Self-association of a nucleoid-binding protein increases with macromolecular crowding in Escherichia coli
Many proteins self-associate to achieve function. Macromolecular crowding enhances protein self-assembly in buffer experiments with added crowders, and crowding could therefore regulate protein function and organization in cells. In eukaryotic cells, protein condensation has been shown to increase with crowding. However, it is unclear what the effect of crowding is on native protein self-assembly in the highly crowded Escherichia coli cell. To determine the role of crowding in the self-assembly of a native protein, we study here the nucleoid-binding H-NS in E. coli and alter macromolecular crowding using a set of perturbations. We followed H-NS self-assembly using a FRET-based method for determining intermolecular interactions with a single genetic intervention. In dilute cell lysate, we see that H-NS self-assembly increases with salts, macromolecular crowding, and its own concentration. In E. coli, the oligomerization increases with crowding. We see that the response of H-NS oligomerization to a sudden crowding change is not immediate but requires time to adapt. Our findings implicate that in-cell crowding affects intracellular organization by promoting self-assembly.