Sum frequency generation vibrational spectroscopy (SFG) was utilized to investigate the interaction between PAP248-286 and the two lipid bilayer systems. The present study also provides spectroscopic evidence to confirm that, although PAP248-286 is unable to penetrate into the hydrophobic core of the lipid bilayers, it is capable of interacting more intimately with the fluid-phase POPG/POPC than with the gel-phase DPPG/DPPC lipid bilayer. The helical structure content of lipid-bound PAP248-286 was also observed to be high, in contrast to the results previously reported using nuclear magnetic resonance (NMR). Collectively, our SFG data suggest that lipid-bound PAP248-286 actually resembles its structure in 50 % 2,2,2-trifluoroethanol better than the structure when the peptide binds to SDS micelles. This present study questions the use of SDS micelles as the model membrane for NMR studies of PAP248-286 due to its protein denaturing activity.
Keywords: Gel-phase and fluid-phase model lipid bilayers; PAP248–286; Peptide conformation; SDS micelles.