Kynurenine 3-monooxygenase (KMO) is a flavoprotein which has been implicated in Huntington’s disease, Alzheimer’s disease and acute pancreatitis. Recently there has been important research published about this enzyme including the structure of a truncated Saccharomyces cerevisiae KMO enzyme and KMO inhibition studies in animal models of disease. In previous work from this research group the complete Pseudomonas fluorescens KMO enzyme has been successfully crystallised both with and without the substrate, L-kynurenine, from which significant insights were gained into function and the potential role of domain movement. To examine substrate binding in KMO and to consolidate previous structural studies, key residues in the active site have been investigated using site directed mutagenesis, crystallography and kinetic analysis using steady-state techniques. This analysis has identified the interactions between the enzyme and the substrate and provides a basis for inhibitor design. The residues implicated in substrate binding are N369, Y404 and R84. For N369 and Y404, minor changes to the amino acid in the mutations N369S and Y404F were shown to cause a decrease in binding affinity of the substrate but the enzyme remained active. For the mutations Y404A and R84K enzyme activity was significantly affected. Crystal structures of N369S, Y404F and R84K were also obtained. Another residue in the active site studied was H320 which is the only amino acid to differ in the active sites of the human and Pseudomonas fluorescens enzymes. This residue was therefore of interest to determine whether the bacterial enzyme used in this work is likely to be a good model for the human enzyme, which has not yet been successfully isolated in significant quantities for in vitro research. Modifying this residue to obtain H320F KMO revealed that this residue does not have a significant role in substrate binding. Potent inhibitor molecules have been studied with this enzyme and shown in kinetic assays to have nanomolar Ki values. These inhibitors are the most potent inhibitors studied with Pseudomonas fluorescens to date and continue previous inhibitor studies carried out with this enzyme. This group of inhibitors contain different substituents in the part of the molecule shown to bind closest to the C-terminal domain of the protein. These novel inhibitors do not allow the flavin to be reduced by NADPH (which results in unwanted peroxide production) unlike a number of previously studied molecules and therefore have the potential to be clinically useful. This research therefore answers many questions about this enzyme, in particular about the role of particular residues in the active site, substrate recognition and inhibition of this important drug target.

Nesse trabalho avaliamos o potencial enzimático de diferentes linhagens de fungos, visando determinar a presença de mono-oxigenases capazes de oxidar cetonas aromáticas e cíclicas. Todas as linhagens empregadas apresentaram atividade de álcool desidrogenase e Baeyer-Villiger mono-oxigenases. Adicionalmente foram sintetizadas oito moléculas bi-funcionalizadas com grupos sulfeto, seleneto e carbonila (cetona). Os produtos das reações biocatalisadas foram isolados e caracterizados. / In this work, we evaluated the enzymatic potential of different Aspergillus strains, through the biotransformations of two substrates: 2- and 4-methylcyclohexanone (1a e 1b). All the strains employed showed alcohol dehydrogenase and Baeyer-Villiger monooxygenase (CPMO and CHMO) activities. These enzymes can perform ketone biorreduction and oxidation. Using the A. terreus SSP 1498 selected from the screening study, we prepared alcohols and lactones in good enantiosselectivity. In this way, other fungal strains were studied aiming to determine the presence of monooxygenase activity by means of the biotransformation of aromatic ketones. Like the Aspergillus, we observed that all strains used in this study showed alcohol dehydrogenase and Baeyer-Villiger monooxygenase (APMO) activities. We selected 1-phenyl-etanone and its para substituted derivates as substrates. Additionally, we synthesized eight examples of bi-functionalized compounds with sulfide, selenide and ketone groups. These compounds were submitted to the action of enzymatic system of different fungi which were selected from the initial screening. The products from the biotransformation were isolated and characterized.

München, Techn. Univ., Diss., 2001. / Computerdatei im Fernzugriff.

München, Techn. Universiẗat, Diss., 2001.

