Darmstadt, Techn. Universiẗat, Diss., 2005. / Dateien im PDF-Format.

Köln, Universiẗat, Diss., 2001.

Konstanz, Universiẗat, Diss., 2000.

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

No description available.

Trypanosoma brucei undergoes developmentally regulated morphological and biochemical changes during its life cycle, being transmitted between the mammalian host and the tsetse fly. It is generally recognized that cellular responses to environmental changes are mediated through signalling pathways, but our understanding of trypanosome signal transduction during differentiation is limited. Protein Tyrosine Phosphatase 1 (TbPTP1) is the one of the few factors identified to be responsible for differentiation from stumpy to procyclic form parasite, whereby TbPTP1 inhibition stimulates transition to insect-form cells (Szoor et al., 2006). In order to characterize the TbPTP1 signalling pathway, a substratetrapping approach was used, which identified a phosphatase TbPIP39 as substrate of TbPTP1. TbPIP39 interacts with, and is dephosphorylated by TbPTP1 in stumpy form cells. Additionally, it has been shown that upon citrate/cis-aconitate (CCA) treatment, phosphorylated TbPIP39 localizes to the parasite glycosomes, the organelles responsible for bloodstream forms metabolism, thereby promoting cellular differentiation to procyclic forms (Szoor et al., 2010). With the aim of further dissecting the TbPTP1 signalling pathway, the substrate-trapping approach was used, which identified one novel TbPTP1 substrate candidate, potentially involved in regulation of differentiation. In addition, the effect of other differentiation triggers, namely protease treatment or mild acid exposure, on the level of TbPIP39 phosphorylation was analyzed, to determine whether these stimuli operate via the same TbPIP39–dependent pathway as CCA signalling. Specifically, changes in the phosphorylation status of TbPIP39 were visualized and quantitated by the use of antibodies detecting either TbPIP39 or the Y278 phosphorylated form of TbPIP39 generated during CCA-dependent differentiation. Both protease treatment and mild acid exposure generated a different pattern of TbPIP39 phosphorylation, thus suggesting a different mechanism of action than CCA. Finally, the possibility of using piggyback strategies targeting TbPTP1 was investigated, as a means to decrease the number of the fly-transmissible stumpy form cells in the bloodstream, thereby controlling parasite transmission. For this purpose, natural and synthetic inhibitors of human PTP1B were tested against the parasite enzyme, since they are being developed by pharmaceutical companies for the treatment of diabetes and obesity. The compounds tested showed a moderate in vitro inhibitory activity against recombinant TbPTP1 and mainly a non-competitive type of inhibition, similarly to that observed for human PTP1B. However, none of the compounds showed in vivo specificity for TbPTP1, indicating that further studies will be needed to identify more specific inhibitors.

No description available.

Hexokinase is the first enzyme in glycolysis, a major pathway for the generation of energy in all eukaryotes. Mammalian cells have four isoforms (I, II, III, IV) that have different tissue distribution and kinetic properties. Among all isoforms, human hexokinase II (hHKII) has been found to be implicated in many cancers with an increased expression which serves a dual role. First, it maintains the high glycolytic rate of malignant cells (Warburg effect) and second it prevents apoptosis when is bound to mitochondria. Trypanosoma brucei is a parasite that causes Human African Trypanosomiasis (HAT) and has two isoforms with extensive sequence similarity (98%), TbHKI (active form) and TbHK2 (inactive form). The bloodstream-form parasites (BSF) depend exclusively on glycolysis for their survival. The enzyme from both organisms is a validated target for drug-discovery against both cancer and HAT. The aim of the present study is the discovery of novel and specific inhibitors of the enzymes based on their structure. Structure-based drug discovery is commonly used in pharmaceutical companies to aid in the discovery of potent lead compounds. In silico studies were performed in this project using the known crystal structure of human hexokinase I and a model of TbHKI generated by the protein modelling tool Phyre2. The docking programs, AutoDock (AD) and AutoDock Vina (Vina), were chosen to perform the docking of ~3 million compounds to the target molecules and scoring functions calculated the predicted binding affinities of each compound. In total, 28 compounds were purchased to test on the target molecules. In the experimental part of the project, the two enzymes were cloned, expressed and purified. hHKII was successfully purified giving a high yield of active and pure protein. The protein was characterised using many biophysical methods to establish the oligomeric state, the homogeneity and the secondary structure. Crystallisation trials failed and for this reason, N and C domains of the hHKII were purified separately. Unfortunately, the domains also failed to crystallise thus SAXS data were collected and analysed to gain information of their shape at low resolution. A novel inhibition assay was developed and used to identify four weak inhibitors against full length hHKII. TbHKI was difficult to express in a soluble form as most of the protein was expressed in inclusion bodies. The purification resulted in a small amount of active protein that was used entirely for biochemical assays. Four compounds were purchased from the docking of the TbHKI model and one was found to inhibit the enzyme over 65% at 100 μM. Because the active site of both enzymes (hHKII, TbHKI) is well conserved the compounds from hHKII docking were also screened against the TbHKI. Four compounds were found to inhibit this enzyme while one of them was also an inhibitor for human isoform. The remaining three were specific for inhibition of TbHKI.

Thesis (doctoral)--Eberhard-Karls-Universität zu Tübingen, 1994.

No description available.