Association of a Model Class A (Apolipoprotein) Amphipathic α Helical Peptide with Lipid

Abstract

Class A amphipathic helical peptides have been shown to mimic apolipoprotein A-I, the major protein component of high density lipoproteins and have been shown to inhibit atherosclerosis in several dyslipidemic mouse models. Previously we reported the NMR structure of Ac-18A-NH 2 , the base-line model class A amphipathic helical peptide in a 50% (v/v) trifluoroethanol-d 3 /water mixture, a membrane-mimic environment (Mishra, V. K., Palgunachari, M. N., Anantharamaiah, G. M., Jones, M. K., Segrest, J. P., and Krishna, N. R. (2001) Peptides 22, 567-573). The peptide Ac-18A-NH 2 forms discoidal nascent high density lipoprotein-like particles with 1,2-dimyristoyl-sn-glycero-3-phosphocholine. Because subtle structural changes in the peptide⅐lipid complexes have been shown to be responsible for their antiatherogenic properties, we undertook high resolution NMR studies to deduce detailed structure of recombinant peptide⅐1,2-dimyristoyl-sn-glycero-3-phosphocholine complexes. The peptide adopts a well defined amphipathic ␣ helical structure in association with the lipid at a 1:1 peptide:lipid weight ratio. Nuclear Overhauser effect spectroscopy revealed a number of intermolecular close contacts between the aromatic residues in the hydrophobic face of the helix and the lipid acyl chain protons. The pattern of observed peptide-lipid nuclear Overhauser effects is consistent with a parallel orientation of the amphipathic ␣ helix, with respect to the plane of the lipid bilayer, on the edge of the disc (the belt model). Based on the results of chemical cross-linking and molecular modeling, we propose that peptide helices are arranged in a head to tail fashion to cover the edge of the disc. This arrangement of peptides is also consistent with the pK a values of the Lys residues determined previously. Taken together, these results provide for the first time a high resolution structural view of the peptide⅐lipid discoidal complexes formed by a class A amphipathic ␣ helical peptide.Lipoproteins are macromolecular complexes of lipids and proteins (apolipoproteins) that serve to transport lipids and lipid-soluble and water-insoluble molecules in blood throughout the body. Epidemiological studies have established an inverse correlation between the plasma levels of high density lipoprotein (HDL) 4 cholesterol and the risk of coronary artery disease. In support of a protective role of human apolipoprotein A-I (apoA-I), the major protein accounting for 70% of the total protein present in HDL, it has been shown that expression of human apoA-I in atherosclerosis-sensitive mouse models leads to inhibition of atherosclerosis (1-4). In addition, recently it has been shown that infusion of recombinant HDL particles consisting of apoA-I Milano regressed already existing lesions in humans (5). Therefore, there is a great deal of interest in understanding structurefunction relationships of HDLs.The common lipid-associating motif identified in apoA-I and other exchangeable apolipoproteins is the amphipathic ␣ helix with opposing polar and apolar...

Conformation of the synaptobrevin transmembrane domain

“…The synaptobrevin transmembrane domain is relatively short, such that the apolar residues (S115 and T116) cannot protrude from the interior leaflet of the membrane, assuming that the thickness of the bilayer is undisturbed by synaptobrevin or other factors. The observed tilt angle allows the tryptophan side chains to be buried in the bilayer as predicted by EPR studies (22) and allows basic residues to ''snorkel'' out of the bilayer to interact favorably with the phosphate region of the lipid bilayer (22,58). The need for snorkeling is particularly evident for K94, which is a full helical turn farther into the bilayer than W90.…”

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

“…NMR structures were calculated on a Silicon Graphics IRIS Indigo work station using X-PLOR (online) version 3.851. The structure calculation protocol involved (a) generation of a "template" coordinate set; (b) bound smoothing, full structure embedding, and regularization to produce a family of 100 distance geometry structures; (c) simulated annealing regularization and refinement for embedded distance geometry structures; and (d) simulated annealing refinement, as described previously (15). Average coordinates of the accepted structures were energyminimized using 200 cycles of conjugate gradient energy minimization.…”

“…Adding an acyl group to the amino terminus of this peptide and an amide to the C-terminal end resulted in Ac-18A-NH 2 (also known as 2F, since the nonpolar face possesses two Phe residues) with increased ␣ helicity and affinity for lipids (13). Recently, we determined the structure of this peptide in 50% (v/v) trifluoroethanol (14) and complexed to lipid (15) using high resolution solution NMR methods. A number of variations of 2F peptide were synthesized by replacing existing nonpolar amino acids with Phe residues on the nonpolar face.…”

Peptide stabilized amphotericin B nanodisks

“…One such peptide, termed 18A, has been extensively studied [4,5]. Derivatives of this have been made by substituting Phe for Leu residues on the nonpolar face of the amphipathic alpha helix [2].…”