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Defined apolipoprotein A-I conformations in reconstituted high density lipoprotein discs
1Department of Biochemistry, College of Medicine at Urbana-Champaign, Illinois 61801.
The Journal of Biological Chemistry
|March 25, 1989
Summary
Researchers created reconstituted high density lipoprotein (r-HDL) particles and found smaller, stable r-HDL species with less phospholipid content exhibit reduced lecithin cholesterol acyltransferase activity. This suggests a model for discoidal r-HDL particle formation and function.
Area of Science:
- Lipid biochemistry
- Protein conformation
- Biophysical characterization
Background:
- High-density lipoproteins (HDL) play a crucial role in reverse cholesterol transport.
- Reconstituted HDL (r-HDL) particles are valuable tools for studying HDL structure-function relationships.
- Understanding the heterogeneity of r-HDL is essential for their therapeutic applications.
Purpose of the Study:
- To prepare and characterize defined reconstituted high density lipoprotein (r-HDL) particles.
- To investigate the structural and functional differences between r-HDL subclasses.
- To propose a model for the origin of discoidal r-HDL particles.
Main Methods:
- Preparation of r-HDL using the sodium cholate method.
- Phospholipid depletion using low-density lipoprotein (LDL).
- Isolation of r-HDL species by gel filtration.
- Characterization by size, alpha-helix content (spectroscopy), and tryptophan fluorescence.
- Assessment of lecithin cholesterol acyltransferase (LCAT) reactivity.
Main Results:
- Isolated discoidal r-HDL particles with 2 and 3 apolipoprotein A-I (apoA-I) molecules/particle and diameters of 77 and 109 Å were obtained.
- Spectral properties indicated distinct apoA-I conformations between smaller (77/109 Å) and larger (86/96 Å) r-HDL particles.
- The 77 and 109 Å particles showed similar, approximately 10-fold lower, LCAT reactivity compared to the 86 and 96 Å particles.
- Stable, limiting r-HDL particles (77/109 Å) arise from larger particles via phospholipid depletion, possessing altered apoA-I conformations and reduced LCAT activation.
Conclusions:
- Stable, discoidal r-HDL particles with specific sizes (77/109 Å) can be formed by phospholipid depletion from larger r-HDL particles.
- These smaller r-HDL particles exhibit decreased alpha-helix content and compact protein regions in apoA-I.
- The altered conformation of apoA-I in smaller r-HDL particles leads to significantly reduced activation of lecithin cholesterol acyltransferase, suggesting a mechanism for HDL subclass formation and function.