Protein Solutions
Calorimetry, Research and Consulting


Protein Solutions provides a range of scientific services such as assistance in experimental research, theory-based interpretation of data, as well as "know how" and consulting in protein/peptide stability and thermodynamics.

Upcoming Events

July 18, 2012

World Drug Target/Deliver Online Symposium Series

Past Events

2011

Lecture presentation at GE Healthcare meeting on label-free technology in Copenhagen University, Denmark

Lecture presentation at TA Instruments workshop and seminar at Roskilde University, Denmark

Differential Scanning Calorimetry (DSC)

The most widely used application of Differential Scanning Calorimetry is the investigation of protein stability. DSC technique utilizes the fact that different protein states (e.g. native and denatured) occupy different energy levels and thus transitions between those levels produce a thermal effect, which can be observed in a calorimeter.

A typical DSC experiment involves heating a protein solution to above its melting temperature and registering the unfolding enthalpy (ΔH) together with the mid-point of the denaturation transition (Tm). These two easily accessible parameters are sometimes misused for a snappy evaluation of macromolecular stability based on a simplistic approach where the higher measured values are equated to a higher stability. Without getting into details and criticizing this primitive (although efficient) tactic I want to stress that DSC does provide an irreplaceable description of protein stability, although it generally requires more than one measurement of Tm and ΔH.

A more challenging and exciting use of DSC is the interpretation of molecular details of the denaturation process. Since protein conformational states are characterized by different intrinsic enthalpy values the shape of the denaturation transition reflects its pathway and thus can lead to a better understanding of the folding/unfolding mechanism.

Analysis of DSC data

Both MicroCal and TA Instruments provide software packages with several basic models, such as two-state or unfolding-coupled-to-dissociation models. Therefore, I prefer to concentrate on the theoretical aspects of data analysis and frequently encountered misunderstandings. A couple of examples follow below and more are coming up:

  • The entropy of unfolding can be calculated at the Tm using the formula ΔS = ΔH/Tm. However, this approach is only valid for the two-state process. Here is why
  • When you fit the data to dissociation-coupled-to-unfolding model, the temperature where ΔG=0, T0, is not the same as Tm evaluated from the maximum of the DSC transition. Here’s an explanation