Diidroorotato desidrogenases (DHODHs) catalisam a quarta e única reação de oxidorredução na via de síntese de novo de nucleotídeos de pirimidina, que envolve a oxidação do diidroorotato (DHO) a orotato (ORO) em um mecanismo dependente do cofator FMN e de aceptores de elétrons. A relevância de pirimidinas para a proliferação e manutenção celular determina a DHODH como um potencial alvo terapêutico. DHODHs são divididas em duas classes baseado em comparações estruturais e na sequência de resíduos: classe 1, a qual é subdividida em classe 1A e 1B, e classe 2. A proteína utilizada como modelo em nosso estudo sobre as DHODHs de tripanosomatídeos classe 1A é a enzima de Leishmania major (LmDHODH). As metas principais desse trabalho foram de contribuir para a compreensão sobre o mecanismo de ação das DHODHs de classe 1A e propor estratégias de inibição seletiva. Inicialmente, ensaios no estado estacionário e pré-estacionário foram realizados para caracterização do ciclo catalítico da LmDHODH e permitiram a análise das etapas redutivas e oxidativa de forma independente e sua comparação com o ciclo global. Foi também analisada a interação da LmDHODH com os produtos da reação por meio de ensaios de cinética, titulação espectral e titulação isotérmica calorimétrica. Após análises topológicas baseadas na estrutura cristalográfica da LmDHODH, diferentes mutantes foram construídos e caracterizados estruturalmente e cineticamente a fim de investigar a importância de alguns sítios na conformação protéica. Durante a etapa de busca de inibidores, bibliotecas químicas de compostos foram analisadas por meio de interferometria de biocamada e ensaio enzimático. Considerando os resultados obtidos, foi possível pela primeira vez identificar um mecanismo cinético cooperativamente positivo frente à ligação do DHO com coeficiente de Hill (h) próximo a 2. Além disso, nossos resultados mostram que o grau da cooperatividade na ligação do DHO é afetado pelo ORO. A comparação entre os parâmetros obtidos para o estado estacionário e pré-estacionário aliada aos estudos da interação da LmDHODH com os produtos da reação, sugerem que a liberação do ORO é a etapa limitante na velocidade global da reação, o que não é verdade para a enzima humana (DHODH classe 2). A partir das análises dos mutantes, foi possível correlacionar o comportamento cooperativo da enzima LmDHODH com a conversa cruzada entre os sítios-ativos mediada pela interface dimérica. Além disso, foi possível observar que a dinâmica conformacional do loop catalítico é extremamente relevante no mecanismo global da reação e existe uma correlação entre os rearranjos do loop catalítico e a interface dimérica. Nossos resultados fornecem uma importante contribuição para o entendimento dos detalhes do mecanismo catalítico adotado pelas DHODHs de classe 1A. Eles também revelam diferenças chave no mecanismo adotado pelas enzimas de classe 1A e classe 2, os quais podem ser explorados no desenvolvimento de inibidores potentes e seletivos contra a LmDHODH. No que se refere à busca por inibidores, alguns hits foram obtidos por meio da varredura da biblioteca de fragmentos do Drug Discovery Unit (DDU) utilizando interferometria de biocamadas. Além disso, um ensaio enzimático de larga escala (hightroughtput) foi desenvolvido para a LmDHODH e permitiu a triagem de alto desempenho nas bibliotecas de fragmentos e diversidade química. Hits foram validados por meio de ensaio de potência e bons inibidores foram encontrados em ambas as bibliotecas. As varreduras identificaram diferentes séries de compostos como pontos de partida para química medicinal e investigações estruturais. Dois hits identificados a partir da biblioteca de diversidade química apresentam excelentes valores de IC50, 260 nM e 1,07 ?M. / Dihydroorotate dehydrogenases (DHODHs) catalyze the fourth and only redox reaction in the de novo pyrimidine biosynthetic pathway, the oxidation of dihydroorotate (DHO) to orotate (ORO) through a mechanism dependent on the FMN cofactor and electron acceptors. The significance of pyrimidine for cell proliferation and maintenance determine DHODH as potential therapeutic target. DHODHs have been distinguished in two major classes based on sequence and structural comparisons: class 1, which is further divided into subclasses 1A and 1B, and class 2. The model protein in our studies on trypanosomatid class 1A DHODHs is the enzyme from Leishmania major (LmDHODH). The essential question in this study was to contribute for the understanding about the catalytic and inhibition mechanisms of class 1A DHODHs . First, steady-state and