Thesis advisor: Charles Hoffman / In both mammals and fission yeast, control of cAMP levels is maintained by adenylyl cyclases (ACs), which synthesize cyclic nucleotide, and by cyclic nucleotide phosphodiesterases (PDEs), which are responsible for its degradation. AC activity is regulated by G proteins, which respond to signals from G protein-coupled receptors (GPCRs) that detect extracellular signaling factors such as hormones. cAMP is a second messenger that has several effectors, with protein kinase A (PKA) being a primary target of activation that phosphorylates several downstream targets and results in modulation of pathways such as cell growth and gluconeogenesis. Aberrant cAMP regulation has been linked to several human disease states, such as McCune-Albright Syndrome, which is the result of elevated cAMP levels. Whereas the targeting of PDEs with drugs and selective inhibitors has been very successful, the AC-inhibiting compounds identified to date are unfavorable for clinical use. Inhibitors may not necessarily bind to and inhibit a given AC directly but instead act on a regulatory pathway such as calmodulin signaling. Theoretically, they also may bind to the G protein, interfere with the AC-G protein stimulatory complex, or regulate a factor of AC transcription. Since more than one AC species is expressed in many human cell types, it is difficult to selectively reduce cAMP levels. Therefore, for an AC inhibitor to be favored as a candidate for drug development, it is likely that the compound should directly bind to and inhibit the AC. This thesis describes my studies on a scaffold of 41 structurally related BCAC compounds, called the BCAC51 scaffold, that was identified in a high-throughput screen (HTS) with Schizosaccharomyces pombe strains transformed with GNAS and either mammalian AC4 or AC7. I carried out a series of experiments to examine whether the compounds bind to and inhibit mammalian ACs directly. The most active compounds were further characterized for potency and specificity against a panel of ACs. Several compounds significantly reduced cAMP production, but it could not be determined if the compounds directly or indirectly altered AC activity. I also cloned and constructed strains expressing the human wild-type AC5 gene and the AC5 R418W mutant, which has shown an increased sensitivity to GNAS. cAMP assays on these strains using various BCAC compounds showed that while most compounds had similar effects on both forms of AC5, BCAC62 was significantly more effective on the wild-type enzyme than on the mutant AC5, although the reason for this is unclear. To test whether the compounds could reduce AC activity in the absence of GNAS (basal activity), a flow cytometry study was carried out using a PKA-repressed GFP reporter. Results suggested that BCAC compounds do reduce basal-AC activity and therefore do not act by binding to and inhibiting GNAS, by interfering with the AC-GNAS stimulatory complex, nor by stimulating PDE. Finally, I developed a molecular genetic screen for mutant alleles of an AC gene that confer compound-resistance. One cycle of the screen is near completion, and the screen provides a foundation for future examination of compound-resistant AC candidates. The results presented in this thesis serve as a basis for further research into members of the BCAC51 compound series being putative direct inhibitors of mammalian ACs. / Thesis (BS) — Boston College, 2022. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Scholar of the College. / Discipline: Biology.

