Self-Assembly of Flexible β-Strands into Immobile Amyloid-Like β-Sheets in Membranes As Revealed by Solid-State ¹⁹F NMR

Abstract

The cationic peptide [KIGAKI](3) was designed as an amphiphilic β-strand and serves as a model for β-sheet aggregation in membranes. Here, we have characterized its molecular conformation, membrane alignment, and dynamic behavior using solid-state (19)F NMR. A detailed structure analysis of selectively (19)F-labeled peptides was carried out in oriented DMPC bilayers. It showed a concentration-dependent transition from monomeric β-strands to oligomeric β-sheets. In both states, the rigid (19)F-labeled side chains project straight into the lipid bilayer but they experience very different mobilities. At low peptide-to-lipid ratios ≤1:400, monomeric [KIGAKI](3) swims around freely on the membrane surface and undergoes considerable motional averaging, with essentially uncoupled φ/ψ torsion angles. The flexibility of the peptide backbone in this 2D plane is reminiscent of intrinsically unstructured proteins in 3D. At high concentrations, [KIGAKI](3) self-assembles into immobilized β-sheets, which are untwisted and lie flat on the membrane surface as amyloid-like fibrils. This is the first time the transition of monomeric β-strands into oligomeric β-sheets has been characterized by solid-state NMR in lipid bilayers. It promises to be a valuable approach for studying membrane-induced amyloid formation of many other, clinically relevant peptide systems.

Peptide Fibrils with Altered Stability, Activity, And Cell Selectivity

“…Impacts of peptide self-assembly on peptide-cell interaction have been revealed in recent publications 21, 30 . Results from this study suggest that peptide aggregation could be as important as the charge and secondary structure of a peptide in affecting peptide-cell interactions.…”

Structural characterization of a C-terminally truncated E5 oncoprotein from papillomavirus in lipid bilayers

“…OCD is a powerful tool for studying the orientation of membrane-active peptides and protein segments in membranes (Lange et al, 2007;Bürck et al, 2008;Strandberg et al, 2008;Wadhwani et al, 2008Wadhwani et al, , 2012Wadhwani et al, , 2014Nolandt et al, 2009;Windisch et al, 2010;Heinzmann et al, 2011;Klein et al, 2012;Muhle-Goll et al, 2012;Steinbrecher et al, 2012;Aberle et al, 2014;Fanghänel et al, 2014). For α-helices, the OCD band at 208 nm can be used to estimate the helix tilt angle relative to the membrane normal (Wu et al, 1990).…”

The cooperative behaviour of antimicrobial peptides in model membranes

“…Three different models for peptidemembrane interaction are commonly used: barrel-stave, toroidal and carpet models [9][10][11]. It was suggested that collective behaviour of peptides can play a role in the bacterial membrane destruction [12][13][14][15][16][17][18][19]. For instance, using 31 P oriented solid-state NMR experiments it was found that at high peptide concentration alamethicin adopts a transmembrane conformation while the novicidin forms a toroidal pore in the membrane [16].…”

“…For instance, using 31 P oriented solid-state NMR experiments it was found that at high peptide concentration alamethicin adopts a transmembrane conformation while the novicidin forms a toroidal pore in the membrane [16]. Using solid-state 19 F NMR it was shown that at low concentration the amphiphilic [KIGAKI] 3 peptide binds to membrane as flexible β-strand, without forming any intra or intermolecular Hbonds [13]. At higher concentrations [KIGAKI] 3 self-assembles into immobilized β-sheets which lie flat on the membrane surface as amyloid-like fibrils.…”