ANALYSIS OF THE MECHANISM OF LIPOPROTEIN(A) ASSEMBLY

We have assessed the ability of a battery of purified recombinant apol ipoprotein(a) (r-apo(a)) derivatives to bind to immobilized low-densit y lipoprotein (LDL) by ELISA. Removal of the apo(a) kringle IV type 8 and type 9 sequences dramatically reduced apo(a) binding to LDL. The b inding of apo(a) to LDL was effectively inhibited by arginine, lysine, the lysine analogue epsilon-aminocaproic acid and proline; comparable inhibition was observed using the 17K and KlV(5-8) r-apo(a) derivativ es, suggesting a direct role for sequences contained in the latter spe cies in mediating the initial non-covalent interactions which precede specific disulfide bond formation. We also determined that r-apo(a) bi nds directly to a synthetic apoB peptide spanning amino acid residues 3732-3745; this interaction appeared to be mediated by sequences prese nt in apo(a) kringle IV types 8 and 9, and could be inhibited by argin ine, lysine and proline. The results of this study indicate that the e fficiency of Lp(a) assembly is a direct function of the initial non-co valent interactions between apo(a) and LDL; in addition, these studies suggest that Cys3734 in apoB mediates covalent linkage with apo(a) by virtue of the ability of the apoB sequences surrounding this residue to directly interact with apo(a) KIV type 9.