No abstract

No abstract

Lipoprotein(a) contains one copy each of apolipoprotein B-100 and apolipoprotein(a). It has been hypothesized that a disulfide bond might exist between Cys4O" of apolipoprotein (a) Lp(a) represent an independent risk factor for the development of premature atherosclerosis (4, 5). Mice transgenic for human apo(a) develop atherosclerosis upon cholesterol feeding (6).Cloning and sequencing of the first complete apo(a) cDNA from human liver (7) revealed a striking homology between apo(a) and plasminogen. Both proteins belong to a protein family characterized by the presence of one or more kringle domains with six highly conserved cysteine residues, which are believed to be involved in three intradomain disulfide bridges. Plasminogen contains single copies of five different kringle domains and a serine protease domain. Referring to the numbering of plasminogen kringles, the first sequenced apo(a) cDNA encoded a glycoprotein with 37 tandemly repeated kringle IV-like domains, a single kringle V domain, and a serine protease domain. Ten distinct kringle IV domains were encoded by the sequenced apo(a) cDNA. One of them occurred in 28 identical copies; the others were unique.In human plasma, almost all apo(a) is present as a macromolecular Lp(a) complex. As the dissociation of the LDL moiety and apo(a) in Lp(a) requires reducing conditions, a

The well documented association between high plasma levels of lipoprotein(a) (Lp(a)) and cardiovascular disease might be mediated by the lysine binding of apolipoprotein(a) (apo(a)), the plasminogen-like, multikringle glycoprotein in Lp(a). We employed a mutational analysis to localize the lysine-binding domains within human apo(a). Recombinant apo(a) (r-apo(a)) with 17 plasminogen kringle IV-like domains, one plasminogen kringle V-like domain, and a protease domain or mutants thereof were expressed in the human hepatocarcinoma cell line HepG2. The lysine binding of plasma Lp(a) and r-apo(a) in the culture supernatants of transfected HepG2 cells was analyzed by lysine-Sepharose affinity chromatography. Wild type recombinant Lp(a) (r-Lp(a)) revealed lysine binding in the range observed for human plasma Lp(a). A single accessible lysine binding site in Lp(a) is indicated by a complete loss of lysine binding observed for r-Lp(a) species that contain either a truncated r-apo(a) lacking kringle IV-37, kringle V, and the protease or a point-mutated r-apo(a) with a Trp-4174-->Arg substitution in the putative lysine-binding pocket of kringle IV-37. Evidence is also presented for additional lysine-binding sites within kringles 32-36 of apo(a) that are masked in Lp(a) as indicated by an increased lysine binding for the point mutant (Cys-4057-->Ser), which is unable to assemble into particles. An important role of these lysine-binding site(s) for Lp(a) assembly is suggested by a decreased assembly efficiency for deletion mutants lacking either kringle 32 or kringles 32-35.

No abstract