available in the literature for mixing times, power draw, and mass transfer (local and global) with measurements at several scales in model fluids (shear thinning) that mimic the rheology of biological media. Models and correlations that derive from this work can be used directly for industrial fermentor design. In order to study mixing, local shear rate and turbulence in detail, PIV is performed in transparent model fluids. The refined hydrodynamic characterisation relies on the dissociation of instantaneous velocity by means of the POD method. The change of key parameters with operating conditions gives relevant information for the scale-up of shear-sensitive micro-organisms.
248

Clonagem e estudos de expressão de enzimas do fungo filamentoso Trichoderma harzianum IOC-3844 envolvidas na degradação de biomassa

Malagó Junior, Wilson 06 July 2012 (has links)
Made available in DSpace on 2016-06-02T20:20:34Z (GMT). No. of bitstreams: 1 4606.pdf: 10556895 bytes, checksum: debf5633a053f88ca7dd4618edef9175 (MD5) Previous issue date: 2012-07-06 / Universidade Federal de Minas Gerais / The plant biomass is a large-scale available resource and one of its more important applications is the second-generation ethanol production. However, the enzyme cost is one of the biggest barriers for economically viable ethanol from biomass. Therefore, it is important to identify fungal strains that can produce high concentrations of plant biomass-degrading enzymes. The aim of this work was to clone, study the gene expression and characterize the plant biomass-degrading transcript set of the filamentous fungus Trichoderma harzianum IOC-3844. A total of 1,543 highquality reads from the Trichoderma harzianum IOC-3844 cellulose induced cDNA library were organized into 1,002 transcripts representing 167 contigs and 835 singlets. Of these 1,002 transcripts 646 had unknown functions and 356 showed associated functions. Among the transcripts with associated functions, we found 20 transcripts related to plant biomass deconstruction. The real time PCR analysis of Trichoderma harzianum IOC-3844 mycelia grown for 36 and 60 hours in cellulose, revealed that the levels of the following mRNAs were induced by at least 2,000-fold when compared to uninduced mycelia: cbh1, cbh2, egl1, egl2, egl3, egl7 and swo1. In some cases, the values were higher than 100,000-fold. Among the transcripts analyzed by real time PCR, cbh1, cbh2 and egl7 exhibited the highest expression levels. The Trichoderma harzianum IOC-3844 exhibited a repertoire with high expression of plant biomassdegrading transcripts. The enzymes EGIII and Xyn2 were recombinantly expressed in Pichia pastoris, showing good quality purification and good enzymatic activity. The heterologous expression assays made possible future studies aiming at the industrial application of the enzymes. Therefore, this strain showed potencial to produce biomassdegrading enzymes for second-generation ethanol production and to be a source of enzymes for the paper industry / A biomassa vegetal é um recurso disponível em larga escala e uma das suas mais imporantes aplicações é a produção de etanol de segunda geração. No entanto, o custo das enzimas é um dos maiores entraves para a produção economicamente viável deste etanol. Neste contexto, é importante encontrar organismos produtores de grandes quantidades de enzimas que degradam a biomassa. Os objetivos deste estudo foram clonar, estudar a expressão gênica e caracterizar o conjunto de enzimas que degradam a biomassa vegetal, do fungo filamentoso Trichoderma harzianum IOC-3844. Um total de 1.543 seqüências de boa qualidade, geradas a partir de uma biblioteca de cDNA do Trichoderma harzianum IOC-3844, induzido por celulose, foi organizado em 1.002 transcritos, sendo 167 representados por mais de uma seqüência e 835 representados por apenas uma seqüência. Destes transcritos, 356 tiveram função associada e 646 não tiveram. Com isso, entre os transcritos com função associada, foram listados 20 transcritos envolvidos com degradação de biomassa vegetal. Análises de PCR em tempo real do micélio de Trichoderma harzianum IOC-3844, crescido por 36 e 60 horas em celulose, mostraram níveis de mRNA mais de 2.000 vezes mais representados para os transcritos cbh1, cbh2, egl1, egl2, egl3, egl7 e swo1, quando comparados com o micélio não induzido. Em alguns casos as maiores representatividades alcançaram valores superiores a 100.000 vezes. Entre os transcritos analisados o cbh1, o cbh2 e o egl7, mostraram os mais altos níveis de expressão. O Trichoderma harzianum IOC-3844 exibiu um repertório com alta expressão de transcritos envolvidas na degradação de biomassa vegetal. As enzimas EGIII e Xyn2 foram expressas em sistema recombinante com uso da levedura Pichia pastoris, apresentando facilidade de purificação e boa atividade enzimática. Os ensaios de expressão heteróloga viabilizaram estudos posteriores que visam a aplicação industrial das enzimas. Assim, esta cepa mostrou potencial para produzir enzimas que degradam a biomassa para a produção de etanol de segunda geração, e para ser fonte de enzimas para a indústria de papel.
249

