Two Homologous Apolipoprotein AI Mimetic Peptides

Abstract

Two related 18-amino acid, class A, amphipathic helical peptides termed 3F-2 and 3F 14 were chosen for this study. Although they have identical amino acid compositions and many similar biophysical properties, 3F-2 is more potent than 3F 14 as an apolipoprotein AI mimetic peptide. The two peptides exhibit similar gross conformational properties, forming structures of high helical content on a membrane surface. However, the thermal denaturation transition of 3F-2 is more cooperative, suggesting a higher degree of oligomerization on the membrane. Both 3F-2 and 3F 14 promote the segregation of cholesterol in membranes containing phosphatidylcholine and cholesterol, but 3F-2 exhibits a greater selectivity for partitioning into cholesterol-depleted regions of the membrane. Magic angle spinning/NMR studies indicate that the aromatic residues of 3F-2 are stacked in the presence of lipid. The aromatic side chains of this peptide also penetrate more deeply into membranes of phosphatidylcholine with cholesterol compared with 3F 14 . Using the fluorescent probe, 1,3-dipyrenylpropane, we monitored the properties of the lipid hydrocarbon environment. 3F-2 had a greater effect in altering the properties of the hydrocarbon region of the membrane. The results are consistent with our proposed model of the effect of peptide shape on the nature of the difference in peptide insertion into the bilayer.There is growing evidence that certain apo 1 A-I mimetic, class A amphipathic helical peptides can be used to inhibit atherosclerosis (1). The oral administration of peptide 4F synthesized from all-D amino acids (D-4F) protects mice from diet-induced atherosclerosis without altering plasma cholesterol levels (2, 3). Preliminary studies also suggest that oral administration of D-4F to LDL receptor null and apo E null mice causes the rapid formation and clearance of small high density lipoprotein-like particles containing peptide, cholesterol, apo A-I and paraoxonase, an enzyme capable of converting pro-inflammatory high density lipoprotein into anti-inflammatory high density lipoprotein (4). The peptide 4F has also been tested in vitro and shown to effectively inhibit lytic peptide-induced hemolysis, inhibit oxidized phospholipid-induced monocyte chemotaxis, scavenge lipid hydroperoxides from LDL (5), and maintain endothelial nitric-oxide synthetase activity in the presence of atherogenic concentrations of LDL (6). To study the relationship of peptide structure to anti-atherosclerogenic potency, we studied the properties of four related 18-amino acid, class A amphipathic helical peptides (5). All of these peptides had identical amino acid compositions and very similar physical properties, yet two of these peptides, 3F-1 and 3F-2, were more potent in inhibiting lytic peptide-induced hemolysis, inhibiting oxidized phospholipid-induced monocyte chemotaxis, and scavenging lipid hydroperoxides from LDL compared with the analogs 3F 3 and 3F 14 (5). In the present work we compare the interaction with phospholipid bilayers with and without chole...

ApoA-I Mimetic Peptides with Differing Ability to Inhibit Atherosclerosis Also Exhibit Differences in Their Interactions with Membrane Bilayers

“…In addition, the effect of 3F 14 is somewhat greater close to the end of the acyl chain but before the terminal methyl group. These results are consistent with 1 H MAS/ NOESY measurements that demonstrated that in pure POPC 3F 14 inserted deeper into the membrane than 3F-2 and that cholesterol inhibited the entry of both peptides into the membrane (26).…”

“…observations is that the active peptide 3F-2, due to -electrons at the center of the nonpolar face (that results in a trapezoidal cross-sectional shape), is not able to bury deeply within the lipid acyl chains (26).…”

The Apoptotic Protein tBid Promotes Leakage by Altering Membrane Curvature

“…Each of these substances was added to 50 M LUV of DOPC:cardiolipin (2:1) or DOPC:DOPE:cardiolipin (1:1:1) to give a final concentration of additive of 7 M. After the addition of Ca 2ϩ and 40 nM tBid (twice the concentration used to obtain the data of Fig. 1), leakage reached a value of 10% or less of the total contents, over the first 200 s. We also tested cyclosporin A, an immunosuppressive peptide that inhibits processes requiring negative curvature (30). At a concentration of 10 M this peptide completely inhibited leakage from DOPG/DOPC/DOPE (1:1:1).…”

“…It has been shown that the membranes of mitochondria of amoeba form structures resembling a lipidic cubic phase, a structure formed by membranes with negative curvature propensity (29). The morphological reorganization of mitochondria observed during apoptosis is inhibited by cyclosporin A (28), a peptide that has been shown to inhibit membrane processes requiring increased negative curvature (30). Furthermore, ceramides, a class of lipids that promotes negative curvature (31), cause the release of cytochrome c from isolated mitochondria (32)(33)(34).…”

Effect of Leucine to Phenylalanine Substitution on the Nonpolar Face of a Class A Amphipathic Helical Peptide on Its Interaction with Lipid

“…We have shown previously that the two homologous apoA-I mimetic peptides, 3F-2 and 3F 14 , differ in their in vitro antiatherogenic properties (50), and the peptide 3F-2 inhibits atherosclerosis in female apoE null mice, whereas 3F 14 does not (51). Using several NMR methods, we have shown that these two peptides insert to different extents into lipid vesicles (51).…”