Kynurenine 3-monooxygenase (KMO) is an enzyme central to the kynurenine pathway of tryptophan degradation. KMO is emerging as an increasingly important target for drug development. The enzyme is implicated in the development and progression of several neurodegenerative disorders, in the regulation of the immune response and in sterile systemic inflammation. Production of recombinant human enzyme is challenging due to the presence of transmembrane domains, which localise KMO to the outer mitochondrial membrane and render KMO insoluble in many in vitro expression systems. Although several in vitro KMO assay techniques have been reported in the literature these methods are typically insensitive or require purified protein for use in high-throughput screening assays of human KMO enzyme. The first report of bacterial expression of soluble active human KMO enzyme is described here. Fusion protein tags were used to optimise soluble expression and enable characterisation and partial purification of the active protein constructs. Functional enzyme was used to develop several novel high-throughput drug screening techniques for the discovery of inhibitors specifically targeting human KMO. These screening techniques were fully characterised and validated using known KMO inhibitors from the patent literature. One of the novel KMO assay techniques was implemented for compound screening and several hit compounds were identified, validated and their in vitro DMPK characteristics determined. In addition to assay development, KMO was characterised at the cellular level when overexpressed in HEK293 cells. These experiments indicated that KMO overexpressing cells undergo bidirectional adaptation via alteration of kynurenine pathway homeostasis. As a result, these cells are protected from cytotoxicity mediated by 3-hydroxykynurenine (3-HK), the toxic product of KMO catalysis. The development of novel high throughput screening techniques targeting KMO has enabled screening of potential new inhibitors specifically targeting the human enzyme. Implementation of these screening assays will allow accelerated and improved discovery and development of novel KMO inhibitors for the potential treatment of numerous disease states.

Natural nitro compounds with diverse structures and biological functions are produced by bacteria, fungi, plants and animals. Little is known about the behavior of such compounds in natural ecosystems. The lack of accumulation in the biosphere implies that they are biodegraded. Microbial strategies for biodegradation of synthetic nitro compounds are well established; however only two pathways are known for degradation of natural nitro compounds. The research described here examines the genes that encode the key enzymes required for biodegradation of 3-nitrotyrosine (3NTyr) and 1-nitro-2-phenylethane (NPE). 3NTyr is a biological marker for disease and inflammation in plants and animals. A 3NTyr degrading microbe, Variovorax sp. JS669 was isolated from soil. We identified the JS669 denA, which encodes an enzyme that catalyzes denitration of 4-hydroxy-3-nitro-phenylacetate, the key step in metabolism of 3NTyr. The isolation of 3NTyr degraders and development of molecular probes specific to denA revealed that 3NTyr degradation is a widespread phenomena in natural habitats and the compound is metabolized by phylogenetically diverse bacteria. Phylogenetic analysis of the 4-hydroxy-3-nitro-phenylacetate denitrase from JS669 revealed it to be the first functionally annotated protein in a clade of unidentified Class A flavin monooxygenases. NPE has been identified from several plants, yet the biodegradation of the compound remained a mystery. Here we report the degradation of NPE and its analog 2-nitropropylbenzene. Discovery of the metabolic pathway revealed a novel microbial strategy to use a meta-ring fission degradation pathway to cleave an undesirable side chain from an aromatic compound and use the remainder of the compound as a carbon and energy source. Two genes that encode enzymes in the biodegradation pathway were identified and both are deeply branched within their respective phylogenetic trees, indicating that both represent highly specialized microbial enzymes. Furthermore, microbial degradation of NPE resulted in the production of 3-nitropropionic acid, a natural toxin that inhibits succinate dehydrogenase and is responsible for livestock illness and death. This is the first report of bacterial production of 3-nitropropionic acid, and might represent a significant source of 3-nitropropionic acid in natural habitats. The findings from these studies contribute to the overall understanding of microbial metabolism. Specifically, this research reveals genes that encode novel enzymes and strategies for the biodegradation of two natural nitro compounds. Furthermore, discovery of mechanisms for the biodegradation of such compounds reveals novel microbial metabolic diversity and provides insight into the evolution of degradation pathways for synthetic compounds.

