In this project, we aim to investigate the structure-function relationships of various soluble and membrane proteins involved in signal transduction and/or energy conversion. We are analysing different hydrogen-converting oxygen-tolerant [NiFe] hydrogenases under specific environmental conditions. In our work on G protein-coupled receptors (e.g., endothelin receptors, melanocortin receptors or rhodopsin), we study the structures bound to agonists and antagonists as well as in complex with their cognate G proteins to understand the mechanism of signal transduction. We also investigate light-regulated proteins such as phytochromes and DNA photolyases. Here we focus on the detailed analysis of the different intermediates of their photocycle and the understanding of their signalling mechanisms. Other areas of research include microbial rhodopsins, ion pumps and guanylate cyclase-activating proteins.