University of Arkansas, Fayetteville


WALP pep tides of sequence acetyl-Gly-Trp-Trp-(Leu-Ala)-Trp-Trp-Ala-ethanolamine insert into lipid bilayers as membrane-spanning a-helices and modulate the lipid phase behavior as functions of n and the lipid acyl chain length. A key feature of the WALP peptides is the positioning of tryptophan (Trp) indole rings at the membrane/water interface. For the examples WALP19 with n = 6.5 and WALP23 with n = 8.5, we have labeled individual indoles with deuterium and incorporated the labeled peptides in oriented, hydrated bilayers of Dimyristoyl-phosphatidylcholine (DMPC). Deuterium NMR spectra from these samples show sharp resonances when the membrane normal is aligned either parallel (Beta = 0°) or perpendicular (Beta = 90°) to the magnetic field. The factor of two reduction in the deuterium quadrupolar splittings when Beta is changed from 0° to 90° indicates rapid molecular rotation about an axis parallel to the membrane normal. The magnitudes and ring assignments of the quadrupolar splittings vary with the position of an indole ring in a WALP sequence and indicate different average ring orientations for different locations in the sequence.