ApoA-I structure on discs and spheres. Variable helix registry and conformational states. J Biol Chem 2002 Oct 18;277(42):39093-101
Date
08/09/2002Pubmed ID
12167653DOI
10.1074/jbc.M206770200Scopus ID
2-s2.0-0037131260 (requires institutional sign-in at Scopus site) 68 CitationsAbstract
Apolipoprotein A-I (apoA-I) readily forms discoidal high density lipoprotein (HDL) particles with phospholipids serving as an ideal transporter of plasma cholesterol. In the lipid-bound conformation, apoA-I activates the enzyme lecithin:cholesterol acyltransferase stimulating the formation of cholesterol esters from free cholesterol. As esterification proceeds cholesterol esters accumulate within the hydrophobic core of the discoidal phospholipid bilayer transforming it into a spherical HDL particle. To investigate the change in apoA-I conformation as it adapts to a spherical surface, fluorescence resonance energy transfer studies were performed. Discoidal rHDL particles containing two lipid-bound apoA-I molecules were prepared with acceptor and donor fluorescent probes attached to cysteine residues located at specific positions. Fluorescence quenching was measured for probe combinations located within repeats 5 and 5 (residue 132), repeats 5 and 6 (residues 132 and 154), and repeats 6 and 6 (residue 154). Results from these experiments indicated that each of the 2 molecules of discoidal bound apoA-I exists in multiple conformations and support the concept of a "variable registry" rather than a "fixed helix-helix registry." Additionally, discoidal rHDL were transformed in vitro to core-containing particles by incubation with lecithin:cholesterol acyltransferase. Compositional analysis showed that core-containing particles contained 11% less phospholipid and 633% more cholesterol ester and a total of 3 apoA-I molecules per particle. Spherical particles showed a lowering of acceptor to donor probe quenching when compared with starting rHDL. Therefore, we conclude that as lipid-bound apoA-I adjusts from a discoidal to a spherical surface its intermolecular interactions are significantly reduced presumably to cover the increased surface area of the particle.
Author List
Li HH, Lyles DS, Pan W, Alexander E, Thomas MJ, Sorci-Thomas MGAuthors
Mary Sorci Thomas PhD Professor in the Medicine department at Medical College of WisconsinMichael J. Thomas PhD Professor in the Pharmacology and Toxicology department at Medical College of Wisconsin
MESH terms used to index this publication - Major topics in bold
Apolipoprotein A-ICholesterol
Cholesterol Esters
Cross-Linking Reagents
Cysteine
Electrophoresis, Polyacrylamide Gel
Fluorescence Resonance Energy Transfer
Humans
Lipid Bilayers
Lipid Metabolism
Lipoproteins, HDL
Lipoproteins, LDL
Plasmids
Protein Binding
Protein Conformation
Spectrometry, Fluorescence
Temperature
Time Factors
