Proteins are the "tools" of our cells—they are essential to all vital tasks. However, they are only able to do their jobs if they fold correctly and adopt their respective, very specific 3D structure. To ensure that nothing goes wrong with the folding process, it is strictly monitored in the cell. The consequences of a flawed quality control can be seen, for example, in the deposition of misfolded proteins in neurodegenerative diseases such as Alzheimer's. Researchers at the Max Planck Institutes of Neurobiology and of Biochemistry have now developed a mouse line that makes the state of protein balance visible in the mammalian brain for the first time. In this way, the processes of protein quality control can now be studied in healthy and diseased neurons in more detail.