pre-steady state kinetic approaches have been used to characterize the catalytic cycle of LmDHODH and have allowed the comparison between the global cycle and each independent half-reaction. Also, the interaction of LmDHODH with the products of the reaction was analyzed by kinetic, spectral titration and isothermal titration calorimetry assays. After topographical analysis based on the LmDHODH crystallographic structure, different mutants were constructed and structurally and kinetically characterized. For inhibitor search, chemical libraries of compounds were screened by using biolayer interferometry binding and enzymatic assays. Based on our results, for the first time, steady-state kinetics analysis of class 1A allowed the observation of a positive cooperativity for DHO binding with a Hill coefficient (h) value close to 2. Moreover, our results show that the degree of cooperativity in DHO binding is affected by ORO. Comparison between steady and pre-steady-state parameters together with studies of interaction for LmDHODH with both products, suggests that ORO release is the rate-limiting step in overall catalysis with is not true to the human enzyme (class 2 DHODH). The hybrid approach used to characterize LmDHODH mutants allowed us to propose that the cooperative behavior is related with the cross-talk between the two active sites mediated by the dimer interface. Also, the conformational dynamics of the catalytic loop is very relevant in the global mechanism of the reaction and there is a correlation between catalytic loop rearrangement and dimer interface. Our results bring an important contribution for a better understanding of the detailed catalytic mechanism adopted by class 1A DHODHs. They also reveal key differences in the enzymatic mechanism adopted by class 1A and class 2 DHODHs, to be exploited in the development of potent and selective LmDHODH inhibitors. Regarding to inhibitors search, few hits were obtained by using screening of Drug Discovery Unit (DDU) fragment library with biolayer interferometry binding assay. Also, an end-point enzymatic assay was developed for LmDHODH and the optimisation carried out at the DDU provided a reliable HTP assay using both DDU\'s fragment library and small diversity set. Hits were validated using a potency assay with good inhibitors found using both libraries. The screens identified a number of series as starting points for medicinal chemistry and structural investigations. Two hits identified from small diversity set exhibit great IC50 values, 260 nM and 1.07 ?M.

Neste trabalho, foi avaliada a reatividade de compostos orgânicos contendo boro frente a reações catalisadas por enzimas. Diferentes exemplos de álcoois secundários quirais contendo boro foram acetilados enantiosseletivamente pela lipase de Candida antarctica (CALB). Todas as reações ocorreram com excelente enantiosseletividade (E >200) e ambos os produtos acetilados, bem como os álcoois remanescentes foram obtidos com alto excesso enantiomérico (ee >99%). Além da resolução cinética enzimática, foi avaliado também o processo de resolução cinética dinâmica quimio-enzimática, empregando complexos de rutênio como agentes de racemização. Após estabelecer as condições adequadas para a reação, foi possível obter o produto acetilado de configuração-(R) com 83% de conversão, mantendo a enantiosseletividade observada na reação de resolução cinética enzimática. Como extensão ao trabalho realizado com os álcoois contendo boro, foi estudada a resolução cinética de aminas primárias quirais contendo boro. Foram avaliadas diversas condições reacionais para alcançar a máxima resolução cinética destas aminas via acilação enantiosseletiva catalisada pela lipase CALB. Excelente enantiosseletividade (E >200) e altos excessos enantioméricos (até >99%) foram obtidos utilizando acetato de etila tanto como reagente doador de acila como solvente da reação. Adicionalmente, foi investigada a reação de biorredução de cetonas pró-quirais contendo boro. Os melhores resultados foram obtidos com as enzimas álcool desidrogenases (ADHs) purificadas dos microorganismos Rhodococcus ruber e Lactobacillus brevis. A ADH de R. ruber (ADH-A) promoveu a biorredução das cetonas aos respectivos álcoois de configuração-(R) com excelente enantiosseletividade (ee >99%), enquanto a ADH de L. brevis (ADH-LB) catalisou a redução de alguns exemplos de cetonas aos respectivos álcoois de configuração-(S), também com excelente enantiosseletividade. / In this work, was evaluated the reactivity of boron-containing organic compounds in enzyme-catalyzed reactions. Different