Studies of the Minimum Hydrophobicity of α-Helical Peptides Required To Maintain a Stable Transmembrane Association with Phospholipid Bilayer Membranes

Abstract

The effects of the hydrophobicity and the distribution of hydrophobic residues on the surfaces of some designed α-helical transmembrane peptides (acetyl-K 2 -L m -A n -K 2 -amide, where m + n = 24) on their solution behavior and interactions with phospholipids were examined. We find that although these peptides exhibit strong α-helix forming propensities in water, membrane-mimetic media, and lipid model membranes, the stability of the helices decreases as the Leu content decreases. Also, their binding to reversed phase high-performance liquid chromatography columns is largely determined by their hydrophobicity and generally decreases with decreases in the Leu/ Ala ratio. However, the retention of these peptides by such columns is also affected by the distribution of hydrophobic residues on their helical surfaces, being further enhanced when peptide helical hydrophobic moments are increased by clustering hydrophobic residues on one side of the helix. This clustering of hydrophobic residues also increases peptide propensity for self-aggregation in aqueous media and enhances partitioning of the peptide into lipid bilayer membranes. We also find that the peptides LA 3 LA 2 [acetyl-K 2 -(LAAALAA) 3 LAA-K 2 -amide] and particularly LA 6 [acetyl-K 2 -(LAAAAAA) 3 LAA-K 2 -amide] associate less strongly with and perturb the thermotropic phase behavior of phosphatidylcholine bilayers much less than peptides with higher L/A ratios. These results are consistent with free energies calculated for the partitioning of these peptides between water and phospholipid bilayers, which suggest that LA 3 LA 2 has an equal tendency to partition into water and into the hydrophobic core of phospholipid model membranes, whereas LA 6 should strongly prefer the aqueous phase. We conclude that for α-helical peptides of this type, Leu/Ala ratios of greater than 7/17 are required for stable transmembrane associations with phospholipid bilayers.The synthetic peptide acetyl-K 2 -G-L 24 -K 2 -A-amide (P 24 )1 and its analogues have been successfully utilized as models of the hydrophobic transmembrane α-helical segments of

Importance of Residue 13 and the C-Terminus for the Structure and Activity of the Antimicrobial Peptide Aurein 2.2

“…To elucidate the mechanism of action of aurein 2.2 and aurein 2.3, and to better understand how a subtle difference in sequence at residue 13 might affect the mode of action, we investigated peptides with mutations at position 13 and peptides with C-terminal truncations. Although a large number of peptides would be needed for a complete and comprehensive study, we were able to use prior information about the effect of mutations on other peptides (34)(35)(36)(37)(38) and limit our focus to five peptides. The first three peptides consisted of a single conservative mutation at residue 13 from one hydrophobic residue (L) to another.…”

Mechanical Properties of Bilayer Lipid Membranes and Protein–Lipid Interactions

“…In contrast with short peptides [100], the mechanism of interaction between the Na,K-ATPase and phospholipids has been studied to a lesser extent. The focus was concentrated on how phospholipid structure and composition affect the functional properties of the protein, including transport rate, ion binding, and turnover.…”

Effect of Lipid Composition on the Topography of Membrane-Associated Hydrophobic Helices: Stabilization of Transmembrane Topography by Anionic Lipids

“…Synthetic hydrophobic peptides, frequently Lys-flanked polyLeu or polyLeu-Ala helices, have been successfully utilized as models for hydrophobic α-helical TM domains by our lab and many others [18][19][20][21][22][23][24] . In this report fluorescence spectroscopy was used to study the lipid compositiondependence of the TM stability of these and closely related sequences.…”