Solid state NMR studies of oligourea foldamers: Interaction of 15N-labelled amphiphilic helices with oriented lipid membranes

Abstract

Synthetic oligomers that are derived from natural polypeptide sequences, albeit with unnatural building blocks, have attracted considerable interest in mimicking bioactive peptides and proteins. Many of those compounds adopt stable folds in aqueous environments that resemble protein structural elements. Here we have chemically prepared aliphatic oligoureas and labeled them at selected positions with (15)N for structural investigations using solid-state NMR spectroscopy. In the first step, the main tensor elements and the molecular alignment of the (15)N chemical shift tensor were analyzed. This was possible by using a two-dimensional heteronuclear chemical shift/dipolar coupling correlation experiment on a model compound that represents the chemical, and thereby also the chemical shift characteristics, of the urea bond. In the next step (15)N labeled versions of an amphipathic oligourea, that exert potent antimicrobial activities and that adopt stable helical structures in aqueous environments, were prepared. These compounds were reconstituted into oriented phospholipid bilayers and the (15)N chemical shift and (1)H-(15)N dipolar couplings of two labeled sites were determined by solid-state NMR spectroscopy. The data are indicative of an alignment of this helix parallel to the membrane surface in excellent agreement with the amphipathic character of the foldamer and consistent with previous models explaining the antimicrobial activities of α-peptides.

Antimicrobial peptidomimetics: reinterpreting nature to deliver innovative therapeutics

“…This permitted to acquire information on the oligomers’ conformation, dynamics, and interactions with model membranes. The acquired data were indicative of an alignment of the oligourea helix parallel to the surface of the phospholipid bilayers, in agreement with the amphipathic character of the foldamer and consistent with previous models explaining the modes of action of AMPs (Aisenbrey et al, 2012). …”

“…High resistant to proteolytic degradation oligoureas have been shown to adopt a remarkably stable helical fold stabilized by 12- and 14-membered H-bonded rings, with helical propensity being enhanced in the presence of phospholipid vesicles, and to possess significant antibacterial activity against Gram-negative and Gram-positive bacteria (Violette et al, 2006; Claudon et al, 2010). Recently, a detailed solid-state NMR structural investigation was performed on aliphatic oligoureas synthesized with 15 N at selected positions (Aisenbrey et al, 2012). This permitted to acquire information on the oligomers’ conformation, dynamics, and interactions with model membranes.…”

Piloting the Membranolytic Activities of Peptides with a Self‐organizing Map

“…[34] This finding is in agreement with previous studies, [35] in particular with work by Bechinger and co-workers, who used solid-state NMR spectroscopy to observe helix formation and orientation of some AMPs upon contact with lipid bilayers. [36] Other biophysical studies confirmed differential interaction of amphipathic AMPs with zwitterionic versus anionic lipids. [37] Using deep-UV Raman spectroscopy Cooley and co-workers provided the first evidence of lipid-dependent secondary structure (helix) formation and aggregation of ME1 peptide in the presence of micelles.…”

Conformational photoswitching of a synthetic peptide foldamer bound within a phospholipid bilayer

“…Solid state nuclear magnetic resonance (ss-NMR (19)) is a powerful analytical technique that can determine structures in non-dissolved systems with quasi-atomic resolution. It can be used to characterize membrane-bound structures (20,21), and it can yield detailed information on the conformation and dynamics of membrane-bound proteins and peptides (22,23,24) and their artificial mimics (25). It has recently been used to investigate both the structure and dynamics of the photoswitchable vision protein rhodopsin (26), and provides evidence that the solution-phase conformational preference of the Aib-rich peptaibol alamethicin is preserved when embedded in phospholipid bilayers (27).…”