Apolipoprotein(a) and plasminogen interactions with fibrin: a study with recombinant apolipoprotein(a) and isolated...

Lipoprotein(a) [Lp(a)], but not low-density lipoprotein (LDL), was previously shown to impair the generation of fibrin-bound plasmin [Rouy et al. (1991) Arterioscler. Thromb. 11, 629-638] by a mechanism involving binding of Lp(a) to fibrin. It was therefore suggested that the binding was mediated by apolipoprotein(a) [apo(a)], a glycoprotein absent from LDL which has a high degree of homology with plasminogen, the precursor of the fibrinolytic enzyme plasmin. Here we have evaluated this hypothesis by performing comparative fibrin binding studies using a recombinant form of apo(a) containing 17 copies of the apo(a) domain resembling kringle 4 of plasminogen, native Lp(a), and Glu-plasminogen (Glu1-Asn791). Attempts were also made to identify the kringle domains involved in such interactions using isolated elastase-derived plasminogen fragments. The binding experiments were performed using a well-characterized model of an intact and of a plasmin-digested fibrin surface as described by Fleury and Anglés-Cano [(1991) Biochemistry 30, 7630-7638]. Binding of r-apo(a) to the fibrin surfaces was of high affinity (Kd = 26 +/- 8.4 nM for intact fibrin and 7.7 +/- 4.6 nM for plasmin-degraded fibrin) and obeyed the Langmuir equation for adsorption at interfaces. The binding to both surfaces was inhibited by the lysine analogue AMCHA and was completely abolished upon treatment of the degraded surface with carboxypeptidase B, indicating that r-apo(a) binds to both the intrachain lysines of intact fibrin and the carboxy-terminal lysines of degraded fibrin. As expected from these results, both r-apo(a) and native Lp(a) inhibited the binding of Glu-plasminogen to the fibrin surfaces.(ABSTRACT TRUNCATED AT 250 WORDS)