Unbiased cold denaturation: Low- and high-temperature unfolding of yeast frataxin under physiological conditions

Since the cold denaturation of most proteins occurs well below 0 degrees C, full access to the cold denatured state is normally limited by water freezing. To circumvent this difficulty the temperature of cold denaturation is normally raised, destabilizing the protein by point mutations and using chemical or physical denaturation. The main drawback of these approaches is that it is not generally possible to extrapolate the results to physiological conditions. Following a different approach, we looked for a protein whose cold denaturation could be studied in a normal buffer at physiological pH without the need of destabilization, in a temperature range accessible to several techniques. Here we describe the cold and heat denaturation of yeast frataxin (Yfh1). Both NMR and CD data were fitted by the same equation, showing that the collapse of the hydrophobic core is exactly paralleled by a decrease of the secondary structure content.