Structure and dynamics of the acyl chain of a transmembrane polypeptide.

We have used acylated analogs of gramicidin as a model to study the interaction between a covalently coupled fatty acid and the hydrophobic part of a membrane-spanning protein in a bilayer environment. The acyl chain was covalently coupled to the C-terminal ethanolamine group of gramicidin which is located near the membrane interface, mimicking a situation found in acylated proteins. Either perdeuterated palmitic acid or palmitic acid deuterated at only C 2 , C 3 , Cs 5-6 , C 7-8 , C 9 , or C 13 was coupled to gramicidin and examined by 2 H-NMR in oriented bilayers of dimyristoylphosphatidylcholine. In this way, quadrupolar splittings of deuterons at specific carbons were assigned