Mode of Membrane Interaction and Fusogenic Properties of a de Novo Transmembrane Model Peptide Depend on the Length of the Hydrophobic Core

Aurélien Lorin,Benoit Charloteaux,Yael Fridmann-Sirkis,Annick Thomas,Yechiel Shai,Robert Brasseur

doi:10.1074/jbc.m700099200

Aurélien Lorin, Benoit Charloteaux + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m700099200

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Abstract

Model peptides composed of alanine and leucine residues are often used to mimic single helical transmembrane domains. Many studies have been carried out to determine how they interact with membranes. However, few studies have investigated their lipid-destabilizing effect. We designed three peptides designated KALRs containing a hydrophobic stretch of 14, 18, or 22 alanines/leucines surrounded by charged amino acids. Molecular modeling simulations in an implicit membrane model as well as attenuated total reflection-Fourier transform infrared analyses show that KALR is a good model of a transmembrane helix. However, tryptophan fluorescence and attenuated total reflection-Fourier transform infrared spectroscopy indicate that the extent of binding and insertion into lipids increases with the length of the peptide hydrophobic core. Although binding can be directly correlated to peptide hydrophobicity, we show that insertion of peptides into a membrane is determined by the length of the peptide hydrophobic core. Functional studies were performed by measuring the ability of peptides to induce lipid mixing and leakage of liposomes. The data reveal that whereas KALR14 does not destabilize liposomal membranes, KALR18 and KALR22 induce 40 and 50% of lipid-mixing, and 65 and 80% of leakage, respectively. These results indicate that a transmembrane model peptide can induce liposome fusion in vitro if it is long enough. The reasons for the link between length and fusogenicity are discussed in relation to studies of transmembrane domains of viral fusion proteins. We propose that fusogenicity depends not only on peptide insertion but also on the ability of peptides to destabilize the two leaflets of the liposome membrane.

Highlights

The effect of hydrophobicity of TM6 model peptides on their interaction with membranes has been studied by several groups [16, 19]
When the length of the hydrophobic stretch of a helical peptide fits the thickness of the membrane hydrophobic core, the peptide inserts into the membrane and adopts a TM orienta
It has been shown that membrane adaptation can result as a response to a hydrophobic mismatch. 2H NMR measurements with lipids containing a perdeuterated acyl chain, x-ray diffraction, and differential scanning calorimetry measurements revealed that a positive mismatch increases the lipid chain order, whereas a negative mismatch increases membrane disorder (38 – 41)

Summary

Introduction

The effect of hydrophobicity of TM6 model peptides on their interaction with membranes has been studied by several groups [16, 19]. Fusogenic Properties of Transmembrane Model Peptides tion [26, 33] When it does not fit, either polar residues are exposed to the apolar medium, or hydrophobic residues are accessible to the water phase. Hofmann et al [42] showed that the fusogenicity of TM model peptides varies with the ratio of helix-promoting leucine and sheet-promoting valine residues and is enhanced if helix-destabilizing residues, such as glycine and proline, are present within their hydrophobic core. They further showed that fusogenicity of these peptides correlates with structural flexibility [42]. Interactions and fusogenic properties of each KALR with a membrane were studied by modeling and experimental approaches

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