J. Am. Chem. Soc., Article ASAP

Chemical Labeling Strategy with (R)- and (S)-Trifluoromethylalanine for Solid State 19F NMR Analysis of Peptaibols in Membranes
Daniel Maisch†, Parvesh Wadhwani‡, Sergii Afonin‡, Christoph Bttcher§, Beate Koksch§ and Anne S. Ulrich*†‡

Abstract
Substitution of a single Aib-residue in a peptaibol with (R)- and (S)-trifluoromethylalanine yields two local orientational constraints θ by solid state 19F NMR. The structure of the membrane-perturbing antibiotic alamethicin in DMPC bilayers was analyzed in terms of two angles τ and ρ from six such constraints, showing that the N-terminus (up to a kink at Pro14) is folded as an α-helix, tilted away from the membrane normal by 8°, and assembled as an oligomer. The new 19F NMR label CF3-Ala has thus been demonstrated to be highly sensitive, virtually unperturbing, and ideally suited to characterize peptaibols in membranes.