The C‐terminal helix of human apolipoprotein AII promotes the fusion of unilamellar liposomes and displaces apolipoprotein AI from high‐density lipoproteins

Abstract

To assess the functional properties of apolipoprotein (apo) AII and to investigate the mechanism leading to the displacement of apo AI from native and reconstituted high-density lipoproteins (HDL and r-HDL) by apo AII, wild-type and variant apo AII peptides were synthesized. The wild-type peptides, residues 53Ϫ70 and 58Ϫ70, correspond to the C-terminal helix of apo AII and are predicted to insert at a tilted angle into a lipid bilayer. We demonstrate that both the apo AII-(53Ϫ70) peptide, and to a lesser extent the apo AII-(58Ϫ70) peptide are able to induce fusion of unilamellar lipid vesicles together with membrane leakage, and to displace apo AI from HDL and r-HDL. Two variants of the apo AII-(53Ϫ70)-wild-type (WT) peptide, designed either to be parallel to the water/lipid interface [apo AII-(53Ϫ70)-0°] or to retain an oblique orientation [apo AII-(53Ϫ70)-30°], were synthesized in order to test the influence of the obliquity on their fusogenic properties and ability to displace apo AI from HDL. The parallel variant did not bind lipids, due to its self-association properties. However, the apo AII-(53Ϫ70)-30°v ariant was fusogenic and promoted the displacement of apo AI from HDL. Moreover, the extent of fusion of the apo AII-(53Ϫ70)-WT, apo AII-(58Ϫ70)-WT and apo AII-(53Ϫ70)-30°peptides was related to the A-helical content of the lipid-bound peptides measured by infrared spectroscopy. Infrared measurements using polarized light also confirmed the oblique orientation of the helical component of the three peptides. In native and r-HDL, the tilted insertion of the C-terminal helix of apo AII resulting in a partial destabilization of the HDL external lipid layer might contribute to the displacement of apo AI by apo AII.Keywords : apolipoprotein AII ; apolipoprotein AI; membrane fusion; lipid-binding; synthetic peptide.The physiological role of apolipoprotein (apo) AII, in the HDL seem less efficient than apo AI-only particles in promoting regulation of plasma high-density lipoprotein (HDL) metabolism the uptake and esterification of cell-derived cholesterol [10], includes the ability to displace apo AI from nascent HDL [1Ϫ contributing to the reverse-cholesterol transport mechanism. The 3], and thereby the negative control on the activity of lecithin amount of cholesterol efflux induced by these particles is how-:cholesterol acyltranferase (LCAT) in these particles [4Ϫ6]. Be-ever highly variable and depends upon the type of cells [11,12]. sides its lipid-binding properties and its ability to displace apo Apo AII further seems less protective against the development AI, apo AII was reported to either activate [7], or inhibit [8,9] of atherosclerosis than apo AI, as trangenic mice overexpressing hepatic lipase, depending upon the assay conditions. Apo AI:AII either human or murine apo AII develop more lesions than human apo AI transgenic or control mice [13Ϫ16], although oppo- Abbreviations. apo, apolipoprotein; HDL, high-density lipoproteins;The C-terminal region of apo AII (i.e. residues 47Ϫ77) was nal domains of ap...

Functional analysis of the missense APOC3 mutation Ala23Thr associated with human hypotriglyceridemia

“…The oblique insertion into the lipid bilayer often causes membrane disruption by promoting highly curved hemifusion intermediates, leading to fusion. Tilted peptides have been discovered in viral fusion proteins as well as in many proteins involved in lipid/ lipoprotein metabolism, such as apoB-100 signal peptide ( 41 ), LPL and hepatic lipase ( 42 ), cholesteryl ester transfer protein ( 42 ), lecithin cholesterol acyltransferase ( 43 ), apoA-II ( 44 ), and MTP ( 45 ). In the case of apoC-III, the predicted oblique peptide has a tilted angle of 40° with the interface plane ( 40 ).…”

Role of the Lid Hydrophobicity Pattern in Pancreatic Lipase Activity

“…The interesting hypothesis in the story of tilted peptides is that tilt might have functional consequences. Tilt was first postulated and further demonstrated to be related to the fusogenic ability of fusion proteins of viruses (13,38), to the secretion yield of secreted proteins (13,15), and to the catalytic activity of some enzymes involved in lipid metabolism (17,35). The reason for this effect was suggested to be in the ability of such fragments to adsorb on and penetrate into the hydrophobic interfaces, and to destabilize the packing of acyl chains.…”

“…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

“…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).…”

“…This method is based on an analysis of the shape and position of hydrophobic clusters in a given protein sequence (13). 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.…”