In this BAG we are investigating the structures and interactions of membrane proteins as well as soluble proteins with relevance to both fundamental and applied sciences. Important basic research projects are concerned with the foundations of proton transport, specifically the concept of proton wires, and the function of unusual, hitherto poorly characterised rhodopsins. In our application-related activities, we are addressing challenges in biotechnology, including the development of novel optogenetic tools (both soluble and membrane-based) as well as the optimisation of microbial enzymes for biomimetic synthesis or efficient hydrogen production, thus contributing to the establishment of sustainable technologies. Moreover, we are exploring the structural biology of selected soluble and membrane protein families with roles in homeostasis, stress response, and pathogenesis, along with innovative ways to modulate their functions, e.g. in anti-cancer or anti-infective therapy.