Contribution of the hydrophobicity gradient of an amphipathic peptide to its mode of association with lipids

Abstract

A class of peptides that associate with lipids, known as oblique-orientated peptides, was recently described [Brasseur R., Pillot, T., Lins, L., Vandekerckhove, J. & Rosseneu, M. (1997) Trends Biochem. Sci. 22, 167Ϫ171]. Due to an asymmetric distribution of hydrophobic residues along the axis of the Ahelix, such peptides adopt an oblique orientation which can destabilise membranes or lipid cores. Variants of these oblique peptides, designed to have an homogeneous distribution of hydrophobic and hydrophilic residues along the helical axis, are classified as regular amphipathic peptides. These peptides are expected to lie parallel to the polar/apolar interface with their hydrophobic residues directed towards the apolar and their hydrophilic residues towards the polar phase. An hydrophobic, oblique-orientated peptide was identified at residues 56Ϫ68 in the sequence of the lecithin-cholesterol acyltransferase (LCAT), enzyme. This peptide is predicted to penetrate a lipid bilayer at an angle of 40°through its more hydrophobic Cterminal end and thereby induce the destabilisation of a membrane or a lipid core. The LCAT-(56Ϫ68) wild-type peptide was synthesised together with the LCAT-(56Ϫ68, 0°) variant, in which the hydrophobicity gradient was abolished through residue permutations. In two other variants, designed to keep their oblique orientation, the W61 residue was shifted either towards the more hydrophilic N-terminal at residue 57, or to position 68 at the hydrophobic C-terminal end of the peptide. Peptide-induced vesicle fusion was demonstrated by fluorescence measurements using pyrene-labeled vesicles and by monitoring of vesicle size by gel filtration. The interaction between peptides and lipids was monitored by measurement of the intrinsic tryptophan fluorescence emission of the peptides. Fluorescence polarisation measurements, using diphenyl hexatriene, were carried out to follow changes in the lipid fluidity. The LCAT-(56Ϫ68) wild-type peptide and the two oblique variants, induced fusion of unilamellar dimyristoylglycerophosphocholine vesicles. Tryptophan fluorescence emission measurements showed a 12Ϫ14 nm blue shift upon addition of the wild-type peptide and of the W61→68 variant to lipids, whereas the fluorescence of the W61→57 variant did not change significantly. This observation supports the insertion of the more hydrophobic C-terminal residues into the lipid phase, as predicted by the theoretical calculations. In contrast, the 0°variant peptide had no fusogenic activity, and it associated with lipids to form small discoidal lipid/peptide complexes. The phospholipid transition temperature was decreased after addition of the wild-type, the W61→68 and W61→57 fusogenic peptides, whereas the opposite effect was observed with the 0°variant. The behaviour of the wild-type and variant LCAT-(56Ϫ68) peptides stresses the contribution of the hydrophobicity gradient along the axis of an amphipathic peptide to the mode of association of this peptide with lipids. This parameter consequently influences the structur...

Bactericidal Activity of Mammalian Cathelicidin-Derived Peptides

“…bicity gradients appear to promote membrane destabilization by causing the peptide to partially penetrate the bilayer (4,7,29). In our series, the peptides with the steepest hydrophobicity gradients, SMAP29 and CAP18, also had the most potent antimicrobial activity (Fig.…”

Role of the Lid Hydrophobicity Pattern in Pancreatic Lipase Activity

“…Tilted peptides have been identified in many proteins and protein fragments interacting with lipids such as viral fusion proteins (14), signal peptides of membrane-translocated proteins (15), and proteins involved in lipid metabolism (16). In the latter, they may increase the accessibility of enzymes to hydrophobic substrates (12,17,18). Hence, in contrast with classical amphipathic helices currently found in proteins and supported to promote protein stability, tilted peptides are a signature for instability (13).…”

Distribution of Hydrophobic Residues Is Crucial for the Fusogenic Properties of the Ebola Virus GP2 Fusion Peptide

“…The 25 to 35 fragment (AIGLAWIPYFG) shows a hydrophobicity profile similar to that of the SIV tilted peptide, well known for its fusogenic properties (22, 26), although, as shown on Fig. 1, the two stretches have no sequence identity.The three-dimensional structure of the 25 to 35 Ebola virus peptide was calculated as previously described, assuming a helical secondary structure (3,6,7,28). Small peptides can adopt ␣ and ␤ type structures (12,22,33).…”

“…It was shown that the ability of the Ebola virus peptide to induce lipid destabilization correlates with an ␣-helical structure, in the absence of Ca 2ϩ (33). Furthermore, the fusogenic activity of the tilted fragments of apolipoprotein A-II and SIV fusion protein increases with the helical content (22,28), stressing the importance of the helix structure for lipid destabilizing capacities. Moreover, nuclear magnetic resonance studies have indicated that the fragments of the fusogenic domain of GP41 and of HA2, which correspond to tilted peptides in terms of hydrophobic/hydrophilic properties, are predominantly ␣-helical in a lipid-like environment (15,16).…”

“…Mutants were then designed via molecular modeling to assess the role of the hydrophobicity gradient in the orientation of the peptide in a membrane and in the fusion process, as has previously been done for viral and neurotoxic tilted peptides (5,26,28). By molecular modeling we designed a mutant with FIG.…”