Kringles of the plasminogen-prothrombin gene family share conformational epitopes with recombinant apolipoprotein (a): specificity of the fibrin-binding site

Monoclonal antibodies directed against recombinant apolipoprotein (a) (r-ap o(a)) lacking plasminogen-like KIV-2 repeats were used to identify structur ally related conformational epitopes in various members of the plasminogen- prothrombin gene family. A number of procedures including a fibrin-binding inhibition immunoassay and surface plasmon resonance studies were used. Two antibodies (A10.1 and A10.4) recognised common conformational structures i n r-apo(a), prothrombin, factor XII, plasminogen and its tissue-type and ur okinase-type activators. In contrast, two other antibodies recognised speci fically an epitope comprising residues of the lysine-binding site (A10.2) o r close to it (A10.5) and inhibited the fibrin-binding function of r-apo(a) (IC50 = 36 pmol/l and 9.76 nmol/l, respectively). Interestingly, these ant ibodies distinctly recognised the elastase-derived fragments of plasminogen K4 (A10.2) and K1+2+3 (A10.5) without affecting plasminogen binding to fib rin. These results suggest that highly conserved conformational regions are common to various proteins of the plasminogen-prothrombin gene family and are in agreement with the concept that these proteins constitute a monophyl etic group derived from an ancestral gene. (C) 2001 Elsevier Science B.V. A ll rights reserved.