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

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journal contribution
posted on 18.04.2012, 00:00 by Parvesh Wadhwani, Erik Strandberg, Nico Heidenreich, Jochen Bürck, Susanne Fanghänel, Anne S. Ulrich
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 19F NMR. A detailed structure analysis of selectively 19F-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 19F-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.