Graduation date: 1998

Graduation date: 1996

There is increasing evidence that hydrogen peroxide (H2O2) can act as a signalling molecule capable of modulating a variety of biochemical and genetic systems. Using Jurkat T-lymphocytes, this study initially investigated the involvement of H2O2 in the activation of a specific signalling protein extracellular signal-regulated protein kinase (ERK). It was found that as a result of H2O2 treatment, mitochondrial complex activities decreased which led to subsequent increase of mitochondrial reactive oxygen species (ROS) production. The increase of ROS resulted in higher cellular H2O2 as well as increased ERK activation. This study demonstrated that in an oxidative stress setting, H2O2 production from the mitochondria was an essential component in maintaining the activation of a signalling protein. One way in which H2O2 could influence protein function is by the oxidation of susceptible thiol groups of cysteine residues. To further understand the variety of signalling pathways that H2O2 may be involved in, an improved proteomics technique was developed to globally identify proteins with susceptible thiol groups. The

Thesis (M.S.)--University of Michigan, 1974.

Thesis (M.S.)--University of Michigan, 1974.

Ribonucleoside diphosphate reductase (RR) from vaccinia virus was recently cloned and overexpressed rn Escherichia coli. The amino acid sequence identities of the small and large subunits between the mouse and the vaccinia virus reductase are approximately 80 and 72 percent, respectively. In addition, vaccinia virus RR displays similar complex allosteric regulation to the mouse enzyme and other eukaryotic reductases. The overall activity of the enzyme, which has two subunits (Rl and R2), is regulated through binding to ATP, which activates the enzyme, and dATP which seryes as an inhibitor. Both nucleotides bind to the same allosteric site, called the activity site, on the large subunit of RR. The specificity of the enzyme towards the four ribonucleoside diphosphate substrates is regulated by the binding of ATP, dATP, dTTP and GTp. Each of these nucleotides affects the reduction of a specific nucleoside diphosphate. Although this enzyme's allosteric regulation is kinetically well understood it has not been possible so far to gain further structural information about the location of the activity site and specificity site. The use of deletion mutants and photoaffinity labeling of the large subunit to identify the location of the binding sites is the incentive for this thesis. With the introduction of 6xHis/Nickel Nitrilo-tri-acetic acid (Ni-NTA) chromatography, the purification of the large subunit was improved in the E. coli and vaccinia virus/T7 RNA polymerase hybrid system. The purification of several deletion mutant forms of the large subunit was also attempted, but it was not possible to purify any of them from either of the expression systems. The purified full-length large subunit obtained with the Ni-NTA-chromatography system was used for a photoaffinity labeling experiment with [³²P]dATP and [³²P]dTTP. The labeled proteins were proteolytically digested to find out about the specificity of the labeling experiment and also to map the binding site of the nucleotide. It was found that labeling of dATP yielded few discrete bands indicating specific binding, while a comparable experiment with dTTP indicated less specific binding, based on a larger number of labeled bands. In competition experiments with non-radioactive nucleotides, vaccinia virus R1 featured the same properties as the mouse and E. coli counterparts. This is consistent with data from kinetic experiments, which also establish the same kinetic properties between vaccinia virus RR with those of mouse and E. coli (RR). To identify the sequence of the fragments carrying the label the digests were subjected to mass spectrometric analysis. However, it was not possible to determine the sequence of the labeled fragment by mass spectrometry due to poor spectral resolution. / Graduation date: 1994

Abstract not available

No description available.

We have synthesized a new class of photoaffinity analogs, 2',3'-O-(2,4,6-trinitrophenyl)-8-azido-ATP, -ADP and -AMP (TNP- 8N₃ATP, -ADP and -AMP), and their radiolabeled derivatives, and characterized their interaction with the sarcoplasmic reticulum Ca²⁺-ATPase. The TNP-8N₃-nucleotides were synthesized from ATP in three steps involving bromination in the 8-position of the adenine ring followed by displacement with an azido group and then trinitrophenylation of the resulting 8N₃-nucleotide with TNBS. Inclusion of the oxidizing agent, DTNB, in the final reaction was found to be necessary to prevent reduction of the azido group by the released sulfite anion and also elevated the yield of trinitrophenylation to about 80%. Purity was determined spectrophotometrically, as well as by anion exchange TLC and reversed phase HPLC. In the dark, the compounds were found to display most of the features of the parent TNP-nucleotides and interacted with the Ca²⁺-ATPase in a similar way. When activated by illumination, the probes were specifically incorporated into SR vesicles with high efficiency at alkaline pH. The site of labeling was identified as being on the A₁ tryptic fragment.

