Differential Scanning Calorimetry of Proteins: an Overview and Some Recent Developments

Abstract

This volume is devoted to emerging techniques in biophysics. Differential scanning calorimetry (DSC) has a long history of interesting and useful applications in the field of protein energetics (and also in the energetic analysis of other biological systems). In fact, DSC studies on protein thermal denaturation have played a central role in the development of current views about the factors that determine protein stability. Reviews on the various aspects of this technique are available in the literature (Privalov 1979, 1982, 1989; Sanchez-Ruiz and Mateo 1987; Freire et al. 1990; Freire 1994, 1995; Makhatadze and Privalov 1995; Sanchez-Ruiz 1995; Makhatadze 1998). It may appear, therefore, that DSC cannot be considered as an «emerging technique» in any sense of the word. However, there have been several recent developments in DSC of proteins that merit special consideration. First and foremost, recent studies (in which DSC has been instrumental) have provided evidence for the downhill (barrierless) character of the folding process for some small proteins. Needless to say, the existence of downhill folding (and the possibility that it may be detected by DSC) may have a huge influence in future studies on protein folding and stability. In addition, studies published in the last few years have made apparent that DSC can be used to probe complex processes involving, for instance, interactions of proteins with other molecules or cooperative changes in protein denatured states. In this chapter we focus on these and other «emerging applications» of DSC (although we also provide a short, general introduction to the technique). Sooner or later, the scientist interested in using DSC will need to confront some classical physical chemistry (including thermodynamics, statistical thermodynamics and even some chemical kinetics) together with the unavoidable mathematics. We believe, however, that many basic concepts in DSC can be explained at a qualitative level without using mathematics and that many readers will find this approach useful, at least on first exposure to the technique. Therefore, no equation is to be found in this chapter. We, of course, make throughout appropriate references to more technical work in the field, where the interested reader may find the physicochemical and mathematical details.