The project aims to investigate structure-function relationships in different groups of soluble and membrane proteins, most of which are involved in signal transduction or energy conversion. We investigate the signalling mechanisms of phytochromes by focusing on the structures of the intermediates of the photocycle and by analysing domain movements or by introducing unnatural amino acids. We analyse the structures of different G protein-coupled receptors (GPCRs; e.g. melanocortin-4 receptor and rhodopsin), either alone or in complex with their cognate G-proteins, to understand their signalling mechanisms. In our work on the biocatalytic splitting of molecular hydrogen into protons and electrons, we analyse the membrane-bound and soluble [NiFe] hydrogenases, proteins of the remarkably small subgroup of hydrogenases that are active under aerobic conditions. Other research areas include mechanosensitive channels, microbial rhodopsins, cytomegalovirus proteins and DNA photolyases.