Theory and practice of Differential Scanning Calorimetry

Differential Scanning Calorimetry (DSC): Theory and practice

Abstract

Differential scanning calorimetry (DSC) is an analytical technique with a proven track record for biomolecular stability studies. The technique is based on forced thermal denaturation of the biomolecules. This white paper discusses the principals of DSC analysis and exemplifies it with basic applications. The benefits and specifics of DSC are discussed.

The key benefit with DSC is that it is based on heat measurements and therefore allows the characterization of native biomolecules. Furthermore, the lack of spectroscopic readings means that the samples do not have to be optically clear. In addition, the characterization is not limited to the melting temperature (Tm), but it also provides data on the forces involved in folding of biomolecules and the mechanisms by which they unfold.

The thermodynamics of biological macromolecules in solution are not easy to interpret in isolation. Measured values are always the net effect of interactions between groups in the molecule and interactions that the same groups could make with the solvent. The energies stabilizing biological systems are thus the difference between many favorable as well as potentially unfavorable interactions. This fact comes as a revelation to many researchers and DSC measurements make the point very clearly. All is not lost, however, and a careful, methodical approach can begin to dissect out the complexity of the interaction. DSC also finds many other uses, based in part on the ability to see the totality of the thermodynamics associated with changes in the forces responsible for stabilizing the macromolecule and the absence of any optical components. DSC can measure how simple effects related to changes in protonation of macromolecules affect the thermodynamics and stability. This approach can be extended to include any noncovalently bound ligand, giving a versatile method of screening for binding. Under favorable circumstances, this approach can be used to determine binding constants. Here the thermodynamic background to DSC measurements is discussed and its application in studying the stability of proteins both alone and interacting with ligands. However, the techniques are equally transferable to other biological macromolecules such as nucleic acids, lipids, and so on.