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Membrane structure and conformational changes of the antibiotic heterodimeric peptide distinctin by solid-state NMR spectroscopy

Resende, Jarbas M., Moraes, Cléria Mendonça, Munhoz, Victor H.O., Aisenbrey, Christopher, Verly, Rodrigo M., Bertani, Philippe, Cesar, Amary, Piló-Veloso, Dorila, Bechinger, Burkhard
Proceedings of the National Academy of Sciences of the United States of America 2009 v.106 no.39 pp. 16639-16644
anti-infective properties, antibiotics, antimicrobial peptides, circular dichroism spectroscopy, deuterium, nitrogen, nuclear magnetic resonance spectroscopy, oxidation, phospholipids, stable isotopes
The heterodimeric antimicrobial peptide distinctin is composed of 2 linear peptide chains of 22- and 25-aa residues that are connected by a single intermolecular S-S bond. This heterodimer has been considered to be a unique example of a previously unrecorded class of bioactive peptides. Here the 2 distinctin chains were prepared by chemical peptide synthesis in quantitative amounts and labeled with ¹⁵N, as well as ¹⁵N and ²H, at selected residues, respectively, and the heterodimer was formed by oxidation. CD spectroscopy indicates a high content of helical secondary structures when associated with POPC/POPG 3:1 vesicles or in membrane-mimetic environments. The propensity for helix formation follows the order heterodimer >chain 2 >chain 1, suggesting that peptide-peptide and peptide-lipid interactions both help in stabilizing this secondary structure. In a subsequent step the peptides were reconstituted into oriented phospholipid bilayers and investigated by ²H and proton-decoupled ¹⁵N solid-state NMR spectroscopy. Whereas chain 2 stably inserts into the membrane at orientations close to perfectly parallel to the membrane surface in the presence or absence of chain 1, the latter adopts a more tilted alignment, which further increases in the heterodimer. The data suggest that membrane interactions result in considerable conformational rearrangements of the heterodimer. Therefore, chain 2 stably anchors the heterodimer in the membrane, whereas chain 1 interacts more loosely with the bilayer. These structural observations are consistent with the antimicrobial activities when the individual chains are compared to the dimer.