Populações de fungos fitopatogênicos e concentrações de nutrientes no solo em pomares de fruteiras temperadas adubados com Dejeto suíno compostado / Pathogenic fungi populations and nutrient concentrations in soil in orchards of temperate fruit trees fertilized with swine manure composted

Costa Junior, Avanor Cidral da 31 July 2014 (has links)
Made available in DSpace on 2016-12-08T16:44:49Z (GMT). No. of bitstreams: 1 PGPV14MA158.pdf: 622907 bytes, checksum: 4bef911008ae5cffa26706180f710db4 (MD5) Previous issue date: 2014-07-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The addition and incorporation of organic matter to the soil, besides favoring crops by improving soil physical, can increase nutrients and add specific biochemicals capable of renewing the native microflora and microfauna. These compounds may, depending on the organic material to act as a suppressant effect and biocontrol. The aim of this study was to evaluate the effect of swine manure compost (DSC) in an orchard of apple, pear and grape vines on the population dynamics of Verticillium dahliae, Fusarium solani, Fusarium oxysporum, Fusarium verticillioides and Trichoderma sp. Soil samples for quantification of fungal colonies and nutrient analysis were collected at a depth of 0-10 cm soil of the orchard with apple, pear and grape vines. The population of pathogenic soil fungi and Trichoderma sp. were obtained by dilution and plating of 10 g of soil samples from soil orchard who received two doses of DSC (50 to 100%) compost and two (50 and 100%), using two culture media (BDA potato-dextrose-agar) and Sabouraud-ágar-chloramphenicol. The application of different doses of DSC and chemical fertilizer began in December 2012, repeated at intervals of 60 days until the 2014 harvest analysis of macronutrients (nitrogen, phosphorus, potassium, calcium and magnesium) and micronutrients (iron, copper, zinc and Manganese) DSC and chemical fertilizer were run using Mehlich-1, spectrophotometry, acid-base titration and Kjeldahl method, all described by Tedesco et al. (1995). Results in the concentration of nutrients was related to the population of Verticillium dahliae, Fusarium solani, Fusarium oxysporum, Fusarium verticillioides and Trichoderma sp. The experimental design was completely randomized, factorial 2 x 5, repeated in time (months). The data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC, v.9.2) and mean comparisons using Tukey least significant difference p &#8804; 0.05. In the apple orchard, Fusarium oxysporum and Fusarium solani showed higher populations in Q100 treatments (0-110 x 103 CFU / g of soil) and Q50 (0-70 x 103 CFU/g of soil) respectively. There were differences in the population periods. Phosphorus, Potassium and Sodium showed significant differences among the treatments tested. In the orchard of pear trees the largest population of Fusarium solani was the S100 treatment (0-50 x 103 CFU/ g of soil). Treatments Q50 and Q100 had higher populations of Verticillium dahliae, Fusarium oxysporum and Fusarium verticillioides in different periods. Concentrations of Nitrogen and Potassium differ between treatments tested. In vineyards the largest populations of Fusarium solani and Fusarium oxysporum were found in December-2012 periods (0-70 x 103 CFU / g of soil) and August 2013 (0-60 x 103 CFU / g of soil) respectively. Concentrations of potassium, phosphorus and sodium were higher in treatment S50 and S100. The orchard of apple, pear and grape vines have different response to chemical and organic fertilization. The intensity of response to fertilization has little influence population dynamics of plant pathogens in soil and Trichoderma / A adição e