examples of boron-containing chiral secondary alcohols were resolved by enantioselective acetylation mediated by lipase from Candida. antarctica (CALB). All reactions showed excellent enantioselectivities (E >200) and both remaining substrates and acetylated product were obtained in high enantiomeric excesses (up to >99%). Besides the enzymatic kinetic resolution, the chemoenzymatic dynamic kinetic resolution was also evaluated, using ruthenium complexes as racemization agents. After establishing the best conditions, the acetylated (R)-product was obtained with 83% conversion, maintaining the high enantioselectivity observed in the enzymatic kinetic resolution. As an expansion of work with boron-containing alcohols, the kinetic resolution of boron-containing chiral amines was studied. Several reaction conditions were studied to achieve the kinetic resolution of boron-containing amines via enantioselective acylation mediated by CAL-B. Excellent enantioselectivity (E >200) and high enantiomeric excess (up to >99%) of both the remaining amines and amides were obtained using ethyl acetate as both acyl donor and the reaction solvent. Additionally, the bioreduction of pro-chiral boron-containing ketones was investigated. The best results were obtained with purified alcohol dehydrogenases (ADH) from Rhodococcus ruber and Lactobacillus brevis. The ADH from R. ruber (ADH-A) mediated the bioreduction of ketones to their respective (R)-alcohols with excellent enantioselectivity (ee >99%), while the ADH from L. brevis (ADH-LB) catalyzed the reduction of some ketones to their respective (S)-alcohols, also with excellent enantioselectivity (ee >99%).

Diante da biodiversidade de micro-organismos existentes na natureza e da necessidade de descobrir novos biocatalisadores para a síntese de bloco de construções quirais e de produtos químicos de alto valor agregado, o presente trabalho teve como objetivo realizar a bioprospeção de micro-organismos para aplicação em reações de oxidação enantiosseletiva de álcoois. Os micro-organismos foram obtidos pelo processo de isolamento induzido de amostras de solo/sedimento coletadas no Parque Estadual Turístico do Alto Ribeira (PETAR) e na Antártica. A partir das amostras coletadas (43 de solo e 13 de sedimento) foram isolados 130 microorganimos mesofílicos (isolados de amostras de solo do PETAR) e 232 microorganimos psicrofílicos/psicrotróficos (isolados de amostras de solo/sedimento da Antártica). Realizamos também a avaliação do espectro de atividade enzimática dos micro-organismos em reações de oxidação enantiosseletiva, e para isso empregamos derivados para substituídos do (R,S)-1-(fenil)etanol. Dentre os micro-organismos estudados, 15 psicrofílicos/psicrotróficos e 11 micro-organismos mesofílicos apresentaram álcool desidrogenases que catalisaram a oxidação do enantiômero (S) do álcool racêmico à sua correspondente cetona. Nesses casos, as linhagens possuem atividade de álcool desidrogenase em que o rendimento de obtenção da cetona foi > 10 % e excesso enantiomérico > 60 %. Por outro lado 6 micro-organismos mesofílicos apresentaram álcool desidrogenases que catalisam a oxidação do enantiômero (R) do álcool racêmico à sua correspondente cetona. Foi realizada a caracterização taxonômica para alguns micro-organismos através do sequenciamento do 16S rDNA. Dentre os micro-organismos caracterizados, destacaram-se as bactérias Flavobacterium sp., Arthrobacter sp., Acinetobacter sp., e o Bacillus sp. por apresentar excelente atividade enzimática. Flavobacterium sp. e a Arthrobacter sp. foram selecionadas para o estudo de otimização da reação de oxidação do (R,S)-1-(4- metilfenil)etanol. Nesse processo foram utilizadas as células ressuspensas em tampão fosfato em diferentes temperaturas (5-30 ºC) e tempos reacionais (24-72 horas). A partir desse estudo, observou-se que a Flavobacterium sp. possui uma excelente atividade enzimática a 10 ºC e a Arthrobacter sp. a 25 ºC. Foram determinadas curvas de crescimentos destas bactérias em 15, 20 e 25 ºC, em que ambas apresentaram crescimento ótimo a 25 ºC, indicando que estas bactérias são psicrotróficas / In the view of the microorganisms biodiversity in nature and the necessity to discover new biocatalysts for chiral synthesis of building blocks and high value-added chemical products, the present work was aimed at making the bioprospection of microorganisms for application in enantioselective oxidation reactions of alcohols. Microorganisms were isolated by enrichment technique from soil/sediment samples collected from the State Park of Alto Ribeira (PETAR) and Antarctic. 