Effects of cholesterol on thermal stability of discoidal high density lipoproteins[S]
- 1To whom correspondence should be addressed. e-mail: shobini{at}bu.edu
Abstract
Reverse cholesterol transport in plasma involves variations in HDL cholesterol concentration. To understand physicochemical and functional implications of such variations, we analyzed stability of reconstituted HDL containing human apolipoproteins (apoA-I, apoA-II, or apoC-I), phosphatidylcholines varying in chain length (12–18 carbons) and unsaturation (0 or 1), and 0–35 mol% cholesterol. Lipoprotein heat denaturation was monitored by circular dichroism for protein unfolding/dissociation and by light scattering for particle fusion. We found that cholesterol stabilizes relatively unstable complexes; for example, incorporation of 10–30 mol% cholesterol in apoC-I:dimyristoyl phosphatidylcholine complexes increased their kinetic stability by δΔG* ≅ 1 kcal/mol. In more stable complexes containing larger proteins and/or longer-chain lipids, incorporation of 10% cholesterol did not significantly alter the disk stability; however, 15% or more cholesterol destabilized the apoA-I-containing complexes and led to vesicle formation. Thus, cholesterol tends to stabilize less stable lipoproteins, apparently by enhancing favorable packing interactions, but in more stable lipoproteins, where such interactions are already highly optimized, the stabilizing effect of cholesterol decreases and, eventually, becomes destabilizing. These results help uncouple the functional roles of particle stability and chain fluidity and suggest that structural disorder in HDL surface, rather than chain fluidity, is an important physicochemical determinant of HDL function.—Jayaraman, S., S. Benjwal, D. L. Gantz, and O. Gursky. Effects of cholesterol on thermal stability of discoidal high density lipoproteins. J. Lipid Res. 2010. 51: 324–333.
- kinetic stability
- protein unfolding rate
- lipoprotein fusion
- acyl chain fluidity
- reverse cholesterol transport
Footnotes
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- Abbreviations:
- apo
- apolipoprotein
- CD
- circular dichroism
- Ch
- unesterified cholesterol
- DLPC
- dilinoleyl phosphatidylcholine
- DMPC
- dimyristoyl phosphatidylcholine
- DPPC
- dipalmitoyl phosphatidylcholine
- DSC
- differential scanning calorimetry
- EM
- electron microscopy
- PC
- phosphatidylcholine
- POPC
- palmitoyl oleoyl phosphatidylcholine
- RCT
- reverse cholesterol transport
- rHDL
- reconstituted high-density lipoprotein
- T-jump
- temperature jump
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This work was supported by the National Institutes of Health Grants GM-67260 and HL-26355. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health.
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↵[S] The online version of this article (available at http://www.jlr.org) contains supplementary data.
- Received August 3, 2009.
- Revision received August 10, 2009.
- Copyright © 2010 by the American Society for Biochemistry and Molecular Biology, Inc.
