Oxidation of methionine residues to methionine sulfoxides does not decrease potential antiatherogenic properties of apolipoprotein A-I.
The initial stage of oxidation of high density lipoproteins (HDL) is accompanied by the lipid hydroperoxide-dependent, selective oxidation of two of the three Met residues of apolipoprotein A-I (apoA-I) to Met sulfoxides (Met(O)). Formation of such selectively oxidized apoA-I (i.e. apoA-I(+32)) may affect the antiatherogenic properties of HDL, because it has been suggested that Met(86) and Met(112) are important for cholesterol efflux and Met(148) is involved in the activation of lecithin:cholesterol acyl transferase (LCAT). We therefore determined which Met residues were oxidized in apoA-I(+32) and how such oxidation of apoA-I affects its secondary structure, the affinity for lipids, and its ability to remove lipids from human macrophages. We also assessed the capacity of discoidal reconstituted HDL containing apoA-I(+32) to act as substrate for LCAT, and the dissociation of apoA-I and apoA-I(+32) from reconstituted HDL. Met(86) and Met(112) were present as Met(O), as determined by amino acid sequencing and mass spectrometry of isolated peptides derived from apoA-I(+32). Selective oxidation did not alter the alpha-helicity of lipid-free and lipid-associated apoA-I as assessed by circular dichroism, and the affinity for LCAT was comparable for reconstituted HDL containing apoA-I or apoA-I(+32). Cholesteryl ester transfer protein mediated the dissociation of apoA-I more readily from reconstituted HDL containing apoA-I(+32) than unoxidized apoA-I. Also, compared with native apoA-I, apoA-I(+32) had a 2- to 3-fold greater affinity for lipid (as determined by the rate of clearance of multilamellar phospholipid vesicles) and its ability to cause efflux of [(3)H]cholesterol, [(3)H]phospholipid, and [(14)C]alpha-tocopherol from lipid-laden human monocyte-derived macrophages was significantly enhanced. By contrast, no difference was observed for cholesterol and alpha-tocopherol efflux to lipid-associated apolipoproteins. Together, these results suggest that selective oxidation of Met residues enhances rather than diminishes known antiatherogenic activities of apoA-I, consistent with the overall hypothesis that detoxification of lipid hydroperoxides by HDL is potentially antiatherogenic.
Panzenböck
U
U
Biochemistry and Clinical Research Groups, The Heart Research Institute, Camperdown, Sydney, New South Wales 2050, Australia.
Kritharides
L
L
Raftery
M
M
Rye
K A
KA
Stocker
R
R
D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000378:metabolism*; D001161:Arteriosclerosis / Q000188:drug therapy; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D013058:Mass Spectrometry; D008715:Methionine / Q000031:analogs & derivatives* / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000378:metabolism; D013997:Time Factors
D016632:Apolipoprotein A-I; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D008715:Methionine; D007862:Phosphatidylcholine-Sterol O-Acyltransferase; D010100:Oxygen; C013111:methionine sulfoxide