The magnitude of macromolecular crowding caused by Dextran and Ficoll for the conformational stability of globular proteins

The polysaccharides Dextran and Ficoll are commonly used as crowding agents to mimic the cellular environment. They usually stabilize the native state of globular proteins, and this effect has been explained by the excluded volume idea: the reduction of the volume available to host the protein molecule shifts the equilibrium towards the folded conformation. However, the experimentally measured stabilization is lower than expected from theoretical models. We would like to show that, applying a classic scaled particle theory approach that considers the density of the solutions, we can provide reliable estimates of their stabilizing effect. Density is a fundamental requirement because it reflects the actual interactions among the solution molecules and allows the calculation of the number density and the volume packing density of the solution, two factors that play a major role in defining the magnitude of the solvent-excluded volume effect. Application of the model to aqueous solutions of glucose, sucrose, Dextran-70 and Ficoll-70 indicates that the stabilization effect of the two polysaccharides is similar to that of glucose and sucrose, and this happens due to the low number density of the polymer solutions.