130 Mesophilic microorganisms were isolated from soil samples of PETAR, and 232 psychrophilic/psychrotrophic microorganisms from soil/sediment samples of Antarctic. We also evaluated the enzymatic activity of the microorganisms in enantioselective oxidation reactions, by using derivatives of substituted para (RS)-1- phenylethanol as substrates. Among the studied microorganisms, 15 psychrophile/psychrotrophic and 11 mesophilic strains contain alcohol dehydrogenases that catalyze the (S)-enantiomer oxidation of racemic alcohols to its corresponding ketone. In these cases, the strains showed alcohol dehydrogenase activity in which the ketone yields were higher than 10 % and the enantiomeric excess >60 %. Moreover, 6 mesophilic microorganisms showed alcohol dehydrogenases that catalyze the R)-enantiomer oxidation of racemic alcohols to its corresponding ketone. It was performed taxonomic characterization for some microorganisms by sequencing the 16S rDNA. Among the characterized microorganisms, Flavobacterium sp., Arthrobacter sp., Acinetobacter sp. and Bacillus sp. showed excellent enzymatic activity. The Flavobacterium sp. and Arthrobacter sp. were selected for optimization study of oxidation of the (R,S)-1-(4-methyl-phenyl)ethanol. In this process, bacterial cells were resuspended in phosphate buffer at different temperatures (5-30 °C) and reaction times (24-72 h). From these studies, it was observed that the Flavobacterium sp. has an excellent enzymatic activity at 10 ºC and Arthrobacter sp. at 25 ºC. We determined the growth curves of these bacteria in 15, 20 and 25 ° C. Both strains showed optimum growth at 25 ° C, indicating that these bacteria are psychrotrophics.

This work is focused on understanding protein function by describing how paralogous proteins with overlapping and distinct functions interact with their substrates and with other proteins. Two model systems are the subject of this research: (1) the stereospecific dehydrogenases R- and S-HPCDH, and (2) the zinc knuckle proteins Air1 and Air2. R- and S-HPCDH are homologous enzymes that are central to the metabolism of propylene and epoxide in the soil bacterium Xanthobacter autotrophicus. The bacterium produces R- and S-HPCDH simultaneously to facilitate transformation of R- and S-enantiomers of epoxypropane to a common achiral product 2-ketopropyl-CoM (2-KPC). Both R- and S-HPCDH are highly stereospecific for their respective substrates as each enzyme displays less than 0.5% activity with the opposite substrate isomer. Presented here are substrate-bound x-ray crystal structures of S-HPCDH. Comparisons to the previously reported product-bound structure of R-HPCDH reveal structural differences that provide each enzyme with a distinct substrate binding pocket. These structures demonstrate how chiral discrimination by R- and S-HPCDH results from alternative binding of the distal end of substrates within each substrate binding pocket, providing a structural basis for stereospecificity displayed by R- and S-HPCDH. Air1 and Air2 are homologous eukaryotic proteins that individually function within a trimeric protein complex called TRAMP. In the nucleus, TRAMP participates in RNA surveillance, processing, and turnover by stimulating the 3’-5’ exonucleolytic degradation of targeted RNAs by the nuclear exosome. Previous studies have indicated that within TRAMP Air1 and Air2 provide crucial protein-protein interactions that link the individual subunits of the complex. However, the mechanistic details of these protein-protein interactions are poorly understood. The work in this dissertation has characterized a previously unknown binding interface between Air2 and another TRAMP component, the helicase Mtr4. This interaction may explain how helicase activity is modulated in TRAMP. In addition to TRAMP protein interactions, preliminary studies have identified a small region of Air1 that is required for modulating the activity of a protein that is not found in TRAMP, the methyltransferase Hmt1. Collectively, these studies provide important characterization of Air1 and Air2 protein-binding interactions, and establish a foundation for future research efforts aimed at exploring Air protein function.

Disc electrophoresis of tissue homogenates from eight species of fringillid birds showed five forms of lactic dehydrogenase. The relative amounts of isozymes were characteristic for each species. This paper classifies some members of the families Fringillidae and Carduelidae in terms of lactic dehydrogenase isozymes and compares the results to other methods of classification.

