Expanding to fill the gap: A possible role for inert biopolymers in regulating the extent of the ‘macromolecular crowding’ effect

We discuss the potential for inert biopolymers existing in cells to play a role in regulating the macromolecular crowding effect via their ability to undergo shape changing structural transitions. We have explored this possibility by the use of theory and experiment. The theoretical component utilized Monte-Carlo based simulations to examine the folding of a hypothetical protein in a concentrated environment of hard spheres which are themselves capable of reversible expansion and contraction. The experimental component of the study involved examination of the effect of different sized crowding agents on the thermally induced denaturation of cytochrome c [in phosphate buffered saline solution containing 1.0 M guanidinium hydrochloride at pH 7.0]. On the basis of our findings we suggest that in a crowded solution environment the presence of a non-reactive polymer capable of reversible expansion/contraction via folding and unfolding may alter the excluded volume component of the solution. This ability would confer on the non-reactive polymer a novel role in influencing other processes in solution affected by macromolecular crowding.