Cold denaturation as a tool to measure protein stability

- Protein stability is not described adequately by unfolding temperature.
- The area under the stability curve offers a better assessment of stability.
- Cold denaturation indirectly offers a simple way to calculate the stability curve.
- Ambiguous cases of protein stability are resolved by area measurement.

Protein stability is an important issue for the interpretation of a wide variety of biological problems but its assessment is at times difficult. The most common parameter employed to describe protein stability is the temperature of melting, at which the populations of folded and unfolded species are identical. This parameter may yield ambiguous results. It would always be preferable to measure the whole stability curve. The calculation of this curve is greatly facilitated whenever it is possible to observe cold denaturation. Using Yfh1, one of the few proteins whose cold denaturation occurs at neutral pH and low ionic strength, we could measure the variation of its full stability curve under several environmental conditions. Here we show the advantages of gauging stability as a function of external variables using stability curves.