Coenzyme nicotinamide adenine dinucleotide (NAD, including the oxidized form-- NAD+ and reduced form--NADH) and the phosphorylated form--nicotinamide adenine dinucleotide phosphate (NADP, including NADP+ and NADPH) are two of the most important biological electron carriers. Most NAD(P) dependent redox enzymes show a preference of either NADP or NAD as an electron acceptor or donor depending on their unique metabolic roles. In biocatalysis, the low enzymatic activities with unnatural coenzymes have made it difficult to replace costly NADP with economically advantageous NAD or other biomimetic coenzyme for catalysis. This is a significant challenge that must be addressed should in vitro biocatalysis be a viable option for the practical production of low-value biocommodities (i.e., biohydrogen). There is a significant need to first address the coenzyme selectivity of the NADP-dependent dehydrogenases and evolve mutated enzymes that accept biomimetic coenzymes. This is a major focus of this dissertation. Establishment of efficient screening methods to identify beneficial mutants from an enzymatic library is the most challenging task of coenzyme engineering of dehydrogenases. To fine tune the coenzyme preference of dehydrogenases to allow economical hydrogen production, we developed a double-layer Petri-dish based screening method to identify positive mutant of the Moorella thermoacetica 6PGDH (Moth6PGDH) with a more than 4,278-fold reversal of coenzyme selectivity from NADP+ to NAD+. This method was also used to screen the thermostable mutant of a highly active glucose 6-phosphate dehydrogenase from the mesophilic host Zymomonas mobilis. The resulting best mutant Mut 4-1 showed a more than 124-fold improvement of half-life times at 60oC without compromising the specific activity. The screening method was further upgraded for the coenzyme engineering of Thermotaga maritima 6PGDH (Tm6PGDH) on the biomimetic coenzyme NMN+. Through six-rounds of directed evolution and screening, the best mutant showed a more than 50-fold improvement in catalytic efficiency on NMN+ and a more than 6-fold increased hydrogen productivity rate from 6-phosphogluconate and NMN+ compared to those of wild-type enzyme. Together, these results demonstrated the effectiveness of screening methods developed in this research for coenzyme engineering of NAD(P) dependent dehydrogenase and efficient use of the less costly coenzyme in ivSB based hydrogen production. / Ph. D.

Les Rétinal déshydrogénases (RALDHs) catalysent irréversiblement la déshydrogénation du Rétinal en Acide Rétinoïque (AR) qui est impliqué dans l’embryogenèse et la différenciation tissulaire. Pour comprendre le rôle dans la biosynthèse de l’AR des RALDHs type 3 et 4 de souris, nous avons déterminé leurs propriétés cinétiques ainsi que leur comportement en présence de différents inhibiteurs. Les tests enzymatiques sont effectués avec une préparation d’enzyme recombinante, tagguée avec 6 histidines, purifiée sur colonne Ni-NTA (Qiagen). L’activité enzymatique est évaluée en quantifiant la production d’AR par chromatographie liquide à haute performance (HPLC) en phase inversée. Les constantes cinétiques ont été déterminées pour les isomères du rétinal tout-trans, 9-cis et 13-cis. La RALDH4 catalyse les isomères 9-cis et 13-cis de rétinal, elle présente un faible KM (3μM) pour les deux isomères et a une efficacité catalytique élevée pour le 9-cis rétinal 3.4 fois supérieure au 13-cis rétinal. La RALDH3 est spécifique au tout-trans rétinal avec un KM de 4 μM et une efficacité élevée. β-Ionone, inhibiteur possible pour la RALDH4, inhibe l’activité avec le rétinal 9-cis et 13-cis, mais n’influence pas l’activité de la RALDH3. Le para-hydroxymercuribenzoïque (p-HMB) inhibe l’activité de deux isoenzymes. Le cation MgCl2 augmente par 3 fois l’oxydation du rétinal 13-cis par la RALDH4, diminue l’oxydation du 9-cis rétinal et influence faiblement la RALDH3. Ces données enrichissent les connaissances sur les caractéristiques cinétiques des RALDHs recombinantes de souris de types 3 et 4 et fournissent des éclaircissements sur la biogenèse de l’acide rétinoïque in vivo. / SUMMARY Retinal dehydrogenases (RALDHs) catalyze the dehydrogenation of retinal into retinoic acids (RA) that are required for embryogenesis and tissue differentiation. This study sought to determine the detailed kinetic properties of 2 mouse RALDHs, namely RALDH3 and 4, for retinal isomer substrates, to better define their specificities in RA isomer synthesis. RALDH3 and 4 were expressed as His-tagged proteins and affinity-purified. RALDH3 oxidized all-trans retinal with high catalytic efficiency but did not show activity for either 9-cis or 13-cis retinal substrates. RALDH4 was inactive for all-trans retinal substrate, exhibited high activity for 9-cis retinal oxidation, and oxidized 13-cis retinal with lower catalytic efficiency. β-ionone, a potent inhibitor of RALDH4 activity, suppressed 9-cis and 13-cis retinal oxidation competitively, but had no effect on RALDH3 activity. The p-HMB inhibited the activity for both RALDH3 and RALDH4. The divalent cation MgCl2 activated 13-cis retinal oxidation by RALDH4 by 3-fold, slightly decreased 9-cis retinal oxidation, and did not significantly influence RALDH3 activity. These data extend the kinetic characterization of RALDH3 and 4, providing their specificities for retinal isomer substrates, which should help in determining their functions in the synthesis of RAs in specific tissues.

