The effect of crowding and confinement: a comparison of Yfh1 stability in different environments.

Crowding and confinement can affect protein stability, favouring the more compact species amongst the folded and unfolded conformations. An unbiased assessment of the relative efficacy of crowded and confined environments has been hampered so far by the paucity of homogeneous comparisons on the same protein. This paper reports spectroscopic studies on yeast frataxin (Yfh1), a protein which provides an excellent model system for stability studies since it undergoes both cold and heat denaturation at measurable temperatures. The stability of Yfh1 was evaluated in the presence of Ficoll 70 and inside the cavities of polyacrylamide gels as means of mimicking crowding and confinement. We find that both effects influence the thermal stability of Yfh1 to a comparable extent thus providing the first direct comparison of crowding and confinement on the same protein. Thanks to the measurement of the full stability curve we also present the first thermodynamic characterization of the stability of a protein in crowding conditions.