Abstract

The structure and alignment of the amphipathic α-helical antimicrobial peptide PGLa in a lipid membrane is determined with high accuracy by solid-state 2H-NMR. Orientational constraints are derived from a series of eight alanine-3,3,3-d 3-labeled peptides, in which either a native alanine is nonperturbingly labeled (4×), or a glycine (2×) or isoleucine (2×) is selectively replaced. The concentration dependent realignment of the α-helix from the surface-bound “S-state” to a tilted “T-state” by 30° is precisely calculated using the quadrupole splittings of the four nonperturbing labels as constraints. The remaining, potentially perturbing alanine-3,3,3-d 3 labels show only minor deviations from the unperturbed peptide structure and help to single out the unique solution. Comparison with previous 19F-NMR constraints from 4-CF 3-phenylglycine labels shows that the structure and orientation of the PGLa peptide is not much disturbed even by these bulky nonnatural side chains, which contain CF 3 groups that offer a 20-fold better NMR sensitivity than CD 3 groups.

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