Fig. 1.

Structure of apo(a). The topologies of plasminogen and apo(a) are aligned to show regions of structural homology. The apo(a) lacks plasminogen kringles I–III and contains single copies of sequences similar to plasminogen KV and protease (P), although the protease domain of apo(a) is nonfunctional. The apo(a) contains 10 different types of kringle related to plasminogen KIV. The apo(a) KIV₂ is present in differing numbers of copies in different apo(a) alleles. The apo(a) KIV₉ contains a free cysteine (–SH) that mediates covalent coupling to apoB-100 in Lp(a). The apo(a) KIV₅–KIV₈ each contain a weak LBS (white asterisks) while KIV₁₀ contains a strong LBS (red asterisk).