The low-resolution structure of nHDL reconstituted with DMPC with and without cholesterol reveals a mechanism for particle expansion

Abstract

Cholesterol from peripheral tissues, such as within the artery wall, is transported to the liver by high density lipoprotein (HDL) particles, which are continuously remodeled in a process called reverse cholesterol transport ( 1, 2 ). HDL particles are highly heterogeneous, varying in protein and lipid content ( 3 ). Apolipoprotein A1 (apoA1) is Abstract Small-angle neutron scattering (SANS) with contrast variation was used to obtain the low-resolution structure of nascent HDL (nHDL) reconstituted with dimyristoyl phosphatidylcholine (DMPC) in the absence and presence of cholesterol, [apoA1:DMPC (1:80, mol:mol) and apoA1:DMPC:cholesterol (1:86:9, mol:mol:mol)]. The overall shape of both particles is discoidal with the low-resolution structure of apoA1 visualized as an open, contorted, and out of plane conformation with three arms in nascent HDL/dimyristoyl phosphatidylcholine without cholesterol (nHDL DMPC ) and two arms in nascent HDL/dimyristoyl phosphatidylcholine with cholesterol (nHDL DMPC+Chol ). The low-resolution shape of the lipid phase in both nHDL DMPC and nHDL DMPC+Chol were oblate ellipsoids, and fi t well within their respective protein shapes. Modeling studies indicate that apoA1 is folded onto itself in nHDL DMPC , making a large hairpin, which was also confi rmed independently by both cross-linking mass spectrometry and hydrogen-deuterium exchange (HDX) mass spectrometry analyses. In nHDL DMPC+Chol , the lipid was expanded and no hairpin was visible. Importantly, despite the overall discoidal shape of the whole particle in both nHDL DMPC Press, January 23, 2013 DOI 10.1194 The low-resolution structure of nHDL reconstituted with DMPC with and without cholesterol reveals a mechanism for particle expansion Abbreviations: DMPC, dimyristoyl phosphatidylcholine; DSH, double super helix; ESR, electron spin resonance; FRET, fl uorescence resonance energy transfer; HDX, hydrogen-deuterium exchange; LUV, large unilamellar vesicle; nHDL, nascent HDL; nHDL DMPC , nascent HDL/dimyristoyl phosphatidylcholine without cholesterol; nHDL DMPC+Chol , nascent HDL/dimyristoyl phosphatidylcholine with cholesterol; nHDL POPC , nascent HDL/POPC and cholesterol; PC, phosphatidyl choline ; POPC, 1-palmitoyl-2-oleoyl-sn -glycero-3-phosphocholine; q , range of momentum transfer; SANS, small-angle neutron scattering; SCX, strong-cation exchange. Published, JLR Papers in

Small-Angle X-Ray Scattering of the Cholesterol Incorporation into Human ApoA1-POPC Discoidal Particles

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Novel Formulation of a Reconstituted High-Density Lipoprotein (CSL112) Dramatically Enhances ABCA1-Dependent Cholesterol Efflux

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