Abstract
Unfolding of mesophilic proteins occurs both at temperatures higher and lower than room temperature: the high temperature transition is generally referred to as “heat denaturation” whereas that at lower temperatures is known as “cold denaturation”. We have recently identified a protein, Yfh1, whose cold denaturation occurs at accessible temperatures close to 0°C and under physiological conditions at pH 7; that is, without the need to add denaturants. The first instance in which this system was used in a general sense to study the stability of proteins was a study on the influence of alcohols at low concentrations. Measuring both thermal denaturations, and hence the stability curve, in the presence of trifluoroethanol, ethanol and methanol, we observed an extended temperature range of protein stability. We suggest that alcohols, at low concentration and physiological pH, stabilize proteins by greatly widening the range of temperatures over which the protein is stable. A second important application is illustrated by titin I28, the second case of a protein undergoing unbiased cold denaturation. The thermal stability of this protein cannot be determined by increasing the temperature because aggregation competes with unfolding. The possibility of measuring cold denaturation hints that it is possible to determine accurately thermal stability of many proteins undergoing aggregation.
Published Version
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