The 14-3-3 family of proteins are important signalling proteins involved in a number of cellular processes. These include cell cycle regulation, apoptosis, signal transduction and cell signalling. There is also considerable evidence in the literature that 14-3-3 proteins play a vital role in the pathology of neurodegenerative diseases, including Alzheimer’s, Parkinson’s, Huntington’s and Prion disease. The neurodegenerative disease of focus in this research is Spinocerebellar Ataxia Type 1 (SCA1). SCA1 is a polyglutamine-repeat disease and the interaction of the disease protein ataxin-1 with 14-3-3 proteins leads to the toxic accumulation and subsequent protein aggregation which is characteristic of this disease. This study focused on attempting to elucidate the structure of various domains of the disease protein and also in identifying potential inhibitors of this deleterious interaction. Unfortunately, structural studies were not successful due to a number of caveats encountered in the expression and purification of the ataxin-1 protein domains. By utilising computational methods and small molecule inhibitors, a number of potential lead compounds which possess the ability to at least partly disrupt the interaction of 14- 3-3ζ have been identified. As 14-3-3 proteins play roles in other neurodegenerative diseases, successful identification of potential drug lead treatments can have far reaching benefits in a number of neurodegenerative diseases including SCA1. Lipid rafts are also involved in neurodegenerative disease pathology. Lipid rafts are cholesterol and sphingolipid rich domains which organise the plasma membrane into discrete microdomains and act as signalling platforms and processing centres which attach specific proteins and lipids. A number of disease proteins are processed at these membrane regions, including those involved in Alzheimer’s, Parkinson’s and Prion disease. This processing is a step which is critical in the pathology of disease and abnormal processing leads to the formation of toxic protein aggregates. Previous research in the lab identified the association of low levels of the five main brain isoforms of 14-3-3 proteins with rafts. This study expanded on this to positively identify the presence of the two phospho-forms of 14-3-3, α and δ. The mechanism by which 14-3-3 proteins associate with rafts was also investigated, indicating that 14-3-3 associates with rafts via an unidentified raftbound protein(s). In addition, the phosphorylation status and quaternary structure of 14-3-3 in the presence of sphingolipids has been explored.

Der erste Teil dieser Arbeit beschreibt die Durchführung eines quantitativen Ansatzes zur Detektion von Protein-Protein-Interaktionen (PPI) mit einem Schwerpunkt für Proteine, die in vier häufigen neurodegenerativen Krankheiten eine Rolle spielen: die Alzheimer-, Parkinson- und Huntington-Krankheit, sowie die spinozerebelläre Ataxie Typ 1 (SCA1). Die Interaktionsstudie kombiniert die stabile Isotopen-Markierung von Aminosäuren in der Zellkultur mit der Affinitätsaufreinigung von Proteinen und hochauflösender Massenspektrometrie. Dieser Ansatz zielt darauf ab, systematisch die Interaktionspartner von gesunden und krankheitsassoziierten Proteinvarianten zu identifizieren und zu quantifizieren. Darüber hinaus wurde das quantitative Interaktionsverfahren genutzt, um zu prüfen ob PPI durch krankheitsassoziierte Mutationen beeinträchtigt werden. Neben der Validierung möglicher Nebeneffekte, sowie dem Vergleich mit Informationen über PPI aus der Literatur, wurde ein Teil der identifizierten Interaktoren durch zusätzliche Koimmunopräzipitations-Experimente in zwei verschiedenen Zelllinien bestätigt. Mit Hilfe von Drosophila SCA1-Krankheitsmodellen und in Kombination mit RNAi-basierter Stummschaltung identifizierter Interaktoren wurde festgestellt, dass ein großer Teil der Kandidaten Neurodegeneration in vivo beeinflusst. Zusätzlich wurden die Alzheimer-spezifischen PPI-Daten auf genomweite Assoziationsstudien übertragen. Bemerkenswerterweise waren Polymorphismen in einzelnen Nukleotiden in den Genen zugehöriger Interaktoren wahrscheinlicher mit solchen Genen assoziiert, die eine Prädisposition für die Alzheimer-Krankheit haben, als mit zufällig ausgewählten Genen. Schlussendlich konnten Folgeexperimente für zwei ausgewählte Interaktionspartner den Nachweis für eine bislang unbekannte Rolle der N-Glykosylierung und einen neuen Zusammenhang zwischen dem RNA-bindenden Protein LRPPRC und mitochondrialer Dysfunktion in der Alzheimer-Krankheit vorlegen. / The first part of the present thesis describes the establishment of a quantitative protein-protein interaction (PPI) screen with a focus on proteins involved in four common neurodegenerative diseases (NDDs): Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD) and spinocerebellar ataxia type 1 (SCA1). The interaction screen combines stable-isotope labeling by amino acids in cell culture (SILAC) with protein affinity purification and high-resolution mass spectrometry. This approach aims to systematically identify and quantify interaction partners of normal and known disease-associated variants of proteins involved in NDDs. Moreover, the quantitative interaction screen was employed to study how PPIs are affected by disease-associated mutations. Along with validation of possible off-target effects and comparison of the data with literature-reported PPIs, a subset of identified interactors was validated by additional co-immunoprecipitation experiments in two different cell lines. Utilizing Drosophila models for SCA1 in combination with RNAi-mediated silencing of identified interactors, a large fraction of candidates was observed to also affect neurodegeneration in vivo. In addition, AD-specific PPI data was mapped to patient cohort data obtained from genome-wide associations studies. Notably, single-nucleotide polymorphisms in the genes of interactors of the disease-associated protein variants were more likely associated with susceptibility to AD than randomly selected genes. Finally, functional follow-ups for two selected interaction partners provided evidence for a yet unreported role of N-linked glycosylation in AD, and a novel link to mitochondrial dysfunction in AD by means of the RNA-binding protein LRPPRC.