MOLECULAR-CLONING OF THE CDNA-ENCODING THE CARBOXY-TERMINAL DOMAIN OFCHIMPANZEE APOLIPOPROTEIN(A) - AN ASP57-]ASN MUTATION IN KRINGLE IV-10 IS ASSOCIATED WITH POOR FIBRIN BINDING

Insight into the structural features of human lipoprotein(a) [Lp(a)] w hich underlie its functional implication in fibrinolysis may be gained from comparative studies of apo(a). Indeed, cloning of rhesus monkey apo(a) has shown that a Trp72 --> Arg mutation in the lysine-binding s ite (LBS) of KIV-10 leads to loss of lysine-binding properties of the rhesus Lp(a) particle. Consequently, comparative studies of apo(a) seq uences in different Old World monkey species should further our unders tanding of the molecular role of Lp(a) in the fibrinolytic process. In contrast to other Old World monkeys, including rhesus monkey, cynomol gus, and baboon, the chimpanzee exhibits an elevated level of Lp(a) an d a distinct isoform distribution as compared to humans [Doucet et al. J. Lipid Res. (1994) 35, 263-270]. Clearly then, the chimpanzee is an interesting animal model for study of the structure, function, and po tential pathophysiological roles of Lp(a). We have cloned and sequence d the region of chimpanzee apo(a) cDNA spanning KIV-3 to the stop codo n. The global organization of this region is similar to that of human apo(a) with the presence of KV, which is absent in rhesus monkey apo(a ). Nucleotide sequence comparison indicates a variation of 1.4% betwee n chimpanzee and man and 5.1% between chimpanzee and rhesus monkey. Th e differences concerned single base changes. An Asp57 --> Asn mutation was detected in KIV-10; this residue is critical to the LBS of KIV-10 in human apo(a). To verify that the Asp57 --> Asn substitution was sp ecific to apo(a), we have also cloned the cDNA-encoding plasminogen, w hich exhibited an Asp at the corresponding position in kringle IV. Usi ng an in vitro binding assay, we have demonstrated that chimpanzee Lp( a) exhibits poor lysine-specific interaction with both intact and plas min-degraded fibrin as compared to its human counterpart. We propose t hat the Asn57 substitution in KIV-10 of chimpanzee apo(a) is responsib le for this property. Chimpanzee Lp(a) therefore represents an appropr iate particle with which to explore the potential effects of Lp(a) on the fibrinolytic system, such as the inhibition of plasminogen activat ion or inhibition of t-PA activity.