incorporação de matéria orgânica ao solo, além de favorecer as culturas pela melhoria física do solo, podem potencializar nutrientes e adicionar compostos bioquímicos específicos capazes de renovar a microfauna e microflora nativas. Estes compostos podem, dependendo do material orgânico, agir como efeito supressor e como biocontrole. O objetivo deste trabalho foi avaliar o efeito da aplicação de dejeto suíno compostado (DSC) em pomar de macieiras, pereiras e videiras, sobre a dinâmica populacional de Verticillium dahliae, Fusarium solani, Fusarium oxysporum, Fusarium verticillioides e Trichoderma sp. Amostras de solo para quantificação de colônias fúngicas e análise de nutrientes foram retiradas na profundidade 0-10 cm de solo do pomar de macieiras, pereiras e videiras. A população de fungos fitopatogênicos de solo e Trichoderma sp. foram obtidas pela diluição e plaqueamento de 10 g de amostras de solo provenientes do solo do pomar que receberam duas doses de DSC (50 e 100%) e duas de adubo químico (50 e 100%), utilizando dois meios de cultura, BDA (batata-dextrose-agar) e Sabouraud ágar-cloranfenicol. A aplicação das diferentes doses de DSC e adubo químico tiveram início em dezembro-2012, repetidas em intervalos de 60 dias até a safra 2014. A análise dos macronutrientes (nitrogênio, fósforo, potássio, cálcio e magnésio) e micronutrientes (ferro,cobre,zinco e Manganês) do DSC e da adubação química foram realizados pelos métodos de Mehlich -1, espectrofotometria, titulação ácido-base e método Kjeldahl, todas descritas por Tedesco et al. (1995). Resultados da concentração de nutrientes foi relacionado à população de Verticillium dahliae, Fusarium solani, Fusarium oxysporum, Fusarium verticillioides e Trichoderma sp. O delineamento experimental foi inteiramente casualisado, em arranjo fatorial 2 x 5, repetidos no tempo (meses). Os dados foram analisados pelo procedimento MIXED do SAS (SAS Inst. Inc., Cary, NC, v.9.2) e as comparações de médias usando a diferença mínima significativa de Tukey p &#8804; 0,05. No pomar de macieiras, Fusarium oxysporum e Fusarium solani apresentaram maiores populações nos tratamentos Q100 (0-110 x 103 UFC/g de solo) e Q50 (0-70 x 103 UFC/g de solo) respectivamente. Houve diferenças da população nos períodos avaliados. Fósforo, Potássio e Sódio apresentaram diferenças significativas entre os tratamentos testados. No pomar de pereiras a maior população de Fusarium solani foi ao tratamento S100 (0-50 x 103 UFC/g de solo). Os tratamentos Q50 e Q100 apresentaram maiores populações de Verticillium dahliae, Fusarium oxysporum e Fusarium verticillioides em diferentes períodos de avaliação. Concentrações de Potássio e Nitrogênio apresentaram diferenças nos tratamentos testados. Na cultura da videira as maiores populações de Fusarium solani e Fusarium oxysporum foram encontradas nos períodos dezembro-2012 (0-70 x 103 UFC/g de solo) e agosto-2013 (0-60 x 103 UFC/g de solo) respectivamente. Concentrações de Potássio, Fósforo e Sódio foram superiores nos tratamento S50 e S100. O pomar de macieiras, pereiras e videiras apresentam diferentes resposta a adubação química e orgânica. A intensidade de resposta da adubação pouco influencia a flutuação da população de fitopatógenos de solo e Trichoderma
250

Estudos por modelagem e dinâmica molecular integradas a técnicas físicas para biomoléculas em solução - interação de receptores nucleares a elementos responsivos no DNA e dinâmica inter-domínios da celobiohidrolase I / Integrated experimental biophysics and molecular dynamics simulations of biomolecules in solution - the interaction of nuclear receptors with DNA response elements and the inter-domain dynamics of Cellobiohydrolase I

