Magic angle spinning NMR study of interaction of N-terminal sequence of dermorphin (Tyr-d-Ala-Phe-Gly) with phospholipids

The influence of the stereochemistry and C-end chemical modification of dermorphin derivatives on the peptide-phospholipid interactions

In this work the conformation of dermorphin, Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH₂, an opioid peptide and its analogues with different stereochemistry of alanine and different C-terminus is studied in aqueous and membrane environments. Using two-dimensional NMR techniques we demonstrate that in D₂O/H₂O peptides with D-alanine have extended conformation, while for the L-isomers more compact conformation is preferred. The analysis of ROESY HR MAS spectra of the peptides interacting with the DMPC bilayer indicates that both stereoisomers have still more extended conformation compared to aqueous phase, as shown by much weaker intermolecular interactions. The influence of Ala residue stereochemistry is also reflected in the interactions of the studied peptides with model membranes, as shown by the ³¹P NMR static spectra, in which the shapes of the phosphorus NMR signals originating from D-isomers correspond to spherically shaped vesicles in the presence of external magnetic field, in comparison to a more elongated ones observed for L-isomers, while TEM photographs shows that upon addition of D-isomers larger lipid vesicles are formed, in contrast to smaller ones for L-isomers. The location of aromatic fragments of dermorphins in the membrane is determined based on static ²H NMR and ¹H¹H RFDR MAS experiments. All aromatic rings were found to be inserted in the hydrophobic part of the bilayer, with the exception of the Tyr5 rings of D-Ala dermorphins. The influence of the C-terminal modification was found to be almost imperceptible.

(19)F-Labeling of Peptides Revealing Long-Range NMR Distances in Fluid Membranes

NMR distance measurements lie at the heart of structural biology. However, long-range distances could not yet be detected in liquid-crystalline biomembranes, because dipolar couplings are partially averaged by the intrinsic molecular mobility. Using conformationally constrained (19)F-labeled amino acids as reporter groups, we could more than double the accessible interatomic distance range by combining a highly sensitive solid-state multipulse (19)F-NMR scheme with a favorable sample geometry. Two rigid 4F-phenylglycine labels were placed into the helical antimicrobial peptide PGLa embedded in fluid oriented membrane samples. A modified Carr-Purcell-Meiboom-Gill sequence yielded an intramolecular distance of 6.6 Å for the labels spanning one helix turn, and 11.0 Å was obtained when the labels spanned two turns. This approach should now also allow the characterization of conformational changes in membrane-active peptides and of oligomeric assemblies in a biologically relevant lipid environment.

Solid-state NMR spectroscopy to study protein-lipid interactions

The appropriate lipid environment is crucial for the proper function of membrane proteins. There is a tremendous variety of lipid molecules in the membrane and so far it is often unclear which component of the lipid matrix is essential for the function of a respective protein. Lipid molecules and proteins mutually influence each other; parameters such as acyl chain order, membrane thickness, membrane elasticity, permeability, lipid-domain and annulus formation are strongly modulated by proteins. More recent data also indicates that the influence of proteins goes beyond a single annulus of next-neighbor boundary lipids. Therefore, a mesoscopic approach to membrane lipid-protein interactions in terms of elastic membrane deformations has been developed. Solid-state NMR has greatly contributed to the understanding of lipid-protein interactions and the modern view of biological membranes. Methods that detect the influence of proteins on the membrane as well as direct lipid-protein interactions have been developed and are reviewed here. Examples for solid-state NMR studies on the interaction of Ras proteins, the antimicrobial peptide protegrin-1, the G protein-coupled receptor rhodopsin, and the K(+) channel KcsA are discussed. This article is part of a Special Issue entitled Tools to study lipid functions.