Effects of Macromolecular Crowding on the Collapse of Biopolymers

Experiments show that macromolecular crowding modestly reduces the size of intrinsically disordered proteins even at a volume fraction (φ) similar to that in the cytosol, whereas DNA undergoes a coil-to-globule transition at very small φ. We show using a combination of scaling arguments and simulations that the polymer size R̄g(φ) depends on x=R̄g(0)/D, where D is the φ-dependent distance between the crowders. If xO(1), there is only a small decrease in R̄g(φ) as φ increases. When xO(1), a cooperative coil-to-globule transition is induced. Our theory quantitatively explains a number of experiments.