Final Activity Report Summary - CROWDED MEMBRANES (Macromolecular crowding in membranes) The goal of the project was to understand how the presence of high concentration of unrelated membrane proteins influenced the function and interaction of membrane proteins. Many membrane proteins had previously been satisfactorily studied in isolated systems; nevertheless, they faced the background of high concentrations of unrelated proteins in their native environment. As an everyday analogy the experiment on an isolated system could be viewed as a swimmer under competition conditions, where detailed knowledge on swimming technique and absolute performance could be gained. In contrast, the native environment in a living cell was similar, however worse, to a swimming pool on a hot summer day. Clearly, even a well trained swimmer would perform very differently if almost half of the water surface was covered by other swimmers. We therefore tried to establish a controlled environment, where the number and size of obstacles could vary and their influence on the swimmers performance could be studied. The project was hindered by unexpected technical challenges which led to the development of new tools for the analysis of membrane proteins which were either in detergent solubilised state or reconstituted in artificial membranes. One of the developed tools, a novel fluorescent activator of a ligand gated ion channel jump, led to the initiation of a side project so as to better understand the mechanism of a ligand gated ion channel, which is the protein responsible for effective signal transduction from nerve cells to muscle cells.