Association of a Model Class A (Apolipoprotein) Amphipathic α Helical Peptide with Lipid: HIGH RESOLUTION NMR STUDIES OF PEPTIDE·LIPID DISCOIDAL COMPLEXES

Vinod K Mishra,G.M Anantharamaiah,Jere P Segrest,Mayakonda N Palgunachari,Manjula Chaddha,S W Simon Sham,N Rama Krishna

doi:10.1074/jbc.m511475200

Vinod K Mishra, G.M Anantharamaiah + Show 5 more

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https://doi.org/10.1074/jbc.m511475200

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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-NH2, the base-line model class A amphipathic helical peptide in a 50% (v/v) trifluoroethanol-d3/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-NH2 forms discoidal nascent high density lipoprotein-like particles with 1,2-dimyristoyl-sn-glycero-3-phosphocholine. Because subtle structural changes in the peptide.lipid complexes have been shown to be responsible for their antiatherogenic properties, we undertook high resolution NMR studies to deduce detailed structure of recombinant peptide.1,2-dimyristoyl-sn-glycero-3-phosphocholine complexes. The peptide adopts a well defined amphipathic alpha 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 alpha 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 pKa values of the Lys residues determined previously. Taken together, these results provide for the first time a high resolution structural view of the peptide.lipid discoidal complexes formed by a class A amphipathic alpha helical peptide.

Highlights

Lipoproteins are macromolecular complexes of lipids and proteins that serve to transport lipids and lipid-soluble and water-insoluble molecules in blood throughout the body
In support of a protective role of human apolipoprotein A-I, the major protein accounting for 70% of the total protein present in high density lipoprotein (HDL), it has been shown that expression of human apoA-I in atherosclerosis-sensitive mouse models leads to inhibition of atherosclerosis [1,2,3,4]
Based on the results of chemical cross-linking of the Lys residues in the peptides on the disc and molecular modeling, we propose that two amphipathic ␣ helices arranged in an antiparallel fashion cover the lipid acyl chains on the edge of the disc. This is in agreement with our earlier 13C NMR studies of the discoidal complexes of Ac-18A-NH2 and DMPC that indicted that Lys9 and Lys13 residues located on the same side of the amphipathic ␣ helix have reduced pKa values because of their exposure to a basic microenvironment [16]

Summary

Introduction

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. We have determined the solution NMR structure of Ac-18A-NH2 in 50% (v/v) trifluoroethanol-d3/H2O mixture, a membrane-mimic environment [14] These studies did not distinguish subtle variations in lipid-associated structures of peptides that may distinguish them from atheroprotective and inactive complexes [15]. Based on the results of chemical cross-linking of the Lys residues in the peptides on the disc and molecular modeling, we propose that two amphipathic ␣ helices arranged in an antiparallel fashion cover the lipid acyl chains on the edge of the disc This is in agreement with our earlier 13C NMR studies of the discoidal complexes of Ac-18A-NH2 and DMPC that indicted that Lys and Lys residues located on the same side (right side, viewing through the axis of the helix from the N terminus) of the amphipathic ␣ helix have reduced pKa values because of their exposure to a basic microenvironment [16]

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