Polarized ATR-FTIR Spectroscopy Reveals Light-Induced Peptide Insertion of LAH4 Into Photoswitchable Membranes

Photoswitchable biomimetic membranes can be controlled by light and offer the possibility to study the role of membrane dynamics for the interaction with antimicrobial peptides. The α-helical peptide LAH4, a well-studied model system, interacts with membranes in a pH-dependent manner. It binds to the membrane surface at acidic pH and inserts into the membrane at basic pH conditions. Polarized attenuated total reflection (ATR) Fourier-transform infrared (FTIR) spectroscopy was employed to probe peptide orientation and structural changes, with particular emphasis on the pH-dependent response of LAH4 to light-induced membrane perturbations. Photoswitchable azoPC lipids were incorporated in large unilamellar vesicles (LUVs) as well as in DIBMA-stabilized nanodiscs, and the light-induced cis-to-trans isomerization of the azobenzene was monitored by characteristic vibrational modes showing a reversible transition between two membrane states for both membrane systems. The measurements reveal that photoswitching between the membrane states induces the reorientation of the surface-bound peptide toward a membrane-inserted state. The findings underline the potential of photoswitchable membranes for the study of lipid-peptide interactions as well as the importance of membrane dynamics for antimicrobial activity.