Under Pressure: Measuring Desolvation of Model α-Helical Peptides

Model helical peptides have been shown to unfold with temperature, but are stabilized with increased pressure 1-3. In these peptides, as pressure increases, the solvent environment becomes ordered allowing for an increase of the helical content of the peptide. Our work investigates hydration of the peptide backbone using both temperature and pressure as modifying conditions. The synthetic peptide sequence, (AAAAK)3-AAAAY is well-characterized and ideal for the study of helix properties3. To measure the coupling of pressure and temperature, Fourier transform infrared spectroscopy (FTIR) monitors the perturbations in the secondary structure via the amide I’ band. FTIR is a sensitive technique for detecting changes in hydrogen bonding and has been used for the estimation of amide photon exchanging with the solvent. Pressure on the peptide is applied using a manually manipulated Diamond Anvil Cell (DAC). Isotopically labeled residues within the peptide have been exploited for probing local interactions due to the shift of the heavier masses of the labeled residues to a lower frequency compared to the global 12C amide I band around 1633 cm−1.Our goal is to compare the location of isotopically edited alanines and the ability to remain desolvated with increasing pressure and temperature. With this technique, it was found that alanines proximal to the lysines were protected from solvent hydrogen interactions due to side chain shielding in the model sequence.(1) Barber-Armstrong, W.; Donaldson, T.; Wijesooriya, H.; Silva, R. A.; Decatur, S. M. J Am Chem Soc 2004, 126, 2339.(2) Gnanakaran, S.; Hochstrasser, R. M.; Garcia, A. E. Proc Natl Acad Sci U S A 2004, 101, 9229.(3) Paschek, D.; Gnanakaran, S.; Garcia, A. E. Proc Natl Acad Sci U S A 2005, 102, 6765.