This work is focused on the RTX (Repeats in ToXin) domains structure of selected RTX toxins and its impact on secretion and protein folding. The structural analysis included RTX domains of ApxI (Actinobacillus pleuropneumoniae-RTX-toxin I) from Actinobacillus pleuropneumoniae, HlyA (Alfa-hemolysin) from Escherichia coli and LtxA (Leukotoxin A) from Aggregatibacter actinomycetemcomitans and blocs 4 a 5 RTX domain CyaA (adenylate cyclase toxin) from Bordetella pertussis. The structures of LtxA RTX domain and CyaA RTX blocs 4 and 5 were obtained and characterized. Two models of CyaA RTX domain were built based on SAXS (Small Angle X-ray Scattering) model, previously solved RTX structures and RTX structures presented here.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20275号 / 医博第4234号 / 新制||医||1021(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 横出 正之, 教授 小西 靖彦, 教授 山下 潤 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Pseudomonas aeruginosa is an important nosocomial infection that has the potential to infect almost every tissue of the human body though it is mainly opportunistic, due to the organism’s intrinsic antibiotic resistance is becoming increasingly difficult to treat. Two-component systems (TCS) rely on a signal sensed from the outside environment by the sensor histidine kinase to initiate phosphotransfer to the response regulator, which may then regulate virulence factors in the organism in response to a changing environment. One important two-component system in P. aeruginosa is the AlgZ/R system. AlgZ, the sensor histidine kinase, has been shown to be co-transcribed with its’ response regulator, AlgR, to affect a myriad of virulence factors, including those related to motility. Pseudomonas species is capable of four types of motility: twitching, swimming, swarming, and gliding. Twitching motility is achieved through the expression of the FimU operon and Type VI pilli, and is most useful when attaching to a solid surface in the initial step of pathogenesis: colonization. Conversely, the swimming phenotype relies on the production of a single polar flagellum upon the activation of the FleQ operon, and allows the organism to move through a fluid environment. A previously unidentified regulator of AlgZ, but not AlgR, has been identified via transposon mutagenesis screening, PA2771, which has a GGDEF domain and predicted diguanylate cyclase activity. The mechanism of PA2771’s action within P. aeruginosa has not been previously studied. The nonpolar deletion mutant was first characterized via various phenotypic assays (including biofilm, rhamnolipid, swimming, and swarming assays) and transcriptional fusions to propose a mechanism in which this predicted diguanylate cyclase (DGC) works with AlgZ to determine the switch in motility from twitching to swimming. When PA2771 is present and active in the cell, cyclic di-GMP levels should be high, leading to the production of Type VI pilli and the upregulation of the FimU operon. In the PA2771 mutant a significant decrease in the expression of the FimU operon, and an increase in the expression of the flagellar genes. Subsequent alterations in swimming and swarming phenotypes were observed, as well as the restoration of these effects via complementation studies. Overexpression of AlgZ in the 2771 mutant showed a restoration of AlgZ expression in the nonmucoid background, and the predicted DGC activity was indirectly verified via a cdrA-lacZ transcriptional fusion.

Cholera toxin (CT) is a bacterial protein toxin responsible for the gastrointestinal disease known as cholera. CT stimulates its own entry into intestinal cells after binding to cell surface receptors. Once internalized, CT is delivered via vesicle-mediated transport to the endoplasmic reticulum (ER), where the CTA1 subunit dissociates from the rest of the toxin and is exported (or translocated) into the cytosol. CTA1 translocates from the ER lumen into the host cytosol by exploiting a host quality control mechanism called ER-associated degradation (ERAD) that facilitates the translocation of misfolded proteins into the cytosol for degradation. Cytosolic CTA1, however, escapes this fate and is then free to activate its target, heterotrimeric G-protein subunit alpha (Gsα), leading to adenlyate cyclase (AC) hyperactivation and increased cAMP concentrations. This causes the secretion of chloride ions and water into the intestinal lumen. The result is severe diarrhea and dehydration which are the major symptoms of cholera. CTA1’s ability to exploit vesicle-mediated transport and ERAD for cytosolic entry demonstrates a potential link between cholera intoxication and a separate quality control mechanism called the unfolded protein response (UPR), which up-regulates vesicle-mediated transport and ERAD during ER stress. Other toxins in the same family such as ricin and Shiga toxin were shown to regulate the UPR, resulting in enhanced intoxication. Here, we show UPR activation by CT, which coincides with a marked increase in cytosolic CTA1 after 4 hours of toxin exposure. Drug induced-UPR activation also increases CTA1 delivery to the cytosol and increases cAMP concentrations during intoxication. We investigated whether CT stimulated UPR activation through Gsα or AC. Chemical activation of Gsα induced the UPR and increased CTA1 delivery to the cytosol. However, AC activation did iv not increase cytosolic CTA1 nor did it activate the UPR. These data provide further insight into the molecular mechanisms that cause cholera intoxication and suggest a novel role for Gsα during intoxication, which is UPR activation via an AC-independent mechanism

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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

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