Methylosinus trichosporium OB3b is a wild type, obligate methanotroph that grows only on one-carbon compounds and, in the absence of copper, produces high levels of soluble methane monooxygenase (sMMO) to metabolize methane to methanol. SMMO has gained a great deal of attention in the bioremediation and chemical industries because of its low substrate specificity and its ability to oxidize chlorinated hydrocarbons. Much literature exists on cultivating this organism on methane, however no one has achieved dry cell weight densities exceeding 18 g/L. Biomass growth is limited due to mass transfer of methane to cells. This study investigated the growth of M. trichosporium on the water soluble carbon source, methanol while retaining sMMO activity. Methanol was found to completely inhibit growth at 40 g/L. For online methanol measurements during fed-batch cultivation, an in situ probe was constructed from autoclavable materials and equipped with a Figaro TGS822 vapor sensor. The probe was designed to prevent the sensor coming in contact with water aerosols which affect its performance. The probe was an essential component of a feedback methanol control system. The cumulative CO2 production (CCP) strategy was used to feed methanol in fed-batch experiments. In an initial bioreactor study, growth nutrients were fed in excess. The yields of biomass to nutrients were determined and the growth medium modified accordingly. A biomass density of 19 g/L (growth rate of 0.013-0.065 h-1) was achieved with sMMO activity of 300 to 500 [µmol naphthol][g of biomass]-1[h]-1. The subsequent bioreactor study involved feeding of nutrients based on their yields in relation to methanol, a biomass density of 62 g/L (growth rate of 0.034- 0.08 h-1) was achieved. The inoculum cultures utilized in the bioreactor studies were maintained on Noble agar plates containing nitrogen minimal salts medium and methane. After 6 months of subsequent plate transfers, M. trichosporium lost the ability to produce high levels of sMMO. The enzyme activity in methanol grown cells was recovered by subculturing in liquid NMS medium with methane as the sole carbon source, the activity increased from 8 to 600 [µmol naphthol][g of biomass]-1[h]-1. It is recommended that further studies be carried out on stimulating sMMO activity during cultivation on methanol. / Thesis (Master, Chemical Engineering) -- Queen's University, 2008-08-21 15:14:42.475

Supernatant protein factor (SPF) is a 46-kDa cytosolic protein that stimulates squalene monooxygenase, which catalyses the second committed step in cholesterol biosynthesis. The mechanism by which SPF stimulates this enzyme is not understood and the goal of these studies was to see if SPF affected cholesterol synthesis in cultured cells. Rat supernatant protein factor-like protein (SPF2) shares 77% sequence identity with human SPF. In my studies SPF2 also stimulated squalene monooxygenase in vitro and incubation of SPF2 with protein kinase A (PKA) and C increased its activity by about 2-fold, as shown earlier with SPF. GTP and GDP prevented the stimulation of squalene monooxygenase by SPF2, suggesting that binding of these nucleotides inhibits SPF2. This inhibition could be prevented by the addition of -tocopherol, although -tocopherol alone had no effect on SPF2 activity in vitro. Expression of human SPF in hepatoma cells, which lack expression of endogenous SPF, increased cholesterol synthesis by 2-fold and addition of dibuytrylcAMP, a PKA activator, to these cells yielded an additional 62% increase whereas addition of a PKA inhibitor completely blocked the ability of SPF to stimulate cholesterol synthesis. To further confirm a role for phosphorylation in the regulation of SPF, substitution of alanine for serine-289 (a putative PKA recognition site) reduced the PKA-mediated activation of SPF in vitro by 50%, as measured with microsomal squalene monooxygenase and completely blocked the ability of SPF to stimulate cholesterol synthesis in hepatoma cells. In further structure-function studies, deletion of the carboxy-terminal Golgi-dynamics domain greatly increased the ability of SPF to stimulate squalene monooxygenase in microsomes, but, paradoxically prevented SPF from stimulating cholesterol synthesis in cell culture. Addition of brefeldin A, which disrupts Golgi formation, also abolished the ability of SPF to stimulate cholesterol synthesis, supporting a role for the Golgi in SPF function. Since squalene monooxygenase is not thought to be rate-limiting with regard to cholesterol synthesis, the possibility that SPF might stimulate other enzymes in the cholesterol biosynthetic pathway was investigated. The substitution of 14Cmevalonate for 14C-acetate completely blocked an SPF-induced 1.5-fold increase in squalene synthesis, suggesting that SPF stimulated mevalonate synthesis at HMGCoA reductase. 2,3-Oxidosqualene synthesis from 14C-mevalonate remained elevated (1.3-fold) with mevalonate demonstrating that SPF also stimulated squalene monooxygenase in hepatoma cells. SPF did not increase HMG-CoA reductase or squalene monooxygenase enzyme levels in cells, indicating that SPF directly activated these enzymes. Indeed, addition of purified recombinant SPF to rat liver microsomes stimulated HMG-CoA reductase by about 1.5-fold. These results reveal that SPF directly stimulates HMG-CoA reductase, the rate-limiting step of the cholesterol biosynthetic pathway, as well as squalene monooxygenase, and, coupled with the ability of PKA-mediated phosphorylation to regulate SPF activity, suggest a new means by which cholesterol synthesis can be rapidly modulated in response to hormonal and environmental signals.