Les toxines Shiga (Stx) sont produites par Shigella dysenteriae et certaines espèces d’E. coli transmisent aux humains par la consommation d'aliments contaminés et causant des maladies graves. La toxine Stx est libérée par les bactéries dans l'intestin et par la suite, traverse les vaisseaux sanguins en aval pour atteindre leurs principaux organes cibles, notamment les reins. Les dommages causés aux reins peuvent entraîner des complications graves notamment Le syndrome hémolytique urémique (SHU). A ce jour, il n’existe aucun traitement disponible contre le SHU. Les toxines Stx usent du transport rétrograde intracellulaire pour infester les cellules endothéliales rénales et atteindre leur cible cytosolique, l'ARN ribosomal 28S. Via un screening à haut débit, il a été démontré que le composé Rétro-2 bloque le trafic rétrograde de Stx à l'interface Endosome-TGN, sans affecter la morphologie des organites cellulaires et le trafic des protéines endogènes. Au cours de cette thèse, une analyse des relations structure fonction du composé Retro-2 nous a permis d’identifier les régions de l'inhibiteur qui sont critiques pour l'activité de protection. Nous avons identifié un dérivé dihydroquinazolinone nommé Rétro-2.1 qui est à ce jour l'inhibiteur le plus puissant contre les toxines Stx. Afin d’identifier la cible moléculaire de Retro-2.1, nous avons développé des sondes photo-activables bio-actives. En outre, les données de diffraction des rayons X ont révélé que de l'activité antitoxine réside principalement dans l’énantiomère S. (S) -Retro-2.1 est 500 fois plus puissant contre Stx (50 nM) que la molécule initiale. Cette étude peut donner lieu à un nouveau concept thérapeutique ciblant la voie de transport rétrograde de la toxine à l'intérieur de la cellule hôte. Une telle stratégie thérapeutique pourrait donc être étendue à d'autres agents pathogènes qui usent également du trafic rétrograde pour une intoxication des cellules hôtes. Ce nouveau concept thérapeutique qui permet de cibler les cellules hôtes et non l'agent pathogène représente une véritable percée dans la découverte de médicaments à large spectre et réduit le risque de développement d’une résistance chez l’agent pathogène. / Shiga toxins (Stx) are produced by Shigella dysenteriae and certain species of E. coli that can be transmitted to humans primarily through consumption of contaminated foods and may cause severe disease. Stx is released by the bacteria in the intestine and subsequently, could cross the downstream blood vessels to reach their main target organs such as kidney. Damage to the kidney can result in serious life-threatening complication hemolytic uremic syndrome, for which there is no proven safe treatment available other than supportive care. Stx invades renal endothelial cells in a retrograde manner from cell surface to the endoplasmic reticulum in order to gain access to its cytosolic target, 28S rRNA. By using HTS, it was previously demonstrated that the compound Retro-2 blocks retrograde trafficking of Stx at the early endosome-TGN interface, without affecting the morphology of cellular organelles and trafficking of other endogenous proteins. In this work, different regions of the lead inhibitor Retro-2 that are critical for the protective activity have been determined by systematic structure-activity relationship studies. It allowed us to identify a dihydroquinazolinone derivative, named Retro-2.1 that is the most potent inhibitor of Stx to date and also to develop bio-active photo-activatable probes with the aim of identifying the molecular target of Retro-2 derivatives. Further, crystal X-ray diffraction data revealed that the antitoxin activity resides mainly in the S-enantiomer. (S)-Retro-2.1 has displayed 500 fold more potency (50 nM) than parent molecule against Stx cytotoxicity. This study may result in a new therapeutic concept - targeting the retrograde transport route of toxin inside host cell - for the treatment of Stx-producing E. coli infections and could therefore be extended to other pathogens that also traffic via the retrograde transport. Such a new therapeutic concept that target the host cells and not the pathogen itself would represent a real breakthrough in drug discovery leading to broad spectrum drugs.