Les Rétinal déshydrogénases (RALDHs) catalysent irréversiblement la déshydrogénation du Rétinal en Acide Rétinoïque (AR) qui est impliqué dans l’embryogenèse et la différenciation tissulaire. Pour comprendre le rôle dans la biosynthèse de l’AR des RALDHs type 3 et 4 de souris, nous avons déterminé leurs propriétés cinétiques ainsi que leur comportement en présence de différents inhibiteurs. Les tests enzymatiques sont effectués avec une préparation d’enzyme recombinante, tagguée avec 6 histidines, purifiée sur colonne Ni-NTA (Qiagen). L’activité enzymatique est évaluée en quantifiant la production d’AR par chromatographie liquide à haute performance (HPLC) en phase inversée. Les constantes cinétiques ont été déterminées pour les isomères du rétinal tout-trans, 9-cis et 13-cis. La RALDH4 catalyse les isomères 9-cis et 13-cis de rétinal, elle présente un faible KM (3μM) pour les deux isomères et a une efficacité catalytique élevée pour le 9-cis rétinal 3.4 fois supérieure au 13-cis rétinal. La RALDH3 est spécifique au tout-trans rétinal avec un KM de 4 μM et une efficacité élevée. β-Ionone, inhibiteur possible pour la RALDH4, inhibe l’activité avec le rétinal 9-cis et 13-cis, mais n’influence pas l’activité de la RALDH3. Le para-hydroxymercuribenzoïque (p-HMB) inhibe l’activité de deux isoenzymes. Le cation MgCl2 augmente par 3 fois l’oxydation du rétinal 13-cis par la RALDH4, diminue l’oxydation du 9-cis rétinal et influence faiblement la RALDH3. Ces données enrichissent les connaissances sur les caractéristiques cinétiques des RALDHs recombinantes de souris de types 3 et 4 et fournissent des éclaircissements sur la biogenèse de l’acide rétinoïque in vivo. / SUMMARY Retinal dehydrogenases (RALDHs) catalyze the dehydrogenation of retinal into retinoic acids (RA) that are required for embryogenesis and tissue differentiation. This study sought to determine the detailed kinetic properties of 2 mouse RALDHs, namely RALDH3 and 4, for retinal isomer substrates, to better define their specificities in RA isomer synthesis. RALDH3 and 4 were expressed as His-tagged proteins and affinity-purified. RALDH3 oxidized all-trans retinal with high catalytic efficiency but did not show activity for either 9-cis or 13-cis retinal substrates. RALDH4 was inactive for all-trans retinal substrate, exhibited high activity for 9-cis retinal oxidation, and oxidized 13-cis retinal with lower catalytic efficiency. β-ionone, a potent inhibitor of RALDH4 activity, suppressed 9-cis and 13-cis retinal oxidation competitively, but had no effect on RALDH3 activity. The p-HMB inhibited the activity for both RALDH3 and RALDH4. The divalent cation MgCl2 activated 13-cis retinal oxidation by RALDH4 by 3-fold, slightly decreased 9-cis retinal oxidation, and did not significantly influence RALDH3 activity. These data extend the kinetic characterization of RALDH3 and 4, providing their specificities for retinal isomer substrates, which should help in determining their functions in the synthesis of RAs in specific tissues.

