Spectroscopic [correction of eSpectroscopic] and structural properties of valine gramicidin A in monolayers at the air-water interface.
Monomolecular films of valine gramicidin A (VGA) were investigated in situ at the air-water interface by x-ray reflectivity and x-ray grazing incidence diffraction as well as polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). These techniques were combined to obtain information on the secondary structure and the orientation of VGA and to characterize the shoulder observed in its pi-A isotherm. The thickness of the film was obtained by x-ray reflectivity, and the secondary structure of VGA was monitored using the frequency position of the amide I band. The PM-IRRAS spectra were compared with the simulated ones to identify the conformation adopted by VGA in monolayer. At large molecular area, VGA shows a disordered secondary structure, whereas at smaller molecular areas, VGA adopts an anti-parallel double-strand intertwined beta(5.6) helical conformation with 30 degrees orientation with respect to the normal with a thickness of 25 A. The interface between bulk water and the VGA monolayer was investigated by x-ray reflectivity as well as by comparing the experimental and the simulated PM-IRRAS spectra on D(2)O and H(2)O, which suggested the presence of oriented water molecules between the bulk and the monolayer.
Lavoie
Hugo
H
Département de Chimie-Biologie, Université du Québec à Trois-Rivières, Trois-Rivières, Québec G9A 5H7, Canada.
Blaudez
Daniel
D
Vaknin
David
D
Desbat
Bernard
B
Ocko
Benjamin M
BM
Salesse
Christian
C
D000388:Air; D003198:Computer Simulation; D017666:Deuterium Oxide / Q000737:chemistry; D006096:Gramicidin / Q000737:chemistry*; D046911:Macromolecular Substances; D008958:Models, Molecular; D011312:Pressure; D011487:Protein Conformation; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D012542:Scattering, Radiation; D013052:Spectrometry, X-Ray Emission / Q000379:methods*; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013499:Surface Properties; D013696:Temperature; D014633:Valine / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D046911:Macromolecular Substances; D014867:Water; D006096:Gramicidin; D014633:Valine; D017666:Deuterium Oxide