Thesis (Ph. D.)--University of Virginia, 2000. / Includes bibliographical references (leaves 104-139). Also available online through Digital Dissertations.

BACKGROUND: Acute pancreatitis (AP) is a sterile initiator of systemic inflammation that can trigger multiple organ dysfunction syndrome (MODS). In the acute phase of AP, the kynurenine pathway of tryptophan metabolism plays an important role in the genesis of AP-MODS in experimental animal models, but it is unknown whether the pathway is activated in human AP. Human data are required to support the rationale for kynurenine 3- monooxygenase (KMO) inhibition as a treatment for AP-MODS and reinforce the translational potential. Additionally, as respiratory dysfunction is frequent in severe AP, the role of lung ultrasonography in severity stratification deserves investigation. Furthermore, the effect of AP-MODS on long-term survival is unknown. OBJECTIVES: My objectives were to: 1) Define the temporal and quantitative relationship of kynurenine metabolites with the onset and severity of APMODS, 2) Investigate the value of lung ultrasonography in the early diagnosis of respiratory dysfunction in human AP-MODS, and 3) Examine whether early AP-MODS impacts on long-term survival. METHODS: 1) A prospective, observational, clinical experimental medicine study titled “Inflammation, Metabolism, and Organ Failure in Acute Pancreatitis” (IMOFAP) was performed. For 90 days, consecutive patients with a potential diagnosis of AP were recruited and venous blood was sampled at 0, 3, 6, 12, 24, 48, 72 and 168 hours post-recruitment. Kynurenine metabolite concentrations were measured by liquid chromatography–tandem mass spectrometry (LC-MS/MS) and analysed in the context of clinical data, disease severity indices, and cytokine profiles. 2) In a nested cohort within IMOFAP, 41 participants underwent lung ultrasonography to evaluate whether this imaging modality can detect respiratory dysfunction in AP. 3) Survival data for a prospectively maintained database of patients with AP was analysed after accounting for in-hospital deaths. RESULTS: 1) During the IMOFAP study, 79 patients were recruited with an elevated serum amylase, of which 57 patients met the diagnostic criteria for AP; 9 had severe disease. Temporal profiling revealed early tryptophan depletion and contemporaneous elevation of plasma concentrations of 3- hydroxykynurenine, which paralleled systemic inflammation and AP severity. 2) Lung ultrasonography findings correlated with respiratory dysfunction. 3) 694 patients were followed up for a median of 8.8 years. AP-MODS conferred a deleterious effect on overall survival which persisted after the exclusion of inhospital deaths (10.0 years, 95% C.I. = 9.4-10.6 years) compared to AP without MODS (11.6 years, 95% C.I. = 11.2-11.9 years; P = 0.001). This effect was independent of age. CONCLUSIONS: In the acute phase of AP, metabolic flux through KMO is elevated and proportionate to AP severity. Lung ultrasonography may be a useful technique for evaluating AP-MODS. AP-MODS is an independent predictor of long-term mortality. Together, this work reinforces the rationale for investigating early phase KMO inhibition as a therapeutic strategy in humans.