Tyrosine Replacing Tryptophan as an Anchor in GWALP Peptides

Abstract

Synthetic model peptides have proven useful for examining fundamental peptide–lipid interactions. A frequently employed peptide design consists of a hydrophobic core of Leu-Ala residues with polar or aromatic amino acids flanking each side at the interfacial positions, which serve to “anchor” a specific transmembrane orientation. For example, WALP family peptides (acetyl-GWW­(LA)_<i>n</i>LWWA-[ethanol]­amide), anchored by four Trp residues, have received particular attention in both experimental and theoretical studies. A recent modification proved successful in reducing the number of Trp anchors to only one near each end of the peptide. The resulting GWALP23 (acetyl-GGALW⁵(LA)₆LW¹⁹LAGA-[ethanol]­amide) displays reduced dynamics and greater sensitivity to lipid–peptide hydrophobic mismatch than traditional WALP peptides. We have further modified GWALP23 to incorporate a single tyrosine, replacing W⁵ with Y⁵. The resulting peptide, Y⁵GWALP23 (acetyl-GGALY⁵(LA)₆LW¹⁹LAGA-amide), has a single Trp residue that is sensitive to fluorescence experiments. By incorporating specific ²H and ¹⁵N labels in the core sequence of Y⁵GWALP23, we were able to use solid-state NMR spectroscopy to examine the peptide orientation in hydrated lipid bilayer membranes. The peptide orients well in membranes and gives well-defined ²H quadrupolar splittings and ¹⁵N/¹H dipolar couplings throughout the core helical sequence between the aromatic residues. The substitution of Y⁵ for W⁵ has remarkably little influence on the tilt or dynamics of GWALP23 in bilayer membranes of the phospholipids DOPC, DMPC, or DLPC. A second analogue of the peptide with one Trp and two Tyr anchors, Y^4,5GWALP23, is generally less responsive to the bilayer thickness and exhibits lower apparent tilt angles with evidence of more extensive dynamics. In general, the peptide behavior with multiple Tyr anchors appears to be quite similar to the situation when multiple Trp anchors are present, as in the original WALP series of model peptides