We have a differential scanning calorimeter (DSC) used for measuring the thermal stability of proteins This can be used to answer questions such as, “does this mutation de-stabilise the protein?” or “what buffer conditions will stabilise the protein?”
Repeat scans allow us to determine reversibility of the unfolding reaction and the effect of the scan rate on the apparent melting temperature. It may be possible to analyse unfolding data to give thermodynamic data such as the enthalpy of unfolding and the heat capacity.
Differential scanning calorimetry (DSC) is used to study thermal transitions in solution, including protein folding, DNA/RNA melting and lipid transitions. The instrument measures the small differences in power input to a sample cell versus a reference cell to maintain the same rate of temperature change during heating or cooling scans. Folding and unfolding transitions in the sample cell release or absorb heat creating a temperature difference between the two cells. The maximum point of a transition gives the melting temperature (Tm). The DSC can scan from 10-130°C with cell pressurisation preventing samples from boiling.
Heat capacities can also be determined with careful preparation and analysis of buffer blanks. Multiple transitions can be deconvoluted from the results by data analysis using the Origin software.
DSC can also be used in "isothermal mode" to monitor heat changes associated with slow processes such as fibril formation or virus assembly.
DSC can be used to analyse protein stability and compare stabilities of wild-type and mutant proteins. It can also be used to analyse nucleic acid folding and unfolding.
DSC corroborates results from unfolding studies using UV hyperchromicity, fluorescence spectroscopy or CD spectroscopy, each of which is sensitive to related, but different, structural properties of a molecule.
DSC requires 2ml per sample to make it easier to flush bubbles from the cell during sample loading, but you get back most of this volume. A concentration of 1mg/ml is a good starting concentration but lower protein concentrations may give useful data. The reference buffer should be matched with the sample, e.g. by dialysis. Degassing samples and buffer reduces problems with bubbles developing during sample heating.