Polarization-modulated FTIR spectroscopy of lipid/gramicidin monolayers at the air/water interface.
Monolayers of gramicidin A, pure and in mixtures with dimyristoylphosphatidylcholine (DMPC), were studied in situ at the air/H2O and air/D2O interfaces by polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Simulations of the entire set of amide I absorption modes were also performed, using complete parameter sets for different conformations based on published normal mode calculations. The structure of gramicidin A in the DMPC monolayer could clearly be assigned to a beta6.3 helix. Quantitative analysis of the amide I bands revealed that film pressures of up to 25-30 mN/m the helix tilt angle from the vertical in the pure gramicidin A layer exceeded 60 degrees. A marked dependence of the peptide orientation on the applied surface pressure was observed for the mixed lipid-peptide monolayers. At low pressure the helix lay flat on the surface, whereas at high pressures the helix was oriented almost parallel to the surface normal.
Laboratoire de Chimie Physique des Polymères et Membranes, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
W P
WP
Ulrich
H
H
Vogel
D000388:Air; D055592:Biophysical Phenomena; D001703:Biophysics; D017666:Deuterium Oxide; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D005454:Fluorescence Polarization; D006096:Gramicidin / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry*; D008956:Models, Chemical; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water
D008563:Membrane Lipids; D014867:Water; D006096:Gramicidin; D017666:Deuterium Oxide; D004134:Dimyristoylphosphatidylcholine