Thesis (PhD (Genetics. Plant Biotechnology))--University of Stellenbosch, 2006. / The young internodes of sugarcane are ideal targets for altering metabolism, through genetic manipulation, to potentially control known fungal diseases such as Smut or to increase sucrose yields in these regions that are currently being discarded. At present, no regulatory sequences that specifically drive transgene expression in young developing sugarcane tissues are available. The objective of this study was therefore to isolate and evaluate such a sequence. The promoter targeted for isolation in this study regulates the expression of UDP-glucose dehydrogenase (EC 1.1.1.22), an enzyme which catalyses the oxidation of UDP-glucose to UDP-glucuronic acid, a precursor for structural polysaccharides which are incorporated into the developing cell wall. A strong correlation between the expression of UDP-glucose dehydrogenase and a demand for structural polysaccharides in developing tissues could therefore be expected. The first part of this study addressed the general practicality of promoter isolation from sugarcane, a complex polyploid. A gene encoding UDP-glucose dehydrogenase was isolated from a sugarcane genomic library. The gene contains an open reading frame (ORF) of 1443 bp, encoding 480 amino acids and one large intron (973 bp), located in the 5’-UTR. The derived amino acid sequence showed 88 – 98% identity with UDP-glucose dehydrogenase from other plant species, and contained highly conserved amino acid motifs required for cofactor binding and catalytic activity. Southern blot analysis indicates a low copy number for UDP-glucose dehydrogenase in sugarcane. The possible expression of multiple gene copies or alleles of this gene was investigated through comparison of sequences amplified from cDNA prepared from different tissues. Although five Single Nucleotide Polymorphisms (SNP) and one small-scale insertion/deletion (INDEL) were identified in the aligned sequences, hundred percent identity of the derived amino acid sequences suggested the expression of different alleles of the same gene rather than expression of multiple copies. The finding that multiple alleles are expressed to provide the required level of a specific enzyme, rather than the increased expression of one dominant allele, is encouraging for sugarcane gene and promoter isolation. In the second part of the study the suitability of UDP-glucose dehydrogenase as a target for the isolation of a developmentally regulated promoter was investigated. The contribution of UDP glucose dehydrogenase to pentan synthesis, as well as the expression pattern and subcellular localisation of the enzyme in mature sugarcane plants was studied at the tissue and cellular level. Radiolabelling with positionally labelled glucose was used to investigate the relative contributions of glycolysis, the oxidative pentose phosphate pathway and pentan synthesis to glucose catabolism. Significantly (P=0.05) more radiolabel was released as CO2 from [6-14C]- glucose than [1-14C]-glucose in younger internodes 3, 4 and 5, demonstrating a significant contribution of UDP-glucose dehydrogenase to glucose oxidation in the younger internodes. In addition, there was significantly (P=0.05) more radiolabel in the cell wall (fiber) component when the tissue was labelled with [1-14C]-glucose rather than [6-14C]-glucose. This also demonstrates a selective decarboxylation of glucose in position 6 prior to incorporation into the cell wall and is consistent with a major role for UDP-glucose dehydrogenase in cell wall synthesis in the younger internodes. Expression analysis showed high levels of expression of both the UDP-glucose dehydrogenase transcript and protein in the leafroll, roots and young internodes. In situ hybridisation showed that the UDP-glucose dehydrogenase transcript is present in virtually all cell types in the sugarcane internode, while immunolocalisation showed that the abundance of the protein declined in all cell types as maturity increased. Results obtained confirmed that this enzyme plays an important role in the provision of hemicellulose precursors in most developing tissues of the sugarcane plant, indicating that UDP-glucose dehydrogenase was indeed a suitable target for promoter isolation. Lastly, the promoter region and first intron, located in the 5’-untranslated region (UTR) of this gene, were isolated and subsequently fused to the GUS reporter gene for transient expression analysis and plant transformation. Transient expression analysis showed that the presence of the intron was essential for strong GUS expression. Analysis of stably transformed transgenic sugarcane plants, evaluated in a green house trial, showed that the isolated promoter is able to drive GUS expression in a tissue specific manner under these conditions.

