3. Stability and stress studies
FTIR spectroscopy is very powerful for comparative purpose. Comparing a control sample (timepoint zero or unstressed sample) with various stability or stressed conditions allows the detection of minor structural changes. It can thus be used as a predictive tool to evaluate the stability of proteins. No dilution, no preparation (which could modify the structural state of the sample) is required. In addition, it is an orthogonal technique to Size Exclusion Chromatography (SEC) in order to assess aggregation. Whereas SEC characterizes aggregates according to the size of the molecules, FTIR spectroscopy analyze aggregation through the secondary structure and the formation of intermolecular beta-sheet.
Finally, for samples with high-scattering properties (proteins adsorbed onto aluminium hydroxide or membrane proteins embedded in lipid bilayer), FTIR spectroscopy is one of the only technique able to provide structural information.
References:
Manning, M.C. Use of infrared spectroscopy to monitor protein structure and stability. Expert Rev. Proteomics 2005, 2, 731–43.
Zheng, Y.; Lai, X.; Ipsen, H.; Larsen, J.N.; Løwenstein, H.; Søndergaard, I.; Jacobsen, S. The structural stability of protein antigens adsorbed by aluminium hydroxide in comparison to the antigens in solutions. Spectroscopy 2007, 21, 257–268.