A role for apolipoprotein(a) in protection of the low-density lipoprotein component of lipoprotein(a) from copper-mediated oxidation.
Low-density lipoprotein (LDL) oxidation is stimulated by copper. Addition of a recombinant form of apolipoprotein(a) (apo(a); the distinguishing protein component of lipoprotein(a)) containing 17 plasminogen kringle IV-like domains (17K r-apo(a)) protects LDL against oxidation by copper. Protection is specific to apo(a) and is not achieved by plasminogen or serum albumin. When Cu(2+) is added to 17K r-apo(a), its intrinsic fluorescence is quenched in a concentration-dependent and saturable manner. Quenching is unchanged whether performed aerobically or anaerobically and is reversible by ethylenediaminetetraacetate, suggesting that it is due to equilibrium binding of Cu(2+) and not to oxidative destruction of tryptophan residues. The fluorescence change exhibits a sigmoid dependence on copper concentration, and time courses of quenching are complex. At copper concentrations below 10 microM there is little quenching, whereas above 10 microM quenching proceeds immediately as a double-exponential decay. The affinity and kinetics of copper binding to 17K r-apo(a) are diminished in the presence of the lysine analogue epsilon -aminocaproic acid. We propose that copper binding to the kringle domains of 17K is mediated by a His-X-His sequence that is located about 5A from the closest tryptophan residue of the lysine binding pocket. Copper binding may account for the natural resistance to copper-mediated oxidation of lipoprotein(a) relative to LDL that has been previously reported and for the protection afforded by apo(a) from copper-mediated oxidation of LDL that we describe in the present study.
Hill
Bruce C
BC
Department of Biochemistry, Queen's University, Kingston, Ont, Canada K7L 3N6.
Becker
Lev
L
Anand
Vijay
V
Kusmierczyk
Andrew
A
Marcovina
Santica M
SM
Rahman
Mona N
MN
Gabel
Brent R
BR
Jia
Zongchao
Z
Boffa
Michael B
MB
Koschinsky
Marlys L
ML
D001054:Apolipoproteins A / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D003300:Copper / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D017270:Lipoprotein(a) / Q000737:chemistry / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010958:Plasminogen / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013050:Spectrometry, Fluorescence
D001054:Apolipoproteins A; D017270:Lipoprotein(a); D008077:Lipoproteins, LDL; D011994:Recombinant Proteins; D003300:Copper; D010958:Plasminogen