Determination of protein stability. Protein thermal stability was assessed by differential scanning calorimetry following protocols that we have previously described in detail. Experiments were performed with protein solutions in HEPES 10 mM NaCl 100 mM pH 8.5. In all cases, a single calorimetric transition was observed. The denaturation temperature, defined as the temperature of the maximum of the calorimetric transition was used as a metric of protein stability.