| Model WALP peptides and "next generation" WALP-derived hydrophobic model peptides were employed to discover principles that govern protein-lipid interactions in biological membranes.;Ternary cholesterol-containing lipid mixtures were examined in the presence of WALP peptides of different lengths (acetyl-GWW(LA)nLWWA-ethanolamide, with n between 3 and 8). Deuterium NMR spectra from labeled lipids reveal that WALP peptides may stabilize lipid ordered "raft" domains and therefore promote lipid phase separation, albeit to a minor extent. The results depend upon whether dioleolyl- or diphytanoyl-phosphatidylcholine is present as the fluid lipid component.;Several WALP peptides were modified to remove anchoring Trp residues from one end or the other, thereby generating "half-anchored" WALP peptides which have aromatic anchor residues on only one side of the bilayer. The longer "half-anchored" WALP peptides (having 19-21 residues) were found to have small apparent average tilt values in DLPC, DMPC and DOPC lipid bilayer membranes. The results from a combined 15N PISEMA and 2H GALA analysis---with various analytical treatments of the peptide dynamics---confirmed the small average tilt angle for one of these peptides in DMPC bilayer membranes. Shorter "half-anchored" WALP peptides with a hydrophobic length theoretically capable of spanning only a monolayer leaflet, however, do not adopt well defined membrane orientations and often aggregate.;To a bilayer-spanning "half-anchored" WALP peptide having Trp17 and Trp18, we incorporated Trp or Arg as a "third" anchor in position 2 or 6. Incorporation of this third anchor increases the peptide tilt. When the third anchor is positioned at residue 6, the transmembrane conformation becomes destabilized.;In GWALP23, acetyl-GGALW(LA)6LWLAGA-ethanolamide, we incorporated Pro-12 (replacing Leu-12) within the transmembrane stretch of the peptide, introducing a distortion in the peptide alpha helix. Based upon combined 2H GALA and 15N PISEMA solid-state NMR experiments and analysis, the segments N-terminal and C-terminal to the proline are tilted by 34°-40° and 27°-29° (+/- 6°), respectively, with respect to the lipid bilayer normal, and the proline-induced kink angle is 20-23°. |
