Displacement of apo A-I from HDL by apo A-II or its C-terminal helix promotes the formation of pre-beta1 migrating particles and decreases LCAT activation.
The displacement of apolipoprotein (apo) A-I by apo A-II is a major event in the remodeling of high density lipoproteins (HDL). In the present study, we investigated the displacement of apo A-I both from native and reconstituted HDL (rHDL) by either apo A-II or by the C-terminal helical peptide (i.e. residues 53-70). We studied the remodeling process of the original particles, the changes in size and composition and in their lecithin:cholesterol acyltransferase (LCAT) activating properties. Using gel filtration, we show that, at low apo A-II/AI ratios, the initial lipid apolipoprotein complex containing 2 mol apo A-I is remodeled into a mixed complex containing apo A-I and apo A-II, involving the displacement of one apo A-I by apo A-II. Upon addition of a larger amount of apo A-II, the rHDL particles become more heterogeneous and of larger size. Immunoblotting of the particles separated by non denaturing gradient gel electrophoresis shows that most of the apo A-I remains associated with the largest particles. The LCAT activation properties of the remodeled complexes decrease upon addition of either apo A-II or its C-terminal helix. This decrease is more pronounced when rHDL are incubated with the apo A-II C-terminal helix than with native apo A-II, as VmaX decreases from 28 to 16 and 7 nmol cholesteryl ester/ml per h respectively, whereas Km remains unchanged. The displacement of apo A-I observed with rHDL also occurred with native HDL particles as demonstrated by two-dimensional gel electrophoresis, using pyrene-phospholipid labeled HDL. Displacement of apo A-I generates pre-beta1 migrating particles containing apo A-I and phospholipids. We therefore propose that apo A-II has a dual effect on the role of HDL in reverse cholesterol transport: displacement of apo A-I from rHDL results in a negative control of the LCAT activity, while generation of pre-beta1 migrating particles enhances the formation of potential acceptors of cellular cholesterol.
Department of Biochemistry, University of Gent, Belgium. christine.labeur@rug.ac.be
C
C
Labeur
G
G
Lambert
T
T
Van Cauteren
N
N
Duverger
B
B
Vanloo
J
J
Chambaz
J
J
Vandekerckhove
G
G
Castro
M
M
Rosseneu
D016632:Apolipoprotein A-I / Q000378:metabolism*; D016633:Apolipoprotein A-II / Q000737:chemistry* / Q000378:metabolism*; D001667:Binding, Competitive / Q000502:physiology; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000502:physiology; D006801:Humans; D015151:Immunoblotting; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008854:Microscopy, Electron; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000378:metabolism*
D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D008075:Lipoproteins, HDL; D007862:Phosphatidylcholine-Sterol O-Acyltransferase