Leonardo Henrique França de Lima 26 September 2011 (has links)
Movimentos coletivos prestam um papel fundamental na dinâmica e energética de biomoléculas em solução. Estes movimentos permitem o acoplamento de regiões significativamente distantes, apresentando considerável influência, por exemplo, no alosterismo para a formação de complexos macromoleculares e no funcionamento integrado de proteínas multidomínios como \"máquinas moleculares\". Neste trabalho de doutoramento, serão apresentados os resultados referentes à aplicação conjunta de técnicas experimentais biofísicas, de modelagem estrutural e de dinâmica molecular no estudo de dois sistemas para os quais estes movimentos coletivos demonstram considerável importância funcional. Para a interação do receptor nuclear do ácido 9-cis-retinóico com seu elemento responsivo específico no DNA (HRE), a comparação de estudos de dinâmica molecular com ensaios de afinidade por anisotropia de fluorescência sugere que a resistência inicial para a associação do monômero, seguida da acentuada colaboratividade na associação do dímero é regida por um impedimento da associação do domínio de ligação ao DNA (DBD) para o primeiro à sequência responsiva devido, em última análise, a uma não complementaridade dos modos coletivos mútuos. Este impedimento para a associação monomérica inicial é mais acentuado para o monômero 5\' (para o qual a menor especificidade de ligação à seqüência específica já é bem documentada), devido aos efeitos conjuntos de um \"defeito\" natural no empacotamento de bases da seqüência responsiva, que se manifesta mais significativamente na interface entre o meio-sítio 5\' e a seqüência espaçadora, e dos modos vibracionais entre os dois sítios decorrentes de seu faseamento relativo na topologia do DNA na seqüência responsiva, caracterizando um mecanismo \"chave e fechadura\" para a interação obrigatoriamente simultânea dos dois monômeros ao DNA. No segundo caso, um estudo integrado utilizando a técnica experimental de espalhamento de raios X a baixos ângulos e uma abordagem de modelagem estrutural baseada em dinâmica molecular foi realizado para a celobiohidrolase I de Trichoderma harziannum. Este estudo permitiu tanto a elaboração de um modelo estrutural de maior resolução para esta enzima de alto potencial biotecnológico como a constatação dos possíveis mecanismos moleculares a partir dos quais as glicosilações no peptídeo conector impõem restrições à orientação e modos vibracionais entre seus dois domínios de forma condizente com sua ação concertada na interação e no deslize da enzima sobre a superfície celulósica, ambos de fundamental importância para a processividade da enzima na hidrólise do substrato microcristalino. / Collective motions play a fundamental role in solution biomolecule dynamics and energetics. These movements can couple very distant regions in the protein structures affection, for instance, allosteric mechanisms, the establishment of macromolecular complexes, and on the integrated function of multidomain proteins as molecullar machines. In this thesis, we present results concerning to the joint use of experimental biophysical techniques, structural modeling and molecular dynamics simulations on the study of two systems for which these collective motions have substantial importance. First, we study the interaction of the nuclear retinoid X receptor with its specific DNA hormone response element (HRE) using a combination of molecular dynamics simulations and affinity assays performed by using fluorescence anisotropy. We find out that collective motions mediate the low binding affinity of monomers and the high cooperative binding of HRE dimers. The lower binding affinity of the monomer is more prominent for 5´ monomers. This occur due to an natural ineffective stacking of the last base pair step at the 5´-half-site and to the phasing of the two binding half-sites in the DNA topology, that impose a collective motions that tends to occlude the 5´ binding site. This behavior, in turn, is concurrent with the well known 3´ polarity and the decreased binding specificity to the 5´ half site for the hRXR&alpha; monomer. This same pattern impose a lock-and-key mechanisms dependent on the binding of the full dimer. Second, an integrated Small angle X ray scattering and molecular dynamics based structural modeling was used to comprehend the interdomain motions of cellobiohydrolase I of Trichoderma harziannum. We manage to build a refined model for this enzime, with important biotechnological potential. We also provide insights into molecular mechanisms of linker and glycosylation imposed restraints on the orientation and vibrational modes of the full-length enzyme, supporting a mechanism of sliding of on the cellulose surface. This mechanism is fundamental for the high processivity on the hydrolysis of microcrystalline cellulose.

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