Formation of spherical, reconstituted high density lipoproteins containing both apolipoproteins A-I and A-II is mediated by lecithin:cholesterol acyltransferase.
Previous studies have provided detailed information on the formation of spherical high density lipoproteins (HDL) containing apolipoprotein (apo) A-I but no apoA-II (A-I HDL) by an lecithin:cholesterol acyltransferase (LCAT)-mediated process. In this study we have investigated the formation of spherical HDL containing both apoA-I and apoA-II (A-I/A-II HDL). Incubations were carried out containing discoidal A-I reconstituted HDL (rHDL), discoidal A-II rHDL, and low density lipoproteins in the absence or presence of LCAT. After the incubation, the rHDL were reisolated and subjected to immunoaffinity chromatography to determine whether A-I/A-II rHDL were formed. In the absence of LCAT, the majority of the rHDL remained as either A-I rHDL or A-II rHDL, with only a small amount of A-I/A-II rHDL present. By contrast, when LCAT was present, a substantial proportion of the reisolated rHDL were A-I/A-II rHDL. The identity of the particles was confirmed using apoA-I rocket electrophoresis. The formation of the A-I/A-II rHDL was influenced by the relative concentrations of the precursor discoidal A-I and A-II rHDL. The A-I/A-II rHDL included several populations of HDL-sized particles; the predominant population having a Stokes' diameter of 9.9 nm. The particles were spherical in shape and had an electrophoretic mobility slightly slower than that of the alpha-migrating HDL in human plasma. The apoA-I:apoA-II molar ratio of the A-I/A-II rHDL was 0.7:1. Their major lipid constituents were phospholipids, unesterified cholesterol, and cholesteryl esters. The results presented are consistent with LCAT promoting fusion of the A-I rHDL and A-II rHDL to form spherical A-I/A-II rHDL. We suggest that this process may be an important source of A-I/A-II HDL in human plasma.
Clay
M A
MA
The University of Adelaide, Department of Medicine, Royal Adelaide Hospital, North Terrace, Adelaide, South Australia 5000, Australia. maclay@camtech.net.au
Pyle
D H
DH
Rye
K A
KA
Barter
P J
PJ
D016632:Apolipoprotein A-I / Q000378:metabolism*; D016633:Apolipoprotein A-II / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D006801:Humans; D008075:Lipoproteins, HDL / Q000378:metabolism* / Q000648:ultrastructure*; D008954:Models, Biological; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000378:metabolism*
D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D002788:Cholesterol Esters; D008075:Lipoproteins, HDL; D007862:Phosphatidylcholine-Sterol O-Acyltransferase