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 (phi) similar to that in the cytosol, whereas DNA undergoes a coil-to-globule transition at very small phi. We show using a combination of scaling arguments and simulations that the polymer size (R) over bar (g)(phi) depends on x = (R) over bar (g)(0)/D, where D is the phi-dependent distance between the crowders. If x <= O(1), there is only a small decrease in (R) over bar (g)(phi) as phi increases. When x >> O(1), a cooperative coil-to-globule transition is induced. Our theory quantitatively explains a number of experiments.