Introdução: A enzima 3-hidroxiacil CoA desidrogenase de cadeia longa (LCHAD) é uma das enzimas envolvidas na beta-oxidação mitocondrial de ácidos graxos e faz parte do complexo enzimático chamado proteína trifuncional. Sua deficiência segue um modelo de herança autossômica recessiva com uma mortalidade maior que 70%, porém um tratamento dietoterápico adequado reduz substancialmente a morbimortalidade. Estudos recentes descreveram que gestantes de fetos homozigóticos para defeitos de LCHAD apresentam grandes chances de desenvolver síndrome HELLP e doença hepática aguda da gestação, com risco de morte materna, fetal e do recém-nascido. A síndrome HELLP é caracterizada por plaquetopenia, enzimas hepáticas elevadas e hemólise, podendo se apresentar na forma completa ou parcial. Estudos mostram que investigar a relação entre síndrome HELLP e defeitos de LCHAD, possibilita a prevenção de futuras gestações de risco por meio de aconselhamento genético e o diagnóstico precoce deste erro inato do metabolismo. Objetivos: Verificar a associação entre gestantes com síndrome HELLP e lactentes com defeitos LCHAD e identificar problemas de saúde gerados pela doença nesses conceptos. Metodologia: Análise de prontuários, necropsias e desfecho atual dos conceptos de 42 gestantes com síndrome HELLP e 84 controles. Resultados: Entre as gestantes que compunham os casos, a maioria apresentou proteinúria; além de sintomas como vômitos e epigastralgia. O parto cesárea foi realizado em 93% das gestantes. Quase metade das puérperas apresentou algum tipo de complicação materna. Quanto ao desfecho perinatal, 90% dos conceptos apresentaram baixo peso ao nascer e 23,8% evoluíram para óbito. Entre esses 10 óbitos, resgatamos 7 imagens histopatológicas com esteatose hepática. Inferimos doença metabólica nesses casos, que levou a uma associação de 11% com a síndrome HELLP. Entre o grupo controle, 46,2% das mulheres já haviam sofrido pelo menos um aborto. Na atual gestação 6,4% desenvolveram pré-eclampsia; entre outras complicações. Encontramos gravidezes subsequentes das gestantes do grupo Caso com recorrência de HELLP e óbito. Conclusão: Os resultados reforçam a importância do diagnóstico precoce de síndrome HELLP, além da investigação da associação do defeito de LCHAD e HELLP mesmo post morten afim de evitar futuras gestações de risco e diminuir a morbimortalidade materna e neonatal. / Long-chain 3-hydroxyacyl CoA dehydrogenase (LCHAD) is one of the enzymes involved in the mitochondrial fatty acids beta-oxidation and part of the enzymatic complex called trifunctional protein. Its deficiency follows an autosomal recessive model with a higher mortality, but an adequate dietary treatment reduces its morbimortality. Recent studies reported that mothers of fetuses homozygous for LCHAD deficiency have higher chances of developing HELLP and acute fatty liver of pregnancy with risk of maternal, infant and fetal death. Thrombocytopenia, elevated liver enzymes and hemolysis characterize HELLP syndrome, which can be diagnosed as complete or partial. Studies demonstrate that investigate the association between HELLP syndrome and LCHAD defects can prevent future risk pregnancies through genetic counseling and early diagnosis of this inborn error of metabolism. Objectives: To investigate the association between pregnant women and concepts with LCHAD deficiency and identify health problems caused by the disease in these fetuses. Methodology: Analysis of medical records, autopsy reports and current outcome of fetuses of 42 pregnant women with HELLP syndrome and 84 controls. Results: In case group, most patients presented proteinuria; as well as symptoms as vomiting and epigastric pain. The cesarean delivery was performed in 93% of pregnant women. Almost half of women presented maternal complications. In perinatal outcome, 90% of fetuses has low weight at birth and 23.8% died. Among these 10 deaths, we rescued 7 hystopathological images with hepatic steatosys. We could infer metabolic disease in these cases, which led to an association of 11% to the HELLP syndrome. Among the control group, 46.2% of women had at least one abortion before this pregnancy. During the pregnancy 6.4% developed pre-eclampsia among other complications. In control group, we find HELLP syndrome recurrence and death in subsequent pregnancy. Conclusion: The results reinforce the importance of early diagnosis of HELLP syndrome, as well as research LCHAD and HELLP association even post mortem to avoid future risk pregnancies and reduce maternal and neonatal morbidity and mortality.