Identification of a novel apolipoprotein(a)-related protein from the European hedgehog (Erinaceus europaeus).

Abstract

We have isolated a cDNA encoding an apo(a)-related protein designated HaRP-1 (Hedgehog apo(a) related protein-1). The HaRP-1 cDNA (2114 bp; corresponding to a 2.6 kb transcript) was isolated from a hedgehog liver cDNA library. The HaRP-1 clone corresponded to an open reading frame of 676 amino acids and contains a signal sequence followed by a preactivation domain and 7 kringle domains which exhibit an average of 57% amino acid identity with hedgehog plasminogen kringle III. We expressed HaRP-1 in human embryonic kidney cells; immunoprecipitation of metabolically-labeled conditioned medium from transfected cells showed the presence of a 74 kDa band corresponding to HaRP-1. Of note, we also observed an approximately 72 kDa species present in hedgehog plasma by western blotting using a human anti-apo(a) monoclonal antibody; we speculate that the 72 kDa plasma species corresponds to HaRP-1. Interestingly, although none of the 7 kringle domains contained a canonical lysine-binding site, we found that recombinant HaRP-1 bound specifically to lysine-Sepharose. It is likely that the evolution of the HaRP-1 gene is coincident with the evolution of hedgehog apo(a), both of which occurred by duplication of the plasminogen kringle III motif. The function of HaRP-1 remains unclear at present, but may constititute a member of the family of apo(a) proteins that functions in the regulation of lysine-dependent proteolysis.