Characterization and biological activities of recombinant human plasminogen kringle 1-3 produced in Escherichia coli

Antiangiogenic kringles derived from human plasminogen and apolipoprotein(a) inhibit fibrinolysis through a mechanism that requires a functional lysine-binding site

Many proteins in the fibrinolysis pathway contain antiangiogenic kringle domains. Owing to the high degree of homology between kringle domains, there has been a safety concern that antiangiogenic kringles could interact with common kringle proteins during fibrinolysis leading to adverse effects in vivo. To address this issue, we investigated the effects of several antiangiogenic kringle proteins including angiostatin, apolipoprotein(a) kringles IV(9)-IV(10)-V (LK68), apolipoprotein(a) kringle V (rhLK8) and a derivative of rhLK8 mutated to produce a functional lysine-binding site (Lys-rhLK8) on the entire fibrinolytic process in vitro and analyzed the role of lysine binding. Angiostatin, LK68 and Lys-rhLK8 increased clot lysis time in a dose-dependent manner, inhibited tissue-type plasminogen activator-mediated plasminogen activation on a thrombin-modified fibrinogen (TMF) surface, showed binding to TMF and significantly decreased the amount of plasminogen bound to TMF. The inhibition of fibrinolysis by these proteins appears to be dependent on their functional lysine-binding sites. However, rhLK8 had no effect on these processes owing to an inability to bind lysine. Collectively, these results indicate that antiangiogenic kringles without lysine binding sites might be safer with respect to physiological fibrinolysis than lysine-binding antiangiogenic kringles. However, the clinical significance of these findings will require further validation in vivo.

Purification and characterization of a recombinant anti-angiogenic kringle fragment expressed in Escherichia coli: Purification and characterization of a tri-kringle fragment from human apolipoprotein (a) (kringle IV (9)–kringle IV (10)–kringle V)

A kringle fragment (type IV (9)-IV (10)-V) from human apolipoprotein (a) (called LK68) was expressed in an inclusion body in Escherichia coli. The LK68 in this inclusion body was rendered soluble with urea, and efficiently refolded via oxidation in the presence of re-dox couple. The refolded LK68 was then purified via two steps of ion exchange chromatography, concentrated via preparative reversed-phase chromatography, and freeze-dried, at a final yield of approximately 30%. The purified LK68 exhibited profound affinity for lysine and fibrinogen, which suggests the proper folding of the kringle fragment, and also indicates that the native characteristics of apolipoprotein (a) were preserved. The purified LK68 was determined to be highly homogeneous upon reversed-phase HPLC analysis and size-exclusion HPLC analysis, in the presence of 20% (v/v) acetonitrile. However, on size-exclusion HPLC analysis without acetonitrile, it was determined to be somewhat heterogeneous, and this was corroborated by native analyses, including native PAGE and IEF.