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- Dahlin, Paul, 1983-
(författare)
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Analysis of sterol metabolism in the pathogenic oomycetes Saprolegnia parasitica and Phytophthora infestans
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The primary objective of this thesis was to investigate the sterol metabolism of two pathogenic oomycetes, specifically the processes of sterol synthesis and sterol acquisition in the fish pathogen Saprolegnia parasitica (Saprolegniales) and the plant pathogen Phytophthora infestans (Peronosporales). Furthermore, the effects of steroidal glycoalkaloids from Solanaceous plants, on P. infestans, were examined. The improved understanding of these processes should help to identify approaches for the identification of new oomycete inhibitors targeting sterol metabolism in agriculture and aquaculture farming systems, and to guide plant-breeding strategies to defend solanaceous plants against oomycetes.For these reasons, the molecular basis of the metabolic pathways of sterol synthesis and/or sterol acquisition was investigated. Sterols are derived from isoprenoids and indispensable in various biological processes. Our biochemical investigation of an oxidosqualene cyclase revealed that sterol synthesis in S. parasitica begins with the formation of lanosterol (Paper I), and a reconstruction of the complete sterol synthesis pathway to the final compound, fucosterol, in S. parasitica was performed using bioinformatics (Paper II). Complementary to this work, the extent to which P. infestans, which is incapable of de novo sterol synthesis, is able to modify exogenously provided sterols was investigated by determining the growth impact of various sterol supplements in the growth media (Paper II). Building on the sterol investigations, the solanaceous sterol derivatives from the glycoalkaloid family were analysed. These compounds contain both a steroidal and a carbohydrate (glycan) moiety. Data obtained by feeding various deuterium-labeled sterols to potato shoots, supported the theory that steroidal glycoalkaloids in Solanum tuberosum are produced from cholesterol (Paper III). Since these steroidal glycoalkaloids are thought to play a role in plant defense, their physiological effects on P. infestans were investigated (Paper IV). Unexpectedly we found that non-glycosylated steroidal alkaloids had a greater inhibitory effect than steroidal glycoalkaloids. Steroidal glycoalkaloids derived from other Solanaceous species exhibited different physiological effects on the growth of P. infestans. This research was conducted on two oomycete species belonging to the Saprolegniales and Peronosporales orders, hence the results presented are likely to be representative of each of these two oomycete orders.
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| 2. |
- Guanglin, Kuang, 1987-
(författare)
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Theoretical Studies of Protein-Ligand Interactions
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The protein-ligand interaction is an important issue in rational drug design and protein function research. This thesis focuses on the study of protein-ligand interactions using various molecular modeling methods, which are used in combination to predict the binding modes and calculate the binding free energies of several important protein-ligand systems, as summarized below.In Paper I, we investigated the binding profile of a type I positive allosteric modulator (PAM) NS-1738 with the α7-nicotinic acetylcholine receptor (α7-nAChR). NS-1738 is found to have three different binding sites on α7-nAChR and has moderate binding affinities to the receptor.In Paper II, we revealed the binding mechanism of a PET radio-ligand [18F]ASEM with α7-nAChR. Using metadynamics simulations, we managed to find a stable state which is not observed in molecular docking and unbiased molecular dynamics simulations. Free energy analysis further confirmed that this stable state is the global minimum with respect to the selected collective variables.In Paper III, we studied the binding modes and binding affinities of two probes (AZD2184 and thioflavin T) for the detection of amyloid β(1-42) fibrils in clinical studies. We found that AZD2184 and thioflavin T are able to bind to several sites of the Aβ(1-42) fibril. Due to the small size, planarity and neutrality of AZD2184, it binds more strongly with Aβ(1-42) fibril at all sites. By contrast, thioflavin T has more significant conformational changes after binding, which is the reason that thioflavin T can be used as a fluorescent probe in in vitro studies.In Paper IV, we studied the binding profile of PtdIns(3,4,5)P3 with the plecsktrin homology (PH) domain of Saprolegnia monoica cellulose synthase. We first studied the binding modes of the inositol groups with the PH domain in solution, the results of which were then used to guide the modeling of the binding mode of PtdIns(3,4,5)P3 in a membrane with the PH domain.
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