Nature uses a special class of histone proteins, histone variants, to modulate the properties of chromatin at defined genomic locations. H2A.B is one of the most divergent H2A variants and is... Show moreNature uses a special class of histone proteins, histone variants, to modulate the properties of chromatin at defined genomic locations. H2A.B is one of the most divergent H2A variants and is involved in important cellular functions, such as transcription and mRNA splicing. Incorporation of H2A.B in nucleosomes causes unwrapping of ~15 bp entry/ exit nucleosomal DNA from the histone octamer core. Yet, the molecular basis of such peculiar nucleosome conformation is unclear. The work described in this thesis aimed to determine the impact of H2A.B incorporation on the structural and dynamical properties of the nucleosome, primarily using nuclear magnetic resonance (NMR) spectroscopy. Show less
The structure of the infectious prion protein (PrPSc), which is responsible for Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy, has escaped all attempts at elucidation due... Show moreThe structure of the infectious prion protein (PrPSc), which is responsible for Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy, has escaped all attempts at elucidation due to its insolubility and propensity to aggregate. PrPSc replicates by converting the non-infectious, cellular prion protein (PrPC) into the misfolded, infectious conformer through an unknown mechanism. PrPSc and its N-terminally truncated variant, PrP 27-30, aggregate into amorphous aggregates, 2D crystals, and amyloid fibrils. The structure of these infectious conformers is essential to understanding prion replication and the development of structure-based therapeutic interventions. Here we used the repetitive organization inherent to GPI-anchorless PrP 27-30 amyloid fibrils to analyze their structure via electron cryomicroscopy. Fourier-transform analyses of averaged fibril segments indicate a repeating unit of 19.1 Å. 3D reconstructions of these fibrils revealed two distinct protofilaments, and, together with a molecular volume of 18,990 Å3, predicted the height of each PrP 27-30 molecule as ~17.7 Å. Together, the data indicate a four-rung β-solenoid structure as a key feature for the architecture of infectious mammalian prions. Furthermore, they allow to formulate a molecular mechanism for the replication of prions. Knowledge of the prion structure will provide important insights into the self-propagation mechanisms of protein misfolding. Show less
Schistosomiasis (Bilharzia) is a tropical parasitic disease caused by schistosomes. At present more than 200 million people are infected by these parasites. If the infection is left untreated, the... Show moreSchistosomiasis (Bilharzia) is a tropical parasitic disease caused by schistosomes. At present more than 200 million people are infected by these parasites. If the infection is left untreated, the parasites can survive within the body for 5 years or more. The parasite has developed r escape mechanisms to escape the immune response of its host. The production by the parasite of heavily glycosylated proteins and lipids is thought to play an important role in this. One important carbohydrate structure expressed in all stages is the trisaccharide Lewis X (Le^x). By measuring the interaction with mono-, di-, and trimeric Lex of antibodies both in vitro and in vivo it has become clear that the humoral immune response to the various oligomeric forms of Le^x is different. This can now be taken into account in further studies in which the humoral and cellular immunogenicity of Le^x is investigated. Next, the elucidation of the crystal structure of a monoclonal antibody in complex with Le^x has led to a better insight in protein-carbohydrage interactions on the molecular level. This new knowledge can be used for further improvement of diagnostic techniques for schistosomiasis, and also for a better understanding of this and other diseases in which Le^x plays a role (e.g. cancer). Show less
