The function of each cell and each organism decisively depends on the dynamic interactions between biological macromolecules and on their correct three-dimensional structure. Faulty interaction and incorrectly folded structures eventually lead to diseases and ageing. Our aim is to understand these interactions and to determine the three-dimensional structure of the protein complexes involved in decisive cellular processes - if possible, in atomic resolution. Beyond that, we develop novel methods for the early diagnosis and treatment of neurodegenerative diseases, with a strong focus on Alzheimer's dementia.