Cells are crowded with macromolecules, which limits the diffusion of proteins, especially in prokaryotic cells without active transport in the cytoplasm. While investigating the relationship between crowding, ionic strength and protein diffusion, University of Groningen biochemists made a fascinating discovery: positively charged proteins stick to the surface of ribosome complexes. This explains why most water-soluble proteins carry an overall negative charge. The discovery will appear soon in the journal eLife.