Proteins complete certain tasks both within and outside cells, like small machines. For example, the COMP and LysC proteins are active in intercellular spaces. But how do these proteins reach their action site following their synthesis in the cell interior? Julia von Blume, who is head of the “Molecular Basis of Protein Trafficking” research group at the Max Planck Institute of Biochemistry in Martinsried, has now succeeded in demonstrating that calcium and the transport protein Cab45 play a central role in the functioning of a special department of the Golgi apparatus, the cell’s distribution centre. The inflow of the calcium signal into the Golgi apparatus causes the Cab45 protein to change shape, accumulate and only come into contact with proteins that carry out their work outside the cell. Hence Cab45 is a central component of the previously unknown sorting mechanism in the cellular export department.