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.
Ulrich
W P
WP
Laboratoire de Chimie Physique des Polymères et Membranes, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Vogel
H
H
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